RESUMO
The sustainable expansion of aquaculture relies on a sufficient supply of eggs and larvae, which are the first step of life cycle management. However, marine fish larval rearing generally depends on live feed production, which needs additional facilities and labor. The flathead grey mullet (Mugil cephalus), a promising species for aquaculture diversification, has a precocious digestive system development, supporting the feasibility of early weaning strategies. For these reasons, this study evaluated survival, growth, proximate and fatty acid composition, and gene expression of Mugil cephalus larvae reared under three different weaning protocols. Three co-feeding treatments, two with different Artemia sp. concentrations (A100 and A50, 2 and 1 Artemia sp. mL-1 day-1, respectively) and one with only rotifers administered as live feed along the feeding trial (A0), were assessed from 22 to 36 days post-hatching (dph). The A0 treatment performed better in survival (64.79 ± 7.40%) than the A100 protocol (32.46 ± 12.82%). In contrast, the larvae of the A100 treatment presented significantly higher final length (15.51 ± 0.86 mm) than those of the A0 treatment (12.19 ± 1.45 mm) and higher final weight (41.28 ± 1.48 mg) than those of the A50 and A0 treatments (31.23 ± 3.65 mg and 24.03 ± 7.99 mg, respectively). On the other hand, the expression of digestive enzyme- and somatotropic factor-related genes did not show differences between treatments. The present results support the convenience of treatment A0 in maximizing survival, as rotifers should be maintained until 30-32 dph (until a total larval length of at least 10 mm). However, to improve growth and minimize size dispersion, Artemia sp. addition is recommended from day 26 to day 29 post-hatching (total larval length of 8 to 9 mm).
RESUMO
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.
