LARVAL PERFORMANCE AND SKELETAL DEFORMITIES IN FARMED GILTHEAD SEABREAM: THE POTENTIAL EFFECTS OF MELATONIN

The gilthead seabream larval rearing in continuous light is a common practice in most Mediterranean hatcheries to increase food intake, improves the conversion rate, and stimulate larval growth in length. Nevertheless, numerous investigations have revealed that continuous light interrupts circadian rhythm alternation, affects larval development and raises the prevalence of skeletal abnormalities. Melatonin, the major output signal of the circadian system, is a crucial pineal neurohormone that stimulates cell proliferation and embryonic development in many teleosts and enhances osseointegration in mice and humans. We believe that inhibiting MEL by continuous light during early life alters larvae growth and development and increases the incidence of skeletal deformities, particularly those affecting the opercular complex. To our knowledge, no study has been conducted on the effect of exogenous melatonin in gilthead seabream larval development. Therefore, our main purpose in the present research was to investigate the effect of orally supplemented melatonin on larval performance and skeletal deformities in farmed gilthead seabream under standard rearing conditions. Melatonin increased the frequency of skeletal deformities, especially those of the operculum, for which we have recorded new typologies. The first signs of the opercular complex deformities were recorded before any sign of mineralization, proving that the abnormalities occur during the onset of the operculum complex bone series. Caudal fin complex was also sensitive to exogenous melatonin administration, and its abnormalities' incidence was increased dose-dependent. In light of our results and bibliographic data, we hypothesize that skeletal deformities detected in experimental groups’ larvae can be induced by the increased PTHrP expression level induced by exogenous melatonin or by a loss of coordination between skeletal muscle and bone growth. Future research should extend and unmask the melatonin- pathways behind muscle and bone growth in gilthead seabream. This is the first study to report the effect of exogenous melatonin on bone deformities and growth of Sparus aurata larvae reared under ordinary hatchery conditions.