INFLUENCE OF DIETARY BULK AGENTS (SILICA, CELLULOSE AND A NATURAL ZEOLITE) ON PROTEIN DIGESTIBILITY, GROWTH, FEED-INTAKE AND FEED TRANSIT-TIME IN EUROPEAN SEA-BASS (DICENTRARCHUS-LABRAX) JUVENILES

The incorporation of various bulk agents by substitution of an equival ent amount of the basal mixture was studied in terms of protein digest ibility, growth performance and body composition in European seabass ( Dicentrarchus labrax) juveniles. During the growth trial, triplicate g roups of 40 seabass (mean initial weight: 7.0 g) were grown in seawate r (salinity: 35; temperature: 18 degrees C) over 60 days. Fish were ha nd-fed, three times a day, one of seven experimental diets. Bulk agent s tested at 10 or 20 % level of incorporation were silica, cellulose a nd a natural zeolite (chabamin). Feeding rates were adjusted in propor tion to the percent dilution of the control diet without bulk incorpor ation. The incorporation of the bulk agents, at a 10 and 20 % level, d id not affect protein digestibility or growth performance. Dietary bul k incorporation reduced feed efficiency values, particularly at the 20 % incorporation level. However, this reduction was mostly caused by t he dietary nutrient dilution of the bulk-incorporated diets, rather th an by a negative effect of the bulk agents as dietary ingredients. In comparison to the control treatment, bulk incorporation at 10 and 20 % level did not affect protein retention values. When compared with the control diet, 20 % bulk agent incorporation changed the evacuation pr ofile of faeces and increased faecal egestion time. (C) Ifremer/Elsevi er, Paris.