ABSTRACT
Mahseers, regarded as a food fish and an excellent sportfish, once attracted the attention of best anglers and naturalist from world over. Of the different species of mahseer belonging to the genus Tor in India, T. khudree is the only important species available in streams and rivers of the Peninsular India and is known to grow to 120-150 cm (40-50 kg). Over the years, the natural stocks of T. khudree have depleted due to anthropogenic activities and hence several in situ and ex situ conservation strategies have been suggested to revive their stocks. The present study was undertaken with a view to throw more light on broodstock care, induced spawning, egg incubation, fry and fingerling rearing of T. khudree.
Feeding captive fish with a special broodstock diet and soya-based extruded feed resulted in early maturity of T. khudree. Of the two spawning agents tested, ovaprim resulted in better spawning response (70%) than ovatide (37.5%). The interval between injection and stripping of eggs ranged between 24 and 36 h at 20-23OC. The number of eggs obtained from ovaprim-injected (o.6 ml/kg) fish varied between 420 and 1680 per female, while for ovatide–injected (0.6 ml/kg) fish it was 240-2100 per female. The fertilization rate obtained for both the hormones was high (77-100%). Dry method of fertilization was found to be better than wet method.
Interestingly, wild–caught broodfish produced 1080 and 3240 eggs, with and without injection, respectively. The egg and embryonic developmental stages proceeded normally, but at a slower rate at 20-23OC (hilly area) and faster at 26-27OC (coastal area). Hatching periods were 80-112 and 63-70 h for the former and the latter areas, respectively. At the hilly region, the hatching rate was poor (13.99%), whereas it was significantly higher (42.8%) at the coastal region. However, there was no difference in the yolk-sac absorption period between the two regions.
Another interesting observation was that for the first time wild T. khudree fry could be collected from a riverine stretch from where the wild brooders of the same species had earlier been collected, suggesting it to be their natural breeding ground. The nursery rearing of the hatchery produced and wild fry indicated that the fry attained 2.03g and 5.63cm (after 37 days) and 1.24g and 4.79cm (after 24 days), respectively, with 99.4-100% survival. The hatchery produced and wild fingerlings of T. khudree reared for a period of 120 days in ponds, attained 96 and 49g, respectively. The survival, specific growth rate, food conversion ratio and protein efficiency ratio were found to be 90-100%, 2.25-2.32%, 1.48-1.49 and 2.54-2.73, respectively after a 120 day culture period. The growth increment during the culture period was 0.74 and 0.38 g/day in hatchery and wild caught fingerlings, respectively.
ABSTRACT
Mahseers, regarded as a food fish and an excellent sportfish, once attracted the attention of best anglers and naturalist from world over. Of the different species of mahseer belonging to the genus Tor in India, T. khudree is the only important species available in streams and rivers of the Peninsular India and is known to grow to 120-150 cm (40-50 kg). Over the years, the natural stocks of T. khudree have depleted due to anthropogenic activities and hence several in situ and ex situ conservation strategies have been suggested to revive their stocks. The present study was undertaken with a view to throw more light on broodstock care, induced spawning, egg incubation, fry and fingerling rearing of T. khudree.
Feeding captive fish with a special broodstock diet and soya-based extruded feed resulted in early maturity of T. khudree. Of the two spawning agents tested, ovaprim resulted in better spawning response (70%) than ovatide (37.5%). The interval between injection and stripping of eggs ranged between 24 and 36 h at 20-23OC. The number of eggs obtained from ovaprim-injected (o.6 ml/kg) fish varied between 420 and 1680 per female, while for ovatide–injected (0.6 ml/kg) fish it was 240-2100 per female. The fertilization rate obtained for both the hormones was high (77-100%). Dry method of fertilization was found to be better than wet method.
Interestingly, wild–caught broodfish produced 1080 and 3240 eggs, with and without injection, respectively. The egg and embryonic developmental stages proceeded normally, but at a slower rate at 20-23OC (hilly area) and faster at 26-27OC (coastal area). Hatching periods were 80-112 and 63-70 h for the former and the latter areas, respectively. At the hilly region, the hatching rate was poor (13.99%), whereas it was significantly higher (42.8%) at the coastal region. However, there was no difference in the yolk-sac absorption period between the two regions.
Another interesting observation was that for the first time wild T. khudree fry could be collected from a riverine stretch from where the wild brooders of the same species had earlier been collected, suggesting it to be their natural breeding ground. The nursery rearing of the hatchery produced and wild fry indicated that the fry attained 2.03g and 5.63cm (after 37 days) and 1.24g and 4.79cm (after 24 days), respectively, with 99.4-100% survival. The hatchery produced and wild fingerlings of T. khudree reared for a period of 120 days in ponds, attained 96 and 49g, respectively. The survival, specific growth rate, food conversion ratio and protein efficiency ratio were found to be 90-100%, 2.25-2.32%, 1.48-1.49 and 2.54-2.73, respectively after a 120 day culture period. The growth increment during the culture period was 0.74 and 0.38 g/day in hatchery and wild caught fingerlings, respectively.