Effect of photoperiod on feeding, intraperitoneal fat, and insulin-like growth factor-I in sunshine bass

Abstract

The length of the photoperiod has been implicated as affecting growth of sunshine bass. This study was done to determine if photoperiod length might affect insulin-like growth factor-I (IGF-I), which is a major hormonal regulator of growth in fish. Growth, feed conversion, peritoneal fat content, and plasma concentrations of IGF-I of sunshine bass were compared on fish held on a short (8 h) or a long (16 h) photoperiod, or after the fish were switched from one photoperiod to the other. Fish were fed daily to apparent satiation for up to 5 wk and were not fed for the last 2 wk of the experiment. Body weight and intraperitoneal fat content increased for the first 2 wk of the experiment and then remained steady for the remainder of the experiment, and feed consumption decreased from 3.5% during the first 2 wk to about 1.5% for the second 2 wk and finally to only 1% during the last week of feeding. Plasma IGF-I concentrations fell steadily during the entire experiment and was at the lowest level during the last 2 wk when the fish were not fed. There was no consistent effect of the photoperiod in any of the conditions; however, feeding and IGF-I concentrations were affected by fish density. © the World Aquaculture Society 2006.