Multifactorial analyses revealed optimal aquaculture modalities improving husbandry fitness without clear effect on stress and immune status of pikeperch Sander lucioperca.

High mortality and impairment in growth rate during pikeperch (Sander lucioperca) ongrowing are among the major bottlenecks for its development in aquaculture. These failures may be related to high stress responsiveness since the rearing conditions are not yet optimized for this species. The objectives were to characterize the stress and immunological responses of pikeperch to major aquaculture modalities, and to identify the optimal aquaculture conditions for improving its welfare status. In a screening experiment, eight factors considered as relevant for the welfare of pikeperch were compared in two modalities using a fractional multifactorial design (28-4). Each experimental unit represented a combination of 8 factors in two modalities including grading, stocking density (15 vs 30kg·m-3), feed type (sinking vs mid-floating), light intensity (10 vs 100 lux), light spectrum (red vs white), photoperiod (long vs short), dissolved oxygen (60 vs 90%) and temperature (21 vs 26°C). Fish sampling occurred on days 36 and 63. Stress markers (glucose, cortisol and brain serotonergic activity), innate immune parameters (plasma lysozyme and complement activities) and expression of some immune genes were assessed. Light intensity and the type of feed clearly appeared as directive factors for pikeperch culture. A strong effect of the feed type was observed on growth parameters while survival was impacted by high light intensity. Light characteristics (intensity, spectrum and photoperiod) and temperature were identified as determining factors for physiological and immune markers. No obvious relation was established between stress status and growth parameters and further investigations are needed to improve management strategies of pikeperch culture and knowledge on the relations between environmental conditions, stress and immunity in percid fish.

The effect of hatching time on the bioenergetics of northern pike (Esox lucius) larvae from a single egg batch during the endogenous feeding period.

Size, caloric value and chemical composition were measured separately in the progeny of two northern pike (Esox lucius) females at 3-day intervals during the endogenous feeding period from hatching to final yolk resorption. Tissue, yolk and entire larvae were analysed separately in three groups of larvae that hatched at different times (between 88 and 106 degree-days post-fertilization). An integrated approach with the Gompertz model was used to compute the yolk conversion efficiency and time to maximum tissue size in early, mid and late hatched larvae. At hatching, unresorbed yolk of early hatched larvae contained more energy (39.20 J) and more protein (0.99 mg) compared to the yolk of larvae that hatched later (38.13 J and 0.92 mg protein for late hatched larvae, p < 0.05). In contrast, a significant reduction in tissue weight (-0.7 mg DW) and protein content (-0.5 mg) was found in early hatched larvae compared to those which hatched later (p < 0.05). Between days 9 and 12 post-hatching (108 and 144 degree-days post-hatching), close to the final yolk resorption, late hatched larvae stopped growing and their tissue began to be resorbed. This tissue resorption time was delayed in early hatched larvae which presented at the end of the experiment a greater tissue weight than late hatched ones. Yolk conversion efficiency in term of energy from hatching to complete yolk resorption stage was significantly higher for early and mid hatched larvae (51%) compared to late hatched ones (44%) (p = 0.004). Furthermore, the time to maximum tissue size was found to be negatively related to hatching time which implies that early hatched larvae take longer time to switch from one developmental stage to the next. The maximum tissue dry weight and energy content were found to be reached at approximately the same age post-fertilization for both early hatched and late hatched larvae, suggesting that the principal steps in a fish's lifespan are better correlated with time of fertilization than hatching time.

Effects of geographic source, rearing system, and season on the nutritional quality of wild and farmed Perca fluviatilis.

The effects of season, geographic source (Lake Geneva, Rhine River), and rearing system (extensive, semiextensive, and intensive systems) on the lipid content and FA composition of fillets of Perca fluviatilis were studied. Significant differences in the total lipid content were found between fish coming from the Rhine River and Lake Geneva (1.21 and 1.48%, respectively). Seasonal effects were investigated quarterly for perch sampled in the Rhine River. Intensively reared perch displayed a higher lipid content (1.48%) than the other farmed perch, i.e., 1.26% for a semiextensive system and 1.16% for an extensive system. No significant difference in lipid content was found (i) between lacustrine fish and intensively reared fish or (ii) among fish from the Rhine River and the semiextensive or extensive rearing systems. The main FA were 22:6n-3 (DHA, 21.3-37.1% of total FA), 16:0 (17.7-20.2%), 20:5n-3 (EPA, 9.2-13.2%), 18:1 (8.0-11.5%), 20:4n-6 [arachidonic acid (ARA), 1.9-10.7%], 16:1 (4.3-6.0%), and 18:2n-6 (2.1-6.0%). In comparison with perch coming from the Rhine River, the lacustrine fish were characterized by higher total n-6 PUFA and a lower proportion of both total monounsaturated FA (MUFA) and total n-3 PUFA. Among rearing systems, extensively farmed fish had higher n-6 PUFA and lower n-3 PUFA contents. Wild fish showed higher ARA and 18:2n-6 than farmed fish. They also had significantly more EPA (12.5-13.2%) than farmed perch (9.2-10.9%). For DHA, no difference existed between (i) the lacustrine fish (31.9% of total FA) and the intensively reared fish (33.0%) and (ii) the Rhine (37.1%) and semiextensively reared fish (36%). Effects of size, diet composition, and environmental conditions on the total lipid contents and FA composition are discussed.

Pesticide pressure and fish farming in barrage pond in northeastern France. Part III: how management can affect pesticide profiles in edible fish?

PURPOSE: The quality of fish produced in ponds needs to be ensured. Indeed, pond is often strongly connected to an agricultural watershed, and pesticides are a main health and environmental issue of concern. In this context, the purpose of this study is to highlight the management practices which could impact the pesticide contamination profiles in edible fish and to give recommendations for better practices. METHODS: A principal component analysis, coupled to a hierarchical cluster analysis, was performed to evaluate temporal evolution of contamination profiles and to assess variability among fish species and among sites according to watershed characteristics. The explicative variables correspond to muscular concentrations of pesticides (azoxystrobin, clomazone, diflufenican, carbendazim, isoproturon, metazachlor, napropamid) in three species of fish (Perca fluviatilis, Cyprinus carpio and Rutilus rutilus), caught in five ponds during two sampling campaigns. Management data are added variables in order to discuss about parameters suspected to be implicated in the contamination profiles recorded. RESULTS: This work shows that high amounts of pesticides applied, short crop rotation durations and bare soil practices led to contamination of sediments and fish and were associated to a "bad" management of watershed. Breeding fish that had low masses and establishing the fishing period at the end of winter seemed to be "bad" management of pond. Aggravating topological parameters were big watershed coupled to small pond and high proportions of sand soils in the watershed. CONCLUSIONS: Reducing amounts of pesticide used (e.g. policy agency plans, farmer acceptance), favouring long-term rotations and inter-cultures, adapting pond creation and fish farming practices to watershed management and topography all could reduce pesticide levels in edible fish and contribute to a better sustainability of the extensive fish farming in pond.