The trend of fish consumption in Indonesia is increasing along with public awareness of the importance of nutrients contained in fish meat. One of the most popular fish commodities for consumption is tilapia. The popularity of tilapia is due to its delicious meat flavour, its high nutritional content compared to other fish, and its relatively economical price.
Among farmers, tilapia is the main choice because it has a fast growth rate, a strong immune system, efficiency in the use of feed, and good adaptability to various conditions of the cultivation environment. One technique commonly used in conventional tilapia farming is the use of earthen ponds. The use of earthen ponds in fisheries activities is very common in Indonesia, especially for fish commodities such as catfish, goldfish, gourami, and tilapia.
In order to obtain maximum results in tilapia farming in earthen ponds, there are several things that need to be considered. According to several studies, before cultivating tilapia in an earthen pond, soil and water management must be done first. This aims to ensure optimal pond conditions for tilapia rearing.
Purpose of earthen pond management
Earthen pond management aims to ensure a healthy and productive aquaculture environment. Some of the main objectives of earthen pond management are:
1. Breaks the cycle of pathogenic bacteria
Pathogens such as Aeromonas hydrophila and Edwardsiella tarda can cause serious diseases in tilapia, such as aeromoniasis and edwardsiellosis. Draining and disinfecting ponds can reduce the risk of pathogen infection by up to 80 percent.
2. Increases oxygen levels in the earth
Oxygen plays a role in supporting the activity of aerobic bacteria responsible for the decomposition of organic matter. Earthen pond that has sufficient oxygen levels can increase the population of Bacillus sp., helpful bacteria to mineralize organic matter.
3. Removing toxins from feed scraps and feces
The accumulation of leftover feed and fish waste produces ammonia and hydrogen sulfide which are toxic to fish. Ammonia concentrations above 0.1 mg/L can cause reduced growth and increased stress in tilapia. With earthen pond management, ammonia content can be reduced to safe levels.
4. Oxidize the earthen pond surface
The process of earthen pond oxidation helps reduce the levels of organic compounds that can lead to anaerobic conditions. Ponds that undergo soil oxidation on a regular basis have a higher farming success rate compared to ponds that are not managed properly.
Stages of earthen pond preparation for tilapia farming
1. Draining the pond
Pond draining is done before starting the tilapia aquaculture cycle. The aim is to break the cycle of pathogenic bacteria formed from the previous cultivation process. The pond drying process lasts for 7-14 days or until the surface of the earthen pond is completely dry. Indicators of successful drying are that the earthen pond looks cracked, brightly colored, and odorless.
However, it should be noted that the earthen pond should not be too dry (the moisture content should remain around 20 percent) because too dry conditions can interfere with the survival of natural food at the bottom of the pond. Forage such as plankton and microorganisms are important in the pond ecosystem and contribute to the provision of food for tilapia.
2. Liming the pond
After the drying process, the next step in managing earthen ponds for tilapia farming is liming. Liming plays an important role in improving the quality of the earthen pond bottom, which affects the water quality and the health of the cultured fish. Some of the main objectives of liming include increasing the pH of the earthen pond to reach a level suitable for tilapia, increasing nitrate levels in the earthen, maintaining the sanitary environment of aquaculture pond waters, and stimulating microbial activity in the process of decomposing organic matter.
Earthen pond bottom that has too low a pH can have a negative impact on tilapia growth. The optimal pH for the growth of freshwater fish, including tilapia, is in the range of 6.5-8.5. If the pH is too low (acidic), the fish will experience stress that can inhibit growth and increase the risk of disease.
Liming is done after the pond has been drained for about 7 days. Before sprinkling lime, the type of earthen at the bottom of the pond needs to be analyzed and tested using a soil pH meter. This analysis aims to determine the appropriate dose of lime so that the earthen pH reaches an optimal condition. If the pH of the earthen pond is too low (<5.5), a higher dose of liming is required. On the other hand, if the earthen pH is close to neutral (6-7), liming can be done in lower doses or even not needed.
The type of lime utilized in earthen pond management is contingent upon the farmer's availability and capabilities. Common types of lime employed in fisheries include agricultural lime (calcite/CaCO₃), dolomite (CaMg(CO₃)₂), and quicklime (CaO). Research indicates that dolomite lime is particularly effective in magnesium-deficient waters, while quicklime has been shown to rapidly increase earth pH. The dosage of lime administered is meticulously calibrated based on the characteristics of the pond's underlying soil and its initial pH level. For instance, to elevate the soil pH from a level below 4 to 6, the application of 500-1,000 kg/ha of quicklime (CaO) is necessary.
Beyond its role in pH regulation, liming also enhances the physical integrity of the pond's substrate. Earth with abundant organic matter often undergoes anaerobic decomposition, yielding toxic compounds such as ammonia (NH₃) and hydrogen sulfide (H₂S). Liming can accelerate the decomposition process by enhancing the activity of aerobic microorganisms that more efficiently break down organic matter. The dosage of lime utilized also depends on the texture of the pond soil. Clay-rich soils generally possess a higher buffering capacity and, as a result, require greater amounts of lime to raise the pH. Conversely, sand-dominated soils possess a low buffering capacity, thereby requiring less lime.
Liming of earthen pond, BPBAT Tatelu
3. Pond fertilization
After the liming stage is complete, the next step in preparing an earthen pond for tilapia farming is fertilization. Fertilization aims to increase the nutrient content in the pond which plays an important role in supporting the growth of microorganisms, especially phytoplankton and zooplankton. Phytoplankton function as primary producers that provide oxygen and become a natural food source for zooplankton and tilapia.
Fertilization is done about three days after liming so that the sown lime has time to react and stabilize the pH of the pond bottom soil. The use of fertilizer will accelerate the growth of plankton, which can be the main food chain in the pond ecosystem. The type of fertilizer used can be either organic or inorganic. Organic fertilizers such as manure can help enrich the organic matter content in the earth and increase microbial activity. Meanwhile, inorganic fertilizers such as urea and TSP (Triple Super Phosphate) can provide the nitrogen and phosphorus elements needed for rapid phytoplankton growth.
The fertilization dose is adjusted to the fertility level of the earthen pond bottom. For organic fertilizers, the recommended dosage ranges from 100-500 grams/m² depending on the organic matter content in the pond. Meanwhile, inorganic fertilizers such as urea and TSP are applied at a lower dose of about 10 grams/m². Excessive fertilizer application can cause algae blooms that have the potential to reduce dissolved oxygen levels in the water, so it needs to be done with the right calculations.
After fertilization, the pond is left for 7-10 days before filling the water. This period is important to ensure that the nutrients from the fertilizer have dissolved and are available for plankton growth. This process also allows microorganisms to develop properly before tilapia are stocked so that the pond will have a stable natural ecosystem.
Earthen pond fertilization, BPBAT Tatelu
4. Filling the pond water
Water filling in tilapia farming ponds should be done gradually to ensure the pond ecosystem develops well before tilapia fry are stocked. This process aims to give time for the growth of phytoplankton, which will be a natural food source for tilapia. In addition, gradual water replenishment helps reduce the risk of water quality fluctuations that can affect the condition of the fish when they are first stocked.
After the fertilization process is complete, the first stage of water filling is done by adding water to a depth of 10-15 cm. At this stage, the nutrients that have been provided through fertilizers will begin to dissolve and support the growth of microorganisms in the pond. The water is then left for 2-3 days so that phytoplankton can develop naturally. Phytoplankton are photosynthetic organisms that play an important role in providing oxygen and food for zooplankton and tilapia fry.
The main sign that phytoplankton has grown well is a change in the color of the pond water to green. This green color is caused by the growth of Chlorophyta algae which are commonly found in aquaculture pond ecosystems. If the water remains clear for a long time, this can be an indication that fertilization is not effective or there are other factors that inhibit plankton growth, such as unstable pH or insufficient nutrient levels.
After the phytoplankton has grown, the next step is to add water to a depth that suits the needs of tilapia farming. The ideal pond depth for tilapia farming generally ranges from 80-120 cm, depending on the rearing system used.
