Constant darkness negatively affects the outcome of hormonally induced reproduction in cultured Eurasian perch females.

This study aimed to assess the effect of constant darkness applied to fish during controlled breeding on reproductive traits in domesticated females of Eurasian perch. Based on the assumption that keeping fish in constant darkness during the reproduction operation may reduce stress, suspected to be responsible for variable spawning effectiveness in this species. Two conditions were assessed (16 h light per day [group 16L] and constant darkness [group 0L], two tank replicates per condition). The reproductive protocol involved a 7-day-long adaptation period for group 0L where photoperiod was reduced by 2.3 h a day down to constant darkness. After the adaptation period, two hormone injections (salmon gonadoliberin analogue) were applied to both groups: priming (10 µg/kg) and resolving (25 µg/kg) with a 7-day interval between them. During the study, morphometric indices were recorded and blood, brain, and pituitary samples were collected to assess stress markers and determine hypothalamic-pituitary-gonadal axis functioning via measuring blood plasma hormones, as well as gonadoliberin and gonadotropins (luteinising hormone [LH] and follicle-stimulating hormone [FSH]) transcript abundance (n = 7 for each group at each sampling point). In addition, kinetics of the final oocyte maturation (FOM) process, ovulation rate, and egg quality of each group was monitored (n = 12 for each group). The results indicated that there were no differences in terms of morphometry, FOM kinetics, and most stress indices between groups throughout the experiment, except haematocrit, which increased immediately following the acclimation period in fish kept in darkness. Constant darkness negatively affected plasma levels of 17α,20ß-dihydroxy-4-pregnen-3-one (DHP) and LH transcript expression at the time of the second hormone injection. This indicated that exposure to constant darkness negatively affected priming of the hormonal dose applied, resulted in the disruption of ovulation, and reduced ovulation rates (50%) for group 0L, as compared to 16L (91%). The findings of this study clearly indicate that constant darkness may have significant deleterious effects on reproductive traits throughout out-of-season induced, hormonally supported, controlled reproduction. Therefore, we advise against the use of constant darkness when managing broodstock reproduction in domesticated Eurasian perch.

D1, but not D2, dopamine receptor regulates steroid levels during the final stages of pikeperch gametogenesis.

In pikeperch, Sander lucioperca, aquaculture hormonal treatment is usually applied to synchronize ovulation. However, the effect of dopamine (DA) receptor antagonists, in particular those blocking the D1 DA receptors, remains unknown. Thus, the aim of the present study was to investigate and compare the effects of D1 and D2 DA receptor antagonists on the sex-steroid production and reproductive performance of the species. Two experiments were performed during which mature pikeperch females were injected with different molecules: NaCl 0.9% (negative control) or human chorionic gonadotropin 500 IU/kg (positive control) in both experiments, metoclopramide (a D2 receptor antagonist; 4 mg/kg or 20 mg/kg) or SCH23390 (a D1 receptor antagonist; 0.8 mg/kg or 4 mg/kg) alone (experiment 1) or in combination with a salmon gonadotropin-releasing hormone analogue (sGnRHa at 25 µg/kg; experiment 2). In experiment 2, fish were also injected with sGnRHa (25 µg/kg) as positive control. Samplings of oocytes and blood were performed on the day of injection and after 24 h (both experiments), after 48 h (experiment 2) and at the time of ovulation (both experiments). In non-ovulating fish, samplings were performed 7 days (experiment 1) or 14 days (experiment 2) after injection. In experiment 2, various zootechnical parameters of fertilized eggs were recorded (survival, hatching and malformation rates). The two antagonists alone were ineffective in inducing the final stages and regulating sex-steroid (testosterone, 11 ketotestosterone, 17ß estradiol and 17,20ß-dihydroxy-4-pregnen-3-one) production. When administered with sGnRHa, both SCH23390 and metoclopramide induced the final stages. However, only SCH23390 stimulated testosterone (4 mg/kg) and 17ß estradiol (0.8 mg/kg) production compared with sGnRHa alone. None of the treatments affected the survival, hatching or malformation rates. This is the first report suggesting that in pikeperch the D1, but not the D2, DA receptor antagonist would be involved in the testosterone and 17ß estradiol production as a potentiator of the sGnRHa effect.

Rearing conditions and life history influence the progress of gametogenesis and reproduction performances in pikeperch males and females.

Pikeperch (Sander lucioperca) is a highly valuable fish in Europe. However, development of aquaculture of pikeperch is highly limited due to seasonality of production. This can be overcome by the controlled reproduction of domesticated fish. The first steps of domestication process may induce changes at anatomical, physiological and molecular levels, thereby affecting a variety of biological functions. While there is abundant literature on their effects on stress and growth for example, these effects on reproduction received limited attention notably in pikeperch, a promising candidate for the development of aquaculture. To answer the question of this life-history effect on pikeperch's reproduction, we compared two groups (weight: 1 kg) originated from Czech Republic and with the same domestication level (F0). The first group was a recirculating aquatic system cultured one (2 years, previously fed with artificial diet, never exposed to natural changes in temperature/photoperiod conditions) and the second one was a pond cultured group (3 to 4 years, bred under natural feeding and temperature/photoperiod). The wild group successfully spawned, while the farmed one did not spawn at all. During the program, gonadosomatic indexes of both males and females were significantly higher for the wild fish, as well as the sexual steroids. Gene expression analysis revealed significantly lower LH transcript levels at the pituitary level for the farmed females and lower FSH transcript levels at the pituitary level for the males. In conclusion this study showed that the previous rearing conditions (e.g. culture system, age, diet, etc.) alter the further progress of gametogenesis and the reproductive performances in response to controlled photothermal program for both sexes in pikeperch.

Does constant photoperiod inhibit the onset of the reproductive cycle in northern pike (Esox lucius) males?

For most temperate and arctic fish species, photoperiod is the key abiotic factor determining the onset of the reproductive cycle, and, for many species, constant long photoperiod seems to have an inhibitory effect. Yet, there is no knowledge about the effect of photoperiod on the onset of the reproductive cycle in northern pike males. The aim of this work was to investigate the potential inhibitory effect of constant long photoperiod on pike males. Batches of fish were reared in triplicate under natural simulated photoperiod (NSP) or constant long photoperiod (CP; 16L:8D) from 14 October 2013 to 14 March 2014. Fish were sampled three times (at the beginning of the photoperiod decrease, at the beginning of the temperature decrease and at the end of the temperature decrease). Morphological parameters, sexual steroid levels and spermatogenetic stages were investigated. Our results showed that CP partially inhibited gonadal development (gonado-somatic index or GSI, %; 2.5% under NSP and 1.2% under CP at day 152), spermatic development (96.2% of spermatozoa under NSP and 69.3% under CP at day 152) and the plasmatic levels of testosterone (7.20 ng/mL under NSP and 2.37 ng/mL under CP at day 152). In conclusion, photoperiod may be one of the determinant factors that control the onset of the reproductive cycle in pike males, but temperature and endogenous rhythms also need to be investigated.

Continuous lighting inhibits the onset of reproductive cycle in pikeperch males and females.

The effect of a constant photoperiod on the inhibition of male and female reproductive cycles was studied in pikeperch Sander lucioperca. Over a 153-day period, batches of pikeperch (2 years, 950 g) breeders were kept under either under natural or artificial photoperiod conditions (24L:0D) (30-35 fish/tank, triplicate) and sampled in late June (start of the photoperiod decrease in natural conditions), late August (start of temperature decrease) and late November (exogenous vitellogenesis) (7-10 fish/tank/sampling date). Morphological parameters, sexual steroids, alkaline-labile phosphate (µg/mL) levels and gamete developmental stages were investigated. Gonado-somatic index (%), developmental stages and sexual steroid levels (17ß-estradiol, testosterone and 11-ketotestosterone, ng/mL) in both sexes and oocyte diameter (µm) and plasma alkaline-labile phosphate (µg/mL) in females were lower in response to a continuous lighting (24L:0D). In both sexes, continuous lighting applied in June for 153 days totally inhibited or delayed the onset of the reproductive cycle. In conclusion, photoperiod manipulation can be used to delay the pikeperch reproductive cycle, even if temperature decreases. This is the first report of the inhibitory effect of photoperiod on the onset of the reproductive cycle in pikeperch.

Can we use stable isotopes for ecotoxicological studies? Effect of DDT on isotopic fractionation in Perca fluviatilis.

Nitrogen and carbon stable isotope analyses are frequently used to assess contaminant biomagnification in animals in the wild. Previous studies, mainly on plant but also on animal tissues, have shown that chemical stress can lead to shifts in delta(15)N. In order to assess if an exposure to DDT at realistic concentration disrupted stable isotope signature in animals, delta(15)N and delta(13)C were studied in several tissues (liver, muscle, gill) of Perca fluviatilis fed with the same commercial diet uncontaminated or contaminated with DDT. We observed no DDT effect on the delta(15)N and delta(13)C of fish tissues. Our results show that stable isotopes can remain useful for field ecotoxicological studies despite food-chain contamination. However, correlations between the delta(13)C or delta(15)N values measured in the different organs were only found in DDT treated fish, suggesting some disruption of major biochemical compound metabolism in tissues.