Abstract

The acute toxicity of L. alopecuriodes to H. bidorsalis fingerlings of mean body weight, 1.99  0.38g and total length 6.32  0.93cm was assessed in a renewal bioassay for 96 h. Five graded concentrations of L. alopecuriodes were prepared as 0.5, 1.0, 1.5, 2.0 and 2.25mg/L and a control experiment (0.00 mg/L).  There were no significant variations observed in the water quality parameters of the test solutions. Toxic reactions exhibited by the fish include hyperventilation, erratic swimming, incessant gulping of air, loss of reflex and death. Opercular beat frequency (OBF) and Tail beat frequency (TBF) decreased with increase in time of exposure but increased with concentration. There were significant interactions between concentration and time of mortality and OBF.  Concentration of the extract shows a positive linear correlation with OBF, TBF and mortality. No death was recorded in the control (0.00mg/L) throughout the period of the experiment. The 96 h LC₅₀ (the concentration required to kill 50% of the fish after 96 h of exposure) value computed was 0.59 mg/L. The median LT₅₀ (the time needed to kill 50% of the fish at various concentration applied) was 83.60 and 19.05 h for 0.50 and 2.25 mg/L, respectively. The results show that L. alopecuriodes is highly toxic to H. bidorsalis fingerlings.

Key words: Acute toxicity, Lepidagathis alopecuroides, opercular beat frequency, tail beat frequency, mortality.