European sea bass growth and N and P loss under different feeding practices

This study was performed to assess growth rate, feed efficiency, and N and P loss of sea bass (initial body weight 3.5 g), held in 500-1 tanks under ambient temperature and natural light, and fed according to the following methods: by automatic feeders that released feed continually in daylight according to feed manufacturers' recommendations (AF100%); half of the above continually in daylight (AF50%); half of the above again but in two meals only (AF50%M); and by self-feeders that supplied feed at low (SFL), medium (SFM) and high (SFH) reward. None of the feeding conditions affected the survival rate of fish. SFL fish had the highest specific growth rate, while AF50% and AF50%M the lowest. Population weight distribution in the restricted automatic-fed fish (AF50% and AF50%M) was more homogenous compared to the other feeding conditions. These two practices produced high feed efficiency ratios (0.93 and 0.95, respectively), compared to the AF100% (0.57) and self-fed ones (SFL: 0.60; SFM: 0.37; SFH: 0.21). Self-feeding at low reward of 0.6 g trigger(-1) could be considered as the optimum feeding practice, combining higher weight gain, lower N and P loss, and intermediate feed supply compared to the other treatments. In the SFH method, fish did not adjust their manipulation of the self-feeders according to their feed needs. Daily feeding activity in all self-fed fish groups was independent of feeding reward. (C) 2000 Elsevier Science B.V. All rights reserved.