Water Quality Management Methods for Tilapia During the Peak Growth Season
June to September is the peak growth season for tilapia, but during this period, as feeding amounts increase, water quality changes most frequently, and severe weather occurs from time to time. If water quality can be well regulated and healthy aquaculture practices implemented, increased production and income can be ensured; if management is neglected, all previous efforts may be wasted. This year the tilapia market is quite promising, but the climate is changeable, so water quality management at this time is crucial. Below, based on practical experience, we discuss water quality management measures for tilapia during the peak growth season, for reference only.
Manage water sources well and create a good water quality foundation
In tilapia aquaculture, the water source is the most basic and also the most important aspect. It determines water quality conditions and the success or failure of aquaculture. Selecting and managing the water source well determines the basic conditions of water quality. Generally, water source conditions require that the water source be stable, sufficient, clean and hygienic, with suitable water temperature, good water quality, no pollution whatsoever, and compliance with national fishery water quality standards. At the same time, it requires convenient water intake and drainage, with separate intake and drainage. Fish-blocking nets must be properly installed at the water intake and drainage outlets, both to prevent harmful organisms and wild trash fish from entering the pond and to prevent fish from escaping. Before water from the source enters the aquaculture pond, it must be filtered and disinfected in a reservoir to kill pathogens and harmful organisms in the water source. Generally, 25 g to 30 g of quicklime or 1 g of bleaching powder (containing more than 25% available chlorine) can be evenly spread over the entire pond, and when pest insects need to be killed, 0.5 g of trichlorfon per cubic meter can also be evenly spread over the entire pond. From June to September, the probability of flooding is relatively high, so the water inlet and drainage outlets must be well managed, filtration facilities must be well constructed, and it is necessary to ensure smooth drainage and irrigation so that embankments are not easily washed away, preventing floods from washing away fish or washing in debris that hinders fish growth.
Apply fertilizer reasonably and cultivate good water quality conditions
The amount of fertilizer affects both the growth of tilapia and changes in water quality. Although tilapia is not very strict about water fertility, during aquaculture, moderate fertilization can keep plankton in a good growth state, increase dissolved oxygen and nutrients in the water body, thereby cultivating good water quality conditions and supporting tilapia growth. From May to June, organic fertilizer should be mainly applied, once every 7 to 10 days; from July to September, chemical fertilizer should be mainly applied, once every 4 to 6 days. Generally, water transparency should be around 25 cm, and the water color should preferably be tea-brown. At the same time, note that a single fertilization amount should not be too much, and emphasis should be placed on applying less but more frequently. For organic fertilizers such as human and livestock manure, 100 kg to 150 kg per mu can be applied each time; for chemical fertilizers, 1 kg of urea or 1.5 kg of ammonium sulfate plus 1 kg to 1.5 kg of superphosphate can be used per mu each time. Biological fertilizers can also be applied according to water temperature and water quality conditions.
Feed scientifically and ensure relatively stable water quality
From June to September, tilapia grows most vigorously, and more feed is put in, which greatly affects water quality. The principle of scientific feeding should be grasped to stabilize water quality and avoid harm. When feeding, the feeding amount should be flexibly controlled according to weather, water quality and fish feeding conditions. Because tilapia is currently one of the main species for high-density flowing water aquaculture or “factory-style” aquaculture, aquaculture requires feeding compound feed with comprehensive nutrition. However, if scientific methods are not grasped during feeding, it will not only waste feed but also spoil water quality and induce various diseases. Therefore, bait feeding must be scientific. Tilapia has a very broad diet. Under artificial rearing conditions, various feeds can be fed, such as wheat, corn, and oilseed cakes, all of which are high-quality feeds for it. In the early stage, the protein content in the feed should be 32% to 35%, and the daily feeding amount should be 3% to 5% of the total fish body weight. When the individual size grows to about 200 g, the feeding amount can be adjusted to 2% of the total fish body weight, and the protein content in the feed should be ensured at 27% to 29%. When the individual reaches about 300 g, tilapia enters the fastest growth period, and the daily feeding amount should be maintained at 1% to 2% of fish body weight, with protein content in the feed above 35%. Feed can be self-mixed, but it is best to process it into pellets for feeding. In feeding methods, the “four fixed” principle should be emphasized. Feed twice a day, at 8 am to 9 am and 3 pm to 4 pm respectively. Each mu of pond also needs 2 to 3 feeding platforms for fixed-point feeding. When the weather is clear, water quality is fresh, and fish feeding is vigorous, more can be fed appropriately; otherwise, feed less or not at all as appropriate. Feeding when fish are floating at the surface in the morning and feeding at night should be strictly controlled to avoid disease.
Regularly add water and regulate and control water quality well
From June to September, water temperature is high, water quality changes quickly, and in addition, feeding and fertilization amounts are relatively large and fish excretion is strong, making it very easy to pollute water quality, so water quality regulation should be strengthened. Water quality regulation is the fundamental way to cultivate good water quality conditions. During pond aquaculture, pond water should be changed frequently to maintain fresh water quality, strictly prevent surface floating and pond turnover, and dissolved oxygen should often be maintained above 3 mg/L. Generally, add and change new water once every 7 to 10 days or so, changing 10 cm to 20 cm each time, keeping the pond water level at about 1.5 m; during continuous high-temperature seasons, the number of water changes can be appropriately increased. During aquaculture, according to weather, water temperature and fish feeding conditions, appropriately turn on aerators to increase oxygen. When the weather changes, air pressure is low, and dissolved oxygen in the water is below 3 mg/L and fish are floating at the surface, the frequency and duration of aerator operation should be increased. During reservoir cage aquaculture, cages should be brushed frequently to wash off cage dirt and attached algae so that the water body can fully exchange, and cages should also be inspected regularly and repaired promptly if damage is found, so as to prevent fish from escaping or fierce fish from entering the cages. When necessary, cages should also be constantly adjusted; as reservoir water levels rise and fall, cages should be adjusted to positions with suitable water depth. When oxygen deficiency is relatively serious, oxygen-increasing drugs can also be used. Generally, quicklime can be used to regulate water quality regularly, usually once every half month by applying 15 kg to 20 kg of quicklime per mu dissolved in water and evenly spread over the entire pond. When surface floating occurs, oxygen-increasing agents and related drugs can also be selected to increase oxygen. At the same time, residual bait and dirt in ponds or on feeding platforms should be removed in a timely manner to prevent water quality pollution.
Strictly prevent disease and do a good job in daily water quality maintenance
From June to September, it is both the best growth season for tilapia and also the period when it is most susceptible to disease infection. Once fish disease occurs, it spreads extremely quickly, pollutes water quality, and causes losses. In tilapia aquaculture, regular disease prevention is the guarantee for cultivating good water quality conditions. Generally, quicklime is more suitable for disease prevention because it can regulate the pH value of the water body, kill harmful bacteria in the water body, and cause bottom mud to release inorganic salts, increasing water fertility. First, regular disinfection is required. During pond aquaculture, apply quicklime every 10 to 15 days at 15 to 20 kg per mu dissolved in water and evenly spread over the entire pond, 1 to 2 times per month, to adjust pond water pH to slightly alkaline, and use biological preparations to improve the microbial structure of the pond and improve water quality. At the same time, aerators should be turned on in a timely manner. When dissolved oxygen is low and fish show slight surface floating, turn on the aerator so that the pH value in pond water remains between 7.0 and 8.0 and transparency remains between 25 cm and 30 cm. During cage aquaculture, regular disinfection and disease prevention can be carried out by hanging medicinal bags or feeding medicated bait to improve water quality conditions. Second, daily management should be strengthened. Persist in patrolling the pond day and night. Measure water temperature and air temperature 3 times every day, measure pH once a week, and measure transparency twice. Patrol the pond once in the early morning and once at night and keep an aquaculture diary. During key periods at dawn, noon and dusk, strictly check feeding conditions and whether there are signs of surface floating. Promptly and frequently remove residual bait and dirt from ponds and feeding platforms, and remove weeds around the ponds. If signs of surface floating are found, stop fertilization and control the feeding amount, and immediately take oxygen-increasing measures. If dead fish are found in the pond, they should be promptly removed, the cause of death checked, and treatment given according to symptoms. At the same time, diseased fish should be buried deeply far away to avoid spoiling water quality, inducing fish disease, or causing fish disease to spread.
Practice rotational catching and stocking to prevent gradual water quality deterioration
From June to September, as tilapia grows rapidly, the fish carrying capacity of ponds rises sharply, and the probability of water quality deterioration grows greater and greater. At this time, pay attention to rotational catching and stocking, release water body space, and control the fish carrying capacity of the water body well, which can achieve the effect of regulating water quality and preventing trouble before it happens. Because by August and September fish grow relatively quickly, as fish bodies grow, when the fish carrying capacity of the water body is exceeded, there will be a danger of oxygen deficiency and fish death. Therefore, large fish should be caught and small ones left, with balanced marketing. If the water body permits, an appropriate number of fingerlings can also be supplemented in a timely manner to lay a foundation for aquaculture in the following year.