Fish population is adversely affected by a number of environmental factors. These are as follows.
- Water Pollution
The problem of water pollution mainly affects marine water fish. A variety of insecticides, pesticides, industrial effluents and domestic sewage find their way into many rivers and pose a serious problem for fisheries. The magnitude of pollution varies with the size of the river, the flow of water etc. Let us take few examples.
(i) The paper mills located on the bank of a river in Orissa consume nearly 270 million litres of water per day. This heavy withdrawal of water together with the discharge of high toxic effluents causes considerable harm to the fisheries for a stretch of nearly 24 km downstream.
(ii) The effluents from fertilizer factory have been found to have adverse effects on fish and prawn. Vast investigations in respect of effluents of paper pulp-textile industries, tannery manufacturing units, sugar distillery, coal, etc. have shown adverse effects on fisheries while sewage used as a fertilizer for fish farm has been found to cause extreme damage to fish culture.
(iii) Thermal pollution caused by the discharge of hot water used for cooling reactors and generators can be a serious problem in tropical waters where the normal temperature itself is high and further increase would be lethal to the fish which are already https://junglefitnessoc.com/diazepam-for-sale/ living in the higher ranges of temperature tolerance. At present, a potential source of pollution is the atomic reactor wastes. Consequences of water pollution are given below.
- Many of favorite fishes like the Bombay Duck have almost disappeared from the Kalu river near Mumbai. This has been due to the release of a number of toxic wastes from the chemical industries into the river.
- Excessive use of chemical fertilizers may lead to the phenomenon of Eutrophication (enrichment of the water body with nutrients). This results in algal bloom, (excessive growth of algae which use up available oxygen) followed by oxygen depletion in water and ultimately the death of fish.
- Thermal (heat) pollution from various heavy industries causes fish mortality.
- Ultra violet radiations affect fish eggs that become non-viable, that is, they fail to develop.
- Leakage of petroleum from ships and off-shore oil wells forms an oil slick on the surface of the water and thus fishes are unable to breathe due to no availability of dissolved Oxygen in the water.
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