Abstract
The present study was designed to investigate acute toxicity of dimethoate on juvenile Clarias gariepinus. Catfish with mean weight and length of 24.01 ± 11.60 g and 13.98 ± 5.66 cm respectively were exposed to sub-lethal levels of dimethoate in static bioassay system for 28 days and mortality data was statistically evaluated using Finney’s Probit analysis. The 96-hour LC50 value for C. gariepinus was estimated as 29.05 mg/l. The value for the LC50 was used in deducing the sub-lethal concentrations (0.01, 0.15and 0.29 mg/l). Biochemical changes in the serum such as glycogen, total protein, cholesterol, urea and creatinine were analyzed after the exposure period (28 days). The glycogenlevel decreased in all sublethal exposures. An increase in cholesterol at lower exposure concentration, followed by slight increase in urea and creatinine among treated groups was recorded. Behavioural changes which includes changes in skin colour, jerking, restlessness, erratic swimming, among others were observed. Based on the result of this study, it was concluded that C. gariepinus juveniles are very sensitive to low concentration of dimethoate. Dimethoate is highly toxic to juvenile catfishes and as such measures must be taken to avoid its run-off into our aquatic environment thus jeopardizing the recruitment of juvenile catfishes into the fishery.
Highlights
Ecological concerns arising from the high persistence of organochlorines have favored extensive use of organophosphates for controlling household, agricultural and public health pests due to their less persistence and high efficacy (Oscan Oruç et al; 2006)
Aquatic ecosystem is faced with the threat of biodiversity loss due to extensive use of pesticide Several physiological and behavioral dysfunctions occur in animals after exposure to low concentrations of organophosphate pesticide (Ambali et al; 2011)
Mortality and Acute Lethal Concentration of Dimethoate: The results of the mortality of C. gariepinus fingerlings and the estimated 24, 48, 72 and 96hour lethal concentrations are presented in Table 2 and 3
Summary
Test substance: Formulated pesticide product with trade name Action 40 which contained 40% EC Dimethoate was purchased from Jiangsu Tenglong. Experimental Animals and Acclimatization: 300 Catfish juveniles with mean weight and length of 24.01 ± 11.60 g and 13.98 ± 5.66 cm respectively procured from Michael Okpara University of Agriculture Fish Farm were acclimated for 14 days (two weeks) in 30 liters’ plastic basins in the laboratory prior to the start of the experiment. During this period the fish were fed with commercial feed (Coppens) twice dailyat 5 % body weight and the water changed daily before the start of the experiment. Sub Lethal Toxicity Test: To evaluate the biochemical effects of dimethoate, 84 catfish (three per group) were randomly divided into one control group (A) and three experimental groups - B, C and D which were treated with 0.01mg/l ,0.15 mg/ and 0.29 mg/l respectively for 28 days each having three replicate
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