In this study, the researchers involved in NewTechAqua project examined the possibility of using constant water temperature throughout the year (supplied by borehole water) to stimulate gametogenesis, and result in spawning of good egg/sperm/embryo in meagre (Argyrosomus regius). If successful, this protocol could be implemented in broodstock management facilities, saving cost from heating and cooling the water in order to provide the expected natural water temperature for reproductive maturation.
Two broodstocks were exposed to simulated natural photoperiod -which is considered the most important environmental cue for reproductive maturation in all animals-, and either attenuated seasonal water temperature (SeasT, 16.4 to 19.6ºC) or constant water temperature (CoT, 19.4 ± 0.6ºC). In the spawning period (May), 4 couples per group were induced to spawn with gonadotropin releasing hormone agonist (GnRHa). Gonadal stage of development, sperm quality parameters and plasma levels of sex steroids were evaluated prior to the GnRHa treatment. Spawning success and egg/sperm quality were examined over the following 4 weeks. Constant temperature allowed the progression of gametogenesis, but exposure to attenuated seasonal water temperature with the inclusion of winter low temperature was more effective in inducing reproductive maturation of both sexes. The mean (±SD) diameter of the largest vitellogenic oocytes prior to GnRHa administration was significantly higher in the SeasT compared to the CoT group (598 ± 27 vs 520 ± 17 μm). Testosterone plasma levels in the females were significantly higher in the SeasT group, but all other hormones were similar in both sexes. SeasT females spawned more consistently with higher relative fecundity, and 24-h embryo survival of the produced eggs. A more pronounced negative effect of constant water temperature was observed in males, since CoT males exhibited a spermiation index of 0 prior to GnRHa treatment, the latter clearly having a beneficial effect over the following 4 weeks. The study demonstrated that meagre do undergo gametogenesis to a significant extent even under constant water temperatures during the year. However, a seasonal thermal regime -even an attenuated one- was necessary for the proper development of the gametes, allowing for the successful spawning induction using the established GnRHa induction protocol.
To have more details about this study, access freely the scientific publication here.