EFFECTS OF AQUATIC POLLUTION ON FISH & FISHERIES

 

 

EFFECTS OF AQUATIC POLLUTION ON FISH & FISHERIES

Definition:

The term pollution is broadly refers to any undesirable change in the natural qualityof environment brought about by physical, chemical, or biological factors. Environmental pollution is unfavorable alteration of our surroundings due to direct or indirect activities of man.The high rate of increase human population, rapid expansion in the industrial and urban activities and modernization of agriculture has resulted in generation of high volume of waste material causing gradual deterioration of valuable resources of biological productivity.

AQUATIC POLLUTION

Aquatic systems are considered as suitable sites for disposal of and recycling the sewage andtoxic wastes and drain off the excess to the sea. However, the increasing pollutant load and theover exploitation of the water resources for potable supplies, irrigation, industries and thermalpower plants to meet the requirements of the ever-increasing population, significantly reducestheir assimilative capacity. Thus, the dual stress exerted on the watercourses is ultimately facedby the biological communities inhabiting them. Of this fish is the most important aquaticcommunity concerning the man.

Definition:

The water pollution has been defined as ‘any man made alternation of physical,chemical or biological quality of the water which results in unacceptable depreciation of theutility of the environmental value of water’. The matter of unacceptability is to be decidedaccording to expectations and requirements at any time, bearing in mind the expectations andrequirements in environmental pollution change as knowledge, experience and perceptionadvance.

Sources of water pollution:

To understand the causes, effect and control of pollution, the sources of pollution shouldbe clearly classified. The sources of water pollution with reference to fisheries can be classifiedinto following categories:1.

 

Domestic sewage2.

 

Soil erosion and sedimentation3.

 

Industrial organic and inorganic wastes4.

 

Agricultural wastes5.

 

Oil and oil dispersants6.

 

Radioactive wastes7.

 

Waste heat8.

 

Solid wastes9.

 

Acid rain

1. Domestic sewage:

In India, raw or partially treated sewage and laundry detergents coming from thehousehold are allowed to discharge into the nearby rivers.Based on the census of 1981, magnitude of sewage pollution in India: It is estimated that nearly33 million tones of sewage is generated daily in our country which is directly proportional to thepopulation of the country. The enormity of sewage pollution in our river water is also reflected inthe river Ganga in which more than 70% of the total pollution load is contributed by the sewage.

2. Soil erosion and sedimentation:

Land erosion is one of the major sources of pollution in the watercourse. The sources of all sediments are soil erosion, which is due to overgrazing, deforestation, intensive agriculturalpractices, high rainfall, and construction of roads, houses etc. and mining activities.Magnitude of siltation in India: In India, nearly, 5,334 million tones of soil are being erodedannually from the cultivable lands and forests. The country’s rivers Cavery an approximatequantity of 2,050 million tones of which nearly 480 million tones is deposited in the reservoirand 1,572 million tones is washed into the sea every year.

3. Industrial organic and inorganic wastes:

In India, pollution of river water takes place at various centers of industrialization, chieflyat Delhi, Bombay, Calcutta, Madras, Kanpur, Hyderabad, Bangalore, Ahmadabad, Baroda,Rourkella, Jamshadpur, Visakhapatnam, Cochin etc. Industries generate a significant quantity of wastewater and discharge it into rivers and lake. Industrial discharges generally contain organicsubstances, solids and mineral acids. Pulp and paper, dairy and textile industries generateputrifiable organic waste, while industries manufacturing organic-chemicals, pesticides,fertilizers, dyes and pigments, non-ferrous metals, steel and chloroalkali generate hazardous andtoxic inorganic waste (heavy metals).

4. Agricultural wastes:

The important pollutants from agricultural drainage include the poisonous pesticideresidues and mineral fertilizers. Unlike industrial effluents, it is very difficult to contain thetransport of the nutrient chemicals and pesticides through agricultural drainage, which is a nonpoint source of pollution. The fertilizers used in the agriculture are the major contributor of residual phosphates and nitrates in surface waters.

5. Oil and oil dispersants:

Oil pollution has become a serious problem of the seawater all over the world. Sourcesof oil pollutions are accidental oil spills, refinery operation, offshore production, normaloperation of oil-carrying tankers, merchant and naval vessels, the disposal of oil waste materials,natural seepage of oil from underwater oil reservoir and transport of oil in the atmosphere and itsprecipitation on the sea surface.Magnitude: Both the east and west coast of India are reported to show pollution due to oilspillage. The water of Mahim Bay of Bombay Coast is heavily contaminated from the effluentsof oil and oil products.

6. Radio active wastes:

Sources of contamination of the aquatic environment by radio active materials are; radioactive fallout-during the period of atmospheric testing of nuclear weapons, Nuclear reactors andplants, nuclear-powered ships and submarines, laboratory experiments with and medicinal use of radioisotopes.

  

7. Waste heat:

Waste heat is a by-product of many industrial processes, especially from the productionof electrical energy. Water is used to cool these power stations becomes quite hot anddischarged into rivers and streams, whose water temperature also rises. 3/40

C increase in watertemperature in Rihand lake is observed after construction of Thermal plant by NTPC in UP.

8. Solid wastes:

Mixture of commercial and household rubbish such as paper, bottles, cans, oldautomobiles and tires, sludges produced in sewage treatment plants, spoils from the dredging of harbours are major sources of solid wastes. The disposal of these solid wastes is a difficultproblem in crowded urban centers and sea disposal of this waste material is being usedincreasingly.

9. Acid rain:

During recent years, industrialized countries are experiencing precipitation which is10-1000 times more acidic than normal. Normal rainfall is slightly acidic (pH=5.6) due to thepresence of CO2in air, which dissolves in water forming a weak carbonic acid. In eastern USA,Canada and Europe, pH of the rain is typically4.5 and some times its is only 4.0. This is due tothe presence of sulphuric acid and nitric acid in rainwater, which is because of the presence of sulphur and nitrogen in air. Burning of fuel (coal) produces SO

2

and NO2, whichreact with watervapour through no of steps, forming acids. As the soil over India has been highly alkaline, rainover Industrial towns like Agra, Kanpur, Delhi, Bombay, Calcutta, Bhopal, Nagpur has remainednon-acidic, but recent studies by scientist of the Indian Institute of Tropical Meteorology at Pune,suggest that this situation is changing.

Changes in the physico-chemical parameters of water due to pollution:

Physical parameters(a)

 

Temperature:

Temperature of water may increase due to thermal pollution when wateris used to cool power stations and due to waste heat from industries.

(b)Turbidity & colour:

Turbidity of water may increase due to soil erosion or heavy algalbloom due to high level of organic and inorganic nutrients from sewage water oragricultural waste. Turbidity, dye and pigment pollutants affect the general colour of water.

 (c)Depth & flow:

Flow and depth of the water body may be reduced due to heavy siltationof sediments coming from land erosion.

 (d)Light:

Due to high turbidity and colouration of the water bodies, penetration of light isreduced.

Chemical parameters(a)

pH:

pH of water may be acidic due to acid rain that originates largely from burning of coal and oil. Acids also originate in large quantities from mines and various industrialprocesses (waste from DDT factory, battery, vinegar, tanneries). Fish usually live at pHlevels between 6.0 and 9.0, although they may not tolerate a sudden change within thisrange.

(b)Dissolved oxygen:

Dissolve oxygen level of water is reduced to greater extent when (i)

 

Heavy sewage pollution or other effluents containing high organic matter aredischarged into it. These are broken down by the microorganisms, which used upthe dissolved O

2.(ii)

 

Inorganic effluents containing readily oxidisable substances such as sulphites andferrous salts can produce a similar effect.(iii)

Eutrophication and turbidity often reduced the dissolve oxygen level of waterbodies.(iv)Presence of synthetic detergents and oils lowering the re-oxygenation rate of water.(v)Discharge of cooling water from industries also reduced the dissolve oxygen levelof water bodies. (c)CO2:Eutrophication and organic pollutants responsible for depletion of

dissolve oxygenincrease the CO2level in water bodies, due to decomposition of undecomposed orpartially decomposed organic matter.

 (d)Alkalinity:

Wastes associated with tanning, wool scouring, the mercerizing of cotton andthe manufacture of certain chemicals (in chloro-alkali industries) may contain causticsoda (NaOH), sodium carbonate or lime. Such alkaline effluents may have a pH of 12-14and lethal to all types of stream life, including bacteria.

 (e)Salinity:

Excessive amount of salts brought by sewage; and effluents from chloro-alkaliindustries increase the chloride level thereby salinity of water, which is responsible forincrease in the osmotic pressure. Salinity also reduces dissolve oxygen level.

(f)Dissolved solids:

  (i) Nitrates and phosphates:

Water polluted by agricultural wastes, soil erosion andorganic pollutants (sewage & biodegradable synthetic detergents) are rich in nitrates andphosphates.

(ii) Heavy metals:Hg, Zn, Ni, Cd, Pb, Mn, Cu, Fe, Cr, As, Se etc are present in naturalwater in very trace amount that’s why they are called trace elements. However, inpolluted waters their concentrations are increased in many folds. They come frommining, refining, paper and pulp industries (Cr), mercury electric appliance industries,vinyl chloride synthesis, caustic soda industries using mercury cell, organo-mercuricfungicides industries, lead processing industries, storage batteries, water pipes (Pb),industrial discharges, metal or plastic pipes (Cd), metal processing and dye industries,mines, drainage (Zn), trade wastes from pickling and anodizing, leather, dye-manufacturing, explosives, ceramics. Heavy metals are non-biodegradable, watersoluble, persistent and strongly bonded to polypeptides and proteins.

ON ECOLOGY1. Eutrophication:

Pollution due to domestic sewage increases the organic load and pollution due to agricultural waste (residual fertilizers) and soil erosion containing nutrients such as nitrates;phosphates, potassium etc. fertilize the water and increase the rate of productivity of the aquatic ecosystem. This results in higher growth of phytoplankton. Water becomes turbid due to excessive growth of phytoplankton and soil eroded particles.Excessive amount of nutrients change the algal community from one of great diversity of species to one of a few; the species which are eliminated are commonly those which form the food of the herbivorous animals which in turn feed the fisheries resources of the area. The species, whichgrow in abundance, are generally the blue-green algae or other species, which are mostlyunsuitable or less valuable as food for fishes and grazing animals. The changes in the plantpopulation thus indirectly cause changes throughout the entire ecosystem, even in organisms,which are not directly effected by the pollution.Aquatic lives face severe oxygen shortage due to;i) Bacterial Decomposition of untreated sewage into their inorganic components assimilatesdissolve oxygen from the water in the process.ii) High turbidity restricts the penetration of sunlight in deeper layers and benthic plants couldnot photosynthesize.iii) When algal bloom die, they sink to the deeper waters and in the process of decomposition, allthe oxygen can be consumed.This leads to anaerobic decomposition and generation of toxic substances like hydrogensulphide, ammonia, mercaptans and organic amines. At times when dissolved oxygen in water isat it’s lowest and these substances at their peak values the water smells bad and becomeunsuitable.The whole process is referred to as ‘eutrophication’, as a result of which there is excessive growth of phytoplankton due to nutrient enrichment, increase in turbidity and death of benthic plants, depletion of dissolved oxygen and consequent suffocation of fish and mollusks that in habit deeper waters.The species able to survive are usually less valuable as fisheries resources from aneconomic point of view. Among the species to disappear from over enriched lakes or estuariesare the trout and salmon, and the survivors are the pollution tolerant cyprinids.2.

Accelerated aging of lakes and ponds:

 Sewage pollution even at in small quantities may change the character of an aquaticenvironment over a period of years. Thus, with the gradual process of aging, deep, clearoligotropic lakes may be sedimented; becoming mesotrophic, then becomes eutrophic andeventually turning into bog.

BIOLOGICAL EFFECTS ON FISH:

Pollutants might effect a given population without being lethal to adult organisms inmany ways.i) Migration: Mechanism used for orientation and navigation by migrating organisms is not wellknown, but in some cases chemo toxicants clearly plays an important role. Sub-lethalconcentration of pollutants may interfere with the normal migration pattern of organisms therebychange the composition of population or species diversity. Salmon, trout and many otheranadromous fishes have been excluded from their home streams by pollution, though it is notknown whether the reason is that a chemical cue has been masked or because the generalchemical environment of pollution is offensive to the fish.On the other hand, heavy siltation and flow of heated coolant water may block migratorychannels and long distance migratory fishes during some phases of their life history maybeadversely affected by highly localized pollution of river.ii) Incidence of diseases: A long-term exposure of sub lethal concentration of pollutants maymake an organism more susceptible to a disease. It is possible that some organic pollutants willprovide an environment suitable for the development of disease producing bacterial and viruses.In such case, even though the pollutant is not directly toxic to the adult organism it could stillhave a profound effect on the population of the species over a longer period.iii) Behaviour: Much of the day-to-day behaviour of a species may also be mediated by means of chemo toxic responses. The finding and capture of food and the search for a mate during thebreeding season are included in this category of activity, and again any pollutant interfering with

   6the chemo receptors of the organism would interfere with the behavioural patterns essential to asurvival of the population.iv) Physiological Processes:Pollutant may interfere with various physiological processes without necessarily causingdeath, which may interfere in the survival of a species. DDT depresses photosynthesis inplanktonic algae, but only at concentrations greater than its solubility in water. Respiration mightalso be adversely affected, as could various other enzymatic processes. The toxic substances andsuspended sediments when injure the mucous membrane of the gills effects the respiration.Heavy metals particularly mercury inhibit the activities of digestive enzymes but it has mostdamaging effect on the nervous system.v) Life cycle:The larval forms of many species are much was sensitive to pollution than the adults. Inmany aquatic species millions of eggs are produced and fertilized but only two of the larvalproduced need to grow to maturity and breed in order to maintain the standing stock of thespecies. For these species, the pre-adult mortalities rate is enormous even under the best of natural conditions. An additional stress on the developing organisms might cause failure of enough individual to survive and maintain the population of the species. Interrupting any stage of the life cycle can be as disastrous for the population as death of the adults from acute toxicity of the environment.Example. Silt sedimentation, eutrophication and increased pollution level had affected thestanding fish stock in many Indian rivers by spectacular mass mortalities.vi) Nutrition and food chain:Pollutants may interfere with the nutrition of organisms by affecting their ability to findpray, by interfering with digestion or assimilation of food, by contaminating the pray species sothat it is not accepted by the predator. On the other hand, if predator species is eliminated bypollution the pray species may have an improved chance of survival. An example of the lattereffect was shown in the Kelp resurgence after the oil spill in Tampico Bay, California (North,1967). The oil kills the sea urchins, which used young, newly developing kelp as food and thekelp beds developed luxurious growth within a few months. Heavy metals and halogenatedhydrocarbons e.g. DDT, BHC, Endosulfan etc. are particularly harmful because they tend to bio-accumulate. These chemicals are easily adsorbed into the body but excreted very slowly resultingin bioaccumulation, which may further enhance in the food chain. Organisms at the bottom of the food chain absorb the chemicals from the water and accumulate it in the tissues. Animals atthe second trophic level, such as fish, feeding on these organisms receive a higher dose, andfurther accumulation takes place in their tissues and so on, up the food chain. Thus, organisms atthe top of the food chain receive the chemical at a much higher level than present in the water.This concentration of the toxic chemicals through the food chain is called ‘bio-magnification’.This is further complicated by the ‘synergistic effects’ i.e. two or more chemicals acting togetherto produce a much more pronounced effect, than the sum of the total of the effects of the twoacting separately.vii) Genetic effects:Many pollutants produce genetic effects, which can have long-range significance for thesurvival of species. Radioactive contamination can cause mutations directly by the action of radiation on the genetic material. Oil and other organic pollutants may include both mutagenic and carcinogenic compounds. A large majority of these mutations is detrimental to the survivalof the young and many are lethal.