Week 14 Flashcards
1
Q
Why are measurements of the fish important?
A
These measurements can then be used to quantify and standardise certain aspects of the morphology of the organism. Through this we can make accurate comparisons between different species, and hypothesise on the reasons behind these differences.
2
Q
What is the standard length of a fish?
A
The standard length of a fish is the distance from tip of the snout to the start of the tail fin (caudal fin). Alternative measurements include, fork length and total length which you will learn about during the practical.
3
Q
What is the aspect ratio of a fish?
A
The aspect ratio of the caudal fin is used to indicate the type of lifestyle or propulsive ability of a fish. It can be used to compare and differentiate different species, such as, fast swimming, pelagic species and slower, bottom dwelling species.
4
Q
What is the equation for calculating aspect ratio?
A
The equation for calculating the aspect ratio of the caudal fin is A = h2 / s where h is the height, and s is the surface area.
Aspect ratio= height2/surface area
5
Q
Why is the gill arch important in this experiment?
A
the gill arch found in teleost fish.
The morphology of the gill arch can vary across species, and can be highly informative as to the ecology of the fish.
6
Q
What are the two teleost fish used in this experiment?
A
Each group has specific features, both ecological and morphological, which you will need to identify in other species.
Pelagic species
Demersal species
7
Q
What are the pelagic species?
A
These species inhabit open waters, and have various adaptations for this habitat
8
Q
What are the Dermersal species?
A
Demersal species are bottom dwelling, benthic organisms. The evolutionary pressures of these species are markedly different from the pelagic teleosts, and their morphology, ecology and behaviour reflect this.
Note that some demersal species can have features similar to pelagic species, but they do not have all the features that pelagic species have.
9
Q
Which of the following are characteristic of pelagic fish species?
A
Forked caudal fin
Streamlined shape
Counter shaded body (dark on top, light underneath)
Found in open water column
10
Q
Which of the following should be included when producing good biological drawings?
A
Good biological drawings should be made up of single pencil lines using a sharp pencil.
Drawings should include a scale bar so the original specimen size can be estimated.
Colours and shading should be described in labels and annotations.
11
Q
_____ fishes evolved at the same time as sharks, some 400 million years ago.
A
Blank 1: Bony
12
Q
Select all that apply
Choose all features typical of most bony fishes.
Lack of swim bladder
Completely symmetrical tails
Internal skeleton made of bone
Thick, protective scales
Highly mobile fins
A
Completely symmetrical tails
Internal skeleton made of bone
Highly mobile fins
13
Q
Two important adaptations that enabled the remarkable success of the bony fishes are the swim ______
and the _____ cover.
A
bladder
gill
14
Q
The oval body releases gas from the _____ bladder of fish, thereby playing a role in their buoyancy.
A
swim
15
Q
Most bony fishes possess a _____ ______ ,a gas-filled sac used to maintain and control buoyancy.
A
swim bladder
16
Q
When did bony fishes evolve?
A
At the same time as sharks
17
Q
Bony fish have a bony ____ and a skin covered in plates or _____.
A
skeleton
scales
18
Q
Select all that apply
Which of the following adaptations were particularly important in the success of the bony fishes?
The lateral line system
The swim bladder
The gill cover
Gill arches
A
The swim bladder
The gill cover
19
Q
The swim bladder of bony fish evolved as a dorsal outpocketing of which of the following structures?
A
Pharynx
20
Q
Select all that apply
Which of the following do not possess a swim bladder?
Tuna Flounder Rays Sharks Skates
A
Rays
Sharks
Skates
21
Q
The ______ is the hard plate that covers the gills in bony fish.
A
operculum
22
Q
Which of the following are features of bony fishes?
All have a bony skeleton
Most have a scale-covered skin
All bony fishes have lungs
Most bony fishes exhibit internal fertilization
A
All have a bony skeleton
Most have a scale-covered skin
23
Q
Which of the following are major groups of bony fish?
Myxini Sarcopterygii Chondrichthyes Actinopterygii Cephalaspidomorphi
A
Sarcopterygii
Actinopterygii
24
Q
In ______-finned fishes, each fin consists entirely of parallel bones and is moved by muscles inside the body, whereas in ______-finned fishes, the fins have muscles and a central core of bones that form an articular joint.
A
ray
lobe
25
The oval body releases gas from the ____ bladder of fish, thereby playing a role in their buoyancy.
swim
26
The ____-finned fishes evolved 390 mya, shortly after the first bony fishes appeared in the fossil record.
lobe
27
When bony fish flex the operculum ____
| is pumped over their gills.
water
28
Which of the following accurately describes the fins of ray-finned fishes and lobe-finned fishes?
In ray-finned fishes, muscles within the fins cause the fins to move
In lobe-finned fishes, each fin is made of a long fleshy muscular lobe
In ray-finned fishes, each fin consists of parallel bony rays
In lobe-finned fishes, there are bony rays at the tips of each fin
In ray-finned fishes, each fin consists of parallel bony rays
In lobe-finned fishes, each fin is made of a long fleshy muscular lobe
In lobe-finned fishes, there are bony rays at the tips of each fin
29
Which of the following classes appeared in the fossil record shortly after the appearance of the first bony fish, around 390 million years ago, and eventually contained members that colonized the land?
Sarcopterygii
30
What are the only living relatives of the jawless vertebrates?
If we look at the jawless vertebrates- you will see that the lampreys and the hagfish, which are the only living representatives of the jawless vertebrates
31
What gave rise to the jawed vertebrates?
You can see that the jawless vertebrates gave rise to the jawed vertebrates. We have a distinct lineage called the placoderms, that is sister to the extent lineages, of the Chondrichthyes and also the bony fish.
32
What does the most recent paleontological evidence indicate?
that there were many lineages of jawless vertebrates, some living (lampreys, hagfish), many extinct (e.g. conodonts).
33
What shares a common ancestry with the living jawed vertebrates?
The placoderms share common ancestry with the living jawed vertebrates, and this combined monophyletic group is the Gnathostomata (Gnathostomes)
34
What does the Gnathostomes contain?
The Gnathostomes contains extant Chondrichthyes (sharks, skates and rays) and Osteichthyes (bony fishes).
35
The Osteichthyes (Osteichthyans) contains the
the ray-finned fishes (Actinopterygii) and the lobe-finned fishes (Sarcopterygii).
36
The lobefins include the
the coelacanths, lungfishes and the tetrapods (amphibians, reptiles and mammals).
37
What can the Osteichthyes be separated in to?
can be separated into two major groups. One of those is the Actinopterygii which are the ray finned fishes. The second is the Sarcopterygii which are the low fins. The low fins include the Coelacanths, lungfish, and all the tetrapods.
38
How are the ray finned fish divided?
The ray finned fishes are divided into three main groups. I) The Chondrostei which comprises the bichirs, sturgeons and paddlefishes. II) The Holostei which comprises the bowfins and the gars. III) The Teleostei, which comprises all other ray finned fishes.
39
How many teleost fishes are there?
There are estimated to be around 30,000 teleost fishes, and they started to diversify around 300 million years ago.
40
What are the Chondrostei Characteristics?
First, focus on the Chondrosteans (Chondrostei). These are a group of bony fishes, that actually have cartilaginous skeletons. However, it is clear from the fossil record that their ancestors had bony skeletons and these have been “secondarily lost”.
1.Secondary loss of bone
Skeleton mainly cartilage
No vertebrae
41
What do the Chondrosteans have the remains of?
also have the remains of a spiracle (which has homology with the first gill slit of the agnathans – the lampreys and hagfishes).
2.Presence of spiracle
Remnant of 1st gill slit of agnathans
42
chondrosteans have
“ganoid” scales, which are characterised by three layers (enamel, vascular bone, lamella bone).
3. Ganoid Scales
- --3 layers- Enamel, Vascular bone and Lamella bone.
43
What are the characteristics of the ganoid scales?
This ganoid scales which are found in the Chondrosteans are also found in the Holostei. They’re quite different from the scales that we see in the Teleosts.
44
How are the Teleosts characterised?
Teleosts are either characterised by their cycloid scales or ctenoid scales, these have only a lamella bone layer with very little mineralisation.
--By contrast the teleosts have cycloid and/or ctenoid scales, and these are much lighter, with only lamella bone without much mineralisation
45
What are the Chondrostei: (Polypteriformes)?
Modern chondrosteans are species poor. There are only two living Orders.
The first Order is the Polypteriformes, otherwise known as bichirs, and there are 12 living species. These are typically found in shallow swampy African freshwaters, and they have paired lungs that can help to breathe in poorly oxygenated waters.
46
What is the second order of the Chondrostei?
The second Order is the Acipensiformes, a group that contains the paddlefishes (1 living species) and the sturgeons (27 living species).
47
Outline the features fof teh American Paddlefish?
Here is the American paddlefish, which live in rivers of North America. They are notably for the extremely long paddle-like rostrum that contains electroreceptors capable of detecting the presence of their favoured prey in the water column. These are essentially filter feeders, they open their mouths up really wide and filter the zoo plankton from the water using their Gill rakers.
A second paddlefish species, the Chinese paddlefish, was native to the Yangtze and Yellow River basins in China. The last sighting was 2003, and it was declared extinct by the IUCN in 2020, as a consequence of overfishing and habitat destruction/fragmentation.
48
What are the sturgeons?
The sturgeons are a group of large migratory species broadly distributed across the northern hemisphere. They are threatened by overharvesting and blocking of migration routes. Caviar (eggs, roe) is harvested from several large species, meaning that they can be valuable for illegal fishers. Anadromous, long lived and 8m long 1.4 tonnes.
49
What are the Holosteans (Holostei)?
Like chondrosteans, these species also have spiracles, but these are non-functioning in gars. They have ossified (bony) skeletons, but this is still partially cartilaginous in bowfins. They have the ganoid scales, also like chondrosteans.
50
What are the three features of Holosteans?
Spiracles present (but not linked to outside in gars)
Ossified (remains of cartilaginous skeleton in bowfins).
Ganoid scales, 3 layers: Enamel, Vascular bone and Lamella bone.
51
What are the two lineages of Holosteans?
There are two main lineages, but these are actually quite distantly related.
The first is the Amiiformes, which only has one living species, the bowfin (Amia calva) that lives in North American freshwaters.
The second is the Lepisosteiformes (Lepisosteidae), or the freshwater gars, which has 7 living species, again mostly in North American freshwaters.
52
What does a phylogenetic tree tell us about the diversity of Teleosts?
Now let’s look at the diversity of teleosts. Here is a phylogenetic tree based on using nuclear DNA sequences, and fossil calibrations.
This tree has confirmed origins of the teleosts date to 300Ma, and have resolved the complex relationships within the group.
Specifically, this tree has identified five major lineages within the teleosts, the Eopomorpha, Osteoglossiformes, Otocephala, Protacanthopterygii and the Neoteleostei. And next we will look briefly at those five major groups.
53
What are the Elopomorpha?
they have two morphologically divergent groups of species, which contains the tarpons and eels, note the shared leptocephali larvae. Laterally compressed almost see through lava, which is unique to this group.
54
What are the Osteoglossoformes?
(bony tongues), which contains the mormyrids, arowana, featherfin knifefishes. Morphologically diverse.
55
What are Otocephala?
which is a very morphologically diverse group of herrings, catfishes, knifefishes, cyprinids. This is a newly defined group based on molecular evidence. Most of these taxa (except the herrings) possess a Weberian apparatus (an anatomical structure connecting the swimbladder to the auditory system),
56
What are Protacanthopterygii?
also a diverse group, but share many characters, including an adipose fin, and they lack a protractible upper jaw. Includes the barreleyes, such as Macropinna.
57
What are the Neoteleostei?
A remarkably diverse group, sharing traits such as the pharyngeal retractor muscle. Includes seahorses etc. range of different habitats.
58
What does evidence suggest about marine and freshwater environments?
Evidence suggests that there have been many evolutionary transitions between marine and freshwater environments (Betancur-R et al. 2015, Ecology Letters). There are also many true euryhaline species (i.e. can live within a wide range of salinities). Maps on the transition between marine and freshwater environments during the evolutionary history of the group. Most likely that the ancestry hosts were marine, but they have repeatedly colonised freshwater environments during their evolutionary history.
59
The teleosts are characterised by the following traits:
High species richness in many teleost lineages, coupled with morphological, ecological and behavioural diversity. Depth, habitat and colour differences among sister species are commonplace.
High species richness in many teleost lineages, with some families within the group possessing 200+ species. Examples of families with high species richness include the freshwater cichlid fishes (=Cichlidae; 1800+ species) and the marine lanternfishes (=Myctophidae; 300+ species).
Sister species commonly differ in depth, substrate, diet and body colouration. Together these patterns suggest that the rapid speciation observed in many teleost lineages has been promoted by both divergent natural (=ecological) selection, and sexual selection.
Here is an example of two pupfishes from a lake in the Bahamas. These are sister species, but one feeds in scale, while the other feeds of molluscs. To study how new species evolve, we often study teleost species pairs like this.
Teleosts have commercial and societal importance. They are extensively used in scientific research, particularly medical research. To understand the function of a vertebrate gene, it is commonly manipulated in zebrafish to determine the outcome. It has been chosen because it has a very fast lifecycle (3 months) and large eggs that are easily harvested.
Finally, teleosts are of considerable commercial importance as a food, both directly for humans, but also indirectly for livestock. Wild (capture) fisheries are now maximally exploited globally, so there is considerable investment in aquaculture, in cages in the sea, cages in lakes, and in ponds.
60
What are the major marine species?
Major marine species: Peruvian anchovy, Alaska pollock, Skipjack tuna etc.
61
What is the swim bladder?
An important feature that sets teleosts apart from other fishes
Can adjust the relative density of the teleost, determining buoyancy.
62
What do Teleost skeletons have?
Teleost skeletons can have a lot of heavily calcified bone - in other words, in addition to cartilage their skeleton contains a lot of calcium phosphate. This makes teleosts relatively heavy in comparison to species with cartilaginous skeletons. Swim Bladders help fish to achieve neutral buoyancy, they have evolved.
63
What essentially are swim bladders?
Swim Bladders are essentially gas bladders, that are situated towards the dorsal surface of the abdominal cavity, and the gas within them can be adjusted, gas can be pumped into the bladder and that will provide more buoyancy but it is also possible for gas to be removed from the bladder, providing less buoyancy. The fish will adjust the content of their swim bladder depending on what the need is of that particular point in time.
64
How does the swimbladder function?
Oxygen-rich blood flows from the aorta (red) through the swimbladder organ capillaries, into the veins (blue).
To pump gas into the bladder, blood flows through the vessels of rete mirabile (a network of capillaries), and into the gas gland, where gas to enters the bladder. The gas gland excretes lactic acid, makes carbon dioxide, causing haemoglobin to lose oxygen (the so-called root effect), which diffuses into the bladder.
65
What does the rete mirabile also do?
However, the rete mirabile also acts like a pump. As it flows back through the rete mirabile from gas gland, excess oxygen and carbon dioxide are absorbed into the neighbouring vessels going into the gas gland, generating pressure, allowing high pressures to develop in the gas bladder. This is how high pressure develops in the gas bladder.
66
How is gas removed from the bladder?
To remove gas from the bladder, blood flows through the ovale (oval window) and the rate of oxygen removal is related to the flow of blood controlled by sphincter muscles.
67
Why does the swim bladder need layers?
To hold gas a high pressure, the swim bladder needs to be both strong and elastic. The outer layer is made of guanine crystals and elastic fibres, while the inner layer is collagen, but also smooth muscle and nerves are present.
68
What is in the outer later of the swim bladder?
guanine crystals and elastic fibres
69
What is in the inner layer of the swim bladder?
Collagen and smooth muscle and nerves.
70
The ability of a swim bladder to function is governed by
the density of the surrounding water.
Here a 1kg teleost fish, without a swimbladder, will sink in freshwater, as it has a higher density (~1.08) than freshwater (~1), and therefore a volume of 1/1.08 = 0.926 litres.
Since that fish would has a volume of 0.926l (=926ml) it would need 74ml of gas to be buoyant.
The same 1kg teleost fish, without a swimbladder, will also sink in seawater, as it has a density (~1.08) than seawater (~1.026), and therefore a volume of 1.026/1.08 = 0.950 litres.
Since that fish would has a volume of 0.950l (=950ml) it would need 50ml of gas to be buoyant.
It is possible to work out how much gas is needed for buoyancy in any particular aquatic environment and second because seawater is denser it requires less gas than freshwater to make a fish achieve neutral buoyancy.
71
Gas-filled swim bladder vs. oils.
The buoyancy provided by air is much greater than that of oils.
A 1kg shark, in seawater needs, 294ml squalene for neutral buoyancy (compared with 49 ml of gas).
In freshwater it would need 444ml squalene (compared with 74 ml of gas).
This is one of reasons that sharks are rare in freshwaters, and are rare in very deep waters because of the amount of squalene that is needed to maintain buoyancy. One of the few deep diving sharks in the basking shark, which has extremely large oil-packed livers to allow it to maintain neutral buoyancy. Those livers were so rich in oils they were historically very valuable for streetlighting.
72
What are the two forms swimbladders come in?
Swimbladders come in two forms open to the gut (physostomus), or closed (physoclistus).
73
What can't species with closed swim bladders do?
Species with closed swim bladders are unable to rapidly change depth.
74
What can species with open swim bladder do?
Fast moving species that regularly change depth often have open swim bladders.
75
What are the benefits of buoyancy?
Pros -
| Are energetically efficient, reduce drag
76
What are the cons of buoyancy?
Cons-
Not ‘Free’
Do not allow rapid changes in depth
77
What is the major benefit of swim bladders?
The major benefit of swimbladders is that they enable easy swimming, but they can be energetically costly, and rapid depth changes are not possible. In some species with closed swim bladders, rapid ascent after capture expands the gas inside, and swimbladder is forced through the mouth.
78
What have some open water species lost?
Some species groups that no longer need to swim in the open water have lost the swimbladder, for example gobies and clingfish.
Swimbladders needed for fish to achieve neutral buoyancy.
Not needed in benthic species or those in turbulent waters.
79
What modifications do Myctophids (‘lanternfishes’)
| have to their swimbladders?
Other species, such as lanternfishes, that undertake very large migrations on a daily basis use a mixture of wax esters and gas in their swimbladders.
Migrate vertically 800m up and down in a day
No gas in bladder of some species- wax esters needed.
80
What are some other modifications to the swim bladder function?
Swim bladders have also been co-opted for other purposes, such as hearing. In the Otocephala (cyprinids, catfishes, characins etc.), there is a structure called the Weberian ossicles linking the swim bladder to the inner ear sensory cells (in the saccule).
Swim bladder have also become modified for different functions other than buoyancy. Sound reception, via Weberian ossicles.
81
How does the Atlantic croaker use the swimbladder?
Meanwhile other species, such as the Atlantic croaker, use the swimbladder for making sound. Here sound is produced using the swimbladder as a drum, and “sonic muscles” function as drumsticks to create vibration.
82
Name the properties of the teleost skeleton.
--Cartilage and calcium phosphate
---Bone can withstand higher force
---Intricate skeleton allows freedom of muscle arrangement
--Now let’s briefly look at the teleost fish skeleton, which is typically heavily ossified. Bone can support appreciably more longitudinal force (i.e. more resistance to buckling).
This is a perch, look at how extensive and complex this ossification has become. This complex skeleton allows more freedom of design in terms of how muscles are attached and arranged.
Here is a better representation of the three dimensional shape of the muscles and the 3D structure of the white myotomal arrangement. In this section you can see the blocks of white muscle above and below the central vertebral axis (familiar as “flakes” of fish, when cooked).
83
In addition to longitudinal support, the vertebrae also support the
the flank muscles via ribs. Those ribs can be external to muscles, or buried deep within them.
84
How are the teleost muscles arranged and what are the types?
Muscle arranged in efficient blocks- myotomes
| Two types; red and white
85
What does the teleost skeleton allow?
The skeleton allows muscle to be arranged in efficient muscle blocks (myotomes) is very complex in teleosts and leads to high forces being developed for swimming/locomotion.
86
What is the function of the red muscles in the teleost skeleton?
Red muscle contains more mitochondria than white muscle, hence the colour. Red muscle is restricted to a thin sheet of muscle just under the skin and typically is restricted to a lateral band of muscle along the flank (like a triangle in cross section). It is used for continuous aerobic swimming.
87
What is the function of the white muscles in the teleost skeleton?
The white muscle fibres lie closer to the centre (median plane) than the red ones, and they run helically rather than parallel to the long axis of the body. This 3D helical structure of the white muscle makes teleosts able to efficiently generate thrust in the water, such as in giant trevally.
88
if you were to dissect a fish through the abdominal cavity, what would you see?
In summary, if you were to dissect a fish through the abdominal cavity (which would normally have intestines, gonads, and various organs in), you would see the vertebra, neural arch protecting the dorsal nerve cord and extending dorsally with the neural spine towards the dorsal fin. Also you can see the white muscle divided into that on the dorsal side (epiaxial muscle) and that on the ventral side (hypaxial). Red muscles will be on triangles, along the flanks.
89
Fishes typically move using
s-waves travel down body displacing water to generate thrust (overcoming the drag).
90
What are the four types of teleost locomotion?
anguilliform
thunniform
Carangiform
Subearangiform
91
What are some examples of the teleost locomotion?
There are extremes; from almost full lateral movement of eels (anguilliform) to the swimming of tunas where movement is concentrated exclusively in the tail (thunniform).
In some species, such as the boxfishes, the body is a rigid box of dermal bone (bone in or close to the skin), so these species swims with small movements of their fins and tail and almost no lateral movement of the body.
Plus, Ostraciiform locomotion, where only tail fin oscillates, e.g Boxfish
Boxfish- lots of dermal bone (in skin for protection)- Locomotion exclusively with fins.
92
Sharks and some of the more primitive fishes have a
heterocercal tail
93
What are the benefits of a heterocercal tail?
require this to produce lift when swimming to counteract shink.
94
Why does the teleost not need a tail?
Because the teleost is more or less neutrally buoyant, largely because of the swim bladder, it does not need a tail to be involved in the production of lift to counteract sinking.
95
What types of tails do teleosts have?
in most teleosts and most have a symmetrical, or homocercal tails that are more efficient at producing propulsive force (not lift).
This is accompanied by a change in the position of the vertebral axis.
96
Since the first Gnathostomes evolved there has been a trend towards
two sets of paired fins: the pelvic fins (lower body) and the pectoral fins (top of body).
97
The vertebrae also directly support the
median fins
98
What are the median fins ?
that is the fins on the midline of the fish: the dorsal fin (or fins), the adipose fin (in some teleosts), the anal fin (always immediately posterior to the anus), and the caudal (tail) fin.
99
Where is the anal fin?
(always immediately posterior to the anus),
100
Median fins-
dorsal, anal, caudal, adipose (in some teleosts).
101
Paired fins-
pelvic and pectorals
102
Dorsal fin can be
split in two but it is still classed as one dorsal fin. But some fish have an additional fin called the adipose fin.
103
What do some species have in relation to their fins?
Some species have pelvic fins placed ‘well back’ (i.e. caudally, towards the tail) on their bodies (e.g. herrings and salmonids).
104
What are the benefits of the pelvic fins being placed well back?
These species tend to be more active and they tend to spend not so much time hovering in the water column. In contrast many teleosts such as the perch, have pelvic fins much further forward, almost under the pectoral fins. This accommodates different life histories. Some species groups lost pelvics altogether.
105
What does the position of the pelvic fin relate to?
Position of pelvic fins related to behaviour. Less motile= further forward. Some species have lost pelvic fins altogether, e.g. pufferfish.
106
What are features of the teleost fin muscles?
Teleost fin muscles are mostly internal and nearly all neatly buried inside the body, which is more streamlined as a result.
107
What is one thing that is responsible for the teleost success?
Fin flexibility and efficiency is probably one reason for the huge success of the teleosts. Unlike elasmobranch fins, which are fixed, teleost fins can be folded and unfolded like a fan and used for generation of exact forces for precise movements, and can be quickly deployed and with fine control.
108
What do teleost fins consist of?
Teleost fins consist of widely spaced, mobile rays known as lepidotrichia, or ‘fin rays’, joined by very thin webs of tissue.
109
What is fin control?
fins folded like a fan and used for generation of exact forces for precise movements.
Internal muscles- streamlined as a result.
110
How many axes of rotational movement do fish have and what are they?
Three
Roll – body “rolling” from side to side.
Pitch - Moving up or down
Yaw - Moving to the right or left
111
How do all the fins benefit the teleost?
The caudal fin provides thrust, and control the fish’s direction (yaw). Pectorals act mostly as rudders and hydroplanes to control yaw and pitch. They also act as very important brakes by causing drag. Pelvic fins mostly control pitch. Dorsal/anal fins control roll.
112
How does the presence of the swim bladder benefit the fins and tail?
Again, because of the presence of the swim bladder, the fins and tail of teleost are free from any need to generate lift. This has allowed the fins of teleosts to undergo diversification in function.
113
What is one of the functions of the fins in teleost?
One function is in sexual selection. This can operate either through females preferring males with the brightest or most elaborate ornaments (direct female choice), or through males competing for access to the females who mate with the winner regardless of their characteristics (indirect female choice). Typically, where you see sexual dimorphism (male-female differences in phenotype), and the male is more showy, then there will be male-male competition facilitating indirect mate choice.
114
Summarise the purpose of the fins in the teleosts?
Fins serve an important function in swimming
But the presence of the swim bladder means the fins are free from any need to generate lift.
Fins have undergone a huge radiation in function, including sexual selection.
115
What are fins also used for?
feeding
116
What is an example of feeding with fins?
Here, for instance, is an anglerfish (also known as monkfish at the fishmongers). In this species the first ray of the dorsal fin has been modified to produce a fishing rod, complete with a lure or esca, which is waved around to attract prey. Note that the edge of the pectoral fins have also got a serrated appearance, and colours match the benthos. This helps in camouflage.
117
What are some features of deep sea anglerfish?
Deep sea (i.e. bathypelagic 2000-10000m) anglerfish are surprising diverse for a group specialising in deep water habitats. The lure is bioluminescent - in other words the esca glows in the dark to attract prey. Between species the lure can vary considerably and is often associated with a concentration of sensory organs. This light is generated by symbiotic bacteria.
118
What are features of Flying fish of the family Exocoetidae?
Flying fish of the genus Exocoetidae have greatly enlarged pectoral fins, giving them “wings”. These fish glide rather than flap their wings and fly like a bird, but can cover 100s of metres in the air, often using the updraft of air in front of advancing waves, enabling them to escape from underwater predators.
119
Although the _______ cannot really fly (they glide) there is one fish, the _______ _______ that actually can (technically)
marine flying fish
| freshwater hatchetfish
120
How can the freshwater hatchetfish fly?
It can develop lift by flapping its pectoral fins (powered flight). For this it has very well-developed muscles in a keel (enlarged sternal region), an arrangement similar to well-developed breast muscles of birds.
121
______ have “legs” that are ______ ______from the ______ fins
Gurnards
modified rays
pectoral
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How do Gurnards use their modified rays?
It uses these to walk around on the sea floor, not so much supporting its weight, but more for sensing the environment to locate food. To help in this they are covered in chemoreceptors allowing the gurnard to sense hidden prey by taste as it moves around.
First three rays if pectoral fin detached and gurnard ‘walks’ on seafloor “legs” covered in chemoreceptors to locate food.
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What are features of Mudskippers- family Oxudercinae?
Highly modified pectoral fins to bear weight and allow movement on land.
But there are fish that use fins for supporting their weight, such as the mudskippers. They can move on land by using pectoral fins which are unusually strong.
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What are features of Gobies- family Gobiidae?
Fused pelvic fins that form a disc-shaped sucker- functions as an anchor in high flow environments.
There are also cases where fins are modified to enable life in fast-moving water. A characteristic feature of gobies is that the pelvic fin has become modified to help attach the fish to smooth substrates (e.g. rocks, macrophytes). The two pelvic fins are more or less fused in the midline of the body and form a sucker.
125
How how has the teleost gill become extremely efficient?
The teleost gill is extremely efficient as a device for collecting oxygen and for getting rid of carbon dioxide. It manages this through a counter current for efficient gas exchange.
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Why are the gills efficient?
Water (in blue on the figure) floods over the gills and through the secondary lamellae. Within the secondary lamellae the blood (sourced from within vessels the gill arches), runs in the opposite direction to the water, for maximum efficiency in gas exchange. This is a counter-current system.
This counter current flow maintains a concentration gradient down which O2 flows over the whole length of the capillary. Because of counter current exchange the lamellae extract about 85% of the O2 dissolved in the water. In contrast if blood flowed in the same direction as the water, the concentration gradient would become less and less steep in the direction of flow. At most the gills could pick up only 50% of the O2 in this arrangement.
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What are gills used for?
Gills are used for osmoregulation. Today teleosts occupy waters of widely varying salinity Some live in “pure” freshwater in which dissolved salts are as low as 0.01 parts per thousand. In comparison, most lakes have concentrations around 1ppt. Other teleosts live in water at the other extreme, in very salty lakes up to 100 ppt. The ocean is 34-36 ppt.
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What level is teleost tissue osmolality?
Despite this range of habitats, teleost tissue osmolality is usually around 300 mOsm/kg, roughly equivalent to 10 ppt, but often a bit higher in saltwater fish and a bit lower in freshwater species. These values are similar to mammals (humans have a tissue osmolality around 273 mOsm/kg).
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There is often a great difference between _____ and ____ _____concentrations, which is solved by pumping ____ and ____.
internal
external ionic
water and ions
130
Why do freshwater fish constantly gain water?
Freshwater fish constantly gain water because they are hypertonic to surroundings. They have:
- low skin permeability to ions and water by having scales, and mucus.
- they produce copious, dilute urine
- they actively take up salts via the gills and, to a lesser extent, in the kidney
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Why do sea water fish lose water?
In contrast, in sea water fish are constantly losing water because they are hypotonic compared with surroundings. In this respect they have the same sort of problems as animals living in deserts. To combat water loss they have:
- low skin permeability to ions and water (as in freshwater case)
- produce little urine
- drink sea water to obtain water
- excrete salts across gills, using the same ion pumps as freshwater fish, in reverse.
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What is the lateral line in teleosts?
The lateral line system of teleosts is a mechanoreceptive system that detects water movement. The clearest manifestation of the lateral line system is along the side of the body (the “trunk canal”), but this is only part of it. Here the trunk canal can be seen in an arowana (top left), butterflyfish (lower left), arapaima (top right) and Atlantic cod (bottom right).
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What does the sensory unit within the lateral line consist of?
The sensory unit within the lateral line system is the neuromast (bottom right). This consists of a set of sensory hairs (ciliary bundles), each connected to a nerve fibre. The hairs are surrounded by a jelly-like cupula. Bending of the cupula due to a change in water flow transmits a signal to the nerve fibres.
Thus, stimulation of the hair cells in lateral lines and inner ears involves the same basic mechanisms that all vertebrates, including humans, use in hearing.
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What can the neuromasts do?
The neuromasts can be free-standing on the outside of the body (superficial neuromasts) or can be inside subdermal fluid-filled canals (canal neuromasts). Superficial neuromasts can be anywhere on the body, but canal neuromasts are found only in the main trunk canal, and set of canals in the head region. The canals are open to the water surrounding the fish via a series of pores (these are the circles on the image of the fish here). The pores link the outside environment to the fluid inside the lateral line canals where changes in the flow field (water movement) around the fish are detected.
It is thought that the superficial neuromasts are able to best detect “environmental flow” changes in the boundary layer of the fish, while canal neuromasts are able to best detect high frequency pulses that may be associated with prey stimuli, for example invertebrates moving in sand.
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Where do species differ?
Species differ substantially in lateral line structure. Deep water fishes that rely heavily on non-visual senses often have expanded lateral line canal systems (and their canal pores are readily visible, such as in this deep sea snailfish).
Even closely related species can differ in lateral line structures. Here are microCT scans of the mandibles of four species from the Lake Malawi cichlid fish radiation. They are viewed from below, and the canal pores differ extensively in size. The species on the left with the largest pores (indicated by the white lines) feeds on benthic invertebrates at night, while other species feed in the day on plankton or algae- so they don't need such large lateral line canal systems to be able to detect any prey.
136
What do jaw modifications allow?
wide variety of feeding modes
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How is the jaw arranged in ancient non-teleost ray-finned fish lineages?
In many of the ancient non-teleost ray-finned fish lineages (such as the gars) the premaxilla and maxilla (upper jaw bones) are fused, meaning that the jaw is similar to ancestral gnathostomes, and it is a simple opening and closing device.
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What is the problem with this jaw arrangement?
The problem with this arrangement is that it is not particularly easily modified for special feeding methods. Essentially, this is an arrangement that is fine for ram feeding (where the predator opens the mouth and moves the body forward), but not suction feeding (where the predator opens the mouth and creates suction bringing the prey in).
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How is the jaw arranged in teleosts?
In teleosts the maxilla and premaxilla can be decoupled (a process called jaw kinesis). This modification makes it possible for teleosts to protrude their jaws outwards from the mouth.
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What is jaw kinesis?
The jaw kinesis essentially a protrusible jaw, and the speed of jaw opening creates a suction force that permits faster attacks.
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What are the functional advantages of jaw protrusion?
Prey can be sucked in from far away
Increases attack velocity by up to 40%
Increased prey handling and swallowing ability
It has been shown that typically jaw kinesis allows further reach (25-50% of the head length), increases attack velocity by up to 40%, and increases the ability of fish to handle and swallow prey (they have a larger oral cavity).
This coupling and decoupling of the maxilla and premaxilla has taken place many times during the evolutionary history of fishes.
Even closely related species can differ in the amount of kinesis, depending on their favoured prey. It is possible to use information on the extent of jaw kinesis to predict diet.
For example, benthic invertebrate eaters often have extensive kinesis, while species that bite algae from rocks have much less.
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What is another feature of teleost jaws?
Pharyngeal jaws, the second set of jaws.
Another feature of many teleosts is the presence of a pharyngeal jaw, which are modified gill arches. These are a second set of jaws in the pharynx that operate completely independently of the oral jaws.
Although these are present in an extremely large number of species groups, they have become particularly important in some.
An example of this is the cichlids. Here the oral jaws are used to seizing the prey, but the pharyngeal jaws are used for processing it (grinding).
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What is linked to the diet of teleosts?
The shape, weight and tooth structure of the lower pharyngeal jaw is very closely linked to the diet. This is now well known from systems such as Lake Tanganyika.
Here algae scrapers have jaws with large surface areas and fine teeth, zoobenthivores have jaws with large surface areas and large teeth for crushing prey, and zooplanktivores/fish eaters have small jaws with small teeth. It is thought that relatively small narrow teeth because not much processing is actually necessary to get the prey into a digestible state.
It has been hypothesised that the evolution of pharyngeal jaws is one of the reasons why teleost fish (and particularly cichlids) have radiated so extensively, as it enables them to occupy a wide range of ecological niches.
A spectacular pharyngeal jaw system is present in moray eels. They have a “raptorial” jaw, which can actively be thrust forward to grab prey within the mouth (Mehta & Wainwright 2007, Nature).
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What are some examples that show that the size and shape of teeth are closely related to diet?
The size and shape of teeth are also closely related to diet. Contrast the sharp narrow teeth of the needlefish, with sharp wide teeth of the moray eel, and the blunt teeth of the sheepshead.
“Viliform” teeth are elongate, needlelike (e.g. viperfish), and handle weakly muscled deep sea fish.
“Blade-like” are triangular and used for slicing prey (e.g. piranhas).
“Caniniform” teeth are fang-like (e.g. snapper), and used for grabbing active muscled prey.
“Cardiform” teeth are numerous, small, pointed and sand-paperlike. They tend to have only a small role in the prey handling, keeping them in place, and are found in ram-feeders such as billfish.
“Molariform” teeth are flattened and used for crushing and grinding hard prey.
145
A simplistic way of classifying the teleosts is into the
“oral manipulators”, the “ram feeders” and the “suction feeders”.
146
What are-
“oral manipulators”,
“ram feeders”
“suction feeders”.
Oral manipulators can use teeth to scrape and bite their prey. Ram feeders can chase down prey and/or filter feed (some species have modified gill rakers to filter zooplankton e.g. sardines and herrings). Suction feeders help for slow moving species that need the extra reach.
147
What can body shape, head shape and dentition help determine?
Collectively, it is possible to use information on body shape, head shape and dentition to determine how fish live their lives and their preferred prey. Here is an example from the fish group called the Terapontoidei, which are closely related but very ecologically divergent.
Each species is one coloured point, and the closer points are species with the most similar morphology. You can see that species with a more similar morphology tend to have a more similar diet.
And there are many novel and bizarre feeding strategies and associated morphologies in fishes, most of which are not well understood from biomechanics perspectives. Here is an example, from the archerfish, a species from the swamps and rivers of South America.
148
What are some reproductive strategies of the teleosts?
There is a vast range of reproductive strategies amongst the teleosts. Most are dioecious (two sexes), oviparous (egg laying), with external fertilisation (eggs and sperm are cast into the water) and have very high fecundity (i.e. produce large numbers of eggs). However, there are many variations within the bony fishes.
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What is broadcast spawning?
There are approximately 12,000 species of marine teleosts, and in ca. 9000 of these eggs float. This is to allow the eggs to disperse in surface waters.
In most marine teleosts, spawning takes place in a “spawning ground”; and the eggs and larvae then drift to another area known as a “nursery ground” where they metamorphose into miniature versions of the adults. As they grow, they will move to adult feeding grounds. After a growth phase, they will migrate back to the spawning grounds.
This is the pattern in most commercial species and emphasises the importance of the preservation of many different habitats if fish stocks are to survive.
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What are some examples of Broadcast spawning?
An example of this is the Atlantic cod (Gadus morhua). This species is a marine broadcast spawner with strictly seasonal spawning. During spring adults aggregate on the spawning grounds, where they lay eggs that float to the surface waters. Eggs hatch into larvae, and those larvae then metamorphose as they settle on the nursery grounds.
An average adult female cod produces an average of around 9 million eggs every time it spawns, and since it spawns once a year and lives for about 20 yrs (if not fished or otherwise killed), this means that in its lifetime a female cod can produce about 180 million eggs.
Since a female cod only needs to replace itself and one mate in the course of its life for population stability, obviously most of these eggs go to waste. In fact Darwin cited the case of the cod in “On the Origin of Species” as evidence of the waste of reproductive potential.
151
What is brood guarder?
In many species, especially freshwater species, floating eggs would be useless and, instead, the eggs are adhesive and stick to sea or river bed. Sometimes elaborate nests are made.
An example of this is from the three-spine stickleback (Gasterosteus aculeatus). Here the males build a nest, court females, and guard the eggs until the fry until they are large enough to look after themselves.
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What are aspects to the livebearing guppies?
Viviparity: live-bearing (transfer nutrients from mother to embryo)
Internal fertilisation with gonopodium = modified anal fin rays.
Gonopodial thrusting- Male attempts to mate with female.
Female mate choice and sneaky matings.
Although most teleosts use external fertilisation, some have evolved methods of internal fertilisation and viviparity (live bearing, with transfer of nutrients from the mother) or ovoviviparity (live bearing but embryos depend on yolk whilst within the mother). For example, guppies (Poecilia reticulata) have internal fertilisation and are viviparous.
Males use a modified ray of the anal fin known as the gonopodium to transfer sperm. Internal fertilisation is associated with mate choice and guppies have elaborate sexual signalling involving movement and colour displays.
Females can select the best quality mates. However, males also very frequently attempt ‘sneaky matings’ which avoid the female’s selective control.
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What are the Anableps anableps (Four-eyed fish)?
Gonopodium- asymmetry
Dextral and synestral males/females.
A fish closely related to the guppy is the four-eyed fish (Anableps anableps). This has unusual ocular optics and appears to have four eyes, though it actually has two, each with a part looking above and a part looking below water).
It also uses a gonopodium to transfer sperm. In this species the gonopodium is asymmetrical and there are right-handed and left-handed males. Similarly, the female reproductive tract has handedness, and so a right handed male must find a right handed female to mate (and vice versa).
154
What is “sequential hermaphroditism”?
Most teleosts remain the same sex throughout their lives. However, some start as one sex and, at some point in their lives, change sex. This is “sequential hermaphroditism”.
155
What is Protogynous (‘first female’) hermaphroditism?
Protogynous (‘first female’) hermaphroditism is a version of this where the sex changes from female to male, and is known in many tropical wrasses. They live in groups of several females and one dominant male. When the male dies the largest female in the harem changes sex to become the new male for the harem. Within a week the transformed individual is producing sperm instead of eggs.
This mechanism appears to be favoured by selection in those situations where individual reproductive output can be maximised first by being female (and having the opportunity to breed) and then males (and having the opportunity to breed).
If there was a genetic controlled 50:50 sex ratio, most males would never get to breed.
156
What is Protandrous (‘first male’) hermaphroditism?
Protandrous (‘first male’) hermaphroditism is version of this where the sex changes from male to female, and is known from several species, such as clownfish. Here, the clownfish need an anemone to breed (which is a limited resource), and without it, they cannot breed. There is only enough room for one female per anemone, and the males are smaller subordinates.
This mechanism appears to be favoured by selection much less often. It seems that individuals may maximise their reproductive output first by being male (and having the opportunity to breed) and then females (and having the opportunity to breed).
If there was a genetic controlled 50:50 sex ratio, most females would never get to breed as there are not enough anemones to go around.
157
What is the true hermaphrodite?
Both ovaries and testes are active in the same individual.
E.g. a tripod fish stands on two elongate pelvic fin rays and on a long caudal fin ray.
True hermaphrodites are unusual in teleosts, but relatively common in deep-sea fishes.
158
A few teleosts are
true simultaneous hermaphrodites; so simultaneously male and female and produce both eggs and sperm at the same time. This strategy is unusual but is most common in deep-sea fishes because in the deep-sea the densities of fish are so low that animals have difficulty finding mates simply due to low encounter rates.
159
What does hermaphroditism ensure?
Hermaphroditism ensures it is always possible to mate when a conspecifics is encountered, and indeed they can mate with themselves if no other options are available.
An example of a hermaphrodite species is the tripod fish (Bathypterois dubius), which stands on two elongate pelvic fin rays and on a long caudal fin ray. It faces into the current and holds its long pectoral fins in the water to sense the potential prey.
160
What are Self-fertilising hermaphrodites?
To our knowledge, self-fertilisation tends to be rare in hermaphrodite bony fish, but there is a species that can regularly self-fertilise, the mangrove killifish Kryptolebias marmoratus. It was recently discovered that this killifish can spend long periods away from rivers – one individual was recorded living for 66 days in logs, burrows and leaf litter. It is possible that the breeding strategy is linked to being able to survive in habitats that fluctuate in water availability seasonally.
161
What is Parthenogenesis?
Another rare mating system is found in the Amazon molly (Poecilia formosa) from Mexico. In this species nearly all individuals are female, there is no sex and reproduction is only by parthenogenesis.
In parthenogenesis the unfertilised egg develops into an embryo, and normally we associate parthenogenesis with animals like aphids.
Female Poecilia formosa still needs to copulate with a male in order to start the parthenogenetic process. This is a problem as there are no males of the species, so they do it with another species of molly. The borrowed sperm penetrates the egg normally, and this stimulates egg development but no nuclear fusion takes place. This is called “pseudofertilization”.
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What is Reproductive frequency in teleosts?
Iteroparity- Reproductive several times during life e.g. most fish.
Semelparity- Breed once (then die)- “Big bang” reproduction. E.g. Pacific salmon, eels.
The frequency of breeding in teleosts is varied. Most teleosts reproduce a number of times in their lives and this is known as iteroparity. Some, however, do it only once in their lives, this is known as semelparity or ‘big bang’ reproduction, after which they die.
Perhaps the most famous examples of semelparous species are the salmon, that run up rivers to breed, and afterwards die.
163
What type of migrations do teleosts follow?
Many teleosts also undergo complex migrations, nearly always related to movement between feeding grounds and breeding grounds. Selection is believed to favour migrations in those cases where juvenile survivorship is enhanced when adults move to breeding grounds. Typically, the adult and juvenile ecological niches are very different in migratory species.
Many species have spawning seasonality
Often associated with migrations to spawning sites
Sometimes over long distance
164
How are fish migrations classified and what are some examples?
Fish migrations are classified depending on the habitat transitions.
Anadromous species migrate from the sea to freshwaters.
Potadromous species migrate entirely in freshwaters, for example between lakes and surrounding rivers.
Oceanodromous species migrate entirely in the marine environment, for example from the open ocean to coastal lagoons.
Catadromous species migrate from freshwaters to the sea.
The European eel is a classic example of a catadromous species with a complex life history. Adult European eels (Anguilla anguilla) live in European freshwaters, but spawn in the Sargasso sea in the mid-Atlantic. We know this because the small larvae (10mm long) are only found in that region. Larger larvae are known from further east, suggesting they follow oceanic currents towards European coastal waters.
165
What are elvers?
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This image (fish not to scale!) shows the transition. In the Sargasso Sea the fertilised eggs rise to the surface and hatch into so called leptocephalus larvae. These leaf-like larvae are only found in eels and their relatives (Elopiformes).
When they arrive at the European coast they enter estuaries and metamorphose into glass elvers.
```
The transparent glass elvers then metamorphose into pigmented elvers as they enter freshwaters.
The eels then stay in fresh water for around 10 years as “yellow eels”. This is the animal’s main growth phase.
When they are ready to spawn, they then migrate down river and metamorphose from “yellow eels” to “silver eels”.
During this transition “yellow eels” to “silver eels” they obtain enlarged eyes (like a deep-sea fish), silver skin (also like a deep-sea fish), and regressed gut (because they don’t feed as silver eels)
They also have very very enlarged gonads. In this form they migrate back across the Atlantic, taking several months, to the reach the Sargasso Sea where they breed and die.
166
What are lobe fins?
```
There are three living groups of the lobefins, otherwise known as the Sarcopterygians.
These are the subclass Actinista (extant groups = coelacanths), the order Dipnoi (extant group = lungfishes) and the superclass Tetrapoda (amphibians, reptiles, birds, mammals).
```
Recently, the phylogenetic relationships of these three groups was confirmed with the sequencing of the first lungfish genome (the Australian lungfish Neoceratodus forsteri). We can be confident that lungfish are the immediate sister group to tetrapods, to the exclusion of the coelacanths (represented here by the African coelacanth Latimeria chalumnae)
167
What are Coelacanths?
Here we will focus first on the coelacanths (which are actually part of big group of fossilised fish called the Actinistia), but coelacanths are the only living representatives of this group.
Living coelacanths are large fish weighing (60kg+) with fleshy fins.
On these fins the muscles are outside the body surrounding the bony structures, similar to tetrapod load-bearing limbs.
Notably coelacanths have pectoral limb bones that are thought to homologous to tetrapod limb bones, specifically the radials (which are finger like bones of early tetrapods).
7) Coelacanths have an extensive fossil record dating back to ~400Ma (million years ago), the Devonian period. They have evolved substantially over this time, and most genera are narrowly restricted to time periods.
The fossil record stops at ~70Ma, and it was thought that the group was extinct.
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What changed when the first living coelacanth was found?
In 1938 that situation changed when the first living coelacanth was found off the coast of South Africa. This species was described as Latimeria chalumnae.
Since then many individuals of this species have been caught off the Comores Islands, Madagascar and the coasts of Mozambique, Tanzania and Kenya. They live in deep water (>100m) around rocky habitats. They are still very rare, and they are recognised as critically endangered.
In 1997 a second coelacanth was discovered in Indonesia. It seems to live at depths around 80-200m. This species has been described as Latimeria menadoensis.
Coelacanths are considered as “living fossils”, as they are morphologically similar today as they appear in the fossil record.
Here is a film of the African coelacanth in its natural deep water rocky habitat.
This image shows the distribution of the two living coelacanths.
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What do molecular clocks tell us about coelacanth populations?
Molecular clock analyses suggest they diverged 30-40 million years ago. It is plausible that other coelacanth populations exist around deep ocean ridges of the Indian Ocean.
We know very little about their behaviour, but we do know they give birth to live young. Genotyping broods of these offspring has shown that broods have single male paternity, so clearly females are choosy about whom they mate with (Lampert et al. 2013 Nature Communications 4, 2488).
The low reproductive potential and rarity make these fish one of the most endangered group of organisms in the world.
170
What are the Dipnoi?
lungfishes, which all belong to the monophyletic order Dipnoi.
They also first appear in Devonian rocks, and so like coelacanths date back around 400 million years.
171
How are lungfishes characterised?
They are characterised by powerful jaws and crushing teeth. Lungfish have paired fins quite unlike those of other bony fish, with a thick central lobe containing bone and muscle and a thin blade supporting fin rays.
Lungfishes have gills and lungs, but the reliance on gills varies between species. The lungs in lungfishes are filled by gulping air at the surface and rates of ventilation vary depending on how useful gills are, which varies between the species and the habitats they are in.
Lungs are not powered by ribs (as in tetrapods). Don’t get the impression that lungs are used by lungfishes to make excursions onto land. They evolved to allow lungfishes to live in stagnant water which has a very low partial pressure of oxygen. The lungs allow the lungfish to stay in water, not to leave it.
Fossils have been interpreted to suggest lungs are a pleisomorphic (i.e. ancestral) character of all jawed vertebrates (gnathostomes) – but this is uncertain.
If this is true, then lungs have been retained in lungfishes, but lost in Chondrichthyes, and turned into the swim bladder in teleosts.
Lungs evolved as out-pockets, or diverticula, of the gut, and even in mammals they still develop this way embryologically.
172
What are the only living genera of lungfishes left?
Today there are only three living genera left. Neoceratodus (1 species) in Australia, Lepidosiren (1 species) in South America and Protopterus (4 species) in Africa.
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What are some aspects of the last three living genera?
Neoceratodus lives in well aerated waters and is the least highly modified and uses its gills for respiration, only coming to the surface every hour or so to gulp air.
Lepidosiren is poorly studied and relative rare.- poorly oxygenates swaps, looks after their young in these conditions.
Protopterus are very common, and often harvested for food
4 species, largely allopatric
Fairly widespread, not particularly threatened
Obligate air breathers as adults
Aestivate during the dry season.
Both Protopterus and Lepidosiren often live in less well aerated water, such as swamps, and are more dependent on their lungs for survival. Both drown if prevented from coming to the surface to breathe.
Lungs have also enabled lungfishes to aestivate (survive periods of hot dry weather by becoming inactive/torpid).
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What occurs when swaps dry up?
Often swamps will dry seasonally in tropical climates.
As swamps dry up, the fish buries itself by biting out mouthfuls of mud using its powerful jaws, and forms a mucus cocoon. African and South American lungfishes become torpid in this way for 4-6 months in dry conditions.
In this state they obtain oxygen by breathing air via a mud tube to the surface and they ventilate the lungs about once an hour.
This habit of aestivation is very ancient, and we know this because fossil lungfish burrows have been found in Devonian rocks.
This adaptation enables them to live in habitats inaccessible to many other aquatic vertebrates.
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What do molecular clocks say about lungfishes?
Molecular clock analyses suggest the living lungfishes share a common ancestor that lived approximately 80-125Ma. Since they are found on continents that were once part of the supercontinent Gondwana until ~120Ma, it seems plausible that the fragmentation of this continent drove their divergence of the living species.
