Development of Nursery Feed for Heteropneustes fossilis with Particular Reference to Salinity Stress Tolerance

Abstract

The present study was conducted to assess the suitability of different larval feeds of Heteropneustesfossllis with particular reference to salinity stress tolerance. For this purpose, 30 days old Heteropneustes fossilis larvae were collected from local hatchery at Cachra in Jessore. The feeding trial was conducted in triplicate with 30 larvae (0.74± 0.0lg; 2.95 ± 0.12 cm) in glass aquaria (54 x 36 x36 cm^3) each containing 30L water. Four different feeding treatments i.e. Tubifex spp. (T1), commercial pellet feed (T2), snail meat (T3) and mixed diet i.e. commercial feed and snail meat on alternative day (T4)were applied. The larvae containing each treatment were fed two times per day with that particular feed until reaching satiation level. The larvae fed with tubificid worms (T1) and mixed diet (T4) showed significantly better results (p<0.05) in terms oflength and weight gain, percent weight gain and specific growth rate (SGR %) compared to the rest two treatments. Water quality parameters were monitored throughout the experimental periods and the parameters did not vary significantly (P>O.05) among the treatments. On the basis of larval development and survival rate, it could be suggested that the live tubificid worms (T1) and mixed diet (T 4) are suitable for Heteropneustes fossilis larvae. For determining particular salinity stress tolerance, there were six treatments, each having three replications, stocked with 30 larvae (4.4 ± O.3cm; 1.59 ± O.l1g) in glass aquarium (54 x 36 x36 cm^3), The larvae were cultured in aquarium with five different salinities 5, 8, 10, 12 and 15 ppt for 30 days to determine the optimum salinity level for direct stocking. The larvae were fed with the best feed (commercial feed and snail meat on alternative day) from the previous experiment. The larvae were exposed to different salinity directly from fresh water. The result reveals that, in case of direct stocking 10ppt, 12ppt and 15ppt are lethal salinity for Heteropneustes fossilis larvae. About 70% survivability was recorded in 8ppt salinity level that is quite satisfactory. But the larvae stocked at 8ppt showed comparatively poor growth rather than 0ppt and 5ppt. In the next part of the experiment, salinity was increased gradually 1ppt in every 3 days. The result revealed 100% survivability up to 7ppt. The survivability rate was also satisfactory at 8ppt (98%), 9ppt (97%) and 10ppt (76%) salinity. The salinity level more than 13ppt can be marked as lethal salinity level for Heteropneustes fossilis larvae. So, the present study suggests that the Heteropneustes fossilis larvae can be stocked directly at 5ppt salinity and can be cultured in 0 to 10ppt salinity level.