Fat-containing bleaching earth as a feed constituent for rainbow trout

Fat-containing bleaching earth (FBE) is a waste product from the bleaching of edible oils in the fat industry. The experiments described were carried out to investigate if FBE may be utilized as an ingredient in feed for rainbow trout (Salmo gairdneri, Richardson). Using bomb calorimetry, a sample of FBE from the bleaching of marine oils was found to contain 3400 kcal/kg. This indicates a fat content of about 36% even though analysis showed an extractable crude fat content of only 23%. The digestibility of the crude fat was estimated at about 80%.Fish growth was very good on all four experimental diets, which contained 0, 10, 20 and 30% FBE. Level of dietary FBE had no measureable effect on fish mortality, condition factor, dressed-out weight, fat content, or fatty acid composition. Fish fed diets containing FBE showed a significantly higher frequency of discoloured livers than fish fed control diets, indicating that the quality of the fat in FBE might be reduced. An organoleptic evaluation conducted on the fish showed differences between fish fed different diets, but no negative effects of FBE.     

Carotenoids in diets for salmonids: II. Epimerization studies with astaxanthin in Atlantic salmon

Atlantic salmon (Salmo salar, L.), kept in sea pens were fed diets containing pure carotenoids. No significant preferential utilization of the (3S,3′S), (3R,3′S) or (3R,3′R) optical isomers of astaxanthin was observed. No epimerization occurred in the flesh at the chiral centres at C-3 and C-3′ in astaxanthin.     

Carbohydrate in rainbow trout diets. III. Growth and chemical composition of fish from different families fed four levels of carbohydrate in the diet

Groups of rainbow trout (Salmo gairdneri) from five different families and five inbred groups were fed four diets similar in protein and energy content but differing in the percentage of metabolizable energy present as carbohydrate. The percentage of metabolizable energy from carbohydrate was 15, 26, 37 and 49%, respectively.Significant differences between fish families were found for growth, condition factor, chemical composition of the fish, relative liver wight, liver colour, digestibility of energy and N-free extracts, dressing percentage amount of intestinal fat and flesh colour.Interaction between diet and family was significant for relative liver weight and liver colour. There was no interaction between diet and family for growth, indicating that the prospects for selectively breeding a strain of rainbow trout specifically better able to utilize carbohydrate are not promising.Growth rate and condition factor increased with decreasing carbohydrate level in diet. The fish fed high levels of carbohydrate had less dry matter, fat and ash in the body, and higher percentage carbohydrate in the liver. They also had higher relative liver weights and more discoloured livers.The fish fed high levels of carbohydrate had significantly better apparent digestibility of energy and protein.There were no significant differences in mortality rate between the groups, and veterinary examination did not reveal any pathological differences in the fish fed different feeding regimes.     

Growth, product quality and immune status of Atlantic salmon, Salmo salar L., fed wet feed with alginate

By-products, by-catch and offal from the fishing industry represent valuable resources of high-quality protein and energy. In order to utilize some of these resources, a method for preparing wet feed for Atlantic salmon, Salmo salar L., using a binder produced from seaweed, Ascophyllum nodosum L., was developed. The feed was formulated with offal from lean fish (haddock, Melanogrammus aegleflnus L., saithe, Pollachius virens L., pollack, Pollachius pollachius L., and cod, Gadus morhua L.) and fatty fish [mackerel, Scomber scombrus L., and argentine, Argentina silus (Ascanius)], fish meal extruded wheat, capelin oil, vitamin and mineral premix, astaxanthin, and seaweed binder. The feed was gellified in a solution of calcium chloride. Equipment for the production of such feed was developed and the feed tested on a large scale at a commercial salmon farm. As control, a high-fat, extruded, commercial dry feed was used. On a dry matter basis, the two feeds were comparable with respect to protein, fat and carbohydrate. Growth rates, appetite and feed conversion were similar for the two experimental groups. Fish fed dry feed seemed to be more active when handled before slaughter and had a higher incidence of skin damage than fish given wet feed. Chemical and sensory analyses of the fish showed no difference (P > 0.05) between the two groups. Fifty fish from each group were analysed for haemoglobin, protein, lysozyme, complement and haemolytic activity in the blood. There was a significantly higher level of lysozyme in the wet feed group than in the dry feed group, implying an immunostimulating effect of alginate. It was clearly shown that producers have an excellent opportunity to improve the utilization of the resources and decrease feed production costs in places where the natural conditions are favourable, i.e. locations where there is an integrated production of fish farming and processing of wild catch.