The use of probiotic microorganisms in aquaculture is gaining a lot of interest. Gnotobiotic model systems are required in order to fully understand the effects and modes-of-action of these microorganisms, as the native microbial communities present in non-sterile animals can lead to false conclusions. In this study, a gnotobiotic sea bass larvae (Dicentrarchus labrax) test system was developed. In order to obtain bacteria-free animals, the eggs were disinfected with glutaraldehyde and subsequently incubated in a solution of rifampicin and ampicillin. Axenity was confirmed using culture-dependent and -independent techniques. The gnotobiotic larvae were fed axenic Artemia sp. from 7 days after hatching onwards. In the challenge test, one of the three opportunistic pathogens, Aeromonas hydrophila, Listonella anguillarum serovar O1 and O2a, was added to the model system via the water and encapsulated in Artemia sp. Only serovar O2a led to increased mortality in the sea bass larvae. The presented gnotobiotic model can be used for research on, among others, reciprocal metabolic effects between microorganisms and the host (e.g. as measured by gene expression), immunostimulants, pharmacological research and the histological development of the gastrointestinal tract and growth of larvae.
-Genetic parameters for carcass quality traits were estimated in 27 families of sea bass (3 dams × 9 sires factorial mating design), raised mixed in the same tanks starting before hatching. Offspring parentage was determined a posteriori using 6 microsatellite loci. Carcass quality traits were recorded at 818 days post fertilization (mean standard length: 32.6 ± 3.1 cm). Genetic parameters were estimated from the sire half sib variance and covariance components. Heritability of body weight (BW) and carcass processing traits (standardized to body weight) percent head weight (Head%), percent viscera weight (Viscera%) and percent visceral fat weight (VisceFat%) were relatively high ranging from 0.48 ± 0.15 (Viscera%) to 0.87 ± 0.23 (Head%); the estimate of heritability for fillet yield (Fillet%) was lower (0.25 ± 0.10) but was significantly greater than zero. Body weight was positively correlated to Fillet%, Viscera%, and VisceFat%, and negatively correlated to Head%. These results indicate that these carcass processing traits can be modified by directional selection and that selection for greater BW would lead to an increase of Fillet%, Viscera% and VisceFat% and a decrease of Head%. Muscle lipid content (MuscleLipid%) was determined using two indirect methods: measurements with a Torry Fish Fatmeter (TorryLipid) and determination of the percentage of dry matter content (MuscleDry%) via desiccation. Both measures were highly correlated to chemical measurements of MuscleLipid%. Regression analysis indicated a superior predictive value of TorryLipid suggesting that MuscleLipid% may be evaluated via rapid, non lethal measurements with a Torry Fish Fatmeter. Heritability estimates of TorryLipid and MuscleDry% differed significantly from zero (TorryLipid: 0.28± 0.12, MuscleDry%: 0.36± 0.14) indicating that MuscleLipid% could be lowered by directional selection. TorryLipid and MuscleDry% were weakly correlated to body weight and carcass processing traits suggesting that simultaneous improvement of MuscleLipid% and other carcass quality traits may require definition of multi-trait selection indices.
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
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