Mortality and non-specific immune response of Eurasian perch, Perca fluviatilis, during the spawning season

Perch breeders showed high mortality rates during the spawning season. This could be linked to immunosuppressive effects of environmental conditions or reproduction.     

Off-Season Spawning of Eurasian Perch Perca Fluviatilis

This study was designed to determine the effects of the selection for body weight and of two final warming durations during an out-of-season reproductive cycle on gonad recrudescence, plasma steroid levels and spawning in Eurasian perch Perca fluviatilis males and females. Two different bodyweight classes (200–250 and 350–400 g) and two different warming periods (1 or 2 months) were studied.At the end of the chilling period, a significant effect of the selection for body weight was observed on gonad development whereas fish were the same age. According to higher levels in testosterone (12 ng mL^–1), a better development was recorded for smaller breeders (P < 0.05). A short water warming period up to 14°C (1 month v.s. 2 months) allowed higher rates of females with completed gonadogenesis (33–38% v.s. 7–8%) and spawning (31–33% v.s. 0%) (P < 0.05). Spontaneous out-of-season spawning (17 ribbons) and larvae were obtained. Relative fecundity was about 100 eggs g^–1 of female body weight. Five ribbons were partly fertilized with a rate ranging from 5 to 90%. These studies have shown that delayed spawning in Eurasian perch can be obtained by a temperature manipulation, but results are not sufficient because of low stimulation rate of females, low spawning rates and high heteroge-neity of fertilization rates. The effects of other environmental factors like photoperiod should be tested in further experiment to improve the protocol inducing out-of-season spawning production.     

Influence of photoperiod regimes on the Eurasian perch gonadogenesis and spawning

The effects of photoperiod regimes under ambient temperature on gonadal growth and spawning were investigated in Eurasian perch, Perca fluviatilis. This study showed that continuous lighting inhibited reproduction in male and female fish with very low sex steroid levels being measured. Constant LD 16:8 resulted in heterogeneous gonad development and sex steroid levels compared to natural regime, with only 54% of females and <?30% of males maturing. Seasonal variations in daylength also seem to be required to control reproduction.     

Involvement of sex steroids in final stages of oogenesis in Eurasian perch, Perca fluviatilis

Significant plasma 17,20β-dihydroxy-4-pregnen-3-one peaks were measured for the first time in female Eurasian perch, Perca fluviatilis, during the pre-ovulatory period, reaching 3.5 ng ml^?1, but was not synchronized with final maturation and ovulation stages.     

Hatching time effect on the intra‐spawning larval morphology and growth in Northern pike (Esox luciusL.)

Based on the analysis of 11 morphometric variables of body (total length, body area and perimeter, myotome height and eye diameter) and yolk sac (length, height, area, perimeter and volume) of pike larvae, the aim of this study was to evaluate how larval size at hatching and growth of larvae hatched from single egg batches vary according to three hatching times: early, mid and late. Hatching time structures strongly pike larval morphometrics. Early hatched larvae have smaller body sizes at hatch, faster growth and higher yolk use efficiency than late hatched ones. Early hatched larvae seem to be premature and hatch at precocious developmental stage whereas late hatched individuals continue their growth within the egg shell and hatch at larger size but with lower reserves (yolk). A compensatory growth phase was observed for the early hatching pike larvae particularly during the first 5 days post hatch. Consequently, no significant difference in body parameters was recorded from day 10 post hatching whatever the hatching time. The higher growth accomplished by early hatched larvae may be related to a particular metabolic activity that converts more efficiently yolk into body tissues.     

The effect of hatching time on the bioenergetics of northern pike (<Emphasis Type="Italic">Esox lucius</Emphasis>) 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.     

Simultaneous effects of nutritional and environmental factors on growth and flesh quality of Perca fluviatilis using a fractional factorial design study

Fractional factorial design is a practical approach for studying multiple factors, with a minimum of experimental units. The objective of this work was to study the simultaneous effects of nutritional and environmental factors on both growth and flesh quality of common perch (Perca fluviatilis), a new inland aquaculture species. This study sought answering the two following questions: (i) which combinations of factors allow improving growth, food efficiency, and technological, sensorial and nutritional qualities? (ii) is it possible to simultaneously improve growth performances and flesh quality? In a first experiment, twelve factors (7 nutritional and 5 environmental factors) were each tested at 2 levels in a fractional factorial design in 24 independent recirculating 500 L tanks. The best 4 combinations identified in this first experiment were then validated in a second experiment. The first phase of the multifactorial approach used here allowed revealing emergent information: i) there is a combination of factors that allows reducing both the heterogeneity of the production and the losses of nitrates and phosphates, while preserving good characteristics of growth and quality of fillets; ii) it is possible to improve the quality of the aquatic production system, without decreasing significantly growth efficiency; iii) the effect of a given factor, even such an important one like diet, temperature or target biomass, depends on the levels of the other rearing factor levels, thus the usual reference optimum used for a given factor has no meaning theoretically and can be questioned according to the levels of the other factors which act altogether on the functioning of the rearing system.The input factor combinations resulting in a significant enhancement of single output variables or several output variables were identified (e.g. improvement of feed efficiency, and/or fillet docosahexanoic acid content). Our results clearly demonstrate a strong interdependence of input factors into the animal rearing system, particularly between nutritional and environmental ones.     

Effects of dietary factors, stocking biomass and domestication on the nutritional and technological quality of the Eurasian perch Perca fluviatilis

The ante mortem determinism of the quality components in fish is multivariate. Among the various influencing factors, the effects of (i) rearing biomass, (ii) dietary features and (iii) domestication process on the technological and nutritional variables in perch Perca fluviatilis here were studied using two-levels fractional factorial design 2^4-1 (resolution IV). This work allowed identifying two main factors, i.e. domestication and diet composition, which influence both technological and nutritional variables. Domestication was the parameter showing the greatest effect on both filleting yield (FY) and total saturated fatty acids (SFA) content, whereas diet composition chiefly influenced viscerosomatic index (VSI) and total poly- and mono-unsaturated fatty acids (PUFA and MUFA) contents. Domesticated fish exhibited higher FY (42.8%) and total SFA (25.1% of total fatty acids or FA) content than wild fish (FY = 40.1%, total SFA = 22.9%). Concerning the effect of food composition, diet including only fish oil as lipid source (FO) induced higher VSI than diet including vegetable oil (FV) VSI = 8.8% vs 7.4%, respectively). Moreover, FV diet induced higher n-6 PUFA but lower n-3 PUFA contents in fillets than did the FO diet (total n-6 PUFA = 6.3% vs 5.4% and total n-3 PUFA = 52.6% vs 55.2% of total FA respectively). FV fish fillets had significantly higher total MUFA (17.7% of total FA) contents in muscle than FO fish (14.8%). Concerning this last variable, domestication played only a role in interaction with diet composition. With FO diet, no difference in total MUFA content between wild and domesticated perch was noticed. However, total MUFA content increased with FV diet and was significantly higher in fillets of wild fish (18.7% vs 16.6% of total FA for domesticated). No effect of either feeding rate or initial biomass on the body composition was noticed. In addition, perivisceral fat content was not influenced by any treatment.