Effects of Different Co-Feeding Protocols on the Early Weaning of Flathead Grey Mullet (<i>Mugil cephalus</i>) Larvae

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 (<i>Mugil cephalus</i>), 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 <i>Mugil cephalus</i> larvae reared under three different weaning protocols. Three co-feeding treatments, two with different <i>Artemia</i> sp. concentrations (A100 and A50, 2 and 1 <i>Artemia</i> 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, <i>Artemia</i> sp. addition is recommended from day 26 to day 29 post-hatching (total larval length of 8 to 9 mm).