Males and females of Rhamdia quelen (Quoy & Gaimard) were subjected to capture and tank transference in order to evaluate the stress response. This process provoked a characteristic stress response in both sexes, with cortisol values reaching a peak in one hour after stress. High levels of cortisol found in females were explained by the increase of energy demand and the mobilization in the vitellogenic phase. Several previous studies have shown that cortisol is strongly correlated to these periods in another cat®sh.
Jundi a (Rhamdia quelen) is an important species for aquaculture in temperate and subtropical climates. In the present study, the results of different forms of GnRH analogue treatments on ovulation in jundi a have been compared with those from treatment with carp pituitary. Seven out of eight females ovulated in groups treated with carp pituitary (4.0 mg kg À1 BW) and Ovaprim (0.5 mL kg À1 BW). Injection with sGnRHa (10 lg kg À1 BW) combined with metoclopramide (20 mg kg À1 BW) caused a significantly lower rate of ovulation with three out of eight females responding. None of the fish injected with sGnRHa (10 lg kg À1 BW) alone ovulated. Mean PGSI [(weight of stripped egg mass/ BW of the female before stripping) 9 100] and mean fertilization rate values were high and similar between treatment groups. The obtained results indicate that in jundi a, there is a strong dopamine inhibitory tone on gonadotropin secretion. The gonadotropin releasing activity of sGnRHa can be potentiated by dopamine receptor antagonists and the combined treatment is effective in inducing ovulation. In this regard, domperidone proved to be more potent than metoclopramide.
The plasma concentrations of testosterone (T) of cultured jundiá Rhamdia quelen increased progressively during spermatogenesis and reached a peak at the beginning of spermiation (e.g. fluidization of the sperm and production of milt). Plasma peaks of T occurred simultaneously to the highest production of T by the testis, however, both plasma concentrations and testis production of T decreased progressively during spermiation. Concentrations of 11-ketotestosterone (11-KT) peaked c. 1 month after the peak of T, concomitant with enhanced production of 11-KT by the testis. The concentrations of 11-KT during the first cycle were extremely high (>1 g ml 1 ), but less during the second and third cycles, suggesting that this steroid is most important during the pubertal phase in male jundiá. Plasma concentrations of both 17-hydroxy-4-pregene-3,20-dione (17-P) and 17,20 -dihydroxy-4-pregen-3-one (17,20 -P) were significantly higher during spermiation than at any other times, and showed little variation. The pattern of steroid changes was cyclical and consistent with their proposed roles in male fish reproduction.2002 Published by Elsevier Science on behalof of The Fisheries Society of the British Isles
Summary
Survival and growth of wels catfish (Silurus glanis L. 1758) larvae (both non‐feeding and feeding), originating from fertilization with cryopreserved sperm were investigated. Non‐feeding (yolk sac) larvae (n = 100 individuals distributed over five replicates) were tested in the laboratory; feeding larvae (100 individuals in five replicates) were tested in both the laboratory and at a commercial fish farm (1000 individuals in triplicates). Water temperature was maintained at 22–23°C during the 4‐day test period on non‐feeding larvae and 10 days on feeding larvae. Larvae originated from cryopreserved or fresh sperm of different males collected in different years. In the laboratory experiments with feeding larvae, changes in standard length (SL), weight, condition factor, specific growth and survival rates were determined after 10 days, while at the fish farm survival and length growth were determined after 10 days. Final SL, weight and survival rate were analyzed on the non‐feeding larvae. In all cases, larvae from fertilization with fresh sperm served as a control. A significant difference (P = 0.034) was found in the 10‐day standard length between larvae originating from cryopreserved sperm (1.92 ± 0.13 cm SL, N = 250) and the control (1.89 ± 0.14 cm SL, N = 250). Significant differences were also observed in the final SL (0.96 ± 0.05 cm in larvae from cryopreserved sperm vs 0.94 ± 0.05 cm in the control, P < 0.001) and weight (10.09 ± 0.37 g in the cryopreserved group vs. 9.02 ± 0.30 g in the control, P = 0.018) of non‐feeding larvae. No significant differences were found in either the survival rates of fry derived from fresh or from cryopreserved sperm. It is postulated that the observed differences can be attributed to the effect of individual males or broodstocks; however, genetic studies are required to confirm this hypothesis. This study gives evidence that the developed cryopreservation technology has no unfavorable effects on the viability of wels catfish larvae.
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