Eye Of The Fish, The
by Nordic Council of Ministers
Category: Nature

Increasing frequencies of cataracts (i.e., opacities in eye lens) have been diagnosed in farmed salmonids during past years. Cataracts have proven a pronounced problem in fish farming because it leads to reduced eyesight and even total blindness of the fish. Norway has been leading research on cataracts because of the economic significance of Atlantic salmon farming. Other issues in respect of stocking and animal welfare have been considered. There are still knowledge gaps on the causes of cataract as well as on its consequences. Furthermore, quantitative information on the severity of the problem is still largely lacking. The report presents results from a number of case studies that have been conducted by the project group and collaborators. The project has shown cataracts to be relatively common in all the six salmonid species included in surveys from Finland and Sweden. The prevalence and severity (coverage of eye lens) were however variable often related to an exposure to Diplostomum spp. parasites that use fish as their intermediate hosts. The result contrasts with findings from Norway about the importance of nutritional imbalance and environmental (abiotic) factors in predisposing fish to cataract development.