Abstract
The use of cleaner fish as a biological control to combat salmon lice (Salmo salar L.) in the Norwegian aquaculture industry has increased, as salmon lice have become resistant to several chemical treatments. Today lumpfish (Cyclopterus lumpus L.) account for the most used cleaner fish species in Norway, but the cleaner fish industry is limited due to lack of knowledge about the optimal diet, rearing procedure and egg quality of lumpfish. Eggs are retrieved from wild caught lumpfish which result in a varying egg quality throughout the year. A varying egg quality will thus affect the further development, survival and delousing efficiency in lumpfish. Good egg quality is known to result in higher fertilization and hatching successes, in addition to survival in marine fish eggs and larvae. It is well established that broodstock diets have an effect on the egg quality of marine fish, but there is no optimal broodstock diet for lumpfish yet. In this master thesis the effects of three broodstock diets with a varying lipid and carbohydrate content (Diet 1 = high lipid & low carbohydrate, Diet 2 = moderate lipid & moderate carbohydrate, Diet 3 = low lipid & high carbohydrate) on the egg quality of captive lumpfish retrieved from NOFIMA´s research station were tested. The egg quality of the captive lumpfish was compared to the egg quality of wild caught lumpfish which were retrieved from two different locations (Skjerneset and Namdalen). The egg quality of the different groups was evaluated by examining the fertilization and hatching success, the egg diameter, the fatty acid composition in unfertilized eggs, bone analysis and the standard length of the newly hatched lumpfish larvae. Results from this experiment show that wild caught lumpfish had better egg quality than the captive lumpfish fed the different broodstock diets. Eggs and larvae from the wild caught lumpfish had the highest hatching and fertilization success, higher levels of DHA and EPA in the unfertilized eggs, earlier bone development but more deformities. Diet 1 seemed to result in better egg quality than the other diet types. This diet type resulted in a higher fertilization and hatching success, in addition to higher levels of DHA and EPA in the unfertilized eggs. Higher ARA levels were found in eggs from fish fed the broodstock diets, which resulted in a lower fertilization and hatching success. Lumpfish fed the broodstock diets also had a higher number of normal larvae, but to what extent the broodstock diets had an effect is uncertain and should be investigated further.