Occurrence and formation of vertebral anomalies in hatchery reared ayu, Plecoglossu altivelis.

The influence of low food supply on the time and order of formation of vertebral column and the occurrences of vertebral anomalies in hatchery-reared ayu, Plecoglossus altivelis, were described and reported. The larvae reared with low food supply, "lack of living micro-crustaceans," grew considerably more slowly than the well fed larvae. The order of cartilaginification and ossification of the vertebral column seemed unaffected by growth rate, but time of formation varied according to the growth rate. The frequencies of abnormal cartilaginous arch and spine, abnormal arch and spine, compressed (shortened) vertebrae and fused vertebrae in fish reared with low food supply were clearly higher than those for fish with high food supply. The slow space of cartilaginification and ossification of vertebral column and the high incidence of vertebral anomalies may be associated with lack of living micro-crustaceans during the larval stage.