Cage Culture of Native Gulsha Fish: BFRI Develops a River Cage Method

Bangladesh's ponds have pushed fish output up year after year, but, as The Agro News reported in April 2025, that growth alone could not keep pace with the demand of a fast-growing population. The report asked a simple question: can the rivers themselves raise fish, and can they do it with the country's own native species?

The answer came from the Bangladesh Fisheries Research Institute (BFRI). According to the report, the institute's Freshwater Station in Mymensingh ran several years of research on raising native fish in floating cages and developed a suitable method for farming gulsha, a tasty, high-value catfish that has become scarce in open waters. This article explains what the station tested, what gulsha is and its IUCN Bangladesh Red List status, how cage culture came to Bangladesh, and what field trials published up to 2024 found about stocking, feeding and costs.

For several years before the report, tilapia had been farmed in cages in a number of rivers in Bangladesh. Native species were a different matter. To test whether pabda, gulsha, magur and shing could also be raised in cages, the BFRI Freshwater Station in Mymensingh took up a research programme, the report said.

After several years of continuous work, the station developed a suitable technology for farming gulsha in floating cages. The report said that if gulsha is farmed in floating cages under sustainable management, it is expected to make a significant contribution to fish production and to meeting the country's nutritional needs. The report gave no stocking or feeding figures; those below come from peer-reviewed trials, credited to their authors.

The report argued that Bangladesh's water resources had not yet been brought into balanced fish production, and that combining open-water management with suitable farming technology could play an important role in food supply and economic activity, and cage culture in rivers is one such technology.

Fish is central to the Bangladeshi diet. In a country presentation published by INFOFISH in October 2024, the Ministry of Fisheries and Livestock put total fish production in 2022-23 at 4.91 million tonnes. It said fish supplies 60 percent of the country's animal protein and gave per capita fish consumption as 67.80 grams a day.

The ministry's presentation also cited FAO statistics for 2024 placing Bangladesh second in the world in inland fish production, fifth in aquaculture production and fourth in tilapia production. It listed 260 freshwater fish species, 12 exotic fish species and 24 freshwater shrimp species in the country's waters.

A 2011 paper on tilapia culture by Md. Asadul Baqui of the Department of Fisheries' Fisheries Training Institute in Chandpur and Ram C. Bhujel of the Asian Institute of Technology noted that with a dense population and farmland being lost to urbanisation, closed water bodies for fish were limited, and vast open waters remained unused.

A fish cage is a frame, usually floating, wrapped in netting and placed in a river, lake or floodplain, so that the fish are held in place while the water flows through. The original report noted that fish have been kept in cages of bamboo or netting since ancient times, when profit and loss were not much considered. Baqui and Bhujel wrote that Asia had led commercial cage culture for about the last three decades and that China, Vietnam, Thailand, Taiwan and Malaysia had raised their national fish output several times over with it.

Bangladesh lagged behind. According to Baqui and Bhujel, the Department of Fisheries, Bangladesh Agricultural University, BFRI and several NGOs tried cages over many years, including trials in Kaptai Lake and in Dhanmondi Lake in Dhaka, and CARE-Bangladesh ran a project called Cage Aquaculture for Greater Economic Security (CAGES) in the Meghna and Gomti rivers from 1995. Almost all of these efforts ran into trouble. The authors listed the main reasons:

• lack of good-quality net;
• lack of suitable floating feed;
• poor choice of fish species for cages;
• lack of technical know-how and of skilled people to run the cages;
• lack of concerted effort;
• social problems such as poaching and conflicts.

The turning point, in their account, came after a group of Department of Fisheries officers trained at the Asian Institute of Technology in Thailand in 2001 on mono-sex tilapia hatcheries and cage culture. In 2002, 40 cages, each 6 m by 3 m by 1.5 m (27 cubic metres), were set up in the Dakatia River in Chandpur. Cage culture spread to Laxmipur district in 2006.

By the time of their 2011 paper, about 3,500 cages were operating along the Dakatia River in Chandpur and 500 along the Meghna in Laxmipur. Farmers stocked 37 to 40 sex-reversed tilapia fry of 20 to 25 grams per cubic metre; the fish grew to about 400 grams in six to seven months, giving around 15 kg per cubic metre with floating feed, mortality under 5 percent and a feed conversion ratio of about 1.75. The cages produced at least 3,200 tonnes of tilapia a year and employed at least 600 people, about 5 percent of them women. The authors also warned that disease problems linked to intensification were threatening the tilapia cage industry.

Gulsha (Mystus cavasius) is a small catfish of the family Bagridae. Its English name is Gangetic mystus, and in Bangladesh it is known as golsha, kabashi tengra or golsha tengra, according to the IUCN Bangladesh Red List of 2015. Beyond Bangladesh it is found in India, Myanmar, Nepal, Pakistan, Sri Lanka and Thailand.

Within Bangladesh, the Red List says, it occurs in the Tista, Padma-Jamuna-Meghna, Surma, Kushiara and Kangsha systems and their beels and haors, and in the tidal rivers of the south. It lives in large rivers with sandy to muddy bottoms and moves into haors, baors, beels, canals and flooded fields. Adults feed mainly on insect larvae, small fish and detritus along the bottom, while the young feed partly on zooplankton.

Researchers value the fish for more than its taste. A 2024 study in the Journal of Fisheries by Shovan Khan Sabuz and colleagues at the University of Rajshahi, citing earlier work, noted that gulsha contains about 13.81 percent protein and 2.26 percent fat and is rich in calcium and phosphorus. The same study said the species can tolerate low oxygen, wide temperature swings and other poor water conditions, and that its high market price and taste make it a strong candidate for farming. A 2023 paper in Aquaculture Reports noted that information on raising it in cages was still limited.

The original report described gulsha as endangered (bilupto-prai, near extinction). The national assessment is more precise. In the Red List of Bangladesh Volume 5: Freshwater Fishes, published by IUCN Bangladesh in 2015 and assessed on 21 August 2014, gulsha is listed as Near Threatened, one step below the threatened categories. It had been assessed as Vulnerable in the earlier IUCN Bangladesh list of 2000.

The Red List explains the decision. The fish is still widely distributed, with an estimated extent of occurrence of 224,068 square kilometres and an area of occupancy of 18,554 square kilometres, both far above the thresholds for a threatened category. But widespread habitat loss and degradation, together with over-exploitation and unplanned fishing, were causing a rapid, continuing decline, and the assessors judged that these threats were unlikely to be halted soon. With no conservation measure aimed at the species, it was listed as Near Threatened, with a decreasing population trend. The 2024 Journal of Fisheries study added that the catch from open water was dwindling because of fishing pressure driven by high market demand, along with habitat destruction and ecological change.

The other fish named in the report sit in different places on the list. Pabda (Ompok pabda) is Endangered: the 2015 assessment, dated 22 September 2014, said the fish was once fairly abundant across Bangladesh but declined drastically in the 1980s through siltation, wetland conversion, over-exploitation and pollution, and that expert opinion suggested a fall of more than 60 percent over the previous ten years. Magur (Clarias batrachus) and shing (Heteropneustes fossilis) were both assessed as Least Concern in 2015.

Across all freshwater fish, IUCN Bangladesh assessed 253 species in 2015 and found 64 of them, or 25.3 percent, threatened: 9 Critically Endangered, 30 Endangered and 25 Vulnerable. Another 27 were Near Threatened, 122 were of Least Concern and 40 were Data Deficient. No fish was found to be extinct or regionally extinct. In the 2000 assessment, 54 of 266 species had been considered threatened, and the 2015 report concluded that the threats to fish in Bangladesh had not been reduced since then.

The cage research is part of a longer BFRI effort on native species. In January 2018, The Daily Star reported that BFRI in Mymensingh had helped preserve 16 endangered local fish varieties over the previous decade through aquaculture, naming pabda, gulsa, tengra, local koi, shingi and magur among them. The report quoted BFRI's then Director General, Dr Yahia Mahmud, as saying: "The native fish varieties are nutritionally dense and more flavoursome."

In September 2020, The Business Standard reported that BFRI had produced fry of 23 nearly lost native species, gulsha and pabda among them, and that the institute had set up a live gene bank of native fish. The same report said pond production of small native fish had risen from 67,340 tonnes in 2009 to 241,000 tonnes in 2017-18. In May 2021, The Financial Express reported that researchers at the BFRI Freshwater Station in Mymensingh had achieved artificial breeding of 24 endangered fish species, including tengra, gulsha and pabda.

Peer-reviewed studies published before April 2025, one with a BFRI scientist among the authors, tested gulsha in cages. Their results apply to the conditions in which they were run and are not official BFRI recommendations.

Stocking density in the Chalan Beel. A study by Md. Abu Sayed Jewel and colleagues of the University of Rajshahi, with partners at Universiti Kebangsaan Malaysia, published in Aquaculture Reports (volume 28, 2023, available online December 2022), ran for 120 days in the Atrai River in the Chalan Beel floodplain at Singra upazila in Natore, which the authors describe as the largest wetland in Bangladesh. Twelve floating cages of nylon netting with 5 mm mesh, each 6 m by 3 m by 2 m (36 cubic metres), were set in a row about 3 metres above the bottom mud. Liners of 0.5 mm acted as a nursery for the first two months and were then removed to keep water flowing. The cages were scrubbed with a hard nylon brush every two weeks to remove fouling.

Fry of about 5.55 grams were stocked at 50, 100, 150 and 200 fish per cubic metre, a range the authors chose from a Department of Fisheries policy brief (2016) that suggests 50 to 250 fish per cubic metre in cages. The fish received a commercial floating pellet with 32 percent protein, twice daily, at 5 percent of body weight for the first two months and 3 percent for the next two. Water temperature was around 26 to 27 degrees Celsius, with dissolved oxygen around 6.4 to 6.5 mg per litre, within the suitable range.

The lowest density did best. At 50 fish per cubic metre, gulsha gained 18.70 grams, survival was 95.84 percent and the feed conversion ratio was 1.75, against a gain of 8.66 grams, 86.66 percent survival and a ratio of 4.09 at 200 per cubic metre. Total production per cage was 88.31 kg at the lowest density and 40.89 kg at the highest. Feed made up between 34 and 95 percent of total cost across the treatments, and the authors recommended 50 fish per cubic metre for a profitable and robust yield.

Feeding to cut costs. Because feed is the biggest expense, a second study tested whether gulsha could be left unfed on some days. Jesmin Ara and colleagues, with Md. Ayenuddin Haque of BFRI in Mymensingh, reported the work in the Journal of Fisheries (volume 11, issue 3, published online October 2023). It ran from 1 July to 28 October 2020 in the Atrai River in the Chalan Beel. The 6 m by 3 m by 2 m cages had stainless steel frames and plastic barrels as floats; each was wrapped in a 0.5 cm mesh net covered by a second 1 cm mesh net, with a gap of 12.7 cm between them to protect the inner net from crabs. Each cage was tied to three blocks so it would not drift.

Hatchery seed of 7.90 to 8.10 grams was stocked at 50 fish per cubic metre and fed a 32 percent protein feed at 5 percent of body weight, 40 percent in the morning and 60 percent at night. Four regimes were compared: feeding every day, and leaving the fish unfed one, two or three days a week. Daily feeding gave the largest fish, but one day without feed each week gave the best feed conversion, the highest production and the greatest benefit. The authors concluded that gulsha stocked at 50 fish per cubic metre with one feed-free day a week is economically feasible for cage culture in running water.

Cages inside ponds. A third study, by Mahmudul Hasan Mithun and colleagues in the Bangladesh Journal of Fisheries (volume 33, number 2, 2021, published March 2022), kept gulsha for 90 days in circular net cages placed in earthen ponds at 200, 300 and 400 fry per cubic metre. Weight gain and survival did not differ significantly, and the highest density gave the greatest gross production, 4.29 kg per cubic metre. The contrast with the river trials shows that the right density depends on the setting: still pond water and running river water are not the same system.

The studies point to lessons their authors drew. Cages in moving water keep water quality steady because the current carries waste away; nets need protecting from crabs and regular cleaning so that water can pass through; hatchery fry are the starting point; and feed is the main cost, so stocking density and feeding schedule decide whether a cage pays.

Conditions differ from river to river and from season to season, and the trials above were research projects, not tested packages for every site. A farmer thinking of cage culture of gulsha or any native fish should first talk to the upazila fisheries officer of the Department of Fisheries and seek guidance from BFRI, whose Freshwater Station in Mymensingh carried out the research described in the report.

Photo: Zeynel Cebeci / Wikimedia Commons (CC BY-SA 4.0)

Sources: The Agro News (Staff Correspondent), IUCN Bangladesh (Red List of Bangladesh Volume 5: Freshwater Fishes, 2015), Aquaculture Reports (Jewel et al., 2023), Journal of Fisheries (Ara et al., 2023; Sabuz et al., 2024), Bangladesh Journal of Fisheries (Mithun et al., 2021), Baqui and Bhujel (Proceedings of the Ninth International Symposium on Tilapia in Aquaculture, 2011), Ministry of Fisheries and Livestock (INFOFISH country presentation, 2024), The Daily Star, The Business Standard, The Financial Express