ReviewEffects of the dietary protein/lipid ratio on growth and nutrient utilization in common dentex (Dentex dentex L.) at different growth stages
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.
Section snippets
Diet preparation and chemical analysis
The dry diets, composition given bellow, were cold pelleted, 3 mm in diameter for the small fish (trial 1) and 4.5 mm in diameter for the larger fish (trial 2), and stored at −4 °C until used. All diets were prepared in the laboratory, after blending the dry ingredients thoroughly in a feed mixer. The same ingredients were used for both trials. A LT fish meal was used as the principal protein source. The required amount of oil and an appropriate amount of water to form a soft dough were added
Experiment 1
As shown in Table 3, daily mean feed intake ranged from 2.75 to 3.05 g/100 g fish and it was affected by the differing energy level of the diets. Thus, fish fed the lowest energy level diet (20 kJ/g) consumed approximately 3 g/100 g of mean body weight per day. But, when the energy level of the diet was increased (22 kJ/g), the intake decreased to roughly 2.8 g/100 g, indicating that feed consumption decreased as the dietary energy level increased. The specific growth rates (SGR) determined in
Discussion
Results of the first trial, using fingerling dentex, showed that all diets tested were well accepted by the fish (Table 3), with feed intake values ranging between 2.75 and 3.05 g/100 g fish. These values were higher than those reported by Tibaldi et al. (1996) and similar to those cited by Company et al. (1999) for the same species of a similar size range. In any case, the feed intake found in our study was similar to those reported for juveniles of sparid fish of a similar size range, such as
Conclusion
This study has demonstrated the capability of dentex fingerlings to spare protein and has indicated the degree to which the lipid content in the diet can be effectively used to promote optimal growth. Diets containing about 23.7 g protein MJ−1 of energy level were adequate for dentex fingerlings to attain maximum growth within certain dietary protein and energy concentrations. The same trend was observed with larger dentex, with a lipid-sparing protein effect that enables good growth
Acknowledgements
This work was supported by a grant from the Spanish Government, ACU00-011-C4-2 of Ministerio de Ciencia y Tecnologı́a (INIA). The authors wish to thank the collaboration of Aquaculture Station of Instituto Español de Oceanografia (Mazarrón, Murcia).
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