The effects of salinity on reproductive development and egg and larvae survival in the spotted scat Scatophagus argus under controlled conditions

In the present study, we report the first successful instance of controlled reproduction in Scatophagus argus, which has recently emerged as a new aquaculture resource. The controlled reproduction process for S. argus was optimized with regard to salinity acclimation. Gonadal maturation was affected by salinity in both sexes. Levels of plasma 17 beta-estradiol (E-2) and 11-ketotestosterone (11-kT) were salinity dependent and increased significantly with the duration of acclimation. Plasma levels of gonadal steroids were higher in fish held at 25 parts per thousand salinity. The highest gonadosomatic indices (GSI), 15.1 +/- 1.6 in the female and 6.4 +/- 1.2 in the male, were also observed at 25 parts per thousand salinity. Nevertheless, the optimal salinity for S. argus embryonic development and larval culture was 15 parts per thousand. Thus, the salinity requirement for gonadal maturation and early development are quite different. The use of advanced reproductive technologies combining salinity acclimation and stimulation of luteinizing hormone-releasing hormone analog (LHRH-A2) resulted in a fertilization rate of 83.2%-91.3% and embryonic survival rates of over 90%. Embryos of S. argus at the 2-cell, blastula, gastrula and pharyngula stages were observed. Most embryos hatched after 21.0 hr of incubation at 28.0 +/- 1.0 degrees C. The development of larvae into juveniles was completed at 40-45 days posthatch (dph). In this study, we provide information about the controlled reproduction of S. argus and identify the optimal environmental parameters for S. argus embryonic and larval culture, with the aim of developing reliable reproductive techniques for its mass production.