Abstract
This study simulated acidic habitat for different life stages of Clarias gariepinus to know the effect on survival, mortality, morphology and behaviour. The fish were exposed to pHs 3, 4, 5, 6 and 8.01 (control) for 35 days. 100% mortality was recorded for all the life stages in pH 3, and 80, 62 and 36% of mortality of fingerlings, juveniles and adults respectively were recorded in pH 4. In pH 5, 30, 26 and 12% mortalities of fingerlings, juveniles and adults respectively were recorded and at pH 6 mortalities of fingerlings, juveniles and adults were 12, 10 and 4% respectively. Control pH mortalities were 10, 6 and 2% for fingerlings, juveniles and adults respectively. Mortality was due to lack of oxygen uptake, stress and circulatory collapse. All these elicited the behavioural responses and morphological abnormalities like erratic swimming, gasping, dark body colouration and lethargy. The study showed that different life stages of C. gariepinus tolerate different acidic pH waters, with high mortalities of the fingerlings, juveniles and adults in pHs 3, pH 4 is sub-lethal to fingerlings, juveniles and adult, pH 5 sub-lethal to fingerlings and sub-optimal for juveniles, and pH 6 optimal for all life stages.
Highlights
Acid rain is a term used to describe the coming in contact of rain water with oxides of sulphur and nitrogen which significantly makes the rain water highly acidic
Despite the acclimatization of the different life stages of C. gariepinus under laboratory conditions, the effects of the acidic media was strongly felt on the fish in terms of survival, mortality, morphology and behaviour
The death of fingerlings, juveniles and adults in pH 3 could be due to toxic action of hydrogen ions which affected oxygen uptake leading to acid stress, precipitation of proteins within the epithelial cells; and acidosis of the blood (Boyd, 1990)
Summary
Acid rain is a term used to describe the coming in contact of rain water with oxides of sulphur and nitrogen which significantly makes the rain water highly acidic. Rainwater becomes more acidic with the pollution of sulphur dioxide and nitrogen oxides to form sulphuric and nitric acids respectively. These pollutants come from burning of fossil fuels in thermal power stations, burning of gasoline in vehicles and heavy equipment and from smelting operations in oil industries and manufacturing industries (Singh & Agrawal, 2008). With urbanization and increasing population especially in developing countries and with no effective act or legislation to reduce these pollutants emission, the problems of acidification of rivers, streams, lakes, ponds and reservoirs which hitherto has not been fully quantified, will manifest in the near future and continue to magnify resulting in declining population of fish species in these aquatic ecosystems
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