The Cortez flounder Paralichthys aestuarius as a candidate species for aquaculture: First report on growth in captivity in response to varying dietary protein levels

•First attempt to evaluate performance of P. aestuarius under controlled conditions.•We examined its biological response to 3 dietary protein levels.•Experimental diets’ basic and acidic degree of hydrolysis was evaluated in vitro.•None of the biological indices differed significantly between dietary treatments.•Aquafeeds with 47% crude protein may support growth of juveniles.

Cortez flounder, Paralichthys aestuarius, like many other flounders, is highly appreciated for culinary purposes because of its top quality meat. It is a native species from the Gulf of California that supports seasonal local commercial fisheries, but production through aquaculture would be welcomed in the domestic fish market as well as an export product. The aim of this study was to determine whether this species can adapt to captivity, and to evaluate its growth in response to varying dietary protein levels in formulated feeds. Three iso-lipidic (8% crude fat) experimental diets with 47, 52 and 55% crude protein (CP) were tested, and their basic and acidic degree of hydrolysis (DH) was evaluated in vitro. A commercial marine fish diet was used as an external control (38% CP). A total of 96 wild juveniles (mean weight 72.038 ± 23.495 g) were caught with cast nets at Santa Rosa, Mexico. Four fish were randomly stocked into each of twenty four 250 L circular tanks and fed the experimental diets for 8 weeks. At the end of the trial, high survival rates (87.5%) were observed in all experimental treatments. No statistical differences for growth were observed among fish fed the experimental diets, and it was comparatively higher than that of animals fed the commercial diet, although they were not included in the statistical analysis. Feed conversion ratio (FCR), protein efficiency ratio (PER), or the basic DH of diets did not show statistical differences among treatments, but the 52% CP diet showed significantly (P = 0.003) lower acidic DH (92.6%). It was concluded that P. aestuarius may be considered a species with aquaculture potential in the Gulf of California, and that aquafeeds with 47% CP may support growth of juveniles, but a more in-depth evaluation of its nutritional requirements is needed to improve FCR and growth rates.