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Overview from the book titled - Effects of Pollution on Fish, Molecular Effects and Population Responses - Lawrence and Hemingway 2004
This book makes an attempt to explain how various types of pollution can affect fish and the entire fishing community. However, molecular biology is not the language of the common man!
This being considered, I tried to simplify some of the most important ideas and facts contained in it.
Basically, Don't Litter! I am sure you have seen these signs on our highways but there should be a way of placing these signs on the world's waterways.
Whether it is garbage bags, fuel oil, or industrial chemicals - eventually this refuse finds its way into the worlds waterways where it will affect fish in various ways. This could be anything from disrupting the way fish reproduce to the formation of benign or malignant tumors. Considering these potential hazards, over-fishing seems to be the lesser evil.
Chemical contaminants such as PCBs, DDT and other halogenated hydrocarbons have been implicated in adversely affecting the reproductive systems of land and marine species. Some of these chemicals are confirmed -others suspected- of having hormonal effects on the sexual organs of fish. Exposure has resulted in male fish producing eggs and the inhibition of female egg production.
Metals can accumulate in the muscle, even in species with low fat muscle tissue. Organic forms of lead, tin, selenium antimony and arsenic are found in the marine environment. The most serious incidence of human consumption of contaminated seafood was the 'Minimata' incident which was caused by an organometal - methylmercury. In this incident, produced by the methylation of industrially discharged mercury, the organometal was taken up by marine invertebrates and fish.Consumption of these products is thought to have been responsible for over a 100 deaths and many cases of severe disability.
Pesticides that contain chlorine (organochlorine pesticides) are the most widely distributed chemicals on the planet and may play a role in sublethal effects on fish. The fish do not necessarily die, instead their health deteriorates. Unfortunately, as with many sublethal affects, the socio-economic consequences of the pesticides in fish are not readily understood in a majority of cases. However, in Uganda the practice of harvesting fish by using pesticides --Thiodan was the compound implicated-- has resulted in the deaths of at least 12 people, the closure of the tilapia fishery and the suspension of exporting Nile perch to the European Union.
In 1991 many fisheries along the coast of California,Washington and Oregon had to be closed due to the high levels of pesticides found in razor clams, mussels and dungeness crabs. Pelicans were killed by the consumption of contaminated anchovies and this led to the closure of the fishery and resultant socio-economic dislocations.
Oil spills have various affects on marine life. In most cases the marine impact depends on the type of oil. The Valdez oil spill was heavy crude and did not readily evaporate or disperse. On the other hand, the Braer oil spill off the Shetland Islands was lighter and easily dispersed by wind and waves.
There was a 23% loss of the wild stock production of pink salmon and a 50% reduction in pacific herring in Prince William Sound after the Valdez spill. Other taxa such as harpacticoid copepods and epibenthic crustaceans (prey resources for the juvenile salmon) were not affected by the spill. In some cases their abundance increased in the areas that were polluted. In addition, toxicity tests were undertaken for finfish and shellfish in the area and the finfish were reported safe to eat. The shellfish, on the other hand, were found to have high concentrations of aromatic contaminants.
Both chemicals and metals are believed to affect the genetic expression of marine animals. Whether fish with 3 eyes, or in one case, a flounder with a tumor on its head which made it look like a 2 headed fish - exposure to these pollutants must be curtailed in order to preserve and enhance fish stocks.
Over the past 2 decades, the effects of pollution on fish have been observed in the formation of tumors of the mouth and livers of fish. These tumors have occurred in both salt and freshwater species. There are many gaps in our current understanding of the chemical processes that effect fish. Presently, there are no comprehensive studies that detail all aspects of the impact of pollution within the aquatic environment.
Clearly, the effects on the reproductive process and it's cumulative effect on population density must be studied in more detail.