A Comparative Study on the Toxicity of a Synthetic Pyrethroid, Deltamethrin and a Neem Based Pesticide, Azadirachtin to Poecilia reticulata Peters 1859 (Cyprinodontiformes: Poeciliidae)

Increased use of chemical pesticide results in the excess inflow of toxic chemicals, mainly into the aquatic ecosystem (Baskaran et al., 1989; Kalavathy et al., 2001). The aquatic flora and fauna are affected by the toxic substances which eventually enter in to their systems or bring about external damages (Pant and Singh, 1983; Hodson, 1988; Johal and Dua, 1995). Several species of fish are susceptible to deleterious effects when exposed to heavy metals, pesticides and other environmental stressors (Khangrat et al., 1988; Areechon and Plump, 1990). Recent emphasis is on the use of natural pesticides, which are usually of plant origin. Azadirachtin derived from neem (Azadirachta indica A. Juss) is a very effective and extensively used pesticid. Pesticides based on azadirachtin may have direct adverse effects on aquatic organisms and their toxicity depends on various factors. It has been reported that neem extracts in aquatic environments are lethal to benthic populations and drastically decrease the number of organisms in the food web and nutrient cycling process (Goktepe et al., 2002; ElShazly et al., 2000). Even though Azadirachtin is not likely to accumulate or cause long-term side effects, toxicity to fish is only moderate and may not kill fish under normal use (Miller and Uetz, 1998). Pesticides containing bioactive compounds from the neemplant, Azadirachta indica Juss are reported to be target specific and comparatively less toxic. Plants are virtually inexhaustible sources of structurally diverse and biologically active substances (Istvan, 2000). Some plants contain compounds of various classes that have insecticidal, piscicidal and molluscicidal properties. Unlike synthetic chemical pesticides, which leave harmful residues in the aquatic environment (Koesomadinata, 1980; Cagauan, 1990; Cagaun and Arce, 1992), botanical insecticides are believed to be more environmentally friendlier because they are easily biodegraded and leave no residues in the environment. Most of the pesticides, both plant based and chemical, applied in the various agro ecosystems reach water bodies through runoff affecting fish, the most abundant aquatic organism, and a variety of other fauna. Persistent chemical molecules with long half-life periods found in chemical pesticides pose a threat to fish and also to the human population consuming the affected fish. The purpose of this study is to establish whether azadirachtin has any non-target effect on fish and to compare its toxic impact with deltamethrin, a powerful chemical pesticide. Based on the results, the use of the less toxic pesticide could be promoted among the agriculturists. It is possible to substitute chemical pesticides with pesticides of plant origin. This needs an extensive study on the properties of the two types of pesticides, especially a study of their toxic effect on aquatic organisms (Lockwood, 1976; Woin, 1988; Glow and Godzi, 1994; Christina, 2004). Fish are considered to be indicators of water pollution (von Westernhagen, 1988). Guppies are common fresh water fish capable of tolerating wide fluctuations in water quality and hence have been selected for this work. Any impact on such hardy species is considered to be ultimate, since other Abstract