In Suthi Mahalao’s Boonsawang farm, the mark of success is when his seabass is accepted by Japanese chefs in Bangkok
The farm harvests 800g fish and will also harvest 5-6kg fish for special markets such as for the Ikejime preparation. Current farmgate prices are THB120kg (USD3.4) for live fish. For chilled fish, prices (in THB) are 80/kg for 400-600g fish; 90/kg for 700-800g fish; 80/kg for 900g-1kg fish; 70/kg for 1.2-2kg fish and 110/kg for 2.2- 3kg fish. The exchange is THB 9.66 for one USD.
Generally, consumers prefer farmed seabass in sea cages rather than those farmed in earthen ponds, mainly because of off-flavour in pond-raised fish. Boonsawang farm prefers to culture fish in earthen ponds with 15-18ppt salinity. It is also easier to manage because of Suthi’s farming experience. He has found ways to address weak points in inland pond culture such as off-flavour, taste, texture, and quality (Figure 1).
Over the last 10 years, Suthi Mahalao has been a happy man. He owns the Boonsawang farm in Bangpakong, Chachengsao Province which has an annual production of more than 700 tonnes of Asian seabass, Lates calcarifer giving a yield of 22.3 tonnes/ha from the 31ha farm. This has been continuous for over 10 years. However, the actual capacity is more than 1,000 tonnes/year, but production has been restricted by demand. Acceptance in high end retail markets is recognition that his seabass production is natural and free of chemicals and antibiotics.
Suthi is not only well known for his farming skills but also as the inventor of a grading bucket now adopted by farmers in Thailand. He has also trained farmers in using pelleted feeds in seabass farming. He is the current chairman of the Thai Marine Fish Farming Association and has received as many as 20 accolades for his contribution to Thailand’s aquaculture industry. Among them are Best Fish Farmer in the Royal Ploughing Ceremony Year 2017, Lert Rat Award in 2018 and Best Fish Farmer of the National Bureau of Agricultural Commodity and Food Standards, Thailand.
Marketing seabass
It is well known that the most discerning buyers are Japanese chefs. Success is when inland cultured seabass meets these chefs’ criteria on quality and freshness. Boonsawang supplies seabass fillets to premium restaurants in Thailand such as the Kensaku Japanese restaurant and premium Copper Buffet where seabass is prepared as sashimi. The farm also supplies fish for Thai raw fish “Ikejime” (Ikejime is a method of killing fish which maintains the quality of its meat). This was possible as the farm’s seabass has passed the test of no off-flavour or muddy taste.
The farming process
The farm starts with 5-inch (12.7cm) fingerlings. Stocking density will depend on target harvest sizes. For harvests of 500g fish, it is 5 fingerlings/m2; for 1 kg fish, it is 3 fingerlings/m2 and for larger fish, it is only 1 fingerling/m2. In general, he says that the stocking density is 3-4kg/m2.
The nursing area is 30% of the farm area and is used for the first month stocking. Fish are disinfected before stocking to be parasite- and pathogen-free. Fingerlings come from a hatchery, which is a member of the Thai Marine Fish Farming Association. Prior to delivery, the hatchery will acclimatise fingerlings to the salinity of pond water at the farm and temperature during transportation is 25-26°C.
Water preparation should be at least a week before stocking. Water is filled to the optimum level and the aerator requirement is 1 HP/tonne of biomass for adequate oxygen demand. The optimum water parameters should be, pH 7.5-8.5, alkalinity >100ppm, transparency 10- 20cm, salinity 15-30ppt, and ammonia nitrite 0. The survival rate is more than 80% for the 6-month cycle. The average daily growth or ADG is around 5.4g.
A leader in seabass farming
Suthi first entered aquaculture in the farming of the monodon shrimp in 1992, as well as acting as a feed distributor. His journey into seabass farming has not been without challenges. In 1995, he began seabass farming using fresh feeds, but he failed. A year later, with the availability of slow sinking feeds, together with another farmer, Suthi continued to farm seabass but again failed. While other farmers left the industry, he persevered with slow sinking pelleted feed, achieving a survival of 20%. He said, “The fish did not look like the seabass but more like a tilapia with a short and plump body. Over the 2 years, I lost USD30,000. I then stopped farming and over the next 8 years, decided to visit farms and learn fish farming from about 300 farmers. In 2004, I restarted, and success came on a yearly basis.”
Secrets of success: Feeding
In a discussion, Suthi identified some techniques which led to his success in seabass farming. It began with him identifying the feeding behaviour of fingerlings and dividing them into five groups. Depending on the feeding behaviour, he will adjust the feeding protocol. In 2004, he was the first farmer to wean 1 inch (2.5 cm) fish onto artificial feeds. He has also modified the feeding rate and management based on fish behaviour i.e., slow and aggressive feeders and those that reject feeds. He has studied the size of feeds required over the culture cycle. The industry uses 4-5 sizes of feeds. Together with Thai Union Feedmill, Suthi has developed 10 sizes of pellets for his farm. The largest size range is 23-30mm.
The broadcasting of feed is in the shape of a traditional Chinese fan with regular speed and force. Feeding is only conducted during low light, i.e., early morning and late afternoon. This is because, according to Suthi, fish are afraid of bright and strong sunlight. He does not use any auto feeder as he wants the feeding team to observe the condition of the fish, understand how to feed and take care of the stock. He also continues to run the aerator during feeding to ensure dissolved oxygen (DO) is sufficient when fish are digesting feed. Attention is on feeding as sometimes fish overconsume when they are stressed.
In general, the feeding protocol includes no feeding over the 2 days after stocking and on the third day, they are fed only for the morning meal. Feeding is within the feeding frame with a blue net with a perimeter of 50m. Broadcasting of feed is aligned to the wind direction and is completed within 10 minutes. Feed amount is 90% of feed demand according to biomass. The team dissects fish and examines left over feed in the fish stomach, identifies sizes of pellets and adjusts feeding accordingly. Some feed conversion ratios (FCR) are shown in Table 1.
At the heart is pond preparation
Suthi has studied in detail soil and water parameters and their management so that he can operate the farm successfully with the principle of “prevention is better than cure.” His technique of pond preparation is a mechanical way of using only water. This is essential so that fish cultured in these ponds have no off-flavour. This is done by switching between dry and wet soil conditions multiple times to eliminate bacteria, snails or weeds and use chain dragging to refresh the pond bottom.
Pond preparation is over 50 days and starts with drying the pond after harvesting until the pond bottom cracks. The pond is then filled with water to a depth of 60cm in the deepest part of the pond. Aeration is for 2 days using a long arm aerator and with 10 dosages of effective microorganisms (Bacillus probiotics) which is also used during the culture period.
Next is chain dragging continuously over 20 days. This is done twice a day, each for 2-3 hours per round during the early morning and evening. This is to stir up all the sediments and mix them with water. According to Suthi, on day 3, toxic gases will burst out creating a stinky, black, and oily surface and on day 7-10, there will be more gas emissions. On day 11-12, the water colour will change from black to gray and by day 15-17, brown bubbles will surface. If this does not happen, it is time to add microorganisms.
From day 18-20, the farmer should examine the soil to ensure cleanliness. Chain dragging is repeated if there is still black soil. Drying will follow until the soil cracks on day 21-22. He cautioned that it may be necessary to repeat chain dragging or extend the process, if at the last crop, there were parasites. Next is to apply lime at around 400- 500kg/acre (1,000-1,235kg/ha), followed by spraying with water and leaving overnight to reduce the bacteria population. Water is then added very slowly to fill up the pond and to cover only 10cm in the shallow area.
Final words
Suthi said, “Inland farming can be better once the farmer learns how to manage the farm properly. What we need is knowledge and know-how. I am always happy to share my experiences and knowledge with anyone with a passion to learn. I love farming fish and sharing what I learnt is important for me.”
“To feed the world with farm seafood is becoming more important and a farmer must value his or her contribution. It is essential to feed our fellow human beings with safe and quality fish. This is our responsibility.”
The article was published in issue Marxh/April 2024 AQUA Culture Asia Pacific
