No abstract

Besides being an indispensable amino acid for protein synthesis, arginine (Arg) is also involved in a number of other physiological functions. Available data on the quantitative requirement for Arg in different teleosts appear to show much variability. So far, there are very limited data on the maintenance requirements of indispensable amino acids (IAA) in fish. In the present study, we compared N and Arg requirements for maintenance and growth of four finfish species: rainbow trout (Oncorhynchus mykiss ), turbot (Psetta maxima ), gilthead seabream (Sparus aurata ) and European seabass (Dicentrarchus labrax ). Groups of fish having an initial body weight close to 5 -7 g were fed semi-purified diets containing graded levels of N (0 to 8 % DM) and Arg (0 to 3 % DM) over 4 to 6 weeks. For each species, N and Arg requirements for maintenance and for growth were calculated regressing daily N gain against daily N or Arg intakes. N requirement for maintenance was estimated to be 37·8, 127·3, 84·7 and 45·1 mg/kg metabolic body weight per d and 2·3, 2·2, 2·6 and 2·5 g for 1 g N accretion, in rainbow trout, turbot, gilthead seabream and European seabass respectively. The four species studied appear to have very low or no dietary Arg requirements for maintenance. Arg requirement for g N accretion was calculated to be 0·86 g in rainbow trout and between 1·04-1·11 g in the three marine species. Turbot required more N for maintenance than the other three species, possibly explaining its reputedly high overall dietary protein requirement. Data suggest a small but sufficient endogenous Arg synthesis to maintain whole body N balance and differences between freshwater and marine species as regards Arg requirement. It is worth verifying this tendency with other IAA.

No abstract

No abstract

The influence of dietary vitamins on growth, survival, and morphogenesis was evaluated until day 38 of posthatching life in European sea bass larvae (Dicentrarchus labrax). A standard vitamin mix (VM), at double the concentration of the U.S. National Research Council's recommendations, was incorporated into larval feeds at 0.5%, 1.5%, 2.5%, 4.0%, and 8.0% to give treatments VM 0.5, VM 1.5, VM 2.5, VM 4.0, and VM 8.0, respectively. The group fed the VM 0.5 diet all died before day 30. At day 38, the larvae group fed VM 1.5 had 33% survival, while the other groups, with higher vitamin levels, showed at least 50% survival. The higher the percentage VM in the diet, the lower the percentage of column deformities. High dietary vitamin levels positively influenced the formation of mineralized bone in larvae: the higher the dietary vitamin level, the higher the ossification status. In the larvae group fed at the highest vitamin levels, we observed a temporal sequence of coordinated growth factor expression, in which the expression of bone morphometric protein (BMP-4) preceded the expression of IGF-1, which stimulated the maturation of osteoblasts (revealed by high osteocalcin expression levels). In groups fed lower proportions of vitamins, elevated proliferator peroxisome-activated receptors (PPAR-gamma) expression coincided with low BMP-4 expression. Our results suggest that high levels of PPAR-gamma transcripts in larvae-fed diets with a low VM content converted some osteoblasts into adipocytes during the first two weeks of life. This loss of osteoblasts is likely to have caused skeletal deformities.