NUTRITIONAL-STATUS ASSESSED IN GROUPS OF SMELTING ATLANTIC SALMON, SALMO-SALAR L, DEVELOPING CATARACTS

There has been an increasing number of reports on cataracts in Norwegi an and international salmon farming. The present study was undertaken to examine physiological and nutritional conditions during an outbreak of cataracts observed in rapidly growing Atlantic salmon, Salmo salar L., smelt with emphasis on zinc status. During this study, the catara cts were classified as irreversible. The outbreak of cataracts was pos itively related to fish growth and negatively related to the condition factor of the fish. Zinc concentrations in liver, eye and plasma were recorded in fish with cataract and in healthy fish from December to M ay. Lower zinc status (around 20%) was found in fish with cataracts co mpared to healthy fish, both over time and with regard to severity of the cataract. The decline in organ zinc concentrations seems to be exp lained by increased relative liver size, lower dry matters in liver an d eye, and lower plasma protein. From the present data, the incidence of cataracts could not be directly related to zinc or any of the other nutrients (vitamin A, iron) examined, although relative deficiencies caused by other unknown rearing factors cannot be excluded. The lower condition factor and differences in organ water composition in fish wi th cataracts indicate that the cataracts may be related to the smoltif ication processes. Smoltification in the fish population was most prob ably accelerated by elevated water temperatures.