The common snook (Centropomus undecimalis) is a protandric hermaphrodite fish that undergoes a sex change during its life cycle. In nature, common snook females develop directly from males shortly after spawning. However, the factors triggering this process remain unknown. This knowledge gap poses challenges for managing the species in captivity. To address this, we conducted a study on sex change induction in three-year-old males using estradiol and evaluated the potential effects of photoperiod manipulation on early maturation. Four treatment groups were employed: (1) fish with estradiol + natural photoperiod; (2) fish without estradiol + natural photoperiod; (3) fish without estradiol + controlled photoperiod; and (4) fish with estradiol + controlled photoperiod. The effectiveness of these treatments was assessed through histological procedures, which allowed for the examination of the fishes’ gonads. Furthermore, the concentration of alkali labile phosphorus in fish plasma was measured and correlated with the histological results. Our findings revealed that administering 2 mg/kg estradiol implants resulted in a remarkable 100% female population within the estradiol-treated groups. No significant effect on fish maturation was observed due to the manipulated photoperiod conditions. This protocol offers improved management strategies for captive broodstock. Firstly, the concentration of estradiol used in this study proved sufficient to induce sex change in this hermaphroditic species, enabling the production of viable females at an early age and smaller size and facilitating easier broodstock manipulation. Secondly, the implementation of the alkali labile phosphorus technique allows for sex identification without the need to sacrifice the fish. In conclusion, our study provides valuable insights into sex change induction and photoperiod manipulation in common snook. The findings contribute to enhanced management practices for captive broodstock. However, further research is needed to explore the underlying mechanisms triggering sex change and to optimize protocols for long-term maintenance and successful reproduction in captivity.

Photoperiod manipulation has been used as an alternative non-invasive method to stimulate sexual maturation in fish. It consists mainly in influencing spatially and temporally the physiological control of the animal over its reproductive period. There are few studies on the effect of photoperiod in male fish and much less for tropical climates. Because of this, the present study focused on inducing gonadic maturation in male grey snapper (Lutjanus griseus), manipulating the duration of the sexual maturation season of five months into two months; the compressed months were March to July. From the fourth week of March (12h and 30 min light), adjustments of 2.4 minutes per day were made until reaching the hours of light corresponding to the maximum estimated peak in the year (13h and 42 min light). All fish confined under artificial photoperiod had a significant response in sperm production. In addition, greater fluidity and greater sperm motility were observed, with a higher number of sperm cells than in the natural photoperiod. These results will allow extending the months of reproductive management of this species using controlled photoperiod.

The Mexican snook (Centropomus poeyi) constitutes an essential artisanal fishery in coastal areas of Mexico containing rivers that discharge into the Gulf of Mexico, and it is considered overfished in general; therefore, aquaculture can provide alternatives to this situation. Induced spawning and Larviculture have been developed in our laboratory for this critical endemic species. Using cholesterol-cellulose implants with LHRH-a, spawning is initiated 30 hours after implantation. A total of 9.5 million fertilized eggs were collected, averaging 700.35 µm in diameter. The fertilization rate was 90%, and the hatching rate was 85%. Two hundred thirteen thousand fish were fed according to a protocol generated for this species, using microalgae, rotifers, and Artemia nauplii. Weaning is initiated 15 days post-hatching using a co-feeding regime combining live food and inert diets designed for marine fish. Survival at the end of the larval period was 1.8%, with fish feeding exclusively on artificial food and acclimated to freshwater.

Vol. 2 No. 1 January-June, 2024