Effects of the dietary protein/lipid ratio on growth and nutrient utilization in common dentex (Dentex dentex L.) at different growth stages

Abstract

Dentex is considered suitable for aquaculture due to its ready adaptation to culture systems, acceptance of formulated feeds and rapid growth rates. However, little information on the nutritional requirements or growth rates under controlled conditions has been reported for this fish. Thus, two feeding trials were performed, at different growth stages, to identify suitable protein and lipid (energy) levels to be used in formulating dry diets for this species. As the first step, a 3×2 factorial experiment was conducted to determine the optimum protein-to-energy (P/E) ratio for fingerling dentex. Triplicate groups were fed to satiation one of six practical diets with increasing levels of protein (50%, 53% and 57% DM) and two energy levels (20 and 22 kJ g⁻¹) within each protein level. Protein utilization was enhanced by a sparing effect of dietary lipid at 19.7%. These data suggest that, when the energy level of the diet is maintained at 22 kJ g⁻¹, the dietary protein level for fingerling dentex can be lowered from 57% to 50%. In the second experiment, with larger fish, triplicate groups of fish were fed one of six diets with two energy levels (20 and 22 kJ g⁻¹) and three P/E ratios (19, 21 and 23 g MJ⁻¹). Thus, the dietary protein level tested ranged from 38.7% to 51.14% DM. The results in the second trial suggest that, when protein efficiency or retention are considered, even dietary levels of 43.4% CP and 19 g protein MJ⁻¹ of P/E, and a calculated available energy level (22 kJ g⁻¹) could be assumed to be adequate levels for formulating practical diets for this species at this growth stage. It can be concluded that, for the two size classes of dentex used, dietary lipid had a protein-sparing effect.

Introduction

Mediterranean marine aquaculture focuses mainly on two fish species: gilthead sea bream and European sea bass, both relying on well-established production technology. The recent increase in gilthead seabream production, however, is causing serious marketing problems, with a rapid price drop. Thus, the quest for new fish species suitable for farming is emerging as a priority in aquaculture research (Abellán, 2000).

Common dentex is a sparid fish that has many qualities ideal for culture (fast growth, consumer acceptance and ease of reproduction in captivity), although many problems remain with larval production (Abellán et al., 1997). Its distribution is from the Mediterranean and the Atlantic, from Biscay to Cape Blanc and Madeira, but not around the British Isles. This species is common at depths of 60 m, but is also found down to 100 m (Morales-Nin and Moranta, 1997). Bini (1968) was the first to have success with weaning of wild dentex fry, which reached a weight of 300 g after 14 months in aquaria. Fingerling fish reared in sea cages with natural feed can reach 830 g in 16–17 months (Riera et al., 1993), with growth rates twice that of European sea bass and gilthead sea bream. Various studies have shown that both juveniles and larger common dentex have rapid growth rates Efthimiou et al., 1994, Riera et al., 1995, Abellán et al., 1997, Tulli and Tibaldi, 1997, Company et al., 1999, Katavic et al., 2000.

Despite the trials mentioned above, little data are available on the nutrient requirements for growth of juvenile dentex (2–30 g initial live weight), using pelleted diets Tibaldi et al., 1996, Cardenete et al., 1997, Company et al., 1999, Espinós et al., 2003. Neither information for nutrient requirements of large dentex is available.

For the determination of optimum growth rates of dentex, it is necessary to determine the protein and energy requirement of this fish. Since the protein content in finfish diets usually constitutes the largest single cost factor in feeds (Watanabe, 2002), the objective is to minimize protein while optimizing growth and survival. In the current paper, we report the results for two trials in which the effects of dietary protein and lipid (energy) levels on the growth performance and whole body composition of both juvenile and growing dentex were investigated.