Energetics

Question 1

What is energetics

Answer 1

How fish species obtain food from the environment to meet metabolic demands – postingestion

Question 2

Do herbivores or carnivores have a longer digestive track

Answer 2

herbivores having longer ones than carnivores

Question 3

How do fish get their food?

Answer 3

most fish do not chew their food, relying instead on physical and chemical breakdown in stomach and upper digestive tract to get nutrients

Some taxonomic groups (e.g., cichlids, telmatherinids, cyprinids) have bony toothed pad that pre-process food prior to stomach called pharyngeal jaws

• Stomach can be highly distendable to store and breakdown food
  Upper pharyngeal jaw

Muscle contractions and acidic secretions function to physically and chemically breakdown food

pyloric caeca and extra folds in digestive tract can allow for more efficient nutrient extractions

Proteolytic enzymes that work at low pH continue the digestion until soupy mix is passed where bile and pancreatic juices(withHCO3- to neutralise pH) continue to digest fats, lipids and proteins.

Question 4

Once metabolic demands are met where can extra nutrients be stored

Answer 4

Carbohydrates: glycogen in liver and muscles
Lipids and protein: muscle / fat tissue as growth

Question 5

What is bioenergetics

Answer 5

The study of the processing of energy by living systems, at any level of biological organization
In fish:
* The bioenergetics of individuals
* Using this information to develop expected energy budgets for populations
* Making predictions about fish production and/or habitat suitability for given species over a given set of environmental conditions

Question 6

Bioenergetic models

Answer 6

Most models try to predict fish growth and so isolate the Growth variable (G)
Using the model over all sizes in a species, and over all species can generate ecosystem-wide expected growth in biomass
estimating growth lets us know if habitat is suitable

Question 7

egestion vs excretion

Answer 7

egestion= leftover nutrients that wasn’t metabolized that does not get processed/digested, goes right through the system
excretion=stuff gets processed but can’t be used like excess nitrates, toxins, etc from digested stuff

Question 8

Energy budgets

Answer 8

varies largely among species and depends on the empirical parameters derived for each species.
Can also model the suitability of a habitat to support the energy requirements and potential growth of a species

Question 9

Empirically derived physiological rate parameters

Answer 9

Framework is based on determining the effects of specific environmental conditions on species-specific physiology from lab-based studies
Physiological rates (e.g., feeding rates or C, or respiration rates R) are characterized by non-linear relationships to key environmental parameters such as temperature

Question 10

physiological rates that impacted by various environmental parameters in similar complex non-linear relationships: (6)

Answer 10

• Temperature
• Salinity
• Dissolved O2
• Prey availability
• Competitive interactions
• Contaminants/stress
• Some of the effects are also not likely independent of one another (

Question 11

Bioenergetics in fisheries management

Answer 11

The Wisconsin Bioenergetics model
Increasing number of species (> 105) are physiologically characterized from empirical studies (lab based) to determine parameters for energy conversion rates (e.g., C, R, etc,..)
Used to predict the status of fish populations and even establish stocking rates within a managed system

Question 12

Energetics and buoyancy regulation

Answer 12

Buoyancy is energetically / metabolically expensive

Many elasmobranchs (cartilaginous fishes) swim extensively, use fins to direct themselves up or down have lighter skeleton = helps minimise energy expenditures

Other species (bottom dwellers) just sink and remain near the bottom

• Lipid or fat infused bones are also lighter and more buoyant and this is often enough to help with buoyancy issues

Question 13

Buoyancy regulation swim bladder

Answer 13

bony fishes (Teleostei) use gas filled “swim bladder” to regulate buoyancy ( gas filled chamber in the gut, permeable to diffusion only at ovale, changes with pressure)

Question 14

Swim bladder and compression

Answer 14

At increasing depths, the swim bladder compresses and the fish will continue to sink

Needs gas injection

• As a fish rises in the water column, pressure lessens and the gas in the bladder expands, and the fish will rise continuously
  Needs gas expulsion

Question 15

Buoyancy regulation for Physostomous fish (more primitive)

Answer 15

trouts and salmons

Pneumatic duct connects swim bladder to esophagus
- Air expelled through duct allows fish to “burp” out air when rising
- Gas must be secreted into swim bladder from blood

Question 16

Buoyancy regulation for Physoclistous fishes

Answer 16

teleost fish
- Pneumatic duct is lost (sometimes during development)
- Gas in swim bladder absorbed or expelled to blood by vascularised rete mirabile and Ovale
- Volumetric regulation by muscle contractions of Ovale and

Question 17

Physiological processes regulating swim bladder

Answer 17

Gas Gland by swim bladder produces lactic acid, which dissociates and decreases pH, promoting O2 dissociation from Hb (by,…Bohr and Root effects)

high lactate concentrations reduce gas solubility in blood near swim bladder, causing O to come out of
solution and flow into bladder (salting out effect)

Countercurrent exchange of blood to and from gas gland keeps gases close to swim bladder

Question 18

Buoyancy regulation metabolism and energetics

Answer 18

process that is routine in fishes but cost energy to maintain and is included in RMR/MMR

Better understanding of processes help clarify how fish are well adapted to the environments