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- Rearing larvae of dusky grouper, Epinephelus marginatus (Lowe, 1834), (Pisces: Serranidae) in a semi-extensive mesocosm | La cría de larvas de mero, Epinephelus marginatus (Lowe, 1834), (Pisces: Serranidae), en un mesocosmos de tecnología semiextensivaPublication . Cunha, M. E.; Quental, H.; Barradas, Ana; Pousão-Ferreira, P.; Cabrita, Elsa; Engrola, S.One of the major obstacles to propagating dusky grouper, Epinephelus marginatus, is the difficulty of rearing the early larvae. We have successfully raised dusky grouper larvae in mesocosms using a mixed diet of endogenous plankton grown in the rearing tank and an exogenous supply of Brachionus plicatilis and Artemia sp. Newly hatched larvae at an initial density of 1.3 ind.l-1 were stocked in partially shaded 3 m3 circular outdoor tanks during the summers of 2007 and 2008. Before introducing newly hatched larvae, the water was left for six days to promote plankton growth. Larval growth occurred at two different rates: i) a faster rate from first feeding to the beginning of metamorphosis, and ii) a slower rate at transformation. Survival at the beginning of metamorphosis was less than 10% (33 DPH) in 2007 and between 25 and 50% (25 DPH) in 2008. High mortalities were observed during larval transformation. The estimated minimum food requirement per grouper larvae increased more than 300% from the beginning of the notochord flexion to the beginning of metamorphosis. To meet such a high feeding requirement the number of larger prey organisms/copepods in the mesocosm should be eight times higher during this time period.
- Successful cryopreservation of sperm from sex-reversed dusky grouper, Epinephelus marginatusPublication . Cabrita, Elsa; Engrola, S.; Conceição, L. E. C.; Pousão-Ferreira, P.; Dinis, Maria TeresaThe dusky grouper, Epinephelus marginatus, is a protogynous monandric hermaphrodite species, since individuals mature firstly as females and later as males. This makes capture and maintenance of males in captivity difficult due to their large size and older age. Thus, the use of techniques that allow controlling sex, obtaining smaller and younger males, as well as cryopreservation techniques to improve sperm availability, may contribute to improve dusky grouper reproduction in captivity. In the present study, immature fish and young females were sex reversed using 2.5 mg/kg BW 17α-methyltestosterone (α-MT) in silastic implants, two months prior gamete extraction. In all individuals a single dose of Lucrin Depot® (20 μg/kg BW, GnRHa) was enough to induce and/or increase sperm production. Volume of sperm, cell concentration, osmolarity, sperm production and motility were registered. Sperm was cryopreserved in 0.5 ml straws using 1% NaCl + 10% DMSO + 10 mg/ml BSA as extender. Post-thawed sperm quality was analysed in terms of motility, viability and fertilization. The sperm volume collected ranged from 5 to 400 μl, cell density from 1.2 to 16.3 × 109 spz/ml and sperm production from 0.04 to 3.9 × 109 spermatozoa. The percentage of motile cells at 15 s post-activation varied from 25% to 93%. Cell viability decreased in post-thawed samples (22.5%) as well as the percentage of motile cells (36.8%). However, sperm velocity (VCL and VSL) and movement pattern (Lin) were not significantly affected by cryopreservation and spermatozoa were able to fertilize the oocytes without a decrease in the fertilization rate. Fertilization rates ranged in thawed samples from 35.9% to 65.1% and only one sample was significantly different from the control (69.5%). Embryo development was impaired in some fertilization trails, registering a significant decrease in the percentage of embryos at G stage when compared with the control. This suggests that the quality of samples may be the principal requirement for improving fertilization rather than the optimization of the cryopreservation protocol. The present study demonstrated that the protocol used for sperm cryopreservation can be successfully used in sex-reversed males for the establishment of a sperm bank. This technique would contribute to the reproduction of this species benefiting production, sea-ranching and species conservation.