EFFECT OF SALINITY ON THE SURVIVAL OF PANGASIUS CATFISH Pangasius hypopthalamus IN SOUTHERN BANGLADESH
The river catfish (Pangasius hypopthalamus) was introduced to Bangladesh in the 1990's from Thailand, and has since become a thriving aquaculture industry with over 3 million tonnes produced annually. Pangasius is typically cultured in freshwater, however with the coastal waters of Southern Bangladesh being affected by salinity encroachment, we sought to determine whether catfish could be cultured in these hyposaline waters. This region is severely impacted by overfishing, and is underutilized due to increasing susceptibility to rising sea levels linked to global climate change. Thus, the aim of the present study was to assess the effect of salinity on growth and survival of Pangasius and in turn, determine the optimum tolerable salinity for culture of this species.
Overwintered Pangasius fingerlings were stocked at a density of 2/m2 in 18 ponds (averaging 400 m2 and 1.3 m deep) within the coastal Patuakhali district of Bangladesh. The experiment consisted of six treatments spanning a range of salinities: T1 (0-5 ppt), T2 (5-7 ppt), and T4 (10-12 ppt) did not involve prior conditioning while T3 (10-12 ppt), T5 (12-18 ppt), and T6 (18-22 ppt) had the fish acclimatized in 6 ppt water for 24 h prior to the start of the experiment. The fish were held at the experimental salinities for 7 days, during which time they were fed twice daily (09:00 and 14:00 h) with commercial feed (Mega floating feed, 28% CP, 7% fat) at a rate of 10% body weight per day. Survival rates were calculated for each treatment at the end of the 7-day period.
In T1 (0-5 ppt) and T2 (7-8 ppt), the survival rate was 100%. For T3 (10-12 ppt), in which the fingerlings were first acclimatized at 6 ppt, the survival rate was also 100% however in T4, where fingerlings were stocked directly at 10-12 ppt, survival rate was 87% with mortalities occurring as early as 5 days. For fish acclimated to 12-15
ppt (T5), survival rate was 30% while at the highest salinity (T6), all fingerlings died within one day. The results indicate that Pangasius catfish are able to survive in waters of up to 12 ppt when allowed a prior acclimation period in more dilute waters (6 ppt). A subsequent 6-month pond study evaluating growth performance of Pangasius catfish in different salinities (0 ppt, 6.5 ppt and 10.8 ppt) was conducted. The survival rate, weight gain, SGR, feed conversion ratio (FCR), yield, and benefit cost ratio (BCR) were similar (P>0.05) among the treatments. The results suggest that Pangasius catfish can be successfully cultured in salinities as high as 12 ppt. The ability to grow Pangasius in hyposaline waters of coastal Bangladesh or other regions can provide additional earnings and food sources for communities impacted by seawater encroachment linked to rising sea levels and climate change. (Supported by the AquaFish Innovation Lab - USAID)