Effects of pollution on eggs, spawn, fry on breeding grounds andfeeding grounds

Effects of pollution on eggs, spawn, fry on breeding grounds andfeeding grounds Effects on fish eggs; spawn and fry:

Fish eggs are much more resistant than the adult fish. Toxicity thresholds for lead, zinc and nickel to be about 20, 40 and 2000 ppm respectively, values for higher than those found forabout animal.Eggs would develop normally between pH 6 to 9. In water more acid than pH 4.0, the eggs displayed exosmosis and collapsed, in water more alkaline than pH 9.0 there was end osmosis, the eggs swelled and yolk became white. The critical oxygen tensions are about 40mm Hg for newly fertilized eggs and rises, as the embryo develops, to about 100 mg Hg (about60% saturation) at the time of hatching. Trout and Salmon lay their eggs in gravel, through which water must percolate while the eggs batch and the fry live on the food from the egg yolk.Then the gravel must allow the fry to emerge. A suitable area must not accumulate silt and sand during the gravel life and it must not freeze or shift with floods. Oxygen shortage due to pollution in the water flowing through the gravel, an insufficient rate of water flow due to deposition of silt in the spawning beds, or a combination of both these adverse factors will holdup the development of fish eggs, delay hatching and proves fatal to the embryos.

Survival of larval fish fry and fingerlings:

(a). Food acquisition:Larval fish is able to feed only on the tiniest of zooplankton and phytoplankton, thus early growth and survival of fish depends upon the densities of small cladocerans and rotifersand phytoplankton. Aquatic pollution is toxic to these plankton and pose threat to survival of fishfry.(b). Predation:Survival of larval fish is probably influenced more by predation than by feeding. These very small fish are vulnerable to virtually every other predator. Not only visual feeding fish butalso other predators such as predaceous copepods may have considerable influence on larval fishdensities.Protective cover, such as aquatic macrophytes must be especially critical in minimizingfish predation on small fish. Any factor(s), such as turbidity, wave action, siltation that would reduce vegetative cover, could also minimize larval fish survivorship. Reducing or lowering thewater level (due to siltation) below the vegetative zone would seem to be especially disastrous tolarval fish.Structural complexity, especially aquatic vegetation, while providing refuge for larvaland fingerlings fish, may reduce the ability of piscivorous fish to feed on small fish.Fry and fingerlings are more susceptible to pollution than adult fish.Resistance to pollution: Egg> Adult>Larvae

Destruction of breeding & spawning grounds:

For any nest, building fish or any fish in which the eggs attach to a particular substratethe nature of the substrate is important in successful spawning. Aquatic vegetation often providesthe very substrate within which or on which eggs are laid and may protect eggs from wave actionand erosion. Gravel bed is good for spawning. The role of nearby structure (gravel) of aquaticvegetation is less clear, but it doubtless makes nest defense from predator more effective.High level of turbidity caused by pollution often precludes the development of substantiallittoral zone vegetation.With increase of water level and flow rate of water, spawning success was found toincrease.

 A lowered level of dissolved oxygen due to the presence of organic pollution, which initself is not toxic to may significantly reduce the chances of salmon reaching the spawninggrounds because of fatigue and reduction of swimming velocity.Base metals in rivers have been shown to cause Atlantic Salmon to return to sea with outspawning, resulting in over all reduce reproduction.Soil particles due to land erosion carried out run-off water and suspended matter presentin sewage and trade wastes gets deposited on the river bed or behind the weirs and cause siltingof the bed. Siltation in river and reservoirs diminishes the (i) quantum of water flow (ii) flow rateof water and (iii) water level, thereby reducing the spawning success. Heavy siltation alsodestroy the nesting materials (e.g. Aquatic vegetation) for fishes and cover the gravel structure by silt deposits thereby natural spawning of fish is prevented due to lack of suitable spawningarea and increases egg mortality. This can be serious in respect of major carps, trouts, salmonid sand other fishes requires special environment for breeding.Either fish failing to reach their spawning or feeding areas, because they avoid pollutedwaters or perhaps because pollutants interfere with their chemical sense and they are not able torecognize their home waters.

Effect on feeds and feeding grounds of fishes:

Turbidity: Silts and clay greatly reduce the euphotic zone in rivers and reservoirs.Turbidity severely restricts the zone within the water body where visually feeding fish canefficiently find and attack their pray. Turbidity also reduces fish vision within the euphotic zone.Siltation: Heavy silt deposits smoothers benthic vegetation and invertebrate checking itsgrowth. This reduces the production of benthic vegetation. Salmonoids in streams need places tofeed and hide from predators. The feeding places are usually in or below the gravel riffles thatproduces aquatic food organisms. This feeding place is destroyed by siltation.Larval fish is able to feed only on the tiniest of zooplankton and phytoplankton, thusearly growth and survival of fish depends upon the densities of small cladocerans and rotifersand phytoplankton. Aquatic pollution is toxic to these plankton and pose threat to survival of fishfry. Eutrophication: Excessive amount of nutrients changes the algal community from one of great diversity of species to one of a few; the species, which are eliminated commonly those, whichfrom the food of the herbivorous animals which in turn feed the fisheries resources of the area.The species, which grow in abundance, are generally the blue-green algae and other species,which are mostly unsuitable as feed for fishes.Heat discharge: Because of this macro algae and sea grass disappear resulting decline of fish product due to lack of shelter for juvenile stages of commercial species of food organisms and reduced food for associated herbivores.

Effects on fishing and fishery products:

Fishing:

  Fishing gear and operations may be adversely affected by various kinds of pollutants.Over fertilization may cause fouling and clogging of nets, traps and other fishing gears by masses of macro algae or other plants and animals drifting in the water or using the materials as substratum. In the areas of oil exploitation nets are frequently clogged by crude oil and lumps of oily tar and catches have had to be discarded because of tainting. The numerous objects caught in the bottom trawls (from plastic containers to explosives) often interfere with fishing operations.Wrecked cars and other junk have hampered fishing particularly in the North sea and the Baltic by mechanical damage to nets and boats, and good fishing areas have been closed because of the danger from dumped military waste such as explosives, cyanide compounds, biological and chemical warfare agents and radio active wastes.

 

 9Fishery products: A common reason for the discarding of catches and the discontinuance of fishing in certain areas is the tainting of the fish by unpleasant ordours and tastes caused bypetroleum derivatives, even at concentrations significantly below lethal levels. Waste fromrefineries and discharges of petroleum from ships are causing increasing damage to fishing inthis respect. 0.01-0.02 ppm concentration is sufficient to cause bad taste in rainbow trout,Japanese mackerel and some other species. Mullet, which is rich in body fat, is likely to acquiretaint more readily than other fish species in the same environment.Colouring: Colouring has a similar effect to tainting on the fish’s marketability that is a fishproduct with a modified colour is practically worthless. The “green Oyster” of Japan andPortugal, coloured by incorporated copper and zinc and “red herring” of Canada due to internalbleeding by elemental phosphorous are examples.There is evidence that pollution can cause morphological changes, teratogenic effects,skin ulcerations and other lesions, as well as various other diseases especially fungal in fish andshellfish. This has generally been associated with water is chronically contaminated by wastefrom industry or municipal sewage and sludge. In some countries fisheries product are eaten rawproviding opportunities for human infection by pathogenic such as viruses, bacteria, andnematodes. Bacterial contamination from domestic sewage is a particular problem to theshellfish (e.g. oysters, mussels, cockles etc.) may be marketed, however, after appropriatetreatment (sterilization, relaying or purification) which, when properly carried out, results inproducts safe for human consumption.Swordfish fishery has suffered economically because of rather high contamination of mercury found in this fish (M.R.L. for Hg 0.05 mg/kg body weight).In some cases, it has been observed that “blooms” of toxic species of plankton wererelated to the disposal of nutrients into the water, as by sewage pollution. The danger toconsumers is evident and mass mortalities of fish and other organisms are frequent consequence.This has led to the temporary closure of certain fishing areas or to the prohibition of the sale of the product.

Ciguatera toxins and paralytic shellfish poisoning:

Ciguatera toxins and paralytic shellfish poisoning are naturally occurring toxins.Ciguatera is the most common nonbacterial food poisoning disease associated with theconsumption of fish primarily in tropical regions of the world, including Caribbean, Atlantic,Indian and Pacific Ocean regions and Middle Eastern and Australian areas. Ciguatera isconsidered a world health problem. Studies have shown that more than 20 toxins are responsiblefor ciguatera phenomenon. The primary toxin, ciguatera toxin, has been isolated from largecarnivores, and in smaller amounts, in herbivores. This is due to the greater lipid solubility of ciguatera. Considerable circumstantial evidence has linked

Gamberdicus toxicus

and otherdinoflagellates to the group of ciguatera toxins. Paralytic shellfish poisoning may occur becauseof ingestion by certain species of bivalves (e.g. mussels, calms, oysters) of planktonic poisonousdinoflagellates such as

Gonyauflux

. Murate et al. (1990) reported the structures of ciguatoxinfrom the morey eel (Gymnothorax javanicus) and has not yet been conclusively demonstratedthat the toxin produced by the dinoflagellate is either identical to, or is a precursor to,ciguatoxin(s) accumulating in fish. However, research workers have suggested recently that therelease of inorganic substances because of mining activities into the water of tropical regions ininsular areas triggers off naturally occurring biotoxicity cycles such as “Ciguatera” and other fishpoisoning. This makes the normally valuable food resource dangerous for human consumptionand thereby instances of human death caused by such poisoning.