Fish feeding behaviour P2

đź“Š Key Variables Affecting Feeding

  1. Temperature:

    • Feeding rate increases with temperature to a point.

    • Ectothermic fish have temperature-dependent metabolic rates.

    • There’s an optimum temperature beyond which feeding may drop or stop (e.g., tropical fish not eating in cold water).

  2. Oxygen Levels:

    • Feeding decreases under hypoxia (low oxygen).

    • Oxygen debt may occur if fish overexert while feeding in low oxygen.

  3. Photoperiod and Light:

    • Many fish feed during daylight hours (diurnal).

    • Light affects visibility and circadian rhythms.

    • Some species (e.g., catfish) feed at night (nocturnal).

  4. Salinity and pH:

    • Extreme conditions (too salty, acidic, or alkaline) can suppress appetite.

    • Optimal feeding requires environmental balance.

  5. Availability of Food:

    • More available food = more likely to feed, up to satiation point.

    • Fish feeding is not linear with food availability—plateaus when full.

âš– Energy Budgets and Growth

  • Food intake contributes to:

    • Growth

    • Maintenance metabolism

    • Reproduction

    • Activity

    • Excretion

  • Equation often used:
    C = P + R + F + U
    Where:

    • C = consumption

    • P = production (growth, reproduction)

    • R = respiration

    • F = faeces

    • U = excretion (mainly nitrogenous waste)

  • Not all consumed food leads to growth—conversion efficiency matters.

🧠 Internal Factors Affecting Feeding

  1. Size and Age:

    • Younger fish eat more relative to body size than older fish.

    • Allometric scaling: Feeding doesn’t increase linearly with size.

  2. Reproductive State:

    • Spawning fish may reduce or stop feeding.

    • Energy diverted to gonad development.

  3. Health and Condition:

    • Parasites or disease can suppress appetite.

    • Poor condition = lower intake and growth.

  4. Stomach Fullness:

    • Fish with full stomachs may reject additional food.

    • Meal frequency varies by species.

🍽 Feeding Strategies

  • Continuous feeders (e.g., filter feeders like anchovies): feed all day.

  • Batch feeders (e.g., predators like pike): feed less frequently but on large prey.

  • Some fish may fast for days between large meals.

🧪 Methods to Measure Feeding

  1. Stomach Content Analysis:

    • Gives short-term data on recent meals.

    • Can be done through dissection or endoscopy.

  2. Growth Models / Energy Budgets:

    • Use lab data to estimate food requirements from observed growth.

    • Accounts for assimilation and metabolic costs.

  3. Radioisotope Tracing:

    • Rare, advanced method for energy/nutrient tracking.

đź’ˇ Applications

  • Understanding how much fish eat helps in:

    • Aquaculture: feeding efficiency, waste management.

    • Wild population management: predicting biomass needs.

    • Ecological studies: food web dynamics.