Muscle growth and changes in chemical composition of spotted wolffish juveniles (Anarhichas minor) fed diets with and without microalgae (Scenedesmus obliquus)

Abstract

Spotted wolffish (Anarhichas minor) is a promising new candidate for cold-water fish farming, but knowledge is needed about its physiology and its capacity to utilize alternative feed ingredients. The aim of the study was to investigate fast muscle growth dynamics, changes in chemical composition as well as growth performance of spotted wolffish when fed diets with or without the microalgae Scenedesmus obliquus incorporated. Juvenile spotted wolffish were fed four diets containing fishmeal as the primary source of protein (CTR diet) or microalgae (Scenedesmus obliquus) replacing 4% (AL4 diet), 8% (AL8 diet) or 12% (AL12 diet) of the fishmeal. During the 12 week experiment, fish grew from an average weight of 140 g to 250 g. The results showed indications of fast muscle cellularity of spotted wolffish being affected by dietary algae inclusion as the control and AL4 groups appeared to be more strongly favored by hypertrophic growth compared to the AL8 and AL12 groups. The CTR and AL4 groups tended towards increased muscle fiber diameters and higher proportions of larger muscle fibers, while the AL8 and AL12 group tended towards similar or increased proportions of smaller muscle fibers at the end of the trial. Probability density functions showed no difference in fast muscle fiber size distributions between dietary groups. Muscle crude protein and fat content tended to increase with growth in all treatment groups and muscle mineral content was reduced in all groups fed diets containing Scenedesmus. At the end of the trial, hepatosomatic index was reduced in all treatment groups. Dietary replacement of fishmeal with Scenedesmus also affected skin coloration, with increasing yellowness observed with increasing microalgae replacement. This study indicates that spotted wolffish has the potential to use microalgae as an alternative to fishmeal in the diet. Keywords: nutrition, sustainable aquafeed, muscle fiber cellularity, muscle growth, proximate composition, histology, alternative feed ingredients