Maintenance requirement and growth utilization efficiency of digestible methionine and cysteine determined for striped catfish (Pangasianodon hypophthalmus) using ration level technique

Abstract

Knowledge of the amino acid (AA) requirements for striped catfish (Pangasianodon hypophthalmus) is very limited. The main objective of the study was to determine maintenance requirements and utilization of digestible methonine (Met) and other essential amino acids (EAA) for growth in juvenile striped catfish. To evaluate the objective, a series of three different trials were carried out. Initially, a 28-d feed deprivation study showed an allometric relationship between energy, protein, or AA losses (y) and geometric body weight (BW), where the relationship was expressed as a power function (y = aBWb) with the exponent values (b) being 0.84 for energy, 0.83 for protein, and 0.81–0.90 for various EAAs. Next, a digestibility trial was carried out to determine apparent digestibility coefficients of energy, protein and AA from the ingredients, including: fish meal, soybean meal, wheat bran, regular and defatted rice bran. These values were then used in the final trial to formulate two diets on a digestible AA basis with similar crude protein (31%), energy (17.1 kJ g−1) and AA composition - except for digestible Met and Met+Cys, which were 0.47% and 0.90% for Diet A, and 0.61% and 1.05% for Diet B. The diets were fed to quadruplicate groups of fish (∼10 g initial weight; 20 fish per tank) at increasing ration levels (∼ 35%, 55%, 77%, 93% and 100% apparent satiation) for 64 days. One group was deprived of feed for 28 days. The results showed that feeding catfish at increasing ration levels significantly improves the growth performance in both dietary treatments. Additionally, the group fed Diet B showed significantly better weight gain than the corresponding group fed Diet A at 93% and 100% satiation. The maintenance requirement was determined to be 21.77 mg digestible (dig) Met kg−0.83 d−1 and 35.3 mg dig Met+Cys kg−0.83 d−1 based on a linear model and to be 18.8 mg digestible (dig) Met kg−0.83 d−1 and 30.7 mg dig Met+Cys kg−0.83 d−1 based on an exponential fit to the data. The efficiency of digestible Met utilization (kDMetassessed based on Diet B) for growth above maintenance was found to be 63% (including data of all ration levels) or 71% (excluding data of 100% satiation), while that for the Met+Cys (kDM+C) was found to be 46% (including data of all ration levels) or 51% (excluding data of 100% satiation). The efficiency of digestible protein utilization for weight gain with Diet B was found to be higher (66%) than that with Diet A (57%), indicating the importance of balancing striped catfish diets for dietary Met. The study also determined maintenance requirements and utilization efficiency of other EAAs which need to be further improved. These data can be used to derive AA requirements for striped catfish based on a factorial modelling approach which relies on maintenance requirements, growth utilization of AA, and targeted growth or protein deposition.