Optimal inclusion of lupin and pea protein concentrates in extruded diets for rainbow trout (Oncorhynchus mykiss)

The aim of this experiment was to determine the optimal inclusion level and ratio of lupin (LPC) and pea protein concentrates (PPC) in multiple essential amino acid-supplemented diets for rainbow trout (Oncorhynchus mykiss). Nine extruded diets, including eight plant protein based diets formulated using four mixtures of LPC and PPC (L/P ratio, 3:0, 2:1, 1:2 and 0:3) with two dietary inclusion levels (300 or 500 g plant protein kg−1 dietary protein) and one diet with LT fish meal as the sole protein source (FM diet) were used. Duplicate tanks of 58 g trout reared in 8.2 °C water were fed the diets for 62 days, followed by a 20-day digestibility experiment. No mortality occurred, an average weight gain (WG) of 181 g and an average feed conversion ratio (FCR) of 0.72 g ingested dry matter (g gain)−1 was obtained. Plant protein inclusion level or L/P ratio did not significantly affect feed intake, WG, body composition (except ash), or retention of nitrogen (N) or energy. High inclusion of plant protein concentrates resulted in significantly higher FCR, apparent digestibility (ADC) of N, lipid, methionine (Met) and tryptophan (Trp) and plasma triacylglycerols level than low inclusion. However, ADC of dry matter, starch and histidine, whole body ash content and plasma cholesterol levels were reduced. The diets with the highest L/P ratio (3:0) resulted in significantly higher FCR than the other diets with less LPC. ADC of starch was reduced by increasing dietary LPC. The diets with the most PPC (L/P ratio = 0:3) inclusion resulted in significantly higher ADC of dry matter, N, starch and energy than other diets with less PPC, and higher plasma cholesterol level than diets with L/P ratio of 3: 0 and 1:2. Lipid digestibility was reduced by increasing LPC at the 500 g protein kg−1 dietary protein inclusion level, but not for 300 g kg−1. The diet with most LPC also resulted in lower trypsin activity in mid-intestine digesta than diets with less LPC and the FM diet. No intestinal inflammation was observed for any of the dietary treatments. However, trout fed the diet with highest inclusion of PPC tended to have a slight decrease in mucosal fold height and a slight increase in fold fusion. In conclusion, any combination of LPC and PPC with essential amino acid-supplementation can be efficiently used when total plant protein inclusion is limited to 300 g kg−1 crude protein in extruded diets for rainbow trout. At higher inclusion, PPC appears to be a preferable source of protein.

► Rapid growth and low FCR with lupin and pea protein in feed for rainbow trout.
► Higher digestibility of amino acids in plant protein diets than from LT fish meal.
► Any mixture of lupin and pea proteins can be used at 300 g kg−1 protein replacement.
► Pea protein concentrate is preferable to lupin concentrate at high inclusion in feed.