Hormone induced spawning and embryogenesis of Cauvery carp, Barbodes carnaticus (Jerdon 1849): implications on commercial culture and conservation.

Abstract

The Cauvery carp Barbodes carnaticus (syn. Puntius carnaticus), an endemic and threatened species of the Western Ghats, was once commercially important species in the Krishnaraja Sagar reservoir, Mysuru but later became scarce due to exploitation. In this study, we attempted conservation and rehabilitation of this species. We raised wild-caught juveniles of Barbodes carnaticus to gonadal maturity in ponds, where male and female took 2 and 3 years to reach first maturity. The females exhibited a higher gonado-somatic index (GSI) than males. Sexing was accomplished based on morphological characteristics and subsequently the fish was induced to ovulate/spawn with ready-to-inject spawning agents viz. ovatide, ovaprim and human chorionic gonadotropin (HCG). The order of performance was ovatide >ovaprim >HCG. The ovatideinjected female produced higher relative fecundity (1462 eggs/kg body wt.) than the females administered ovaprim (814 eggs/kg body wt.). The ripe oocytes had a diameter of 0.98 mm, and the water-hardened eggs were of 1.90 mm. The injected fish responded to hormones between15 and 30 h at 25.6-28.5ºC. The fertilization rates were generally high (50-100%). However, the hatch rates were low (0-27%). The quantity of yolk-sac fry obtained was higher in ovatide trial (336 fry/kg body wt.) than the ovaprim trial (293 fry/kg body wt.). The performance of HCG was much lower than that of ovatide and ovaprim. The early development of B. carnaticus from activation of egg to yolk-sac absorption stage was recorded using live eggs, embryos and early fry. Five embryonic steps (blastodisc formation, cleavage, epiboly, organogenesis and blood circulation) and free embryo consisting of five larval steps were identified. Hatching occurred between 37 and 48 h (post-activation), the free embryo period lasting up to 5 days post-hatching. The transition from larva to juvenile occurred in 25 days when the fish were fully scaled and the lateral line organ clearly visible, with a distinct black blotch on caudal peduncle. A few deformed eggs with asymmetrical cleavage and embryos with yolk-sac malformations, spinal cord and tail curvatures were observed. When the fry were reared in manured and fed pond, they showed faster growth, reaching fingerling stage (3.5 g; 7.5 cm) in 50 days, with more than 95% survival. Spermatozoa motility duration (13-60 s) and percentage (16-63%) were moderate, while the spermatozoa density and spermatocrit were high.