Abstract
Salinity intrusion in freshwater ecosystems of low-lying coastal areas poses a major threat to aquaculture and agricultural production. An experiment was conducted to observe the effects of salinity on early life development of the freshwater aquaculture species pabda, Ompok pabda. Fish embryos (n = 200) and fry (n = 100) were exposed to five different salinity concentrations viz., 0 (control), 2.5, 5.0, 7.5 and 10.0 ppt with three replications. The LC50 values were calculated by probit analysis. The 24 h LC50 values recorded for embryos was 15.07 ppt and hatching success decreased significantly as salinity concentration increased. The 48 h LC50 values recorded for larvae was 5.07 ppt and larval developmental rate was reduced in response to an increase in salinity concentration. Mostly larval deformities were found from 5.0 to 10.0 ppt salinity. The 72 h LC50 values of fry was denoted as 2.42 ppt and fry mortality was augmented significantly with exposure time and salinity concentration. Fry mostly survived at 0 (92.67 %) and 2.5 ppt (65.67 %) salinities after 24 h exposure, but none survived at 5.0 and 7.5 ppt salinities after 48 h. 100 % fry mortalities occurred at 10 ppt salinity after 24 h exposure. Thus, the present findings provide useful information on salinity effects on early life development of Ompok pabda and sensitivity for embryonic development. It is expected that current findings will be helpful to raise awareness of the sensitivity of salinity for freshwater aquaculture species.
Highlights
Salinity intrusion is considered a remarkable threat for freshwater ecosystems of low-lying coastal countries, such as Bangladesh
Certain freshwater fish species can hatch in low salinity levels such as silver carp, Hypophthalmuchthys molitrix (Gao, 1965), and yundu, Heterobranchus longifilis (Bombata and Busari, 2003) and similar findings were reported by Nadirah et al (2014)
The present study reported the salinity toxicity bioassay of Ompok pabda
Summary
Salinity intrusion is considered a remarkable threat for freshwater ecosystems of low-lying coastal countries, such as Bangladesh. Increasing water salinity has led to changes in the physical environment of coastal ecosystems which may have adverse effects on the aquatic flora and fauna. Over the last 4 decades water salinity level increased about 26 % in coastal area of Bangladesh (Alam et al, 2017). As a result of salinity intrusion and seasonal fluctuation of water salinity in coastal freshwater regions, many aquatic organisms including wild stock of commercially important fish species may be subjected to salinity stress. It was evident that 12, 19 and 24 % inland freshwater and brackish water fishes become extinct, en dangered and threatened, respectively due to salinity intrusion in the riverine system across the coastal zone of Bangladesh (Alam et al, 2017). Very limited virtual information is available regarding saltwater toxicity to freshwater fish species
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