The effect of some selected pesticides on the growth and reproduction of freshwater Oreochromis niloticus, Chrysicthys nigridigitatus and Clarias gariepinus

Studies were carried out to determine the toxicity of some selected pesticides on fresh water fish in a tropical environment. The uptake of the pesticides lindane, pentachlorophenol (PCP), and propoxur, which are frequently used on farms, and in industries as well as by loggers and timber men on wood were studied in concrete ponds at the University of Cape Coast, in Ghana. The fish used for the study were Oreochromis niloticus, Clarias gariepinus, and Chrysicthys nigrodigitatus. They were obtained from cultured ponds in the Cape Coast and Mankessim districts in the Central Region and Weija Dam, in the Greater Accra region of Ghana. Single high lethal concentration (SD) or acute treatment and cumulative/chronic (or multiple minor) lethal concentration (CD) treatment were employed in administering the pesticides to the fish via water. Gas chromatograph electron capture detector analysis was done on the dead fish to see the extent of ingestion. The LC(50 )values obtained for lindane on the three fish samples were as follows: Chrysicthys - 0.38 mg L(-1); Oreochromis - 0.42 mg L(-1), and Clarias - 1.2 mg L(-1). Mortalities occurred in fish within 3-5 days of application. For the PCP on Chrysicthys, Oreochromis, and Clarias species the LC(50) values were 0.42, 0.32 and 0.64 mg L(-1), respectively, for over a 2- to 3-day period. For a three-time influx period of propoxur the LC(50) for Chrysicthys, Oreochromis, and Clarias, were 22.0, 30.40, and 45.04 (all in mg L(-1)), respectively. The results obtained indicated that the pesticides had adverse effects on the general growth and reproduction of fish as shown by gonadosomatic indices.

Using gas chromatography with an electron capture detector (GC-ECD) to analyze dead fish tissue, the team calculated the precise lethal concentration values (the lethal concentration required to kill 50% of the test population)

Lindane Toxicity (3–5 Day Acute Window): Chrysichthys was found to be the most vulnerable with an LC 50 of 0.38mg/L. Oreochromis followed closely at 0.42 mg/L, while Clarias was significantly more resilient, requiring 1.2 mg/L to achieve 50% mortality.

PCP Toxicity (2–3 Day Acute Window): The lethal limits for Oreochromis, Chrysichthys, and Clarias were established at 0.32 mg/L, 0.42 mg/L, and 0.64mg/L respectively, showcasing immediate toxic impacts on tilapia species. 

Propoxur Toxicity (Chronic Exposure): Carbamates required much higher relative volumes to cause death, yielding LC50 markers of 22.0 mg/L, (Chrysichthys) 30.40 mg/L, (Oreochromis) and 45.04mg/L (Clarias).