Comparison of the lysine utilization efficiency in different plant protein sources supplemented with l-lysine·HCl in rainbow trout (Oncorhynchus mykiss) fry

The efficiency of lysine (Lys) utilization has recently received much attention in dietary formulation for fish especially for plant protein based diets. However, it remains unclear whether supplemental Lys utilization is similar in fish fed diets containing different plant protein sources equally limiting in Lys. In the present study, we compared the Lys retention efficiency in rainbow trout fry fed each of three plant protein based diets containing six graded levels of Lys (10, 12, 14, 16, 18, 20g/kg dry matter). Three groups of isonitrogenous (74.1 ± 0.9g N/kg dry matter) and isoenergetic (24.7 ± 0.2MJ gross energy) diets were formulated using l-Lys·HCL, crystalline amino acids and one of three plant protein sources: wheat gluten (WG), maize gluten (MG) or a mixture of sesame oil cake (39%) and wheat gluten (61%) (SW). Each diet was offered to one group of 70 rainbow trout fry with an initial mean body weight of 0.92 ± 0.01g over a period of 30days at 15 ± 0.6°C. Lys utilization efficiency in fish was assessed by comparative regression analysis. The results showed that Lys gain, protein deposition, liveweight gain and voluntary feed intake increased linearly with increasing dietary Lys content or Lys intake (P < 0.01). Voluntary feed intake was lower for fry fed the MG diets compared to fry fed the SW and WG diets at all levels of supplemental l-Lys·HCl. Lys retention efficiency above maintenance was higher for fish fed the WG diets with respect to trout fed the MG and SW based diets (0.75 vs. 0.63, P = 0.058). In the present study, we demonstrated for the first time that the utilization efficiency of supplemented Lys varies with the plant protein source that is supplemented. This variation should be taken into account in the formulation of plant protein based diets.