Taurine is a β-amino acid containing a sulfonate instead of a carboxylic group in α-amino acids. It is vital for organ development and aging but not for protein synthesis. Taurine is needed for membrane stabilization, has cytoprotective and cell volume regulation effects, and maintains calcium homeostasis and signalling.
Taurine deficiency impairs growth, fertility, triggers immune deficiency, muscle atrophy, and increased susceptibility of diseases, resulting in a pathological condition known as green liver in strictly marine species due to bile pigments accumulation. Under normal nutritional conditions, fish can produce taurine via methionine-cysteine metabolism pathway.
It is well known that a steady decline of fish meal inclusion levels in aqua cultural feeds has pushed higher inclusion levels of plant protein rich ingredients supplemented crystalline methionine. We assume that the higher level of dietary methionine supplementation might provide a sufficient taurine precursor to support growth rate in fish. However, Gaylord et al (2007) indicated dietary taurine supplementation was indeed beneficial fort rout fed all-plant protein diets, but supplementation of methionine above the requirement could not spare taurine.
Based on the control diet without supplemental methionine and taurine, taurine and methionine were supplemented at 0, 5, or 10 g/kg diet in a 3 x3 factorial design, respectively (figure 1).
Figure 1. 9 experimental diets in 3×3 factorial design.
The relative body weight gains in 9 dietary treatments were shown in Figure 2. There was no interaction (P > 0.05) between Taurine and methionine supplementation. Adding about extra 6.5 g/kg taurine could optimize Rainbow Trout body weight gain.
Figure 2. Relative body weight gain in response to taurine and methionine supplementation