Mixtures of lupin and pea protein concentrates can efficiently replace high-quality fish meal in extruded diets for juvenile black sea bream (Acanthopagrus schlegeli)

A 60-day feeding experiment was carried out to investigate the effects of including lupin protein concentrate (LPC) and pea protein concentrate (PPC) in multiple essential amino acid-supplemented extruded diets for black sea bream (Acanthopagrus schlegeli). Nine diets, including eight diets formulated to contain 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 high-quality fish meal as the sole protein source (FM diet) were fed to 18 tanks of 13-g black sea bream. Growth performance, nutrient utilization, and brush-border membrane bound maltase activities were evaluated. An average weight gain (WG) of 32.7 g fish− 1 and an average feed conversion ratio (FCR) of 1.13 g ingested dry matter (g gain)− 1 were obtained. Neither plant protein inclusion level nor L/P ratio significantly affected body composition (except ash), fish somatic indices or plasma parameters. The high inclusion of 500 g kg− 1 resulted in significantly higher FCR than what was obtained with 300 g kg− 1 inclusion. The WG, whole body ash content, and nitrogen (N) and energy retentions of these fish were, however, significantly lower than that of the fish fed diets with low plant protein inclusion (300 g kg− 1). The highest LPC inclusion (L/P ratio = 3:0) resulted in significantly higher feed intake and FCR, and lower N retention than the treatments with less LPC, but did not affect the growth rates or energy retentions. The diet with the highest PPC inclusion resulted in significantly reduced maltase activity in distal intestine. Any combination of LPC and PPC in essential amino acid-supplemented extruded diets, accounting for up to half of dietary protein, can be used without impairing fish growth. At high inclusion, combinations with more PPC are preferred, due to less efficient feed conversion caused by the LPC.

► FCR of 1.1 in black sea bream fed extruded diets with plant protein concentrates.
► Black sea bream grew from 13 to 46 g in 60 days on plant protein concentrate diets.
► Any mixture of lupin and pea proteins can be used at 300 g kg− 1 protein replacement.
► Combinations high in pea protein rather than lupin are preferred at high dietary inclusion.