Deleterious effects of food restrictions in yellowtail kingfish Seriola lalandi during early development

The effects of delayed first feeding and food deprivation on the structure and function of the digestive system in yellowtail kingfish Seriola lalandi larvae and juveniles were studied through histological examinations and enzymatic analyses. The experimental design included a conventional feeding regime with initial feeding from 3 days after hatching (DAH) as a control, delayed first feeding until 5 DAH, a first 3-d food deprivation from 12 to 15 DAH, and a second 3-d food deprivation from 33 to 36 DAH. Fish samples for histological and enzymatic analyses were taken on 5, 15, and 36 DAH, respectively. The delay of first feeding and a 3-d food deprivation on 15 DAH significantly reduced the height of enterocyte cells in the midgut, but a 3-d food deprivation on 36 DAH did not significantly reduce the cell height. Lipid vacuoles and supranuclear vacuoles disappeared from the epithelial cells after the fish had experienced the delay of first feeding or a 3-d food deprivation on 15 DAH. Total and specific activities of trypsin and amylase were reduced by the delay of first feeding. The 3-d food deprivation on 15 DAH reduced specific activities of trypsin, amylase and alkaline phosphatase, and total activity of amylase, but the 3-d food deprivation on 36 DAH only reduced the amylase activity. This study indicates that yellowtail kingfish larvae are more vulnerable to starvation in the first 2 weeks after the start of first feeding but fish become more tolerant to a short-term starvation after 33 DAH. Therefore, any delay of feeding during the first 2 weeks may impair histological structure and cause malfunction of the digestive system in yellowtail kingfish larvae. Our data also suggest that the enterocyte morphology, the number of supranuclear vacuoles in the intestine and the activity of digestive enzymes can be used as indicators of the nutritional condition of fish larvae.