Water temperature regimes affect cataract development in smolting Atlantic salmon, Salmo salar L.

The effect of fluctuation in water temperature during the freshwater rearing stage on cataract development in Atlantic salmon was investigated. Presmolts were exposed to either constant low or high temperatures, or high temperature with coldwater fluctuations. Temperature fluctuations caused the fastest growth rate and most severe cataracts, whilst low temperature resulted in slow growth and minor cataracts. The fish were then individually marked and maintained together in a seawater net pen for 7 months. Cataract progressed in all groups, fish from the low temperature group showed the fastest subsequent growth, and developed cataracts to the same degree as fish from the other groups. There were no statistically significant differences in selenium-dependent glutathione peroxidase levels in pooled samples of aqueous humour, lens and plasma from fish with or without cataract, except from the last freshwater samples, where cataractous fish showed lower plasma activity. Plasma cortisol and glucose levels did not differ, nor did whole eye riboflavin levels. Higher concentrations of some free amino acids in whole eyes were found in fish with cataract. This study shows that fluctuation in water temperature may cause both increased growth rate and cataract development in Atlantic salmon and that cataract development initiated in the freshwater rearing phase continues after transfers to seawater.