Utilisation parChrysichthys nigrodigitatus(Bagridae) d'ensilage chimique ou biologique de poisson

Abstract

These studies were undertaken to test the nutritional value of marine fish offal products preserved by different silage methods and used as an ingredient in african catfish (Clziysiclzflzys izigrodigitatus) feeds. The first experiment concerned cooked tuna waste silage prepared by addition of 3% formic acid. After incubation for 16 days, a desirable and stable pH of 4.03 was obtained. The hydrolysate, containing 66.7% of crude protein (N x 6.25) on a dry matter (DM) basis, was incorporated with a basal mixture to formulate feeds containing 38% crude protein which were fed to Clziysichflzys izigrodigitatus. A commercial fish meal was used as control on an iso-nitrogenous basis. Diets were distributed to 6 groups of 50 catfish of an initial weight of 34 g for 56 days at 3% (dry) of fish body weight. The zootechnical performances obtained with fish fed with the experimental diet (CNE) were better in terms of the daily weight gain (0.86 g.d-’), food conversion ratio (FCR: 1.79) and protein efficiency ratio (PER: 1.46), compared to those of the control diet (no significant difference). During the second experiment, fish silage was prepared by fermentation with 65% (wet weight, wlw) cooked and ground small sardines, 25% (w/w) corn flour, 5% sugar and 5% (wlw) fermented cassava used as fermentation starter. After 35 days, a stable pH of 4.18 was attained and the source of fermentation substrate did not affect the nitrogen content of the hydrolysate after 15 days storage. The liquid silage (cosilage) containing 35.65% crude protein (DM) was also added to a mixture and tested against control fish meal on an iso-nitrogenous basis in experimental conditions identical to those described above. The incorporation of cosilage in the diet (CE) resulted in an increase in the daily weight gain (0.94 g.d-’), FCR (1.77) and PER (1.61) compared to control diet. In both experiments, the increase in growth rate and the presence of greater amount of lipids in the body of fishes receiving silage are partially due to greater food ingestion, owing probably to a different texture of the pellets or the possible presence of food attractants. The acceptability of fish silage as an ingredient in catfish feed, as shown in these studies, constitutes an akernative to fish meal in utilizing marine fish waste or low value fish.