Pierrick Haffray

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).

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.

Production of meiotic gynogenetic and triploidsea bass, Dicentrarchus labrax L. 1. Performances, maturation and carcass quality

Abstract Meiotic gynogenetic and triploid sea bass were produced by pressure shocks according to a previously published protocol. Pressure-treated groups did not survive as well as controls during early development and larval rearing. Performances, sexual maturation and carcass quality were examined over a period of 34–45 months. At the age of 34 months, growth of the gynogenetic fish was comparable to that of the control but inferior in the triploid fish. A predominance of male fish was found within the triploid groups, while diploid and meiotic gynogenetic fish showed equal proportions of the sexes. Gonadal maturation in triploid fish was significantly impaired, particularly in the females that showed rudimentary ovaries. Triploid males exhibited primary maturation but proved to be gametically sterile. Pressure-induced triploids did not grow as well as diploids, but these results might be ascribed to specific on-growing conditions (communal rearing). The performance of gynogenetic sea bass was comparable to that of control. The superiority of diploid fish over their triploid counterparts was confirmed during the final growing period and more clearly so in females. Performances of triploids varied according to their maternal origin. Overall, striking qualitative differences between diploid and triploid fish were found at the age of 34 and 45 months, although the results varied in a gender-specific manner. A strong maternal effect was also observed. The potential advantages of triploid sea bass for aquaculture purposes are discussed.

Saline preferendum for the European sea bass, Dicentrarchus labrax, larvae and juveniles: effect of salinity on early development and sex determination

Abstract The sea bass, Dicentrarchus labrax , is an eurhyaline marine fish. Juveniles of this species are known to frequent estuaries and lagoons where salinity is lower than in the open sea. Sex determination occurs during this phase of fish life and has been shown labile and sensitive to environmental factors. In this work, the effect of rearing salinity on sex determination and early development of the sea bass was investigated. An excess of males (87%) was found in all groups and the salinity level [(natural sea water salinity, mean: 37‰) vs. (15‰)], when maintained constant, had no effect on the sex-ratio. The transfer from low to high salinity at 93 days post-fertilization (p.f.) increased the percentage of males (93%) suggesting that sexual differentiation in this species may be influenced by such an osmotic stress. Growth was improved by a 15‰ salinity at the beginning of larval rearing (14 days p.f.) and at the end of pre-growing (234–458 days p.f.), periods during which low temperatures were applied. Survival during larval rearing and nursery were also improved in the groups reared at low salinity and so was swimbladder inflation. These results show that sea bass juveniles have a low saline preferendum, a finding that corresponds to the conditions they actually encounter in the wild during their juvenile ecophase; sex determination is not directly modulated by the salinity level but seems to be subjected to complex environmental regulations.

Quality traits of brown trouts (Salmo trutta) cutlets described by automated color image analysis

Twenty-seven-month-old brown trout from two genotypes, i.e., control and lines selected for growth, were reared in seawater cages and fed two diets containing 16% and 26% fat (LFR and HFR) during the last 4 months of growth to maximise heterogeneity at slaughtering at 3.8 kg (n=48). Image segmentation methods were developed and applied to quantify quality traits on cutlets by color image analysis including flesh color (L*a*b), myoseptes (visible fat), myomera, and peripheral surfaces. Results were also compared to lipids evaluated by Soxhlet or by NMR. Color image analysis provided results on the effects of feeding and selection on the development of various tissues representing edible flesh.

Different growth and processing traits in males and females of European catfish, Silurus glanis

Two experiments were developed in France to assess whether growth and processing traits differ for males and females in the European catfish, Silurus glanis. In the first experiment, fish were raised from 5 to 200 g in a pond for 7 months. A significant sex effect is demonstrated in males for live weight at the end of the experiment (males 147.5±5.4 g vs females 132.9±4.9 g) and head index (males 20.6±0.1 % vs females 21.2±0.1 %, P < 0.05). In the second experiment, fish were raised from 885±196 g to 2 266±418 g in a recirculated system at 20.7±1.4 °C for 120 days. A differential growth between the sexes is also registered. Males are heavier and longer (+ 357 g or + 17.0 % and + 6.2 % in length at day 120) and present a higher gutted weight and yield (+ 367 g or + 18.7 %; 95.0±0.9 % vs 93.8±1.8 %) and fillet weight (+ 233 g or + 20.9 %) than females after slaughter.

Parentage assignment with genomic markers: a major advance for understanding and exploiting genetic variation of quantitative traits in farmed aquatic animals

Since the middle of the 1990s, parentage assignment using microsatellite markers has been introduced as a tool in aquaculture breeding. It now allows close to 100% assignment success, and offered new ways to develop aquaculture breeding using mixed family designs in commercial conditions. Its main achievements are the knowledge and control of family representation and inbreeding, especially in mass spawning species, above all the capacity to estimate reliable genetic parameters in any species and rearing system with no prior investment in structures, and the development of new breeding programs in many species. Parentage assignment should not be seen as a way to replace physical tagging, but as a new way to conceive breeding programs, which have to be optimized with its specific constraints, one of the most important being to well define the number of individuals to genotype to limit costs, maximize genetic gain while minimizing inbreeding. The recent possible shift to (for the moment) more costly single nucleotide polymorphism markers should benefit from future developments in genomics and marker-assisted selection to combine parentage assignment and indirect prediction of breeding values.

Rapid quantification of muscle fat content and subcutaneous adipose tissue in fish using MRI

The potentiality of MRI to quantify fat content in flesh and subcutaneous fat in fish cutlets was investigated. Low measurement time was aimed at in a view to handling large number of samples needed in selective breeding programs for example. Results on fresh and frozen-thawed cutlets were compared to assess this way of conservation. As MRI generates unwanted spatial variations of the signal, a correction method was developed enabling the measurement on several cutlets simultaneously in less than 3 min per sample. For subcutaneous fat, the results were compared with vision measurements. High correlations between both techniques were found (R(2)=0.77 and 0.87 for the ventral and dorsal part). Fat in flesh was validated vs NMR measurements. No statistical difference was found between fresh and frozen-thawed cutlets. RMSE was respectively 0.8% and 0.89%. These results confirmed the potentiality of MRI for fat measurement in fish particularly for a large number of samples.

Changes in motility, ATP content, morphology and fertilisation capacity during the movement phase of tetraploid Pacific oyster (Crassostrea gigas) sperm

Changes in sperm features during the movement phase are especially interesting to study in external fertilization species whose sperm duration movement is long because this implies a significant adaptation of moving cells to the external medium. This study describes the changes in tetraploid Pacific oyster sperm characteristics in relation to time post activation. Sperm individually collected on three tetraploid males were activated in seawater. Their features were analysed over a 24h period and compared to a sperm pool collected on three diploid males as a reference. The percentage of motile spermatozoa, the intracellular ATP content, and the fine structure of spermatozoa were studied in relation to time post activation. Furthermore, the fertilisation capacity of sperm individually collected on five diploid males was assessed after 1 and 24h post activation. A forward progressive movement was maintained for at least a 20h duration. Compared to diploid males, the percentage of motile spermatozoa was lower in tetraploid males. The intracellular ATP concentration was higher in spermatozoa from tetraploid males than in spermatozoa from diploid males. A decrease in ATP content was observed in the first 6h post activation and severe alterations were observed in sperm morphology after 24h. Then, a lower fertilisation capacity of sperm from diploid males was observed at the end of the movement phase. The cessation of Pacific oyster sperm motility was unlikely caused by ATP consumption as ATP concentration was still high at the end of sperm movement but rather caused by drastic changes in sperm morphology. Compared to sperm collected on diploid males, the lower quality of sperm from tetraploid males was emphasized by a shorter movement duration and deeper morphological alterations at the end of the movement phase.

Comparison of growth performances of three French strains of common carp (Cyprinus carpio) using hemi-isogenic scaly carp as internal control

Three strains of mirror carp originating from important regions of carp culture in France (Brenne, Dombes, Forez) were compared for growth at 5 weeks, 1 summer and 2 summers of age in ponds using a paternal cross on the same Dombes dams. An internal scaly control was produced by crossing an homozygous inbred strain on the same dams and mixed with the tested strains in all ponds in a proportion of 1:3. No between-strain differences in weight were seen at any time when taking into account the weight of the internal control. However, the internal control weight at 2 summers of age was lower than that of the tested strains (P<0.05). The use of the internal control divides the number of replicates needed to have a good statistical power by 5 at 5 weeks and by 8 at 2 summers, when compared to separate testing without control. No genotype by environment or strain-control interactions were detected. The validity and optimisation of the use of an internal control in strain testing are discussed.