Extensive asynchrony of sexual maturation is characteristic of salmonid females, and, for various reasons, the spawning season can be extended for 4 months, although it generally extends over a 3 week to 2 month period, as in brook trout and northern whitefish. In aquaculture, to ensure high fertilization and egg survival rates, it is recommended that identification of ovulating females be undertaken at least twice weekly. This is time-consuming when keeping large numbers of broodstock with an extended spawning season, and risk of stress damage to fish increases. Ensuring sufficient Arctic grayling broodstock relies on capture of wild animals from natural waters before onset of the spawning season. Capture and long-term holding of wild stocks is associated with high pre-spawning mortality. Due to the high ovulation synchronizing effect, GnRHa is practical for induction of ovulation 1?1.5 months prior to the natural spawning season. This work focused on optimization of methods of hormone-controlled reproduction using GnRHa in brook trout, northern whitefish, and Arctic grayling from Siberia. Because this is the first report of use of GnRHa in these species, emphasis was on optimization of the hormone dose and delivery method along with assessment of effects of GnRHa treatment on postspawning broodstock mortality, egg size, and egg viability. As in other salmonids, GnRHa treatment effectively synchronizes the onset of ovulation in brook trout and northern whitefish. This gives accurate information about ovulatory status of the broodstock and enables planning of the stripping schedule. The most convenient methods were the double acute injection at 25 ?g.kg-1 ?-Arg6,Pro9-NHEt-sGnRHa administered 3 days apart and injection of 25 ?g.kg-1 of emulsified ?-Arg6,Pro9-NHEt-sGnRHa in Freund´s incomplete adjuvant, which prolongs and more effectively stimulates LH secretion and requires only a single injection. Double acute injection at 10 ?g.kg-1 of ?-Tle6,Pro9-NHEt-mGnRHa (Supergestran) was sufficient to induce ovulation in Arctic grayling 1?1.5 months prior to natural spawning, and enabled accelerated stripping and return of wild broodstock to their natural habitat. Single acute injection proved to be ineffective or unreliable in most cases and therefore cannot be recommended. No negative effect of GnRHa or GnRHa-FIA treatments on post-spawning mortality of broodstock was observed. It has to be noted that that to the extent of law Nr. 166/1999 statute book (Czech veterinary law)injective procedures can be carried out just by the veterinarian or by a verinarian-authorized person in veterinarian presence. GnRHa treatment has side-effects and alters egg quality. Apart from in brook trout, egg survival was significantly lower (5?20%) in treated females. Increased hormone dose did not influence egg survival at the levels tested. Egg and hatchling size was lower in treated females compared to untreated specimens irrespective of dose or hormone delivery method. Reduced egg size is, however, not the likely source of reduced viability. In general, our results corroborate results of studies dealing with assessment of effects of hormone treatment on egg quality. Based on current experimental designs it is impossible to identify the cause of the side-effects with certainty. Solving this problem should be priority for future research.
| Identifer | oai:union.ndltd.org:nusl.cz/oai:invenio.nusl.cz:156251 |
| Date | January 2013 |
| Creators | ŠVINGER, Viktor William |
| Source Sets | Czech ETDs |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis |
| Rights | info:eu-repo/semantics/restrictedAccess |
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