Introduction Directory UMM :Data Elmu:jurnal:A:Aquaculture:Vol184.Issue1-2.Apr2000:

1. Introduction

Successful feeding of intensively cultured fish species requires detailed knowledge of which nutritional requirements and feeding practices best contribute to the improvement of rearing in terms of growth rate and feed efficiency. In sea bass, Dicentrarchus labrax, one of the most popular and highly produced species in the Mediterranean region, improvement of feeding is one of the main priorities of farmers because the cost Ž . of feed accounts for up to one-third of running expenses Stefanis, 1995 . Despite this, Ž investigation of feeding practice in sea bass is limited Tsevis et al., 1992; Boujard et al., . 1996; Azzaydi et al., 1998 , compared to the abundant literature on the effect of feed Ž composition on the growth of this species Carrillo et al., 1986; Tibaldi et al., 1991; Santulli et al., 1993; Ballestrazzi et al., 1994; Garcia-Alcazar et al., 1994; Perez et al., ´ ´ . 1997; Diaz et al., 1998 . Ž Ration size Reddy et al., 1994; Ryer and Olla, 1996; Fontaine et al., 1997; Azevedo . et al., 1998 has been shown to be essential in fish fed daily with a fixed amount of feed. In the case of free access to feed, as in self-feeding, the determinant factor of feed Ž efficiency is the reward level, i.e., the instant ration per self-feeder actuation Alanara, ¨ ¨ . 1996 . None of the parameters have been studied thoroughly in sea bass, although fixed feeding mainly by automatic feeders, is used empirically and self-feeding is a promising Ž feeding method for sea bass culture Kentouri et al., 1986; Anthouard et al., 1993; . Divanach et al., 1993; Boujard et al., 1996; Azzaydi et al., 1998 . According to Paspatis Ž . et al. 1999 , sea bais juveniles, when fed by self-feeders are fed to satiation and exhibit similar growth and feed efficiency to fish fed by hand. The improvement of feeding is not only a priority because of the cost of feed, but also because, given the rapid development of fish farming in the world, a better knowledge of waste output is crucial so that aquaculture be environmentally sustainable Ž . Cho and Bureau, 1998; Kaushik, 1998 . This is especially important in the case of open sea farming using cages, as is the case for the majority of sea bass farms. Under such conditions, uneaten feed and faecal and metabolic losses have a direct impact on the environment. The effect of dietary composition on nutritional waste of sea bass has been Ž studied by several authors Ballestrazzi et al., 1994; Dosdat et al., 1996; Diaz et al., . 1998; Kaushik, 1998 , but the effect of feeding practice on waste production has apparently never been studied in this species. This study was conducted to determine the effect of different feeding practices Ž . different automatic feeding protocols and self-feeding with different feed rewards on Ž . growth, feed efficiency ratio FER , and N and P loss in sea bass juveniles. In addition, daily feeding activity in self-fed fish was investigated to define the consequences of feed rewards on fish feed demands.

2. Materials and methods