The Economics of Fish Growth
Feed is the single largest operating cost in aquaculture, accounting for 40–60% of total production expenses. The feed conversion ratio — kilograms of feed required to produce one kilogram of fish — determines whether a farm is profitable or bankrupt. Fish are remarkably efficient converters of feed to flesh, outperforming cattle (FCR 6–8) and even poultry (FCR 1.7–2.0) because they are cold-blooded and neutrally buoyant, spending no energy on body heat or fighting gravity.
Temperature and Metabolic Rate
As ectotherms, fish metabolic rate roughly doubles for every 10°C increase in water temperature (Q₁₀ ≈ 2). This means fish in warm tropical waters eat more, grow faster, and reach market size sooner — but only within their species-specific thermal optimum. Beyond the optimum, stress hormones suppress appetite and growth, and FCR deteriorates rapidly as energy is diverted to physiological survival mechanisms.
Protein: The Growth Engine
Protein quality and quantity are the primary nutritional determinants of fish growth. Unlike mammals, fish can efficiently use protein directly for energy, but this is wasteful — each gram of excess protein produces 0.34 grams of ammonia via deamination in the liver. Modern feed formulation uses the ideal protein concept, balancing essential amino acids to maximize retention and minimize nitrogenous waste.
Growth Curves and Prediction
This simulation models fish growth as a temperature-dependent exponential curve modified by feed rate and protein content. Adjust parameters to explore how feeding strategy affects FCR, growth rate, and feed cost. Notice how the optimal feeding rate shifts with temperature — overfeeding at low temperatures wastes feed and pollutes water, while underfeeding at high temperatures leaves growth potential unrealized.