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

Abstract

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, 17β estradiol and 17,20β-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 17β 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 17β estradiol production as a potentiator of the sGnRHa effect.

Time of response to hormonal treatment but not the type of a spawning agent affects the reproductive effectiveness in domesticated pikeperch, Sander lucioperca

“…In contrast, the T level was nearly 20 times higher after injection compared to wild fish (Pourhosein Sarameh et al, 2012). A similar discrepancy in terms of sex steroid levels was reported by Roche et al (2018), where pond-reared fish (originating from a wild-like environment) had much lower T levels compared to domesticated fish. Therefore, the results obtained here clearly show that hormonal stimulation, irrespective of the type of spawning agent, very effectively stimulated T production in domesticated broodstock.…”

“…in an Eppendorf tube just prior to fertilisation. Next, the eggs were fertilised according to the method described by Roche et al (2018): the so-called 'wet method' on glass Petri dishes (diameter 50 mm), to which the fertilised eggs adhered. Briefly, to each individually labelled Petri dish, 5 mL of hatchery water was added and a small portion of eggs (approximately 100) was placed on it simultaneously with 50 µl of the pooled sperm sample.…”

“…Research on hormonal stimulation of ovulation in pikeperch has mostly been conducted with wild fish (Żarski et al, 2015), and only a few studies have been performed with domesticated fish grown fully in RAS (Ljubobratović et al, 2017;Roche et al, 2018;Zakęś et al, 2013). Because the domestication process, rearing conditions and life history (Khendek et al, 2017 influence fish reproductive physiology and performance, there is an urgent need to develop hormonal treatment protocols for fish commercially grown in RAS, where both hCG and GnRH should be tested.…”

Domestication modulates the expression of genes involved in neurogenesis in high‐quality eggs of Sander lucioperca

“…Each collected egg portion during both spawning operations (of domesticated and wild fish) was first aliquoted into several cryotubes and then snap‐frozen in liquid nitrogen. The remaining eggs were used for evaluation of their quality as described by Roche et al (2018). Briefly, 5 ml of hatchery water was poured over a glass Petri dish (30 mm diameter).…”

A novel approach for induced out-of-season spawning of Eurasian perch, Perca fluviatilis

“…Importantly, the application of dopamine antagonists was reported to have an inhibitory effect on ovulation in Eurasian perch (Rónyai and Lengyel, 2010). Moreover, recent findings of Roche et al (2018) indicate that the application of dopamine antagonists did not have any effect in a closely related species of pikeperch (Sander lucioperca). This result confirms the earlier reports that the application of GnRHa alone is effective in Eurasian perch (Kouril et al, 1997) and pikeperch (Křišt'an et al, 2013;Żarski et al, 2019).…”