Deleterious effects of food restrictions in yellowtail kingfish Seriola lalandi during early development Ben Nan Chen a, ⁎ ,1 , Jian G. Qin a , John F. Carragher b , Steven M. Clarke b , Martin S. Kumar b , Wayne G. Hutchinson b a School of Biological Sciences, Flinders University, GPO Box 2100, Adelaide, SA 5001, Australia b South Australian Research and Development Institute, PO Box 120, Henley Beach, SA 5022, Australia Received 13 November 2006; received in revised form 5 April 2007; accepted 10 April 2007 Abstract 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. © 2007 Elsevier B.V. All rights reserved. Keywords: Digestive enzyme; Digestive system; Histology; Larvae; Starvation; Yellowtail kingfish 1. Introduction Starvation is probably one of the major causes of larval fish mortality in nature (May, 1974; Margulies, 1993) and in aquaculture (Dou et al., 2002). In larval fish, even a short period of starvation after the onset of exogenous feeding can cause severe nutritional pro- blems, leading to drastic mortality and deformity in the early stage (Kjorsvik et al., 1991). Although a plenty of live food is supplied into the culture tank, fish may still be suffering from starvation due to poor vision and mouth gape limitation (Planas and Cunha, 1999). The digestive tract of larval fish and its associated glands, Aquaculture 271 (2007) 326 – 335 www.elsevier.com/locate/aqua-online ⁎ Corresponding author. Tel.: +61 8 83037721; fax: +61 8 82075481. E-mail address: chen.bennan@saugov.sa.gov.au (B.N. Chen). 1 Present address: South Australian Research and Development Institute, PO Box 120, Henley Beach, SA 5022, Australia. 0044-8486/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaculture.2007.04.016