Research and development to optimise hatchery production of ballan wrasse (Labrus bergylta): bacterial control and nutritional aspects

Abstract

Farmed ballan wrasse (Labrus bergylta) is recognised an efficient biological control of sea lice (Lepeophtheirus salmonis) infections in farmed Atlantic salmon (Salmo salar). Wild caught harvesting is putting increased pressure on wild stocks to meet growing demand, therefore, the production of disease free, farmed populations is a priority. Two main bottlenecks to be addressed are low larvae survival rates and slow juvenile growth during the hatchery phase. A first study compared egg disinfection protocols using bronopol as an alternative to the commercial use of formalin. Bronopol concentration of 100ppm applied for 240min on the first day of egg incubation followed by daily treatment with 25ppm for 30min is recommended for disinfection to control bacterial growth without affecting egg survival and hatching. A follow up study investigated the need for bacterial control at early larvae stages. Results showed positive effects of synergetic use of probiotics and bronopol on survival rate and microbial analyses identified opportunistic bacteria in the rearing environment and fish. The work then compared commercially available diets developed for weaning and on growing of other marine fish species. Benchmarking experiments confirmed the importance of developing ballan wrasse tailored diets based on specific raw materials, and provided a stepping stone to rationalise growth potential, feed intake, digestive and liver function, against which to compare in future studies. Clear differences in survival and growth were observed during weaning with improved survival in larvae weaned onto a diet including shrimp and cod fillet meal. During on-growing, results indicated improved FCR and growth compared to previous studies, potentially reducing time required to reach deployment size from 20–24 month to 16–19 month period. Overall, this study provides new knowledge that can be directly applied to help tackle major bottlenecks in commercial exploitation of farmed ballan wrasse.