Aquaculture Nutrition and Feed Management: A Guide

The nutrients fish need, how requirements differ by species and life stage, feed types, feed conversion ratio, feeding rates, fishmeal replacement, and the link between feeding and water quality.

Overview

Feed is usually the largest operating cost in fed aquaculture, so nutrition and feed management strongly affect both profitability and the environment. Fish need a balanced supply of nutrients, delivered as feed that matches the species and life stage, in amounts that the fish can actually use. Underfeeding slows growth, while overfeeding wastes money and pollutes the water.

Essential nutrients

FAO groups dietary nutrients into proteins and amino acids, lipids, carbohydrates, vitamins and minerals. Protein supplies the amino acids needed to build tissue; FAO notes that fish and shrimp require ten essential amino acids that must come from the diet. Lipids supply concentrated energy and essential fatty acids. Carbohydrates are an energy source that omnivores digest better than carnivores. Vitamins and minerals are needed in small amounts for metabolism, bone and many body functions.

Protein requirements by species and stage

FAO reports that farmed fish and shrimp have a uniformly high dietary protein requirement, broadly in the range of about 24 to 57 percent of the diet. Carnivorous species such as sea bass and bream generally need higher dietary protein, on the order of 40 to 55 percent, while omnivorous species such as carp and tilapia need less, roughly 25 to 38 percent. Within a species, young fish need a higher protein percentage than older fish; FAO cites sea bass fingerlings needing about 52 to 55 percent protein at 5 g, declining toward about 45 percent at 50 g.

Feed types

By stage: starter feeds for early life, grower feeds for the main growth phase, and finisher feeds for market size.
By form: mash or paste, and pellets that are either expanded (floating) or compacted (sinking).
By role: complete feeds that supply all nutritional needs, and supplementary feeds that complement natural food.

Feed conversion ratio

The feed conversion ratio (FCR) is the weight of feed consumed per unit of fish weight gained; a lower FCR means more efficient feed use. FAO illustrates this with values such as about 4.5:1 for trash fish versus about 1.8:1 for dry pellets, showing that formulated pellets are far more efficient. FCR is worsened by overfeeding, poor feed quality, poor water quality and stress, and improved by matching feed and ration to the fish.

Feeding rate and frequency

Feeding rate is commonly expressed as a percentage of fish body weight per day, and it decreases as fish grow because larger fish eat proportionally less. FAO gives an example of sea bass fed at about 15 percent of body weight daily as small fish, falling to about 5 percent as they grow, with the equivalent dry-pellet rate near 4 percent. Smaller fish are fed more often, and the amount is adjusted to temperature and appetite so that feed is eaten rather than wasted.

Fishmeal, fish oil and replacements

Fishmeal and fish oil have traditionally supplied much of the protein and the essential fatty acids in feeds for carnivorous species, but their use is being reduced. Wikipedia notes that salmon feeds have moved from being based only on fishmeal and oil to containing around 40 percent plant protein, and that the wild fish needed per kilogram of farmed salmon fell from about 7.5 kg in 1995 toward roughly 4.9 kg by 2006. Plant proteins and processing by-products increasingly replace whole wild fish.