Mullets population, such as Mugil incilis, have recently gained significance in aquaculture due to their considerable potential. The Caribbean species exhibits an annual maturation cycle, limited to two or three months each year (from November to January), the characteristics of which are just beginning to be understood. Hormonal management may or may not aid in the growth of female gametes in this species, with the aim of achieving maturation in captivity. Therefore, the objective of this study was to assess the growth of M. incilis oocytes through hormonal induction, taking into account the male-to-female ratio. The response to treatment was evaluated by monitoring in vivo oocyte growth rates. A total of 20 fish were captured during their breeding season with the assistance of local artisanal fishermen from the Ciénaga Grande de Santa Marta, and subsequently transported to the Aquaculture Laboratory at the University of Magdalena. There, they were acclimatized in circular PVC tanks (250L), in freshwater at a temperature of 28 °C, and fed with commercial feed containing 34% protein at 3.2% of their biomass. All animals were anesthetized for the collection of biometric parameters. The identification of sexes was conducted through the extraction of gametes using a 4mm diameter cannula. These were examined under a microscope (40X), and the oocytes were measured using the ImageJ 64-bit software. Out of the 20 lisas specimens, five mature females (109.8±11.5g, 24±0.8cm) were selected, exhibiting a swollen and soft abdomen along with a reddish and rounded genital papilla. The animals were allocated into two 250L tanks filled with freshwater, maintaining a ratio of 2 and 3 females per 2 males for a duration of 15 days. At the beginning of the experiment, a cannulation was performed, revealing an initial average oocyte diameter of 411±22.7 µm. By day 10 of the experiment, when the eggs reached an average diameter of 517±10.76 µm, induction was carried out using Ovaprim at a dosage of 0.5 mL/kg, administered in two doses with a 24-hour interval. The fish were monitored for five days following the treatment. The results indicated that after hormonal stimulation, there was a decrease in the growth of the oocytes in the females housed in the 2:2 ratio tanks (-3.05 µm/day), whereas the females in the 3:2 ratio exhibited an increase in oocyte diameter of 1.73 µm/day. In the end, the overall growth of the oocytes was measured at 6.21 and 7.6 µm/day over the 15-day duration of the experiment in each of the sampled tanks. In conclusion, although the use of the hormone Ovaprim for oocyte maturation in M. incilis yielded variable results, it can be inferred that stimulation may enhance oocyte maturation in this species. Nevertheless, it is advisable to conduct further studies concerning the application of various hormonal treatments to optimize maturation protocols.
Project funded by the general system of royalties in Colombia: Ensayos de producción de Mugil cephalus en condiciones controladas. Cod. 82521; 890 - 1027-2021.