The high quality of fishmeal proteins makes substitution difficult. However, partial substitutions are being made (Li et al. 2002, Li and Selle 2002, Tabe et al. 2002, Chen et al. 2002). Tacon (1987) recommended a crude protein level varying from 35% to 42% for omnivorous fish without affecting growth.
For optimal growth fish require not only a minimum level of protein, but also that the essential amino acids are balanced to meet the requirements of each single one. This can easily be done by using fishmeal as the main protein source. However, the amount of fishmeal on a world wide basis is not high enough to cover the need for the constantly growing aquaculture industry. Protein requirements vary between species (Finke et al. 1987), but are generally high (>30%) even for most omnivorous species (Tacon 1987) where all the protein (98%) can come from a mixture of plant protein - in commercial diets mainly from soybean. Using this almost “all-veggie” feed still results in satisfactory growth and feed utilisation.