Béatrice Chatain

Abnormal swimbladder development and lordosis in sea bass (Dicentrarchus labrax) and sea bream (Sparus auratus)

Abstract Many types of skeletal malformations are found in species reared in intensive conditions. Lordosis, characterized by a more or less acute V-shaped spine, is the most common. It may be congenitally or post-natally induced. Poor rearing conditions are usually the cause of postnatal lordosis. A correlation between the appearance of lordosis in 0.7–4 g juvenile Dicentrarchus labrax and Sparus auratus and the lack of functional swimbladders was found in larval forms of both species. Lordosis was present in all fish which were forced to swim against a current of at least 20 cm/s, while only 20–30% of fish reared in static waters were affected, thus suggesting a mechanical cause of this deformity. Spinal curvatures were mainly in the area of vertebrae 14–15 which is the area where muscle pressure is highest during swimming. The curvature of the deformed fish increased with weight and from less than 10° in 0.7-g fish to 60° in 4-g sea bass and 120° in 150-g sea bream. Late swimbladder inflation was observed in S. auratus of about 7 g and over. However, late swimbladder inflation did not reduce spinal curvatures in fish with chronic lordosis starting at the larval phase.

Improved rate of initial swim bladder inflation in intensively reared Sparus auratus.

Abstract Initial swimbladder inflation in Sparus auratus was artificially inhibited by covering the surface of the rearing tanks with a layer of liquid paraffin. The results showed that the larvae must gulp air to achieve inflation. They also suggested that the low rates of inflation (

A Polygenic Hypothesis for Sex Determination in the European Sea Bass Dicentrarchus labrax

Polygenic sex determination, although suspected in several species, is thought to be evolutionarily unstable and has been proven in very few cases. In the European sea bass, temperature is known to influence the sex ratio. We set up a factorial mating, producing 5.893 individuals from 253 full-sib families, all reared in a single batch to avoid any between-families environmental effects. The proportion of females in the offspring was 18.3%, with a large variation between families. Interpreting sex as a threshold trait, the heritability estimate was 0.62 ± 0.12. The observed distribution of family sex ratios was in accordance with a polygenic model or with a four-sex-factors system with environmental variance and could not be explained by any genetic model without environmental variance. We showed that there was a positive genetic correlation between weight and sex (rA = 0.50 ± 0.09), apart from the phenotypic sex dimorphism in favor of females. This supports the hypothesis that a minimum size is required for sea bass juveniles to differentiate as females. An evolution of sex ratio by frequency-dependent selection is expected during the domestication process of Dicentrarchus labrax populations, raising concern about the release of such fish in the wild.

The application of microsatellite markers to breeding programmes in the sea bass, Dicentrarchus labrax

Microsatellite markers isolated from a genomic library of sea bass, Dicentrarchus labrax, were used to assess parentage in a breeding programme. The progenies were obtained from a complete factorial design between three males and three females, and mass-reared in a single tank. Three samples of 329, 97 and 360 larvae respectively aged 11, 40 and 116 days-old, were genotyped with microsatellite loci. The parentage of all individuals was determined unambiguously with only two microsatellite loci. A genetic analysis of quantitative characters (survival, body weight, length and malformation, condition coefficient) was realized on the larvae identified in this way. Each of the families appeared significantly different for the analyzed traits. We argue that microsatellites will be a valuable tool in: (i) breed identification (ii) family selection programs in which genetic tagging will allow different genotypes to be reared together, thus greatly reducing the impact of environmental variance and the number of replicate needed ponds.

Physiological mechanisms underlying a trade-off between growth rate and tolerance of feed deprivation in the European sea bass (Dicentrarchus labrax)

SUMMARY The specific growth rate (SGR) of a cohort of 2000 tagged juvenile European sea bass was measured in a common tank, during two sequential cycles comprising three-weeks feed deprivation followed by three-weeks ad libitum re-feeding. After correction for initial size at age as fork length, there was a direct correlation between negative SGR (rate of mass loss) during feed deprivation and positive SGR (rate of compensatory growth) during re-feeding (Spearman rank correlation R=0.388, P=0.000002). Following a period of rearing under standard culture conditions, individuals representing ‘high growth’ phenotypes (GP) and ‘high tolerance of feed deprivation’ phenotypes (DP) were selected from either end of the SGR spectrum. Static and swimming respirometry could not demonstrate lower routine or standard metabolic rate in DP to account for greater tolerance of feed deprivation. Increased rates of compensatory growth in GP were not linked to greater maximum metabolic rate, aerobic metabolic scope or maximum cardiac performance than DP. When fed a standard ration, however, GP completed the specific dynamic action (SDA) response significantly faster than DP. Therefore, higher growth rate in GP was linked to greater capacity to process food. There was no difference in SDA coefficient, an indicator of energetic efficiency. The results indicate that individual variation in growth rate in sea bass reflects, in part, a trade-off against tolerance of food deprivation. The two phenotypes represented the opposing ends of a spectrum. The GP aims to exploit available resources and grow as rapidly as possible but at a cost of physiological and/or behavioural attributes, which lead to increased energy dissipation when food is not available. An opposing strategy, exemplified by DP, is less ‘boom and bust’, with a lower physiological capacity to exploit resources but which is less costly to sustain during periods of food deprivation.

Sexual growth dimorphism in sea bass Dicentrarchus labrax

Abstract The growth of 100 sea bass feminized by estradiol treatment and 200 individually tagged controls was followed from the age of 10 months [27±1.7 g, mean±confidence interval (95%)] to 45 months (1160±46 g) in order to analyze the evolution of sexual dimorphism as a function of the age and sexual maturity. One hundred percent females were found in the treated group ( n =94) versus 55% in the control nontreated group ( n =171). Males remained significantly smaller than both females and feminized fish from the beginning of the experiment. The resulting weight advantage [(female mean weight−male mean weight)/male mean weight, expressed as a percentage] for females was much more pronounced during the early stages of development (67% at 10 months of age), decreased in the second year of life and then became stabilized around 25%. Females and feminized fish retained the same growth, suggesting that growth is related to phenotypic sex in the sea bass. The growth rate was influenced by sex in the fourth year of life, period during which the females grew faster in terms of both weight and length. Compared to the males, they had a relatively higher ratio of digestive tract to body weight (+26%), but lower ratios of visceral fat to body weight (−49%) and muscle lipid content (−16%) at slaughtering, at which time they had finished their second vitellogenic cycle (45 months).

Tank wall colour and light level affect growth and survival of Eurasian perch larvae (Perca fluviatilis L.)

The influence of interaction between light intensity and tank wall colours on survival and growth of perch larvae (Perca fluviatilis L.) was investigated for 15 days after hatching. Three light intensities (250, 400 and 800 lx) and four wall colours (black, dark grey, light grey and white) were used. At the end of the experiment, survival rates ranged between 1% and 26%, and varied according to the different treatments (P=0.0001; df=11). A global effect of light intensity was detected (P=0.0001; df=2) and the highest survival rate was observed under 250 lx. Survival was also influenced by the tank wall colour (P=0.0001; df=3): light grey showed the best result (17%). The greatest growth in weight and length was observed in tanks with light grey and white walls, which were strongly illuminated, while the lowest growth was recorded in the tank with black walls and 250 lx illumination.

Pressure and cold shock induction of meiotic gynogenesis and triploidy in the European sea bass, Dicentrarchus labrax L.: relative efficiency of methods and parental variability.

The optimal conditions for the retention of the second polar body in sea bass eggs were investigated by altering the timing, intensity and duration of application of pressure and cold shocks. Treatment optima for cold shocks were 0–1°C for 15–20 min at 5 min after fertilisation (a.f.) and 8500 psi for 2 min at 6 min a.f. for pressure shocks. Meiogenesis was obtained by fertilising eggs with UV-irradiated homologous sperm (32,000 erg mm −2 ) and pressure or cold shocking eggs as above. 100% triploidy was induced following definition of liable periods for the disruption of the meiotic spindle obtained in gynogenesis. Ploidy investigations were performed on experimental groups by flow-cytometry. Verification of uniparental transmission in meiogens was carried out by microsatellite marker loci analysis. This work highlights the degree of variation in individual responses of selected broodstock to these agents. Finally, some preliminary results on heterologous fertilisation in sea bass with potential applications for gynogenetic studies are also provided.

Organogenesis of the exocrine pancreas in the sea bass, Dicentrarchus labrax L., reared extensively and intensively

Organogenesis of the exocrine pancreas in the sea bass, Dicentrarchus labrax, was found to comprise three main phases: (i) appearance of a primordium at hatching, in the form of a dorsal bud on the digestive tract which migrated to the right side, (ii) differentiation of exocrine cells and appearance of excretory ducts and blood vessels during the second half of the prelarval phase, and (iii) growth of the organ in larvae and juveniles. The pancreatic primordium appeared as a stratification of the dorsal wall of the digestive tract. Its migration was related to morphogenetic movements combined with twisting of the digestive tract. The first visible sign of exocrine cell differentiation was polarization. The first zymogen granules appeared 3 days after hatching and became abundant at the onset of the trophic phase, regardless of the rearing method. This synthesis coincided with the appearance of tubules and the common duct, but no excretion could yet be seen in their lumina. Until the time of mouth opening, the developmental sequence of cell differentiation did not depend on the rearing conditions and appeared to be genetically programmed. In contrast, the activity of the exocrine gland during the larval and juvenile periods appeared to depend more on dietary conditions. During these stages, the exocrine pancreas of intensively reared individuals fed ad libitum on Artemia was more active than that of extensively reared individuals, whose food was much less abundant. Larvae fed on artificial granules did not appear to secrete enzymes even though their digestive tract was full of food.

Effects of rearing density, size grading and parental factors on sex ratios of the sea bass (Dicentrarchus labrax L.) in intensive aquaculture

Abstract The effects of rearing density and size grading on sex ratios in 30 families of sea bass reared in the same tank from the fertilization stage onwards were investigated. Two extreme density treatments (high versus low) were applied in quadruplicates throughout the labile period for sex determination. An excess of males (88%) was found in all groups. Growth was faster under low density from 49 to 191 days post fertilization (p.f.) (27–10% relative difference in length) and was then equivalent between the two groups until the end of the treatments (414 days p.f.). Density had no effect on sex ratio, suggesting that the high densities usually applied in aquaculture are not involved in the systematic excess of males reported in farmed populations. The fish were genotyped at three to six microsatellite loci. This allowed them to be assigned to the individual breeders used in the mating design. The percentage of females was significantly influenced by both the dam and the sire, highlighting the existence of genetic variation of sex ratio. Repeated size grading performed from 84 to 199 days p.f. had no effect on the sex ratio of the overall population studied showing that sex determination had not been affected by the treatment. However, the highest percentages of females were found in the lead classes from 84 days p.f. Most of the fish in this lead group were descended from one dam and the percentage of females found in the individual families were higher in this class than in the non-graded group. These results show that females start growing faster than males long before morphological sexual differentiation occurs.