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	Broodstock management and hormonal control of reproduction Control of the reproductive cycle in commercial fish hatcheries is essential for their self-sufficiency in eggs and fry. It also enables the production of eggs on a year-round basis for the more uniform supply of seed and edible fish. In the IMBC, research in fish reproductive biology examines various influences on the reproductive cycle of commercially important species. These include rearing conditions (photoperiod, thermoperiod), broodstock organisation and external hormone manipulations. Research examines the endocrine control of gametogenesis, final maturation and spawning; the influence of social factors, behaviour and management stress on the quality of gametes; and the utilization of controlled-release hormone delivery systems for the induction of ovulation, spermiation and spawning. Control of reproductive processes in cultured fishes can be accomplished in two ways. The first phase of the reproductive cycle (gametogenesis) can be influenced using photothermal manipulations, while the second phase (final maturation and spawning) can be controlled using exogenous hormones. Photothermal manipulations resulting in phase-shifting of the annual environmental cycle allows off-season production of eggs and fingerlings. Such seasonally changing photothermal cycles have been successfully applied to sea bass, sea bream and common dentex. Hormonal manipulations are used in cultured fishes in order to induce ovulation in species which do not normally undergo final oocyte maturation in captivity, such as the dusky grouper, the white grouper (E. aeneus) and the Mediterranean yellowtail, or exercise greater control over the ovulation, spermiation and spawning of certain species, so that egg production can become more efficient and on demand (e.g., sea bass, red porgy, common dentex, shi drum). Hormonal manipulations can be done using a variety of hormones, including human chorionic gonadotropin (hCG) and synthetic agonists of gonadotropin-releasing hormone (GnRHa). Depending on the reproductive physiology of the species of interest, these hormones can be applied in the form of regular injections, or the more recently employed sustained-release delivery systems. Another area of active research is the reproductive biology of new potential species for commercial cultivation, such as the common dentex, sharpsnout bream, red porgy, shi drum and the dusky grouper.
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