Farming Requirements and Site Selection Criteria

1. Salinity
   Asian sea bass is a euryhaline species, meaning it can thrive in varying salinity levels from freshwater to seawater. However, farming is most effective in brackish waters with salinity levels ranging between 10-30 ppt. Coastal and estuarine regions are ideal for farming due to the stable salinity conditions.
2. Temperature
   Optimal growth is achieved in warm waters of 26-32°C. Temperatures below 20°C for prolonged periods can cause mortalities, making warm climates essential for successful farming.
3. Water Quality
   The preferred water parameters for Asian sea bass farming include:
   • pH: 7.5-8.5
   • Dissolved Oxygen (DO): 4-9 ppm, with floating net cages offering 7-8 ppm due to constant water flow.
     Sites with low microbial loads are necessary to ensure healthy fish growth and minimise disease risks.
4. Water Exchange
   Locations with strong currents (1-2 knots or 50-100 cm/sec) and tidal fluctuations (2-3 m) help maintain clean water in cages. Floating net cages placed at least 2 m above the seabed prevent siltation and waste accumulation.
5. Protection from Strong Winds
   Farms should be established in protected bays, lagoons, or coves to shield cages from strong winds and large shipping activities.
6. Biofouling and Predation
   Sites should be assessed for biofouling organisms and predator risks, as these factors significantly affect maintenance efforts and fish survival.

Advantages of Cage Farming for Asian Sea Bass

1. Rapid Growth and High Yield
   Asian sea bass grows quickly under optimal conditions, contributing to large-scale production and meeting high consumer demand.
2. Economic Viability
   Cage farming requires lower land investment compared to traditional pond farming, making it cost-effective. The species’ high market value ensures a strong return on investment.
3. Efficient Water Flow and Oxygen Levels
   Floating net cages facilitate continuous water exchange, providing ample dissolved oxygen and removing waste, which supports fish health and growth.
4. Adaptability to Diverse Environments
   The species thrives in freshwater, brackish water, and seawater, making it suitable for diverse farming locations.

Challenges of Cage Farming for Asian Sea Bass

1. Cannibalism and Feeding Challenges
   Asian sea bass is highly cannibalistic, particularly during its juvenile stages, requiring careful size grading and monitoring to prevent stock losses.
2. Biofouling and Predator Risks
   Biofouling organisms increase net maintenance efforts, while predators like larger fish and birds pose threats to stock.
3. Temperature Sensitivity
   Farming is unsuitable in regions with fluctuating or cooler temperatures, limiting its geographical scope.
4. Site Maintenance and Monitoring
   Cage farming demands regular cleaning of nets and close monitoring of water quality, adding to operational costs.
5. Environmental Impact
   Without proper waste management, uneaten feed and fish waste can accumulate beneath cages, affecting local ecosystems.

Asian sea bass cage farming presents a lucrative opportunity for aquaculture due to its fast growth, high market demand, and adaptability. However, challenges such as biofouling, cannibalism, and environmental management require careful attention. With proper planning, adherence to best practices, and environmental sustainability measures, cage farming for Asian sea bass can significantly contribute to meeting the rising demand for seafood while supporting economic growth in the aquaculture industry.

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While institutions connected to extension are aiming to increase seabass culture, other organizations in Bangladesh, particularly scientific institutions, are focused on producing seabass fries artificially. Bangladesh Fisheries Research Institute (BFRI) also started an experimental project on coral fish farming in cages in the Andharmanik river in Patuakhali’s Kalapara upazila. Initiatives are being conducted by the Palli Karma-Sahayak Foundation (PKSF)’s fisheries division to reach out to impoverished farmers in isolated coastal districts with high-value seabass cultivation. Programs including field days, carp and seabass farming demos, training, billboard installation, market linkage workshops, farmer-motivation tours, and the establishment of local seabass marketing centers and depots are all being carried out as part of the plan.

Culture Techniques:

Seabass has been farmed in Bangladesh’s coastal regions using a traditional and semi-intensive method that involves seedlings stocked in natural resources. Few nurseries in Bangladesh produce fingerlings from naturally occurring eggs and fry. The primary issue here, though, is that the seabass has not acclimated to additional commercial fish feed in culture ponds, forcing the farmer to employ live feed in the form of silver carp or tilapia fish fries.

The nursing stage:

The tide water then carries the eggs and larvae to the estuary following ovulation. The larvae migrate from the estuary to the upper reaches of the river, where they are caught by local fishermen. Larvae placed in ponds have a very high probability of dying. Rather, one of two methods is used to develop larvae from natural sources to produce juveniles that are up to three to five inches in length.

In nursery tanks or ponds, fries with a length of 0.5 to 1.0 inches are stocked at a density of 800-1100 per cubic meter and fed moderate amounts of nursery feed. A lot of people are also used to consuming shrimp and fish flesh, particularly those who will eventually farm naturally with little to no live food. Every three to four days, the bigger fries are chosen and separated, and while the seabass consume the smaller fish, the same-sized fry are raised in the tank using the grading process. Approximately one-third of the water in the nursing tank is changed each day.

The water in the tank is kept at a semi-brackish level, about 10 parts per thousand. Once the fish have been raised in the tanks for 30 to 40 days, the typical size of the fish that are retrieved for stocking ponds is between 3 and 5 inches, with a survival rate of 70–80%.

Grow-out Stage:

1.     Pond Preparation:

Pond renovations are started by seabass growers in February and March. Generally, the pond is prepared by clearing it of all fish, letting it dry out, and adding lime. When the pond is ready, the producers get in touch with the fry providers to order seabass fish fries.

• Optimum water quality parameter:

Standard water quality parameter should be Temperature: 26–32°C, Salinity: 10–30 ppt, Dissolved oxygen: 4–9 ppm, pH: 7.5–8.5, Turbidity: less than 10 ppm, H2S: less than 0.3 ppm, NH3: less than 1 ppm. Regularly, water quality parameter monitoring is necessary.

The amount of clay in a site is crucial because it prevents acid-sulfate soil and can retain water. Prior to stocking, an inorganic fertilizer can be used and an organic manure application of up to 2000 kg per hectare can be made.

3.     Stocking density:

In mixed aquaculture, tiny fish species, carp, tilapia, and seabass are all raised together. These farmers’ farms range in size from 15 to 40 decimal places. Typically, 5 kg of tilapia fish fries of the same size are stored in storage at the same time as 25–35 pieces of seabass fry, measuring 1.5–3.0 inches in size, are stocked each decimal. Small tilapia and zooplankton are the main sources of food for seabass; later, larger tilapia and carp fish fry.  Fresh tilapia fish fries are discharged when the population of tilapia declines, and eels and rubbish fish are frequently fed. In this instance, feeding seabass with 5 kg of carp or tilapia fish fry per decimal every month produces good outcomes. Seabass gains 2-3 kg with this procedure and reaches a salable weight in a year.

4.     Feed Management:

As it stands, waste fish is the only additional feed source for seabass culture. 10% to 5% of the total biomass might be applied to ground or chopped trash fish. After the first feeding, the application of feeding might continue for up to ninety days. It is recommended to feed them twice a day. A 1.5 kg/day/100 fish application of chopped fish is possible, although. In this instance, feeding seabass with 5 kg of carp or tilapia fish fry per decimal every month produces good outcomes. Seabass gains 2-3 kg with this procedure and reaches a salable weight in a year.

5.     Monitoring:

Frequent water exchange through the entrance is crucial for maintaining the proper salinity of the water needed for seabass culture as well as a healthy aquatic habitat. It is necessary to regularly check or inspect the area for pests and predators like crabs and water snakes. Waterfowl should be removed using a soft brush, and parasites should be removed as well. To prevent more pollution of the water, dead fish should be removed from the pond.

6.     Marketing:

Seabass prices are largely determined by weight on the market, just like the prices of most other fish. Fish that are larger in size tend to cost more per kilogram.

Bangladesh offers enormous potential for mariculture due to its large coastal water bodies and ideal climate. Either in ponds or cages, seabass culture has the potential to advance mariculture and strengthen the economy.

Farhana Islam
Agriculturist, Researcher
Fisheries Resource Management, CVASU

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Now, why should we care about Vetki / Koral fish? Well, they’re not just tasty; they play a vital role in keeping our ecosystem in check. These fish are like the clean-up crew, getting rid of dead organic waste. And guess what? They’re loaded with good stuff like fatty acids and Omega-3, which are great for lowering bad cholesterol and reducing the risk of diabetes and cancer. Plus, they’re packed with nutrients like protein, zinc, calcium, and magnesium, all of which are good for our bones. And let’s not forget the vitamin A, which keeps our eyes in top shape. So, eating Vetki fish is not just a treat; it’s like a health boost.

But there’s a catch. Despite being popular, Koral fish face some challenges in Bangladesh. Illegal fishing and environmental damage are causing problems. People are trying to farm these fish during the off-season by using leftover nets from prawn fishing, and it’s showing some promise. The little Vetki fish grow fast, and the big ones are in high demand, making it a good way to make money.

However, there’s still work to be done. Bangladesh is doing great in freshwater fish farming, but when it comes to farming in the sea fish, especially Asian Seabass, we’re a bit behind. We need to figure out how to make more Asia Seabass babies in a controlled way. Though there’s a recent success on artificial breeding by a local hatchery in Cox’s Bazaar named “Greenhouse Mariculture”. Now, its time to see how it turns out in commercial way, lets say we give more or less 3-5 years and hopefully something sustainable can be expected. Currently, many coastal fish farmers are already practicing Vetki farming, collecting fingerlings of imported brood from local hatcheries. Along with many the main challenge for rearing Asian Seabass, is the right food for the growth. There are some smart folks are already experimenting with different types of fish food to help Asian Seabass grow faster, but it can be expensive.

So, the bottom line is, there’s a lot of potential in farming Vetki fish, but we need to tackle the challenges like illegal fishing and figure out how to make it work in the aquaculture / Mariculture. If we can do that, we’ll not only get to enjoy more delicious Vetki dishes but also help our coastal waters stay healthy and diverse. Win-win!

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