Dogfish offal, ensiled or frozen, as feed for salmonids

Abstract

An underutilized feed source, offal from filleting of picked dogfish ( Squalus acanthias, L.), was tested as a source of protein in moist diets for salmon ( Salmo salar, L.) and rainbow trout ( Salmo gairdneri, Richardson). The offal was divided into two lots; one was preserved by freezing and the other by the addition of formic acid, 2.5% (w/w). Two experimental diets were tested in which either frozen or ensiled dogfish replaced an industrial fishery catch, consisting mainly of argentine ( Argentina silus, Ascanius), which was the wet component in the control diet. In both experimental diets, 47% of the wet weight, or 30% of the total N, was supplied by dogfish. No negative effects were observed in feed consistency or in the fish's weight increase, health, chemical composition or organoleptic properties in any of the groups. The apparent digestibility of the dogfish protein was as high as that of the protein from argentine and of the binder meal, and it was highest for dogfish preserved by formic acid. Of the total N, 20–30% is urea N and must be subtracted when comparing the protein value of the dogfish offal with other filleting offals.