No abstract

European sea bass Dicentrarchus labrax of the north-western (NW) and south-eastern (SE) Mediterranean Sea strains were exposed to different temperatures (13, 17 or 21 C) during the larval rearing (11-51 days post hatching, dph) or nursery periods (55-95 dph), in order to examine the effects of temperature on sex differentiation and subsequent growth during the first year of life. Higher growth was observed during exposure to higher temperatures, but fish of the NW strain exposed to 13 or 17 C during larval rearing exhibited compensatory growth once exposure to the lower temperatures finished, and as a result their final size at 300 dph was similar or greater to the group exposed to 21 C. Fish exposed to 17 C during the nursery period also had similar size to fish exposed to 21 C after 300 days of rearing, but the fish exposed to 13 C remained significantly smaller (ANOVA, n ¼ 55-100, P < 0Á05). There were significant differences in the sex ratio among the fish exposed to different temperatures during the two periods of rearing, with high temperature (21 C) resulting in a significantly higher percentage of males in the population, both in the NW (ANOVA, n ¼ 2, P < 0Á04) and SE populations (ANOVA, n ¼ 2, P < 0Á01). The masculinization effect of high temperature was significantly stronger during the larval rearing stage, both in the NW (ANOVA, n ¼ 2, P < 0Á005) and SE populations (ANOVA, n ¼ 2, P < 0Á01). None of the temperature manipulations could produce 100% females, suggesting that there is a part of the genetic component in sex differentiation which is not labile to environmental influence. # 2005 The Fisheries Society of the British Isles

No abstract

No abstract

Chantier qualité GASea bass is a major species in Mediterranean aquaculture, but has a distribution area ranging from North Atlantic to South Mediterranean, with a population structure previously revealed by population genetics. To test the farming performances of wild sea bass populations, we produced a partial diallel cross mating scheme, using sires originating from North Atlantic (NAT), South Atlantic (SAT), West Mediterranean (WEM), North-East Mediterranean (NEM) and South-East Mediterranean (SEM). Fifteen sires per origin were mated in a full-factorial design using artificial fertilization with 9 NAT dams and 17 WEM dams, producing 10 population crosses and 1950 potential full-sib families. All fish were reared together, then tagged at an average weight of 20 g and distributed to four different sites (1800 fish per site). They were grown to an objective of 200 g mean weight, where 737 to 775 fish were slaughtered in each site, and their parentage was recovered using 6 to 7 microsatellite loci, resulting in 98.9% unique assignments. All populations had similar growth rates until tagging size (20 g), but differences appeared later on. No heterosis appeared for growth rate, and genotype by environment interaction (G × E) at the population level was limited, with a significant re-ranking only in one rearing site, while strong G × E for growth rate was observed within populations. Populations were different in shape, muscular fat content, and carcass yield, but not in fillet yield. In general, heterosis was absent and G × E was very limited between populations. No "ideal" population combining all favorable traits was identified. Differences between extreme populations ranged between 3 and 49% of the mean, depending on the traits. Interestingly, in almost all cases, these differences were within the reach of one generation of intense (5%) phenotypic selection