Energy Balance & Metabolism

What is Metabolism?

The chemical changes in living cells by which energy is provided for vita processes and activities, and new material is assimilated

What are bioenergetics?

Energy partitioning induced by the metabolic processes that occur for organisms to stay alive, grow, and reproduce. Can apply at molecular, cell, organism, and population levels.

How are metabolism and bioenergetics relevant to fisheries?

• Energy expenditure/costs (margins)

• Forage choices

• Integrated ecosystem management

How are metabolism and bioenergetics relevant to aquaculture?

• estimate energy requirements of farmed fish (>maintenance; <fat deposition)

• Develop feed to maximize uptake efficiency and growth

• predict the growth of animals according to feeding regimes

What is the general pathway for energy partioning

1. Food

2. Ingestion (Metabolism)

3. Digestion (Metabolism)

4. Assimilation (Metabolism)

5. 4 options

   1. Maintenance (Farm) (Wild)

   2. Growth (Farm) (Wild)

   3. Reproduction (Wild)

   4. Storage (Wild)

What factors often impact nutrient partitioning

• Environmental ones

  • Biotic

  • Abiotic

Wild fish energy partitioning is dependent on…

• Change in season and climate

• Forage availability

• Food G margin

Aquaculture energy partitioning depends on…

• Photo-thermal control

• Biofilter/Gas regulation

• Formulated Fish Diets

• Max energy margin

What extrinsically influences metabolism (Similar to growth)

• Salinity

• Dissolved Oxygen

• Temperature

• Stressors

• Photoperiod

What instrinsically influences metabolism

• Nutritional Status

• Life Stage

• Genetics

• Reproductive Status

• Photoperiod

What affects energy expenditure and metabolic rates of poikilothermic ectotherms?

• Temperature

• Oxygen availability

• activity (O2 demand)

• feeding (G availability)

What are the metabolic costs of eating?

• Breaking food down into substrates

  • physically processing food (Digestion, nutrient absorption)

  • Deamination of proteins and lipids, synthesis of excretory products like ammonia

  • Biosynthesis of macromolecules, cellular turnover, tissue synthesis

What is the aerobic metabolic scope?

The capacity to provide O₂ for aerobic activity above rest

How is Aerobic metabolic scope defined?

The change between the oxygen uptake rates at a given temperature

As temperature increases, how does aerobic scope get impacted generally speaking?

It increases up to an optimal temperature (T_opt), and then begins to fall

When graphing the Aerobic metabolic scope, what is the bottom line? top line?

bottom: maintenance

top: maximum rate of O₂ uptake at temp.

What can lower aerobic metabolic scope?

Stress or low O₂ saturation

What are the steps from food intake to out (include byproducts for each step where relevant)

1. Feed Intake

2. Absorbed Nutrients → Feces (Bp)

3. Digestion + absorption of energy

4. Protein metabolism → Ammonia/Urine (Bp)

5. Metabolize energy

6. Retained energy

7. Production (Somatic growth)

In an aquaculture context, how is feeding relevant/

• Fish need feed intake for metabolism

• poor fish diets will pollute their environment with feces and urine (ammonia)

• If fish are digesting too much, O₂ can be taken up too fast, resulting in die offs

What is FCR?

The ratio of food intake to weight gain

Is the FCR of a “domesticated” fish or a wild fish higher?

The wild fish has a higher FCR

Why do domesticated fish have a lower FCR?

• Minimized foraging energy

• Maximized energy retention

Fish, compared to many land animals, have a significantly (lower, higher) FCR

Higher

How many lbs of fish are typically produced per unit of food

between 1-1.5

Why might fish’s efficiency in their diet be slightly misleading?

• They are fed very high quality, protein rich food compared to land animals

• They don’t have to maintain body heat

commercial fishmeal consists of what % protein, fishmeal?

15% fishmeal, 30-50% protein

What are some potential alternative protein sources?

• Legumes/Grains

• Animal Processing Byproducts

• Human food waste

• industrial microalgae, bacteria, and yeast

• insects

What are some anti-nutritional factors to consider when finding alternative protein sources for fish diets?

• Interference with protein digestion and absorption

• bind to minerals, reducing their bioavailability

• act as anti-vitamins

• interfere with metabolic pathways

• disrupt endocrine signaling

IN a wild context, what is different compared to farm?

Most notably, there is variability in food abundance. This causes…

• realistic competition requiring foraging strategies

• fish must avoid wasting energy in times of low abundance

• fish need to alter behavior; develop social adaptations to improve net energy intake to increase their G margin

How do wild fish decide what they want to eat?

Food is ranked on net energetic value; if something is too costly to catch relative to it’s worth, it isn’t worth it.

What’s the gamble in foraging?

Fish can eat low G food at the expense of time that could be spent foraging for high G food, but high G food comes with a risk of failure.

Ideally, a wild fish want’s it’s forage to be…

High G, abundant

Least ideally, fish forage would be…

low energy… variable

Wild fish must choose the forage that will…

be best to get most energy in the least time while spending the least energy

Competition is an example of…

bioenergetics at the population level

What is competition determined by, what does it determine?

• Determined by food abundance

• Determines distribution of feeding animals

What more specifically is competition related to?

food abundance relative to # of competitors (can be the same or a different species)

ecosystem health is largely dependent on… (Integrated ecosystem mgmt)

relative prey:predator ratio

what is a generalist feeder?

a feeder that can adapt to most abundant food sources

what is a specialist feeder?

a feeder that will exploit niche abundant food sources

as fish move through different life stages, they will occupy new…

ontogenetic niches

why might a fish change ecological niches through it’s life cycle?

A location beneficial or small fish may not be appropriate for a larger, more mature fish.

• Fish change habitat (depth, structure, competition, food they eat)

Avoiding predation while eating adds…

energetic costs

how do fish reduce the time they spend at risk of predation?

they modify their tactics

One way fish modify their tactics is by sing spatial and temporal refuse… what could this be?

• Shelter (Burrows, coral reefs, weeds, crevices)

• tolerance or ability to survive somewhere predators cannot

• sensory organs allowing for finding food where/when predators aren’t around

• seasonal occurrence to avoid predators

What are the cons of safe refuse?

it leads to a concentration of competing foragers avoiding predators

What are special tactics to avoid predation?

• avoiding detection (Camouflage)

• special morphology

  • spikes, toxins, armor

• communication with predator to convince them not to attack

  • poison warnings

• specialized behaviors to assist in escape

  • flight, bloating

How are predators an important resource for prey?

Greater feeding opportunities in high risk conditions, allowing foragers who can mitigate risk to feed while others cannot

What is the tradeoff for defenses?

Defenses typically come at an energetic costs; if the predator disappears, now the defense has become a liability and the forager has lost it’s niche

Predators are key for _____ ecosystems

stabilizing