Researchers at the Universidade de São Paulo in Brasil have determined that swine liver hydrolyzate can be included in carnivorous fish diets. 

Their study evaluated the performance of juvenile dourado Salminus brasiliensis, a carnivorous Characin, fed with increasing levels of swine liver hydrolysate. Results found that feeding dourados with up to 140 g kg− 1 swine liver hydrolysate promoted better immune and hematologic indices in the fish. 

However, free amino acids limit the inclusion level of the  hydrolyzate. \"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 research team hypothesizes that ultrafiltration of swine liver hydrolysates may help solve the issue and allow for the increase in the proportion of the product in fish diets. \"Further studies on the economic feasibility of swine liver hydrolysate may shed additional light regarding its use as surrogate protein sources.\"

The study is published in the January 2018 issue of Aquaculture