Partial utilization efficiencies of protein and methionine by barramundi (Lates calcarifer) in response to dietary methionine source and form

An experiment was conducted with barramundi (Lates calcarifer) juveniles (initial weight 10.3g +/- 0.3g) to examine the partial efficiency of utilization of methionine (Met) from intact protein (fishmeal or lupin protein concentrate) and a crystalline DL-Met source. Fish were fed at one of three ration levels: Low (0.4g/fish/day), Moderate (0.8g/fish/day) and High (1.6g/fish/day). Those fed the fishmeal-based diet (Diet FML) at the highest ration level grew to an average weight of 37.3 +/- 0.46g, whereas those fed the Lupin Protein Concentrate (LPC)-based diet fortified with all EAA (Diet LPCM) at the highest ration level grew to 25.4 +/- 2.27g. The weight of the fish fed the LPC diet with no additional Met (Diet LPC) even at the highest ration level declined over the course of the experiment resulting in a final weight of 9.2 +/- 0.88g, clearly demonstrating the impact of dietary Met deficiency. The partial efficiency of protein utilization was also significantly reduced when Met was limiting (a coefficient of 0.06, compared to 0.39 in the Met-supplemented LPC diet). The results suggested that the partial efficiencies (coefficients) of both Met and protein utilization in diets where crystalline Met is the primary source of Met (Diet LPCM: 0.26 and 0.39 respectively) were significantly poorer than from an intact protein source (Diet FML: 0.89 and 0.67 respectively) when Met is provided in excess.