COMPARATIVE LYSINE REQUIREMENT OF TWO STRAINS OF JUVENILE RAINBOW TROUT Oncorhynchus mykiss

Seunghan Lee, Brian C. Small, Biswamitra Patro and Ronald W. Hardy
 
University of Idaho, Hagerman Fish Culture Experiment Station
3059F National Fish Hatchery Rd, Hagerman, ID 83332
seunghanl@uidaho.edu
 

Lysine is one of the limiting amino acids in formulated fish diets containing plant protein sources and is estimated to be 2.4% of the diet for rainbow trout (NRC 2011). However, genetic selection has increased trout growth rate, even when fish are fed a plant-protein diet. We pose the question: does a fast-growing trout strain require more lysine in the diet than a slow-growing strain? In other animals, it has been shown that nutrient requirements vary in terms of daily feed intake but not necessarily in terms of nutrient content of the diet. It is not known if nutrient requirements vary with fish strain. The objective of this study was to evaluate the lysine requirement of two domestic strains of rainbow trout, a selectively bred fast-growing strain (UI-ARS strain) vs. a randomly bred strain (Hayspur).

Five isonitrogenous (37% digestible protein) and isocaloric (5.0 kcal kg-1 digestible energy) diets were formulated to be supplemented with L-Lysine HCl in increments of 0.40% (1.80, 2.20, 2.60, 3.00 and 3.40% diet). UI-ARS select strain (12.2±0.3 g) and Hayspur non-selected strain (8.54±0.19 g) trout were randomly stocked into fifteen (n=3) 145-L tanks each at 35 fish per tank. Fish were fed to apparent satiation three times daily.

After 12 weeks of the feeding trial, UI-ARS fish had significantly higher weight gain (%) and daily feed intake (g/fish) compared to Hayspur fish. Using the broken-line regression analysis, based on nitrogen retention (%), the optimum lysine level for UI-ARS and Hayspur strains were 2.69% and 2.24% of the diet, respectively. This level was similar to levels needed to support maximum weight gain and feed conversion ratio. Conclusively, these results demonstrate that the fast-growing strain (UI-ARS) consumes more feed and requires more lysine (as a % of diet) than the slow-growing strain (Hayspur) of rainbow trout.