Effects of pesticides on fish and other aquatic organisms: Production of indigenous small fish in Bangladesh decreases vary sharply day by day. Generally our indigenous small fish (Anabas festudineous, Heteropneusted fossil, Clarias batrachus,m Mustus tengara, Glossogobius giureis Channa punctuates, Nonoptetus notoptesus, Puntius sophore etc.) uses paddy fields as breeding ground. Now all of paddy fields are polluted by the agricultural pesticides. That is why, fish mortality occurs in the paddy fields. Normal physiological functions, affacing and breeding behaviour are inhibited by the effects of pesticides and fish may be sterile by the same.In open water, fish mortality and fish diseases occurs .due to the use of pesticides in agricultural fields. In assessing the toxicity of pesticides to other aquatic invertebrates and vertebrate it is found that most of the pesticides are highly toxic to phytoplankton, zooplankton and other aquatic organisms. Many of the aquatic invertebrates, especially crustaceans, cladocerans, copepods and insect larvae that form an important source of food for many species of fish, are reported to be more sensible to pesticides than fish. Various types of pesticide were tested at the Fisheries Research Institute of Riverine Station.
Residual effects of pesticides on fish and other aquatic organisms: Pesticides that are transported to the aquatic environment are primarily of agricultural origin. They may also raise as effluents to manufacturing and formulating plants, urban sewage, careless handling of the spraying equipment and used containers is another source of pesticides residues to the aquatic environment. How much pesticides molecules wash out from agricultural lands to aquatic environment depends on soil texture, soil type (mineral or organic), surface geology, slope and drainage density and also soil chemistry. Water bodies closer to agricultural lands understandably have high residue levels. The residue concentrations of animals found higher to lower are enclosed ponds, free flowing creeks, larger water bodies like lake and contiogouus esturaies respectively. The distribution residues in different parts of the fish body varies; bead slices of fish which usually have more lipid and are also reported to have higher concentration. Relatively high concentrations of residues were found in testes, ovaries and eggs in fish. The changes which may occur in fish and other aquatic organisms due to the residual effects of pesticides are given below.
1. Physiological changes: Due to the residual effects of pesticides some important organs, viz. Kidney, liver, gills, stomach, brain, muscles and genital organs are damaged. Development of testes and ovaries are 50 inhibited by the effect of pesticides because its effects also hamper the spermatogenesis and genesis process. Pesticides affected eggs have very low hatching rate and fry dies soon after hatching.
2. Changes of breeding ground: Some pesticides residues are accumulated by the aquatic vegetation. Many fishes release their eggs on that aquatic vegetation. For this reason, the released eggs become toxic and damm damaged all types of breeding grounds are polluted by the pesticides residues. Therefore, the fisheries sector is known endanger position.
3. Changes of feeding ground: Most of the pesticides are highly toxic to both of aquatic invertebrates and vertebrates. Many aquatic invertebrates and vertebrates are used as fish food. Their feeding and breeding grounds are not suitable for rearing and spawning due to the residual effects of pesticides. Due to the aquatic environment degradation, natural fish feeds have already started declining significantly.