Eye health in juvenile Atlantic halibut, Hippoglossus hippoglossus L., at two commercial production densities

Abstract

Eye damages have been known to occur in commercial halibut farming, and are expected at elevated biomass densities. As one part of intensifying halibut production, the present study was performed to investigate the effect of biomass density on growth and eye health of juvenile (14.4 g) halibut, Hippoglossus hippoglossus L., reared commercially at two densities; normal (12.5 kg m − 2 ) and high (18.2 kg m − 2 ) density for 18 wks. At start and three sampling points, growth, mortality, eye health and cataract score were recorded, and since histidine status has been related to eye health in farmed Atlantic salmon, lenses and white muscle were sampled for analysis of free histidine amino acids (imidazoles). No differences in growth and mortality were found between the two densities during the experiment. Cataractous changes did not occur, while the incidence of eye damage increased to eventually affect 33% and 23% of the fish reared in normal and high density, respectively. High lens and muscle free imidazole concentrations support the finding of no cataract in the present study. We conclude that the higher fish density under the present rearing conditions does not impact feeding and growth, and rather reduce the development of eye damages in juvenile halibut. The present hyper oxygenated inlet water (151% O 2) at high water flow may be a production factor in the formation of gas bubbles and damages in the eyes.