DEVELOPMENT OF DRY FOOD FOR LARVAE OF COREGONUS-LAVARETUS L .1. GROWTH, FOOD DIGESTION AND FAT-ABSORPTION

Four different dry diets (diets I, II and IV containing yeast, III without yeast) were tested for suitability for rearing larvae of Coregonus lavaretus L. Living zooplankton was used as a reference diet. Feeding zooplankton resulted in the best growth and survival. Among the four dry diets, growth obtained with the diet free of yeast was not significantly different from that obtained with the diets containing yeast. In the intestine, ingested zooplankton were broken down almost completely within the anterior parts of the intestinal tube. For diet IV, the microscopical appearance of the food items changed with transition from the stomach to the intestine. The other dry diets underwent almost no alterations during passage through the gut. Dry diets I-III, and to a lesser degree dry diet IV, evoked higher activities of the enterocytic enzymes aminopeptidase, maltase and unspecific esterase than did zooplankton. The dry diets I-III led to the appearance of large lipid droplets within the enterocytes, whereas zooplankton-fed larvae showed small droplets, with an intermediary size of lipid droplets for diet IV. The histological findings suggest that (a) in zooplankton-fed coregonid larvae a more complete break-down of food items can be achieved with lower enzyme activities, and (b) dry diet formulation and composition can clearly modify the digestive response of the larvae. © 1990.