Reproduction of hatchery-produced meagre Argyrosomus regius in captivity III. Comparison between GnRHa implants and injections on spawning kinetics and egg/larval performance parameters

Abstract

Hatchery-produced meagre (Argyrosomus regius) were induced to spawn using either controlled-release delivery systems (implants) loaded with gonadotropin-releasing hormone agonist (GnRHa) or GnRHa injections. Over two consecutive years, individual females were paired with single males after treatment with a GnRHa implant (40–104 μg kg− 1) or a GnRHa injection (15–25 μg kg− 1). Three consecutive GnRHa implants were given every 20–30 days, while five (in 2012) or seven (in 2013) consecutive GnRHa injections were given every 10 days. Fecundity and fertilization success was evaluated the day of spawning, and embryo/larval development was evaluated using 96-well microtiter plates. The first implantation with GnRHa produced up to 23 almost daily spawns, but most females failed to spawn repeatedly after the second implantation, even though their ovaries contained significant numbers of post-vitellogenic oocytes. Most of the eggs were produced in the first 3–4 spawns after GnRHa implantation, while the remaining batches were of low fecundity, which related directly to low fertilization. On the other hand, GnRHa injections produced consistently two spawns on days 2 and 3 after each treatment. Fecundity also decreased over time in response to the subsequent injections, but the response was more gradual and less dramatic than in GnRHa implanted females. Although both methods produced similar overall results in terms of total fecundity and egg/larval quality, multiple GnRHa injections resulted in more consistent spawning results and better egg production control, and this method may offer significant advantages over the use of controlled-release GnRHa implants. We present an efficient spawning induction method for meagre, which is the result of extensive experimentation both in previously published works, as well as in this one. The resulting method is proposed for its effectiveness and efficiency to the aquaculture industry.