LAUSR

Abstract A 12-week feeding experiment was conducted to determine the lysine requirement for Totoaba macdonaldi juveniles. Five isonitrogenous and isocaloric diets, with 420 g kg−1 crude protein and 21 MJ kg−1, were formulated and produced to contain increasing levels of dietary lysine. After HPLC analysis the actual lysine dietary levels were found to be 16, 17.7, 22, 25.1, and 27.8 g kg−1 of diet dry matter. Each diet was randomly assigned to triplicate groups of 10 fish and fed to apparent satiation by hand, three times a day. Growth in terms of weight and length, survival and feed utilization (as feed conversion rate, protein efficiency ratio, and protein productive value) were used as response variables. Lysine digestibility of diets was estimated using acid-insoluble ash as an internal marker. Results revealed that final weight and weight gain significantly increased with increasing levels of lysine in the diet, from 16 up to 17.7 g kg−1 of the dry matter (DM). Thermal growth coefficient was the response variable used to estimate the lysine requirement using a quadratic broken-line model (R2 = 0.82). The model estimated that highest growth is obtained with a dietary lysine level of 19.3 ± 0.8 g kg−1 DM or 46 g kg−1 of dietary crude protein (equivalent to 16.4 g kg−1 of digestible lysine). Using the results here obtained, estimates of other amino acid requirements were calculated using the quantified lysine requirement and totoaba whole-body amino acid concentrations, which can serve as a base-line to formulate practical diets for juvenile totoaba, summing for the further development of the commercial culture of this promising species.