Fish

Question 1

What are the general properties of fish?

Answer 1

• There are 20-30,000 species of fish
• Vast range in size, from less than a cm to 16m (whale shark)
• Found in wide range of habitats, including both fresh and salt water
• Mostly ectothermic (‘cold blooded’), can produce some heat via metabolism, but most of this is lost as the blood passes through the gills. This means that body temperature is usually within 1-2˚C of the water temperature, but there are exceptions.
• Efficient gill system to extract oxygen from water
• Fertilisation usually external, though some fish can bear live young

Question 2

What is the Linnaean system of classification for rainbow trout?

Answer 2

Class: osteichthyes (have jaws, bone skeletons)
Sub-class: actinopterygii (membranous fins strengthened by bony rays)
Infra-class: teleostei (no ganoine in sclaes, upper jaw only attached to skull at snout)
Order: salmoniformes
Family: salmonid

Question 3

Describe the outer anatomy of the eyes.

Answer 3

Eyes are large and do not have eyelids but the cornea is covered by transparent integument

Question 4

Describe the outer anatomy of the ears and olfactory system.

Answer 4

No external ear is present in fish.

There are olfactory pits/nares which are used to detect scents in the water. There are 2 small openings rostral to the eye on both sides of the fish. Theses are connected by a small U shaped tube, which contains a vascular sensory epithelium. Water passes in through 1 opening and out the other and scents in the water are detected when water passes through the tube.

Question 5

Describe the outer anatomy of the mouth and gills.

Answer 5

• Large mouth that is lined with teeth
• Maxilla is fixed cranially at the snout but free caudally. This is a feature of teleost fish.
• Operculum is a flap of skin covering the gills at each side of the caudal head. Supported by 4 thin bones. It is fixed cranially but free caudally and it can be lifted to expose the gills.
• Ventrally, the operculum is continued by a fold of skin called the branchiostegal membrane, which is supported by several small bones called the branchiostegal rays.
• Caudal edge of the operculum forms the boundary between the head and trunk.

Question 6

List the features of the external anatomy.

Answer 6

Olfactory pit
Maxilla
Operculum
Lateral line
Pectoral fin - paired
Cranial dorsal fin
Pelvic fin - paired
Caudal dorsal/adipose fin
Anus/vent
Urogenital aperture
Anal fin
Caudal/tail fin

Question 7

What is the position of the 2 openings on the trunk?

Answer 7

The trunk is marked by 2 openings on the ventral edge. Anus/vent is cranial while the urogenital aperture is more caudal.

Question 8

What is the lateral line?

Answer 8

Lateral line is a dark line running along the length of the trunk. This continues as far as the caudal/tail fin. There are pits in this line containing sensory cells called neuromast cells. These have delicate hairs, protected by a gel-like cap and are used to detect movement and vibration in the surrounding water.

Question 9

What is the collective purpose of the fins?

Answer 9

Fins are responsible for the fish’s ability to manoeuvre and remain stable in water. There are paired and unpaired fins.

Question 10

Name and describe the 4 unpaired fins.

Answer 10

Cranial dorsal fin – on dorsal edge, protects the fish against rolling so stabilises the fish and assists in sudden stops and turns.

Caudal dorsal/adipose fin – soft and fleshy, absent in many fish but present in salmonids.

Anal fin – ventral edge, caudal to the urogenital aperture, used to stabilise the fish.

Caudal/tail fin – vertical, has species variations on shape, salmonids have homocercal tail where the fin is arranged symmetrically around the tip of the body. Tail is moved from side to side by the body muscles and propels the fish forwards.

Question 11

Name and describe the 2 paired fins.

Answer 11

Pectoral fins – equivalent of forelimbs, for braking, balancing and turning, cranial.

Pelvic fins - equivalent of hindlimbs, for braking, balancing and turning, caudal.

Question 12

List the layers of the integument of fish.

Answer 12

Cuticle/mucous/slime layer is outermost
Epidermis
Dermis
Scales

Question 13

Describe the cuticle layer of the integument.

Answer 13

Has a protective function. Can make the fish more difficult to grab hold of so protects from predation, it reduces friction in water, contains anti-pathogenic immunoglobulins that act as an initial barrier to infection, slows down water transfer across the skin important for osmoregulation, retards decomposition of fish for food trade. If you catch a fish with the intention of returning it to water, you must be gentle so as not to disturb this layer. Excess mucous can be a sign of disease.

Question 14

Describe the epidermis of the integument.

Answer 14

Cells retain capacity for cell division. Mucus secreting cells are abundant, producing the mucous to help form the cuticle layer. Relatively thin. Stratified squamous epithelium with mucous secreting cells between them.

Question 15

Describe the dermis of the integument.

Answer 15

Divided into outer stratum spongiosum and inner stratum compactum. It contains chromatophores and scales, scales project towards the epidermis.

Question 16

Describe the scales of the integument.

Answer 16

Calcified plates originating in the dermis and covered by the epidermis.

Question 17

Name the 2 types of teleost scales.

Answer 17

Cycloid and ctenoid

Question 18

Distinguish the 2 types of teleost scales.

Answer 18

Flat almost circular plates of bone that is laid down in concentric rings, which represent seasonal growth rates, so a fish could be theoretically aged with these

Cycloid scales have a smooth contour while ctenoid scales have stiff spikes protruding from one edge like a comb.

Question 19

Describe the scales of the rainbow trout.

Answer 19

• Rainbow trout have cycloid scales
• Can have chromatophores associated with them.
• In trout, these are mainly melanophores that contain black or brown melanin granules, which can be concentrated or dispersed to allow colour to change.
• Dispersed granules give a darker colour as light disperses when passing through them.

Question 20

What is cranial kinesis?

Answer 20

Maxilla is free caudally so movement is possible between the upper jaw and the cranium. This is cranial kinesis. Also occurs in reptiles and birds and is important to allow a wider gape.

Question 21

Where are the teeth in teleost fish?

Answer 21

Most of the bones around the mouth cavity are equipped with teeth, which vary in shape and size depending on diet. Sharp pointed teeth indicate predatory feeding. Teeth can also be present inside the buccal cavity and lining the larynx and tongue.

Question 22

Where are the branchial arches?

Answer 22

• Bones of the operculum are attached to the caudal aspect of the skull and overlap the bones of the branchial arches.
• Branchial arches are part of the gill apparatus and help form the wall of the pharynx.
• Each arch is a V shaped rod with the apex pointing caudally.
• There are 4 on each side of the fish.
• Dorsally and ventrally, the arches unite with others on the same side and those of the other side to form the pharynx.

Question 23

Where is muscle distributed along the body?

Answer 23

• Complex musculature for head and fins
• Bulk of muscle is in trunk and tail. Muscle blocks arranged either side of the axial skeleton and attached to the vertebral column.
• Split into epaxial and hypaxial muscles

Question 24

How is muscle arranged?

Answer 24

• Arranged in myomeres, zig-zag blocks. Each myomere has both cranial and caudal extensions, which extend under neighbouring myomeres. This overlap ensures the smooth transition of contractile force along the myomeres.
• Zigzag blocks separate by myosepta, which are connective tissue sheets.
• Coordinated contraction – undulations. Sequential contraction of muscle blocks allow movement.

Question 25

Distinguish red and white muscle in fish.

Answer 25

Mixture of red lateral slow muscle fibres, sued for slow cruising and maintaining position within a current, and dorsal and ventral white fast fibres, used for essential bursts of speed. Red muscle fibres have a very good blood supply and are a good site for injections when a rapid distribution throughout the body is needed.

Question 26

Name and describe the 2 coelomic cavities in fish.

Answer 26

Cranial pericardial cavity, which contains the heart and lined by pericardium, and a much larger peritoneal/abdominal cavity, which stretches the length of the trunk and contains the rest of the viscera.

The 2 cavities are separates by a strong septum.

Question 27

Describe the respiratory system of fish.

Answer 27

Gill apparatus is very efficient – can extract 80% of the oxygen in the water passing over the gills.

Question 28

Describe the function of the gill apparatus.

Answer 28

• When the mouth opens, water is drawn into the buccal cavity and pharynx and when the mouth closes, the water is pushed out through the spaces between the gills on both sides.
• Gills are supported by skeletal/branchial arches, which attach dorsally and ventrally to the walls of the pharynx.
• Each gill arch has projections from its cranial surface called gill rakers, which are small curved teeth that act as filters to protect the delicate gills from ingested particles which could damage them.
• Gill rays are on the caudal surface of the gills, also called filaments.

Question 29

What is the arrangement of gill rays and lamellae?

Answer 29

Alternate rays are set at an angle to each other and are caudally projected to form a v shaped double row. Each ray is covered in epithelium and together they are called primary lamellae. These have dorsal and ventral projections known as secondary lamellae. Lamellae act to increase the surface area. They have a close relationship with the capillary network reaching the gills so that the diffusion distance for respiratory exchange is minimal.

Question 30

What is the function of counter current flow?

Answer 30

Another reason why exchange is so efficient is because blood flow through the capillaries in the lamellae has counter current flow/opposite to the flow of water through the gills. Ensures blood always meets water with a higher oxygen content so that the diffusion gradient is maintained, so oxygen passes out of the water and into the blood.

Question 31

What are the 3 reasons for efficient oxygen extraction in gills?

Answer 31

• Large surface area
• Minimal diffusion distance for respiratory exchange
• Counter current flow

Question 32

What are spiracles?

Answer 32

• Large opening on dorsal surface, caudal to eyes
• Majority of water will flow into the buccal cavity via this opening, rather than the downward pointing mouth in these species.
• Connects pharynx to dorsal surface, acts as channel for inflow of water
• Smaller in other cartilaginous fish

Question 33

Which species are spiracles present in?

Answer 33

• In skates and rays
• Cartilaginous fish, including some shark species
• Also found in some primitive teleosts, such as sturgeon

Question 34

Describe the cardiovascular circulation pattern in fish.

Answer 34

• Fish have a single circulatory pattern
• Blood passes through the heart only once per circulation
• Heart works under low pressure as to not damage the delicate gills

Question 35

Where does the heart lie in fish?

Answer 35

• Lies within the pericardial cavity
• There are only 2 proper chambers: thin walled atrium and a thicker walled muscular ventricle.

Question 36

Describe the path of blood through the heart.

Answer 36

• Deoxygenated blood returning from the body via various veins enters the atrium via a sac-like compartment called the sinus venosus.
• Sinus venosus > atrium > ventricle > ventricle aorta

Question 37

What is the bulbous arteriosus?

Answer 37

First part of the ventricular aorta is enlarged and called the bulbous arteriosus. This is a fibrous connective tissue structure so appears white. It acts as a shock absorber, further protecting the gills from damage caused by high pressures.

Question 38

What is the purpose of the valves in the heart and the sinoatrial valve?

Answer 38

• Blood flow through the chambers is maintained by valves.
• There is a sinoatrial valve between the sinus venosus and the atrium and the atrioventricular valve between the atrium and ventricle. There are also flaps leading from the ventricle into the aorta

Question 39

Describe whole body circulation in fish.

Answer 39

• Have both a dorsal and ventral aorta.
• Ventral aorta runs along the ventral floor, giving off 4 branches to the individual gills, these are the afferent branchial arteries. These carry deoxygenated blood.
• Oxygen is extracted from the water as the blood passes through the gills.
• Oxygenated blood drains into the efferent branchial arteries.
• The 1st and 2nd efferent branchial arteries from the lateral dorsal aorta on their own side. This fuses rostrally and caudally to make a circle with the equivalent vessel from the other side.
• From the rostral end of the circle, paired vessels pass to the brain, ensuring that this gets well oxygenated blood.
• A single dorsal aorta runs caudally from the circle, joined by the 3rd and 4rth efferent branchial arteries.
• Dorsal aorta gives off branches to the muscles and a single coeliacomesenteric artery, which supplies the organs in the body cavity.

Question 40

Describe the venous system in fish.

Answer 40

Renal portal system present on addition to hepatic portal system. All blood draining from the caudal part of the fish drains to the kidney first before draining more cranially.

Question 41

Describe the upper alimentary system.

Answer 41

• Mouth, buccal cavity and pharynx
• Teeth found along jaws, inside buccal cavity/pharynx and on tongue
• Gill rakers filter food and prevents is going to the gills and directs it towards the oesophagus.
• Epithelial lining of the buccal cavity contains taste receptors and mucous glands, mucous produced aids swallowing.

Question 42

Describe the pharynx and oesophagus in the alimentary tract.

Answer 42

• Pharynx continues as the oesophagus, which continues into the muscular stomach, with no obvious division between the 2.
• An opening into the gas/swim bladder form the oesophagus.

Question 43

Describe the stomach in the alimentary tract.

Answer 43

Stomach is J shaped and the larger part is dorsal while the shorter more ventral limb runs cranially and is the pyloric part, which continues into the intestine and is separated from the intestine by a sphincter.

Question 44

Describe the intestine in the alimentary tract.

Answer 44

• U shaped.
• Ascending limb continues from the stomach and crosses left to right to the liver, and continues as the descending limb.
• The intestine continues as the rectum, which runs in the midline and opens at the anus/vent in the floor of the ventral cavity. Its mucosa is arranged in these annular folds, which mark the junction between the intestine and rectum.

Question 45

What is unique about the intestine of rainbow trout*?

Answer 45

In the rainbow trout, the ascending limb is covered in 40-60 finger like projections, called the pyloric or intestinal caeca. Not present in all fish. They are approximately 5cm long and 3-4 mm in diameter. They are caudally directed so are closely related to the stomach. The mucosal surface inside the caeca is similar to the intestine. They are believed to secrete digestive enzymes and absorb nutrients.

Question 46

Describe the liver in the alimentary tract.

Answer 46

• Liver is the most cranial organ and lies against the septum dividing the pericardial cavity from the peritoneal cavity. It is large and reddish-brown in colour and is indistinctly lobed.
• Gall bladder is present.

Question 47

Describe the pancreatic tissue in the alimentary tract.

Answer 47

Pancreatic tissue is found amongst the pyloric or intestinal caeca. This is a diffuse irregular organ compared with the mammalian one.

Question 48

Describe the spleen in the alimentary tract.

Answer 48

Spleen is a dark red-black organ and may be divided into several parts. Usually located ventral to the caudal edge of the stomach.

Question 49

What is the structure of the swim/gas bladder?

Answer 49

• An unpaired, thin-walled sac located in the dorsal part of the abdominal cavity.
• Shiny and nearly transparent and runs the whole length of the body cavity and lies ventral to the kidney.
• 7% of the total body volume.
• In some species, like carp, it is divided into 2 separate chambers, connected by a small tube.

Question 50

What are 3 roles of the swim bladder?

Answer 50

Buoyancy
Hearing
Sound protection

Question 51

Why is buoyancy an advantage to fish?

Answer 51

Fish swallow air to keep themselves buoyant. Fish have developed ways to reduce their body density to avoid sinking and can decrease the amount of energy required to keep themselves at a given depth. Fish do this by keeping gases in the swim bladder.

Question 52

How is the swim bladder involved in hearing?

Answer 52

Gas bladder also has a role in hearing, as some fish can sense vibrations through it. Other fish use the gas bladder for sound production.

Question 53

Distinguish physostomous and physoclistous fish.

Answer 53

The amount of gas within the gas bladder needs to be adjustable. So gas bladder is connected by a short tube to the oesophagus so they can expel gas through the mouth and gill and add gas to the bladder by swallowing air at the water surface. These fish are said to be physostomous.

Physoclistous fish have a closed system where they rely on the transfer of gases from the gas bladder to adjoining blood capillaries and back again.

Question 54

Describe the kidneys in the urogenital system.

Answer 54

• Kidneys are a long dark red structure which lies dorsal to the gas bladder.
• Kidneys are fused in salmonids but do develop as paired organs. They form 1 mass immediately ventral and extending either side of the vertebral column and occupy almost the whole length of the abdominal cavity.
• Excretory, endocrine and haematopoietic functions

Question 55

Describe the ureters and urogenital aperture in the urogenital system.

Answer 55

• In caudal part of the kidney the paired ureters leave the ventral surface. These unite into a single urogenital sinus. This is a small space in which the gonadal ducts in both male and female.
• This opens to the outside at the urogenital aperture, which lies immediately caudal to the anus.

Question 56

Where do the gonads lie?

Answer 56

Elongated gonads lie alongside kidney in paired organs in both male and female. They are suspended from the dorsal body wall by the peritoneum.

Question 57

Describe the male reproductive system in fish.

Answer 57

• In the male, the caudal end of each testis continues into a testicular duct which opens into the urogenital sinus.
• In fish the mixture of sperm and the fluid medium is called milt.
• In mature males, the testis are elongated, white, slightly pinkish, paired organs, known as soft roe.

Question 58

Describe the female reproductive system in fish.

Answer 58

• In the adult female, the ovaries can be enormous distending the body cavity and consist almost completely of ova. When they reach maturity, the ova are discharged into the coelom from the lateral surface of the ovaries and pass into the urogenital sinus via the paired oviducts and then to the outside at the urogenital aperture.
• Paired ovaries in adult females are enormous when ripe. They appear as clusters of orange white spheres. These are known as hard roe.

Question 59

Describe fertilisation in fish.

Answer 59

Fertilisation is external. Female deposits her eggs and a waiting male will eject a cloud of milt over the eggs.

Question 60

What layer of the integument do the scales arise from?

Answer 60

Found within the stratum spongiosum of the dermis. They project towards the epidermis and do not penetrate it and overlap forming a protective armour. Chromatophores/pigment can also be found in this region.

Question 61

What art of the fish brain is the largest in teleost fish and why?

Answer 61

Optic lobe as they are visual feeders.

Question 62

A fish which has a pneumatic duct connecting its swim bladder its alimentary canal is what type of fish?

Answer 62

Physostome