Performance, hematology and immunology of Salminus brasiliensis fed diets containing swine liver hydrolysate

•Swine liver hydrolyzate can be included in carnivorous fish diets.•Free amino acids limits inclusion level of swine liver hydrolyzate in carnivorous fish diets.•Feeding dourados with up to 140 g kg− 1 swine liver hydrolysate promoted better immune and hematologic indices.

Diets for carnivorous fish ordinarily contain large proportion of fish meal (FM), a high-cost and restricted feedstuff. Animal by-product hydrolysates are high-quality feedstuffs and potential surrogates to FM in fish diets. This study evaluated the performance of juvenile dourado Salminus brasiliensis, a carnivorous Characin, fed with increasing levels of swine liver hydrolysate. Juvenile dourado (4.57 ± 1.25 g) were stocked into 20,300-L, indoor plastic tanks (15 fish per tank), closed-loop recirculating system in a totally randomized experimental design (n = 4), and fed to apparent satiation for 61 days with practical diets containing graded levels of swine liver hydrolysate - SLH (0, 70, 140, 210 and 280 g kg− 1). Fish fed the SLH14 diet had higher feed intake and weight gain. Fish fed the SLH28 diet had the lowest rates of feed efficiency ratio (FER), protein efficiency ratio (PER), energy retention ratio (EER) and protein retention ratio (PRR). Diets containing in excess of 140 g SLH kg− 1 probably caused reduction of protein synthesis by fish, possibly resulting from higher proportion of small peptides and free amino acids in the feedstuff, which possibly elicited higher amino acid catalysis and increased nitrogen excretion. The lowest values of blood lysozyme were recorded for fish fed diet SLH7; on the other hand the oxidative burst was not influenced by the diet. Higher nitrogen excretion was recorded for in fish fed diets containing the highest levels of hydrolysate. Ultrafiltration of swine liver hydrolysates may elicit increasing the proportion of the product in fish diets and further studies on the economic feasibility of swine liver hydrolysate may shed additional light regarding its use as surrogate protein sources.