Effects of Temperature on the Incidence of Scoliosis and Cataract in Chum Salmon Fry Caused by Tryptophan Deficiency

So far, scoliosis caused by tryptophan (TRP) deficiency has been noted only in salmonids which are coldwater fishes, but not in warmwater fishes.This suggests that environmental temperature has some relation to the incidence of scoliosis or that this is a particular phenomenon occurring only in salmonids.In this study, therefore, chum salmon fry were reared for 4 weeks on a TRP-deficient diet at three different water temperatures, and the incidence of scoliosis was compared among the three groups to confirm our assumptions.At the same time, the cataract which is known to be one of the symptoms of tryptophan deficiency was also checked.The experimental conditions, experimental fish, test diet and sampling methods for serotonin (5-HT) analysis were the same as reported previously.1)No significant difference in weight gain was detected among the three groups (Table 1).Feed efficiency improved and food consumption decreased as the rearing temperature was lowered.There was no mortality in any group throughout the experimental period.The incidence of scoliotic fish at the end of the experiment significantly increased from 23 to 90% as the rearing temperature was lowered (Fig. 1), and the scoliosis became severer.This fact apparently indicated that water temperature affected the occurrence of scoliosis.No difference was detected in 5-HT contents of the brain among experimental groups (Table 1).Although the 5-HT level in the brain is an important factor responsible for the occurrence of scoliosis as suggested in our previous paper,1) the turnover of 5 HT also should be considered when the thermal condition is different.