Water Characteristics to Consider for Optimum Aquaculture Water Management

By Bryan Low

The specific requirements of fish and other marine animals mean that water must have the right composition and optimum oxygen content to promote fish and marine life in aquaculture. The right chemical composition in pond aquaculture will determine the success or failure of any business built on fish and marine life. However, there is more to successful fish farming than just a simple determination of the composition of the water. Suitable water sources, the right volume of water taking into account evaporation rates and seepage, and a host of other factors work together to ensure the optimum growth of fish and other marine organisms.

Understanding Water for Aquaculture Water Management
There are several characteristics of water that maintain life. However, the importance of an aquatic environment is seen in two areas of fish and marine life, namely:
  • capacity to act as a temperature buffer
  • maintain the water balance in fish
Water has the ability to prevent rapid fluctuations in temperature which is essential for the maintenance of marine life because it can hold large amounts of heat before the temperature rises dramatically. The larger the body of water, the harder it is to raise the temperature by a degree. This is essential for maintaining marine life since organisms take on the temperature of water and most cannot tolerate sudden temperature changes in their environment. Water can also dissolve more substances than any other liquid out there, which makes it essential in the provision of minerals and other nutrients that are needed by fish and other marine life.

Water is also essential in keeping the chemical balance in fish. Since water is the natural environment of fish, it naturally plays an important part in the internal homeostasis of fish and other marine animals. Specifically, the gills, which are permeable to water and salts are the main modes of excretion for fish. Because the salinity in water is higher compared to that of fish, water is ingested by fish and it turn excretes salt-concentrated urine out. This is the normal process of excretion in salt water fish, although the reverse is true in freshwater species, where the fish lose the majority of the salt concentration in their systems through the gills. Naturally, this leads to a lower salt concentration in the urine that is excreted by the freshwater fish.

It is also important to note that the physical characteristics of water determine what kind of gases are dissolved. Cooler water temperature allows more gases to be dissolved. The way that water reacts to temperature also results to thermal stratification where different substances are distributed in different layers in the water depending on how they dissolve in water. In the spring, where the water temperature is more or less consistent in various levels of the water, dissolved gases and fish wastes are distributed more evenly in the water. In warmer seasons, upper layers of water become warmer and lighter. The bottom layer of water is cooler and denser and circulation is decreased due to the difference in densities between these two layers. More oxygen is present in the upper layers due to its lighter nature and its access to air, while the opposite is true for the bottom part of the water. Oxygen levels in the bottom layer is further decreased with the presence of fish waste which, being heavier, naturally float down and settle in the bottom. This often leads to localized oxygen depletion which can pose a problem for most fish farmers. Stratification becomes a heavier problem in deeper farm ponds since the condition can last for several weeks. Prolonged stratification explains fish kills in the summer months that is followed by summer rain.

Water Sources for Aquaculture
Commercial aquaculture relies on reliable and suitable sources of water. This means choosing a suitable source for water that can maintain marine life. These include wells, springs, rivers, lakes as well as groundwater. Water from wells and springs are often considered to provide a consistent quality for aquaculture. Of course, water quality analysis will be done no matter how suitable the source is. This is a crucial part of a feasibility study where a quantitative and qualitative appraisal of the water coming the source is done. This includes measuring the dissolved oxygen, pH, temperatures, and the chemical composition of the water to determine its suitability. An analysis for metals and depending on the location of the source, the presence of chemicals such as pesticides and herbicides coming from the surrounding areas. The results are then compared to the optimum water quality criteria for fish farming.

Determining the Suitable Water Quantity for Aquaculture
The water quantity is also an essential factor in ensuring the success of fish farming. The minimum rate would be 13 gallons per minute per surface acre of pond. The volume must be adequate for the needs of fish taking into account the rates of seepage and evaporation. It is also important to note that the quantity of water needed may change depending on the seasons. For example,the spawning season will necessitate more water requirements for certain species of fish. In farms that depend on groundwater sources, studies must be made to determine the yield potentials of each source. This includes doing exploratory drilling and test pumping in order to adequately assess the groundwater resource in each area.

Aquaculturists who want to ensure the maximum quality of the water need to understand a few things about the best quality of environment for fish. These include the physical characteristics of water, the interaction between water balance and fish, the quantity of water versus the quantity of fish present in the water and the physical and chemical factors of water. The water quality is a top priority because fish and other marine animals perform all bodily functions important for life in water. Fish breathe, eat, reproduce and excrete wastes in water. Biological activities of fish and other living organisms can drastically alter the chemical composition of water which necessitates the use of water management solutions, provided by Malaysian companies such as Syndel, to ensure that all factors are maintained at the levels that fit marine life.

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