Introduction

Environment is complex and diverse. It includes several distinct ecosystem types. Environmental pollution is the act of introduction by man of extraneous substances or energy in the environment that induces unfavourable changes. During the last few decades the indiscriminate use of pesticides has created havoc in the environment and has become the reason for various ailments in human and other fauna and flora.

The Indian pesticide industry, with an estimated 79,800 metric tonnes (MT) of production for 2007 – 2008, is ranked second in Asia (behind China) and twelfth globally. In value terms, the size of the Indian pesticide industry was estimated at US$ 1500 million, including exports of US$ 622 million. The importance of pesticides in India can be understood from the fact that agriculture is a major component of the Indian economy: it contributes 22% of the nation’s GDP and is the livelihood of nearly 70% the country’s workforce14. Monocrotophos is a water-soluble organophosphate insecticide with high oral and moderate dermal toxicity. The toxicologically relevant mode of action is the inhibition of ChE activities12. In the present investigation the effects of monocrotophos on the enzyme activity of the grass carp Ctenopharyngodon idella has been analysed.

Materials and Methods

Ctenopharyngodon idella is an herbivorous fresh water fish. The healthy varieties were acclimatized to lab conditions for 15 days, prior to experimentation. Fish species of similar size and weight were subjected to acute toxicity test with 7-8 narrow range concentrations and was observed for 24,48,72,96 hrs and % of mortality was calculated4. The 96 hrs exposed species are subjected to chronic toxicity test; where 60%, 70%, 80%, 90% of 96 hrs Lc50 were subjected to sub-lethal concentration for 7 days. A control was also maintained1.

Later the exposed species were subjected to undergo the bioassay of Acid Phosphatase (AcP) and Alkaline Phosphatase (AlP)3 and Lactate Dehydrogenase (LDH)6 with samples taken from gill, liver and kidney.

Results and Discussion

Acute stress Tolerance of Fish

Susceptibility of the fish to monocrotophos proved that the percentage of mortality increased with increasing concentration of the pesticide. The tolerance level of C. idella to monocrotophos was determined after exposing them to known pesticide concentrations for 24, 48, 72 and 96hrs (Table 1). The enzyme activity was determined from the control and treated fishes. In the control fish, the enzyme activity in gill, liver, and kidney were recorded as 158.00 ± 2.31, 190.00 ± 4.62 and 218.00 ± 4.62 IU/l respectively. Gills are generally considered good indicator of water quality, since the gills are the primary route for the entry of pesticide13.

TABLE 1: Tolerance limit of Ctenopharyngodon Idella exposed to Monocrotophos.

The gill tissues showed lowest AlP activity compared to liver and kidney. In 70% pesticide treated fish, gill tissues showed the moderate AlP activity. In 80% pesticide treated fish, the liver tissues showed the lowest AlP activity. In 90% pesticide activity, the liver tissues showed the lowest AlP activity.

Acid phosphatase activity in the gill, liver and kidney of C. idella exposed to 60%, 70%, 80%, and 90% of concentration of monocrotophos. The gill tissues showed the lowest AcP activity compared to liver and kidney. The Lactose dehydrogenase activity in the gill, liver and kidney of C. idella exposed to 60%, 70%, 80% and 90% of concentration of monocrotophos. In control- liver tissues showed high LDH activity. The same was the result for all 60%, 70%, 80%, and 90% treated fish species for 7 days (Table 2).

Table 2: Activity of Alkaline phosphatise (AlP), Acid phosphatise (AcP) and Lactate dehydrogenase (LDH) (IU/L units)in the tissues of Ctenopharyngodon idella exposed to sublethal concentrations of Monocrotophos for 7 days.

Pesticides eventually reach the aquatic systems in considerable amounts via the agricultural runoff and atmosphere fall out through rain etc., acute toxicity tests are used to detect and evaluate the potential toxicological effect of any chemical or toxicant. In the present study susceptibility of the fresh water fish C. idella increased with decrease in the concentration concomitantly the Lc50 values of pesticides range from 7.7, 7.4, 7.4, and 7.3 ppm for 24, 48, 72 and 96 hrs of exposure of monocrotophos. Impact of sub- lethal concentration of pesticides on enzyme activity revealed significant decline in the activity of AlP, AcP and LDH in the tissues of C. idella.

The impact on phosphates activity was high in the fishes exposed to the highest of the three sub- lethal concentration. Acid and alkaline phosphatases are hydrolytic lysosomal enzymes and have a role in certain detoxification function. Evidences indicate that membrane system of cell is the important sites of pesticides toxicity9 which is true in present investigation. A significant increase in concentration of pesticide and exposure time indicated an increased inhibition of the enzyme. Uncoupling of oxidative phosphorylation is the main cause for inhibition of phosphatises. Depleted levels of phosphatases activity was reported in Channa gachua exposed to pesticides and toxicants2. The findings of the present investigations are in accordance with the report of Gill et al.,5 on Puntius conchonius exposed to aldicarb, phosphamidon and endosulfan.

According to Shaoguo Ru et al.,10 the AChE activity goes down progressively with the increase of monocrotophos concentration in Sciaenops ocellatus. Increased activities of acid and alkaline phosphatase of blood plasma of Channa punctatusexposed to monocrotophos indicated hepatic tissue damage11. Sub-lethal doses (176.95 and 75.5 ppm) of monocrotophos on gonads of female and male Chrotogonus trachypterus (Blanchard) produced drastic changes in alkaline phosphatase and acid phosphatase8.

Behavioral responses of the fish Cyprinus carpio were significant in lethal exposures due to intoxication. Fish showed hyper excitation, erratic swimming, jumping, and lethargy due to low breathing frequency followed by muscular rigidity and abundant mucous secretion over the gills when exposed to sublethal concentrations of monocrotophos7.