Charles Mélard

Size heterogeneity, cannibalism and competition in cultured predatory fish larvae: biotic and abiotic influences

Growth heterogeneity is a central problem in larviculture and especially in predatory species. It can be influenced by a wide range of intrinsic and environmental factors, of which the respective influences are largely unknown. The role of non-interactive (temperature, day length, light intensity, food availability and composition) and interactive factors (stocking density, initial size heterogeneity, hatching time) on growth, survival and size heterogeneity was measured in larvae and post-larvae of the European seabass Dicentrarchus labrax and Eurasian perch Perca fluviatilis. Embryos hatching later than others were found less competitive than those hatching earlier in both species, but to a greater extent in perch. By contrast, the final size heterogeneity in both species was independent from the initial size heterogeneity or recurrent size sorting. High stocking density had a positive effect on perch larvae, no effect on seabass larvae and a negative impact on the post-larvae of both species, owing principally to density-dependent access to food. Day length and light intensity produced contrasting results in larvae and post-larvae. Larvae of both species performed better under bright light and continuous day length. Post-larvae of seabass performed equally well at different light levels but did better under short day lengths, whereas post-larvae of perch were unaffected by day length but performed better under reduced light levels. Increasing food availability resulted in increasing performance of perch larvae, although cannibalism was higher for submaximal than for maintenance rations. The similarity between the two species at the larval stage, and differences at the post-larval stage can be accounted for by the increasing specialisation towards specific environments and niches. Regarding the impact of rearing factors on growth, survival and size heterogeneity, interactive variables impacted essentially on growth and survival, whereas size heterogeneity was chiefly influenced by non-interactive variables, either directly or indirectly via interactive mechanisms such as cannibalism and size-dependent mortality.

The effect of PIT tags on growth and physiology of age-0 cultured Eurasian perch Perca fluviatilis of variable size.

Abstract For many biological reasons, it is often necessary to tag and monitor fish from a very early age. However, tagging can adversely affect fish, especially for high tag to body weight ratios. To determine the minimum size for passive integrated transponders (PIT) tagging in juvenile perch Perca fluviatilis , surgical implantation was evaluated in fish ranging from 1.67 to 10.62 g (55–96 mm FL). The survival, gonadal development, and capacity of tagged perch to store abdominal fat was affected neither by the tagging procedure, tag presence, nor tag to body weight ratio. Four months after tagging, no tag had caused internal damage or had been expelled, despite about 95% of them becoming encapsulated by host tissues. Negative effects from tagging were restricted to slower healing rates, and depressed growth of fish with high tag to body weight ratios during the first post-tagging days, which was compensated for by catch-up growth within less than 2 weeks. Surgical PIT tagging can be confidently applied to perch weighing less than 2 g, but the collection of biological data should be delayed by about 2 weeks after tagging. X-ray photographs revealed variable orientations of tags (95% CI: 26°) and slight (ca. 4°) changes of orientation over time. These discrepancies may affect the probability that the tag is detected by automatic data entry stations, and should be compensated for by using smaller antennas (≤87% of maximal antenna size).

EVALUATION OF IMPLANTATION PROCEDURES FOR PIT-TAGGING JUVENILE NILE TILAPIA

Abstract We evaluated three alternative procedures for tagging juvenile Nile tilapia Oreochromis niloticus (1.9–13.7 g) with passive integrated transponder (PIT) tags: injection with hypodermic syringe injectors (N = 40) and abdominal surgery with or without suturing (N = 55 and 40, respectively). The survival of Nile tilapia tagged with injectors was low (10–50% at 10 d) and proportional to fish size because of the difficulty of controlling the penetration of the syringe into the intraperitoneal cavity following the piercing of the body wall. Surgically implanted fish had much higher survival rates (78–100% at 10 d). Suturing reduced the risks of tag expulsion and protrusion of the viscera through the open incision within the first 3 d following surgery (10% risk in the nonsutured fish). Over the first 3 d after tagging, tagged fish showed depressed growth rates (to a greater extent in smaller fish and proportionally greater in sutured fish) but showed normal growth later on. These results demonstrate th...

Effect of stocking density on the dynamics of cannibalism in sibling larvae of Perca fluviatilis under controlled conditions

The effect of stocking density (10, 31.6 and 100 larvae l 1 ; three replicates per treatment) on the day-by-day dynamics of survival, growth and cannibalism was examined in sibling perch larvae reared from eyed-egg stage in 100-l cages (16L:8D, 20.0F0.5 jC, O2z6.0 mg l 1 ; feeding in excess with live Artemia nauplii during the photophase) during the first 3 weeks of exogenous feeding. Larvae unable to achieve the transition to exogenous feeding died in between 7 and 11 days post-hatch. Later, mortality from causes other than cannibalism never exceeded 1% day 1 . Cannibalism did not start before days 10–11 and first consisted in the incomplete ingestion of prey attacked tail first, exclusively. This type of cannibalism never caused losses higher than 2.0% of the initial stock, and ceased after days 16–18. From days 12–14 onwards, differential growth was apparent, and cannibals turned to complete cannibalism of small prey ingested head first, which caused greater losses (28–53% of the stock). Increasing the stocking density did not compromise growth and decreased the overall impact of cannibalism through several complementary mechanisms: (i) a postponed emergence of cannibalism, (ii) a lower proportion of cannibals in the population, and (iii) probably a lower rate of cannibalism per capita as predation was complicated and less directed at high stocking density. D 2003 Elsevier Science B.V. All rights reserved.

Growth and nutritional status of Eurasian perch Perca fluviatilis fed graded levels of dietary lipids with or without added ethoxyquin.

Abstract An 8-week experiment was conducted to establish the optimal dietary lipid levels in relation to feed intake, growth rate, lipid storage and nutritional status of juvenile Eurasian perch. All diets contained 40% crude protein and graded levels (ranging from 6% to 18%) of stabilized (addition of ethoxyquin as antioxidant) or unstabilized (no addition of ethoxyquin) menhaden oil as lipid source. Feed intake was high in all groups fed diets containing stabilized lipid and intermediate in fish fed 6% dietary lipid without ethoxyquin. On the other hand, feed intake was significantly lower in fish fed 12% and 18% unstabilized dietary lipid but increased during the experiment, indicating an habituation of perch to accept oxidised lipid diets. Dietary lipid concentrations and addition of ethoxyquin significantly influenced weight gain and feed efficiency, the best results being obtained at 12% and 18% stabilized lipid, while the poorest growth was recorded at high concentration of unstabilized lipids (18%). Fatty acid composition of perch tissues (muscle, viscera and liver) was significantly affected by the dietary treatments. At 12% and 18% dietary lipid, the addition of ethoxyquin significantly increased the total polyunsaturated fatty acid concentration in perch liver and muscle as well as the n−3/n−6 ratio. Concentrations of linolenic, eicosapentaenoic and docosapentaenoic acids were low in fish fed unstabilized lipid diets while docosahexaenoic acid was not influenced by the absence of ethoxyquin. Ultrastructure observations revealed noticeable modifications in the hepatocytes of fish fed high lipid diets, with a large accumulation of lipid droplets in the cytoplasm and a marked reduction of mitochondria and rough endoplasmic reticulum.

Effects of dietary fat levels on growth, feed efficiency and biochemical compositions of Eurasian perch Perca fluviatilis

A feeding experiment was conducted for 10 weeks with Eurasian perchPerca fluviatilis juveniles (33.1–35.9ginitial body weight) using three dietary fat levels (11.7, 15 and 19.3%). Theresults showed that increasing dietary fat content increased growth, feedefficiency and protein utilization of perch (P < 0.05) but did not affectmortality. Lipid analysis showed that the composition of some perch tissueswerealso significantly affected by increasing dietary fat content, with an increaseof lipid deposition in the viscera (from 64.9% in fish fed 11.7 % fat to 78.8%in fish fed 19.3% fat) and liver (from 12.4 to 23.8%) (P < 0.05), while themuscle composition was not affected by the dietary treament. Highdocosahexaenoic acid (22:6n-3, DHA) and high docosahexaenoicacid/eicosapentoenoic acid (20:5n-3, EPA) ratios were found in the liver andmuscle lipids as compared to the dietary fatty acid compositions, suggestingthat Eurasian perch might possess a high capability of converting the longchainhighly unsaturated fatty acids, especially DHA from its dietary precursors.

Effect of ambient water temperature on sex determinism in the blue tilapia Oreochromis aureus

Fry from six egg batches of Oreochromis aureus were reared at 21°C (40 days), 27°C and 34°C (25 days) then at 27°C and sexed. High temperature regimes produced high male ratios (mean male percentage: 97.8%) while intermediate thermal regime gave balanced ratios (mean male percentage: 63.0%). Low temperature delayed the differentiation of gonads. Perspectives of using high temperature for the production of monosex populations are discussed.

Skin mucus of Cyprinus carpio inhibits cyprinid herpesvirus 3 binding to epidermal cells.

Cyprinid herpesvirus 3 (CyHV-3) is the aetiological agent of a mortal and highly contagious disease in common and koi carp. The skin is the major portal of entry of CyHV-3 in carp after immersion in water containing the virus. In the present study, we used in vivo bioluminescence imaging to investigate the effect of skin mucus removal and skin epidermis lesion on CyHV-3 entry. Physical treatments inducing removal of the mucus up to complete erosion of the epidermis were applied on a defined area of carp skin just before inoculation by immersion in infectious water. CyHV-3 entry in carp was drastically enhanced on the area of the skin where the mucus was removed with or without associated epidermal lesion. To investigate whether skin mucus inhibits CyHV-3 binding to epidermal cells, tail fins with an intact mucus layer or without mucus were inoculated ex vivo. While electron microscopy examination revealed numerous viral particles bound on the fins inoculated after mucus removal, no particle could be detected after infection of mucus-covered fins. Finally, anti-CyHV-3 neutralising activity of mucus extract was tested in vitro. Incubation of CyHV-3 with mucus extract reduced its infectivity in a dose dependent manner. The present study demonstrates that skin mucus removal and epidermal lesions enhance CyHV-3 entry in carp. It highlights the role of fish skin mucus as an innate immune protection against viral epidermal entry.

Effect of water temperature on survival, growth and phenotypic sex of mixed (XX–XY) progenies of Nile tilapia Oreochromis niloticus

Abstract The ambient temperature during early ontogeny affects the phenotypic sex of various fish species, including the Nile tilapia. Forty-seven groups of Nile tilapia (220 to 350 fish each) from 11 progenies were exposed to different rearing temperatures (20.4–39.0°C) during the first 28 days of exogenous feeding (50-l aquariums, 12L:12D, feeding ad libitum) to model the relationship between ambient temperature and (a) the reversal of phenotypic sex in this species, (b) fish growth and survival rates. The efficacy of the masculinising treatment was estimated with respect to the survival rates in the treatment and control groups (i.e., T ° of circa 27°C), and to their respective sex ratios, in order to take into account the possibility that mortality affected mainly females (minimum efficacy, E m i ) or males (maximum efficacy, E M i ), depending on ambient temperature, and parental influence. Ranges of masculinising efficacy were given by log-logistic equations ln( E m i (1− E m i ) −1 )=−27.495+0.757 T ° ( R 2 =0.548) and ln( E M i (1− E M i ) −1 )=−36.707+1.050 T ° ( R 2 =0.709). The corresponding temperatures giving a masculinising efficacy of 90% were 37.8°C and 39.2°C, for E M i and E m i , respectively. As a corollary, high percentage male progenies could only be obtained at very high temperatures, close to the upper incipient lethal temperature (UILT) of juvenile tilapia (38.5–39.0°C). During the treatment period, the survival and growth of fish reared at circa 37°C averaged 41.9% and 74.5% of those of fish reared at 27–33°C, resulting in a production loss of over 70%, which was not compensated after the temperature was returned to 27°C. These results suggest that the advantage of producing faster growing males of Nile tilapia at high temperature would hardly compensate the loss of production incurred during the masculinising treatment, unless after the selection of the most thermosensitive strains or breeders.

Spleen immune status is affected after acute handling stress but not regulated by cortisol in Eurasian perch, Perca fluviatilis.

The effects of acute stress on immune status and its regulation by cortisol/corticosteroid receptors have received little attention in percids. To address that question, we investigated the physiological and immune responses of Eurasian perch, Perca fluviatilis to acute stress. We exposed immature perch to an 1-min exondation and measured at 1 h, 6 h, 24 h and 72 h post-stress: (1) stress-related parameters including plasma cortisol and glucose levels, (2) immune parameters in the plasma and in the spleen (complement, respiratory burst and lysozyme activity, total immunoglobulins; gene expression of lysozyme, complement unit 3, apolipoprotein A1 and 14 kDa, hepcidin and chemotaxin) (3) the corticosteroid receptors gene expression in the spleen after having cloned them. In addition, the in vitro effects of cortisol on the spleen immune parameters were also investigated. Plasma cortisol and glucose levels increased markedly 1h post-stress and returned at basal levels after 24 h. P. fluviatilis mineralocorticoid receptor, but not glucocorticoid receptors, was significantly up-regulated both in vivo after the stress and in vitro by cortisol at a physiological concentration (100 ng/ml). The plasma immune parameters were not significantly affected by the stress. In contrast, spleno-somatic index, spleen lysozyme activity, lysozyme and hepcidin gene expression were depleted and total immunoglobulins increased along the whole time-course (1-72 h). But, these immune parameters were not regulated in vitro by cortisol at physiological or supra-physiological doses. Our results indicate that handling stress may affect spleen antibacterial defences without clear effects on circulating immune compounds and that the elevation of plasma cortisol after handling stress may not be related to the regulation of this splenic response.