Blood electrolytes of the freshwater catfish Heteropneustes fossilis in response to treatment with a botanical pesticide (latex of Euphorbia royleana).

The aim of the present study was to determine changes in blood electrolytes (calcium and phosphate) in the freshwater catfish Heteropneustes fossilis following short- and long-term exposure to latex of Euphorbia royleana. To investigate the effects of short-term exposure, fish were exposed to 80% of the 96-h LC(50) of E. royleana latex (2.47 mg/L) for 96 h. To assess the effects of long-term exposure, fish were exposed to 20% of the 96-h LC(50) of E. royleana latex (0.618 mg/L) for 28 days. Fish were killed after 24, 48, 72 and 96 h (short-term experiments) or after 7, 14, 21 and 28 days (long-term experiments). Blood samples were collected and sera were analyzed to determine calcium and inorganic phosphate levels. Serum calcium levels decreased progressively in H. fossilis after 48 h exposure to E. royleana latex. This decrease persisted until the end of the experiment (96 h). Serum inorganic phosphate levels in treated fish decreased progressively from 72 h. After 7 days exposure to E. royleana latex, decreased serum calcium levels were noted in H. fossilis that persisted until the end of the experiment. Serum phosphate levels were decreased in H. fossilis on days 21 and 28 of exposure to E. royleana latex. It is concluded that E. royleana latex alters the blood electrolyte content of the fish. The change in these electrolytes, particularly calcium levels, may cause disturbances in the normal vital physiological functions of the fish, its growth rate, and even its ability to survive in nature.