The impact of raw material freshness and processing temperature for fish meal on growth, feed efficiency and chemical composition of Atlantic halibut (Hippoglossus hippoglossus)

Quality of fish meal is determined both by freshness of the raw material used and by nutrient digestibility due to different processing conditions of the fish meal. Pilot plant, experimentally produced fish meals were used to investigate separately these quality factors in long term growth experiments with Atlantic halibut. The results were compared with those obtained using commercial fish meals. The effects of fish meal quality on growth, feed efficiency and chemical composition of the fish were studied. The first experiment studied the biological effect of using two fish meals made from fresh raw material, in four diets varying in protein digestibility, as measured by a standardized assay using mink (DCmink) as the test animal. The second experiment studied the biological effect of using two fish meals produced at the same processing conditions, but varying in raw material freshness in four experimental diets. The level of biogenic amines in the fish meals and diets were used to assess the raw material freshness. The third experiment was performed similarly by using six commercial fish meals varying in both DCmink and cadaverine (CAD). Experiments 1, 2 and 3 started with 17 g, 214 g and 7 g halibut, respectively, and lasted for 208, 152 and 481 days until the fish were about 120 g, 500 g and 400 g. The halibuts were hand fed to obtain close to satiation feeding. Generally the fish showed good growth, high feed efficiency (FE) and good survival during the experimental periods. The first experiment showed a significant linear correlation between DCmink and specific growth rate (% per day) (SGR) and FE. Similarly, Experiment 2 revealed a significant negative relation with the fourth exponential of cadaverine (CAD(4)) in the diets (g kg(-1)) both for SGR and for FE. The experiment with the commercial fish meals also showed dependencies both on DCmink and dietary level of CAD. The impact of the dietary level of CAD on growth and FE was very much less in the commercial fish meals than in the experimentally produced fish meals, while dependency on DCmink was somewhat lower. Both raw material freshness, as evaluated by the level of biogenic amines and processing conditions as measured by DCmink, are useful and important for the assessment of fish meal quality for halibut. Reduced fish meal quality due to digestibility was compensated for by increased feed intake. This was not the case when fish meal quality was reduced due to raw material spoilage.