Spawning induction and larval rearing in the thinlip gray mullet (Chelon ramada): The use of the slow release gonadotropin releasing hormone analog (GnRHa) preparation, leuprorelin acetate.

ABSTRACT

The thinlip gray mullet (Chelon ramada) belongs to the Mugilidae family, it is a low-trophic, euryhaline species adapted to a wide range of environmental conditions. As such, it represent a candidate to diversify aquaculture production toward more sustainable species. Nonetheless, several bottlenecks have to be overcome before production is undertaken at commercial scale. Indeed, C. ramada mature females do not spawn without hormonal treatments in captivity. This report describes the use of the gonadotropin releasing hormone analog (GnRHa), leuprorelin acetate as an effective single-dose inducer of spawning in this species. Wild mature females (n = 10; 29 ± 1 cm total length, TL and 199 ± 20 g body weight, BW) exhibiting protruded papilla and bulging abdomen, presenting vitellogenic oocytes (diameters higher than 657 µm) and fluent males (n = 21; 28 ± 1 cm TL and 181 ± 80 g BW) were treated with a single injection of leuprorelin acetate. Breeders spawned more than 500,000 eggs with a mean fertilization and hatching rate of 92 ± 3 and 91.4 ± 0.4 %, respectively. Larvae grew according to the equation y = 2.6841e0.044x, mean survival rate at 19 dph was 13.8 ± 1.5 %. Mean SGR% day-1 slightly decreased concomitantly with tail flexion, probably for a greater investment on ontogenic development rather than growth. Present results suggest that mature C. ramada presents easily recognizable reproductive traits, adapts without difficulty to captive conditions, and can be easily induced to spawn administrating a single dose of leuprorelin acetate. The protocol used in our study resulted in high fertilization and hatching rates, as well as promising larval survival minimizing broodstock stress.