Organic fish farming: the rules, the benefits and why it matters

Pull a net through a village pond on a winter morning and the rui and catla that come up carry the green smell of the water they grew in. More and more buyers in Bangladeshi markets now want to know where a fish came from and what it ate. That question has put organic fish farming back in the conversation. The idea is to raise fish on the strength of the pond itself, without chemical fertiliser, pesticide or any synthetic input. The method is spreading around the world because the fish it produces is wholesome and the way it is farmed keeps soil and water safe.

Organic fish farming puts nature's own cycle to work. When sunlight falls on pond water, countless tiny plants grow in it, almost invisible to the eye. Scientists call them phytoplankton. Even tinier animals, the zooplankton, feed on them. Together these two are the main natural food of the country's native carp. Cow dung, poultry litter or compost added to the pond makes more of this food grow, so the fish can put on weight without factory pellets or chemical fertiliser.

One point needs to be clear from the start. Organic does not mean a neglected pond. It takes more planning, not less. Where the pond sits, how deep the water is, which fish go in and how many, when manure is added, what happens when a fish falls sick: every step follows a rule. Followed properly, those rules raise output and improve the quality of the fish.

In Bangladesh fish is both food and livelihood. According to the Department of Fisheries, the country produced about 4.915 million tonnes of fish in the 2022-23 fiscal year, and more than half of it came from ponds, enclosures and farms rather than open water. The Bangladesh Bureau of Statistics' household income and expenditure survey found that in 2022 the average person ate about 67.8 grams of fish a day, more than in 2016.

As farmed fish grows in volume, so do questions about feed, medicines and water quality. Commercial farms often stock fish densely and depend on pelleted feed and a range of chemicals. The organic route is an alternative: output may rise a little more slowly, but buyers can trust what they eat. The government itself adopted a National Organic Agriculture Policy in 2016 to encourage organic practice in farming.

The first step is choosing the right pond. It should sit where monsoon floods cannot reach it. When floodwater gets in, farmed fish escape, while predatory fish, disease and dirt come in from outside. The banks need to be high and solid.

The second requirement is sunlight. The pond should be in the sun for most of the day. Without light the phytoplankton do not grow, and without them the whole natural food chain weakens. If big trees stand on the bank, it helps to trim their branches so that falling leaves do not foul the water and shade does not cover the pond.

Before any fish go in, the pond has to be cleaned. Weeds, unwanted water plants and unwanted fish all come out. Predators such as snakehead and boal eat young fingerlings. Instead of poisoning them, the organic approach is to dry the pond where possible or to net it repeatedly until they are gone.

Then the water is tested. Its acidity is measured on the pH scale: 7 is neutral, lower is acidic, higher is alkaline. Water in a fish pond should sit between pH 6.5 and 8.5. Cheap test strips and small meters are sold in local markets, and the upazila fisheries office gives advice. If the water is too acidic, lime is added while the pond is being prepared; lime is a mineral that brings acidity back into balance.

Depth matters too. A depth of 1.5 to 2.5 metres is recommended. A very shallow pond heats up fast in summer and chills fast in winter. A very deep one gets no light at the bottom, and oxygen runs short there. At a middling depth the fish stay comfortable all year round.

Organic manure is the heart of the method. Cow dung, poultry litter and compost build up the fertility of the pond bottom and the water. Guidance on fish farming published by the Agriculture Information Service suggests 5 to 7 kilograms of cow dung per decimal (about 40 square metres) when the pond is prepared. The manure releases nutrients slowly into the water, and algae, phytoplankton and zooplankton grow on them.

Within a few days the water turns light green or brownish green. Experienced farmers read that colour as a sign that the pond is producing food. Too much manure at once backfires, however. As it rots it strips oxygen from the water, and the pond can turn thick green and foul-smelling. Adding manure little by little, watching the colour of the water, is the safe way.

Checking the colour of the water once a day after manuring is a good habit. If the water stays perfectly clear, little food is forming, and a small dose of manure can go in again. If it turns dark green with a scum on top, manuring stops and, where possible, some fresh water is added. This small daily check does more than chemical fertiliser ever could, because the colour of the water tells the farmer what the pond needs.

Compost can be made from what lies around the homestead: straw, leaves, vegetable peelings and cow dung left to rot together in a pit. It costs little and puts household waste to use.

Alongside manure, the advice is to keep some water plants in the pond. A limited patch of water hyacinth held in a bamboo frame in one corner gives small fish shade and shelter and keeps part of the water cool on hot days. Napier grass planted on the bank holds the soil together, and its young leaves can be cut and thrown to grass-eating fish.

The plants must not take over, though. Water hyacinth spreads very fast. If it covers the surface, light cannot get in, the phytoplankton die and oxygen falls. So the plants are kept to a fenced-off area and the excess is pulled out regularly.

Species that are at home in local conditions suit organic farming best. Rui, catla, mrigal and puti (pool barb) have lived in this climate for centuries and suffer relatively little disease. Tilapia, which came originally from Africa, has also settled well in the country's ponds and can grow on natural food. Stocked together, these fish use every level of the pond.

Think of the pond as a three-storey house. Catla live on the top floor, near the surface, feeding on plankton there. Rui move through the middle layer. Mrigal live on the ground floor, picking organic particles and decaying matter out of the mud. The three do not compete for the same food, and nothing in the pond goes to waste. The method is called polyculture, or layered stocking.

Mixed stocking also spreads the risk. If one species fails to grow well for some reason, the others still yield. If the price of one fish falls in the market, selling another can make up the loss. For a small farmer, that security matters a great deal.

A small fish such as puti brings extra benefits. It grows fast, can be harvested more than once a year and puts nutrition on the family's plate. How many of each fish to stock depends on the size of the pond and the quality of the water, and it is worth talking it through with the upazila fisheries officer, because overstocking leaves too little natural food to go round.

In organic farming the fish rely mainly on natural food. As they grow, or when natural food thins out in winter, they need something extra. Instead of commercial feed with chemical additives, farmers can give rice soaked in water, wheat bran and organic feed made from vegetables. Banana leaves, bottle gourd leaves, the outer leaves of cabbage and young grass are favourites of grass-eating fish.

A word of caution belongs here. Farmers need to know whether bran or oil cake bought in the market has chemicals or synthetic additives mixed in. One wrong input can undo the whole organic effort. Where possible, rice from the farmer's own field, greens from the garden and dung from the cowshed are the safest supplies.

One habit helps: feed at the same time every day, in the same spot. The fish learn the routine and less feed is wasted. How much they eat today decides how much goes in tomorrow. Leftover feed rots and spoils the water, so no more than is needed should go in.

Checking water quality and water level regularly is one of the main duties of an organic fish farmer. When the water drops in the dry season, clean water from a tube well or another source is added. In the monsoon there has to be an outlet for surplus water so that the pond does not overflow and carry the fish away.

What fish need most is oxygen dissolved in the water. On cloudy days, in sultry heat and towards dawn, oxygen in a pond falls. Fish then gasp at the surface, a clear danger sign. At such times an aerator, a machine that mixes air into the water, keeps oxygen up. It adds no chemicals; it only stirs the water. Where there is no machine, village methods work too, such as beating the water with bamboo poles or swimming through it to stir it.

Organic farming leans on natural materials rather than antibiotics or chemical drugs to prevent disease. Neem leaf, garlic and turmeric are familiar in every Bangladeshi household, and fish farmers use them to keep disease at bay. How much to use depends on the pond and the state of the fish, so it is safest to ask a fisheries officer first.

The most effective protection, though, is daily watching. Farmers observe how the fish behave and how they are growing. Are they eating? Are they circling oddly at the surface? Are red spots or sores showing on their bodies? Noticing such signs catches disease early. Netting a few fish now and then to check their weight and appearance shows whether growth is on track.

Winter is the season of ulcer disease in the country's ponds, when red sores appear on the fish. The standard fisheries advice is to add 1 kilogram of lime and 1 kilogram of salt per decimal before the cold sets in, at the end of the Bengali month of Ashwin or the start of Kartik (roughly mid-October). Lime and salt are both minerals, so this sits comfortably with the organic approach.

Harvesting at the right time is part of the job. Once the fish reach market size it pays to catch them without delay, since keeping them longer raises the feed bill while growth slows. Many farmers do not empty the pond at once but pick out the larger fish, leaving the smaller ones room to grow.

Organic fish has an advantage in the market. Demand for it is high, and so is the price. Earning that premium means earning the buyer's trust: building a group of regular customers at the local market, letting buyers see the pond, being open about what the fish are fed. Selling under an organic label abroad or in large supermarket chains usually requires certification from a recognised body, and it is worth finding out about that well in advance.

The gains from organic fish farming reach beyond the environment to people's health and farmers' incomes. The main ones at a glance:

• Wholesome produce: fish raised without chemicals are safe and nutritious to eat.
• Protection of the environment: no chemical fertiliser or pesticide is used, so soil and water keep their quality.
• Lower production costs: cow dung, compost, bran and greens from the homestead replace bought inputs.
• A better market price: demand for organic fish is high, and so is what it fetches.
• Aquatic biodiversity: because the natural food chain keeps working, the balance of life in the water holds.

Cost is the point that matters most to many farmers. On commercial fish farms a large share of total spending goes on bought feed. In organic farming the pond itself supplies much of the food, and the rest comes from the house and the fields. That means a smallholder with little capital can start this way too.

Biodiversity is no small matter either. With no chemicals in the water, frogs, snails, aquatic insects and many kinds of plants survive in the pond. They are part of its food chain, and the fields and water bodies nearby are healthier for it.

Seen on a larger scale, the importance of organic fish farming becomes plainer. First, it makes fish farming sustainable over the long term. After a few years of chemical-heavy farming, toxic sludge builds up on the pond floor, disease rises and so do costs. An organically managed pond stays healthy year after year.

Second, it is kind to the environment. The method prevents pollution of soil and water. Using less synthetic fertiliser and fewer chemicals also helps to reduce the pressures behind climate change, since making and transporting those inputs burns energy.

Third, food security. Fish raised organically are wholesome and full of nutrients. In a country where fish supplies much of the animal protein people eat, producing more safe fish is a step towards making sure families are well fed.

Small fish such as puti deserve a special mention on nutrition. Because they are eaten whole, bones and all, they supply micronutrients such as calcium, iron and vitamins that are especially valuable for children and mothers. Keeping such small fish alongside the big carp turns the pond from a market product into a store of nutrition for the family.

Fourth, economic gain. The higher market price of organic fish leaves farmers better off. Low costs and a good price together can turn even a small pond into a steady source of family income.

Fifth, public awareness. As organic methods are promoted, people become more conscious of chemical-free food. Buyers learn to ask questions, and farmers are encouraged to adopt good practice. That two-way pressure slowly pushes the whole sector towards safer farming.

Organic fish farming is not free of risk. Because it depends on natural food, fish may grow more slowly than on a commercial farm. A pond cannot hold very many fish. Persuading buyers that the higher price is justified takes time. Starting small, with a mixed stock of native fish in one modest pond, is the sensible way to gain experience.

Keeping a notebook helps as well. When and how many fingerlings went in, how much manure and feed was given, when fish were caught and at what price they sold: with all of that written down, the year's profit or loss is plain to see. The same record also shows buyers that the farming really was organic.

The upazila fisheries office gives free advice on pond preparation, choosing fingerlings, testing water and managing disease. Finding a reliable hatchery with healthy fingerlings matters just as much: start with sickly fish and all the care in the world may be wasted.

Organic fish farming is a promising field, with a real part to play in the environment, public health and rural incomes. Done by the rules, it pays the farmer and does the environment good. It can begin in the same village pond where the net is pulled at dawn. Given what lies ahead for food and the environment, spreading this method is now a need of the times.

Photo: Fishing in a village pond, Md Nahid Hasan bin Jafor / Wikimedia Commons (CC BY-SA 4.0)