Water is the most important part of the environment in aquaculture ponds for the aquatic organisms. Shrimp farming is directly related to the water quality of shrimp ponds, so that if the water and soil quality of the ponds is not maintained to the desired level, the shrimp will not feed well and will become sensitive to diseases and their survival will be reduced. Therefore, maintaining the optimal quality of this environment depends on proper and optimal water management during the farming period. The water used in aquaculture contains organic and mineral materials, and soluble mineral ions, soluble gases, suspended solids, soluble organic compounds, and microorganisms all affect water quality. Water quality in shrimp ponds is affected by various external factors (such as weather conditions and the quality of water entering the ponds) and various internal factors (food quality, bed conditions, etc.). Thus, management strategies in this area should be regulated in such a way that compensatory, confrontational or preventive measures should be adopted for uncontrollable factors, and appropriate measures should be considered for internal factors. In fact, aquaculture practitioners need to learn how to manage water in order to know in what situation, what control measures should be taken to prevent damage to their products.
Reservoir ponds
These ponds occupy between 25 and 30 percent of the total area under cultivation and the water needed to fill aquaculture pools, after pumping from the main source (water canal, estuary, sea, ocean, etc.), first enters these ponds and then is directed to other ponds. In farms that use reservoir ponds, depending on the purpose of construction, centralized or separate reservoir ponds may be built for sedimentation, storage and water treatment.
Filtration
In recent years, the use of reverse sand filter system (overflow) has played an important role in removing physical and biological unwanted materials. Pond vacuum net filter, incoming water supply pipe net filter, reverse sand filter, one millimeter filters and chamber filters with fabric filters are among the various types of filters used in aquaculture farms.
Physico - chemical parameters
Dissolved oxygen
The most important consumers of dissolved oxygen in aquaculture ponds are black bottom soils, which consume about 55 to 75 percent of the dissolved oxygen, followed by phytoplankton and shrimp, which consume 25 to 40 percent and 5 percent of the dissolved oxygen, respectively. The most important reasons for the decrease in dissolved oxygen include over feeding, over bloom, an increase in water temperature, temperature stratification, an increase in salinity and cloudy weather for several consecutive days.
Oxidation - reduction potential (ORP)
The low level of this indicator indicates the oxidation capacity of the environment, which usually occurs in aquaculture farms in cases of black bottom soil accumulation. The appropriate amount of ORP in aquaculture ponds is between 150 and 250.
Temperature
Pathogens usually grow more at temperatures of 35 to 40 degrees Celsius. Vannamei shrimp feed well at temperatures of 27 to 32 degrees Celsius. Below this temperature, shrimp feeding rate decreases. Between 33 and 35 degrees Celsius, although shrimp feeding rate increases, the excretion rate also increases. Shrimp feeding rate reduces above 35 degrees Celsius.
Alkalinity
Alkalinity prevents the pH from fluctuating sharply day and night. Factors affecting pH fluctuations in shrimp ponds are as follows: Acidic soils (high in aluminum), rainfall, buffering capacity of water, high density, over feeding, accumulation of sludge in the bed, the presence of many microorganisms in the bed, excessive bloom in the water as well as respiration of shrimp and other organisms or their competitors and unwanted organisms in the pond.
Salinity
The salinity tolerance of vannamei shrimp ranges from 5.0 to 55 ppt and the optimal range is between 15 and 35 ppt. In salinity much lower than the desired range, shrimp need to perform osmoregulation (with energy consumption) and at a higher range than this, they need to pump solutes out of the body.
Aerator performance in the pond
Factors that cause the transfer and diffusion of oxygen from the air into the water include the direct diffusion of oxygen from the atmosphere into the water. Other factors that produce oxygen in ponds are the mechanical aerators, which increase the oxygen content in ponds by mixing pond water with air and creating current (water exchange) and waves. As a result, interactions for the decomposition of organic matter in ponds are reduced.
Proper arrangement of aerators in the pond
The arrangement of aerators in the pond is varied based on the purpose of aeration. If the main purpose of using aerators is to provide oxygen along with directing the waste to the center of the pond, the arrangement of aerators should be such that it can create a proper flow of water around the center of the pond. If the use of aerators is only for oxygen supply to water (in injection, respiration and vertical pump types), it is necessary to place the aerator in critical points or in the water inlet path. Placing aerators in the corners of the pond causes solids to accumulate in the center of the pond. If the ponds have proper drainage, these solids will be drained or removed during drying of the ponds. Depending on the size of the pond, placing more aerators in the middle of the pond will provide more oxygen and better water circulation. Usually, the aerator with the power of 10 - 20 hp / ha is considered in the super - intensive shrimp farming and high feeding rate.
As mentioned, the management of shrimp farms involves a chain of factors, some of which are influenced by other factors and in other words are dependent. For example, pH and oxygen are affected by various factors such as phytoplankton bloom (photosynthesis process), wind, stocking density and temperature as well as salinity. Some factors are independent such as temperature and salinity. Therefore, in the pond environment, our role in controlling these factors is insignificant. On the other hand, the role of food in the quality of the bed and, of course, the quality of the water seems obvious. Therefore, it should be noted that poor quality feed can be the source of significant changes in water such as reduced oxygen levels and high pH fluctuations, which of course affects the growth rate of shrimp. It is recommended that water quality parameters such as salinity, temperature, oxygen, pH, ammonium and nitrite be measured regularly. If the amount of oxygen is low, it is necessary to change the water or use aerators in order to supply oxygen and remove toxins and excretion of shrimp from the ponds. Sampling of phytoplankton to regulate algal biomass (the degree of transparency) should also be on the agenda. Experiments and studies of researchers indicated that fluctuations in most important physicochemical parameters such as pH, oxygen, organic matter load, ammonia, nitrite and the bloom of a particular phytoplankton species as well as water quality and sediment quality are mainly affected by low feed quality. Therefore, it is recommended to use feed pellets that contain the ingredients needed for shrimp at different stages of growth, which of course affects the growth rate of shrimp. However, some factors such as temperature and salinity act independently or in other words, our role in controlling these factors is insignificant.