Quantifying methionine requirement of juvenile African catfish (Clarias gariepinus)

Abstract

This study was conducted to estimate the methionine (Met) requirement of African Catfish (Clarias gariepinus). A basal diet was formulated to contain 32% crude protein, 12% lipids, and 0.44% cysteine using only protein from legume ingredients as intact protein. This diet was supplemented with graded levels of crystalline DL- methionine (0, 0.12, 0.24, 0.36, 0.48, 0.60, and 0.84%), which resulted in seven dietary methionine levels ranging from 12.2 to 36.0 g kg−1 crude protein.

Triplicate groups of 40 fish (78 g) were restrictively fed one of the seven diets for six weeks. Dietary methionine level significantly affected growth rate, feed conversion ratio, retained nitrogen, methionine efficiency and body composition. All parameters were fitted to dietary digestible methionine content expressed per unit of digestible protein (dMetDP) to estimate the Met requirement using; the linear plateau model (LP), broken line model (BL), or quadratic regression model (QR). LP and BL recorded similar values for requirement estimates while QR evidently recorded a 57% higher requirement estimates across different parameters.

The digestible methionine requirement of African catfish for growth (using LP) ranges between 18.7 and 21.4 g kg−1 per unit of digestible protein. This equates to a minimum dietary methionine level of 6.3 g kg−1 diet (19.2 g kg−1 Crude protein), which is lower than was has been previously reported for this species.