Comparative assessment of the acute and sub-acute effects of some plant based Ichthyotoxins on aquatic organisms: a case study of Clarias gariepinus

Abstract

Plant-based ichthyotoxins are increasingly used for commercial fishing activities in many countries all over the world. This study investigated the acute and sub-acute effects of the aqueous extracts of some plant-based ichthyotoxins, commonly used in Nigeria, on Clarias gariepinus. Ichthyotoxins in the bark of Anarcadium occidentale, seeds of Carica papaya, nuts of Raphia vinifera and leaves of Manihot esculenta were extracted using referenced methods. Acute effect of the ichthyotoxins to Clarias gariepinus was assessed using static bioassays for a 96-h period and sub-acute effect on the biochemical processes in the fish was assessed using static renewal bioassays for 28 days. Acute toxicity studies showed that A. occidentale was the most toxic to the fish with a 96h LC50 value of 35.159 mg/L compared to the other ichthyotoxins. The 96h LC50 values of C. papaya, R. vinifera and M. esculenta were 539.236 mg/L, 828.741 mg/L and 1160.233 mg/L respectively. Sub-acute toxicity studies showed that the ichthyotoxins had minimal effects on the biochemical processes in the fish. Activities of the antioxidant and liver function enzymes investigated did not increase in exposed fish compared to the control. This study showed that some plant-based ichthyotoxins can be acutely toxic to fish at low concentrations and their general application on surface waters expose target and non-target macro invertebrates to the acute effects of the toxins. Hence, there is a need to enlighten indigenous fishermen and regulate the use of plant-based ichthyotoxins which are presumed to be safer than synthetic ichthyotoxins.