Aquaculture Articles on Water Quality

Aquaculture is concerned with 'the propagation and rearing of aquatic organisms under complete human control involving manipulation of at least one stage of an aquatic organism's life before harvest, in order to increase its production'. Fish catches from the marine environment have been steadily declining in many parts of the world due to over-exploitation and pollution, making many people turning to aquaculture to improve the food production and to contribute for economic development. Aquaculture, has made encouraging progress in the past two decades producing significant quantities of food, income and employment. Aquaculture, particularly, shrimp like Penaeus monodon, Penaeus japonicus, Penaeus vannamei, prawn like Macrobrachium rosenbergii, and various fish species has extensively been practiced all along major water sources in Asia, the major contributor. Increased production is being achieved by expansion of culture areas and the use of modern methods.

One of the most common reasons for disease and mortality in land-based aquaculture in Australia, is due to problems with water quality. Water quality has a direct effect on the health of aquatic animals. Some of the most influential factors affecting water quality are temperature, dissolved oxygen, pH, salinity, suspended solids, toxic waste levels such as ammonia and flow rates.

Carp, or white amur, have been used for aquatic vegetation control in Mississippi for the past two decades. These fish, used as a "biological control" for aquatic vegetation, can be effective and cost efficient when stocked at appropriate rates and when the problem-weed species is a plant preferred by carp. Although these fish are voracious herbivores, they exhibit preferences for the softer, low-fiber, high-moisture plants when given a choice. Even when there is no alternative, grass carp will not always provide adequate control of certain plants that they do not prefer to eat.

Brown blood disease occurs in fish when water contains high nitrite concentrations. Nitrite enters a fish culture system after feed is digested by fish and the excess nitrogen is converted into ammonia, which is then excreted as waste into the water. Total ammonia nitrogen (TAN; NH3 and NH4+) is then converted to nitrite (NO2) that, under normal conditions, is quickly converted to nontoxic nitrate (NO3) by naturally occurring bacteria. Uneaten (wasted) feed and other organic material also break down into ammonia, nitrite, and nitrate in a similar manner.

Potassium permanganate, KMnO4 , is a chemical oxidizing agent that will react with any organic matter in a pond including algae, bacteria, fish, particulate and dissolved organic, and organic bottom sediments. It has been used in fish ponds to treat common fish pathogens such as gill parasites and external bacterial and fungal infections. Contrary to some reports, potassium permanganate does not add significant amounts of oxygen to water and can actually decrease dissolved oxygen concentrations by killing algae that produce much of the oxygen in ponds.