Farming with fish

FarmingFishing

By Bob Hansford.

Good farmers look after their crops. Before planting they make sure the soil is well prepared. They select good seed or seedlings. They water the young plants regularly and remove weeds. They use manure or fertiliser to increase growth and watch out for pests or diseases. Hard work produces a good crop, but laziness or neglect will result in a poor harvest!

It is the same for farming fish. The fish become the crop, the pond is the field. Weeds are the wild or predatory fish which compete for food or eat the fish. Pests and diseases are there too! Pests are the animals and birds which attack the fish. Diseases are not too common, but patches of woolly fungus sometimes appear on the skin or gills and parasitic creatures may invade the gills or stomach.

A successful fish farmer must provide for the needs of the fish and protect them from their enemies. Farmers who neglect their fish will probably fail!

Fish need…

  • Water  
  •  Food 
  •  Oxygen  
  •  Safety

Water

This is their most obvious and immediate need, but there has to be the right quantity and quality.

Depth The water should be 1–2 metres deep at one end, with a shallower end 30cm) if the fish are to breed.

Drought can be dangerous for fish. Ideally, water should be present for the whole year, although some types of fish grow quickly enough to give a crop in temporary ponds (for about six months of the year).

Floods may overflow the pond banks during times of heavy rainfall, allowing fish to escape. Make sure the pond banks are high enough to withstand the highest recorded flooding in your area. Fit a screened overflow pipe or channel to take away surplus water.

Water quality depends on substances dissolved or suspended in the water. If the right nutrients are there in sufficient quantity then the pond will produce a lot of microscopic organisms called plankton. Stream water flowing through fertile farmland will be rich in these nutrients and good for the pond. Water from a spring or well may not be so good, depending on the underlying rock.

Food

There are two sources of fish food: natural and supplementary.

Natural foods – plants and animals living in the pond and dead or decaying organic material on the pond bottom. Different types of fish eat different natural foods. Some will search along the bottom for insects and worms. Some will eat submerged or trailing plants; others will strain out tiny plants and animals from the water.

Organic fertilisers (compost and manure) are usually the best and the cheapest. Compost is made by mixing vegetable wastes, straw and animal manure in a pile away from the pond. Cover to protect from the rain, and leave to rot for 2–3 months. Sprinkling a handful of triple super phosphate will increase its effectiveness (1 part TSP to 40 parts compost).

Add organic fertiliser once a week to a basket in the corner of the pond. For a pond measuring 10 metres by 15 metres you will need…

  • 10kg of compost
  • or 5kg of well rotted cattle manure
  • or 2.5kg of well rotted chicken manure.

If instead, you choose chemical fertilisers, it is best to seek advice from the government fisheries department, as many different fertilisers are available. As a guide, 150gm of urea and 400gm of TSP would be needed for a 10m x 15m pond each week. Reduce the amount of fertiliser (organic or chemical) in the dry season, when there is less water in the pond.

Muddy water does not contain much food. It is often seen in new ponds or ponds with bare soil around the banks. Muddiness can be reduced by planting grass on the pond banks and by adding a measured quantity of lime to the water. Consult the government fisheries department for advice. A general quideline is two teaspoons of lime per square metre.

Supplementary foods are brought in from outside as extra feed. The types used will depend on the type of fish and the availability of suitable materials at a cheap price. Examples include:

  • rice bran
  • kitchen waste and scraps
  • termites
  • chopped grass
  • various oil cakes (some may first need heat treatment to destroy toxins)
  • cassava peelings.

How much food? Generally fish will eat about 5% of their weight in supplementary food every day. For example, 100 fish weighing 250gm each (25kg total weight) will require about 1.25kg of supplementary feed each day.

Food should be supplied from the same place each day, preferably half in the morning, half in the evening. Fish will soon form the habit of coming for food. If some food is uneaten, then reduce the amount given the next day.

Oxygen

The unseen need of fish is oxygen to breathe. Fish obtain oxygen from the water as it passes through their gills. Some types of fish (such as catfish) can survive in water with very little oxygen because they can breathe from the air.

The amount of oxygen in the water rises during the day, but falls during the night with the lowest level around dawn.

Oxygen shortage is usually caused by one of the following…

  • too much organic matter rotting in the pond (dead leaves, uneaten food, excess compost)
  • too many fish
  • too many plants or green algae in the water (the water will look very green and there may be a green scum on the water).

Action required…

  • Add clean stream water to the pond, taking care to screen or net the inlet pipe. (Well or spring water will not help because they contain very little oxygen.)
  • Reduce the amount of food, perhaps stopping altogether for a few days.
  • Remove the compost basket, if there is one, from the pond.
  • Harvest some of the fish.
  • Beat the water surface with bamboo branches.

Do not enter the pond, as the stirring up of the pond bed may make the problem worse.

Safety

Fish need to be protected from their enemies. These include predatory fish, otters (or other fish-eating animals), birds, snakes and fish thieves!

Predatory fish can enter a pond by various routes:

  • an open ditch, drain or pipe – so protect using screens, nets or fine fish traps
  • mixed with baby fish – examine them carefully and buy from a trusted supplier
  • as eggs in the mud at the pond bottom – make sure the pond is dried and treated with lime before filling and stocking.

Otters are known as udh in Bengali. You may have other names for them. The only protection is to build a closed fence around the pond or to have a human guard!

Birds can be scared away by people. It is helpful to dig the pond close to where people live or work.

Snakes are difficult to keep out. Try keeping the edges of the pond clear of long grass or building tightly woven fences.

Thieves usually strike during the night and use nets and other ways of catching fish. Some farmers fix sharp bamboo poles into the bed of the pond or lay tree branches in the water. This makes theft more difficult.

Poisons Fish also need protection against poisons. There are three main sources…

  • pesticides – used against insects in the home or field
  • cattle/sheep dips – used to control skin parasites
  • seeds from trees.

Never wash out a pesticide container or spray machine in or near a fish pond. Cut down the branches of any seed bearing trees which hang over the pond.

Stocking the pond

To get started you will need a supply of fish. Some of the common fish species used are carp, tilapia and catfish. If you are going to have more than one kind of fish, make sure they can live together easily. For example, catfish eat other baby fish. If you keep only catfish you may have to buy or raise small fish to feed them.

Transporting fish is stressful for them and should always be done as quickly as possible. So the closer your fish supply is, the better it is for the fish. When you get your baby fish, leave the container of fish sitting in the pond until the water in the container is the same temperature as the water in the pond. The fish can then be let out very gradually into the pond.

Suggested stocking levels for tilapia…

Fish size

Quantity

per square metre

Quantity in

10m x 15m

pond

50gm

2

300

200gm

1

150

 

The number of fish which can live in a pond depends on four factors…

  • the size of the pond
  • the types of fish stocked
  • the size of the fish
  •  the amount of extra food you are able to give the fish
  • the depth of water.

If you have a government fisheries department or other fisheries project near you, ask their advice. If you stock at a high rate to begin with when the fish are small, you must reduce the numbers rapidly as the fish grow larger. For tilapia, it is recommended that you start with a stocking rate of two per square metre. With Indian and Chinese carp, the stocking rates are lower – less than one fish per square metre (100 in a pond 10m x 15m).

Fish production

This will be determined by the type and number of fish in the pond, the amount of supplementary feeding and the level of management. Typical production figures range from 20kg to 50kg of fish per year from a 10m x 15m pond (equivalent to 1,250–3,370kg per hectare per year).

Know your Fish !

Tilapia (Oreochromis species) Oreochromis niloticus is considered the best for warm countries.









Will it hold water? 

Dig a hole 1–1.5m deep on the proposed site of your pond. If it fills with water from below, the site is likely to give you enough water. If it doesn’t fill naturally, pour in some buckets of water. Come back the next day. If the water has gone, then the site is likely to be too dry unless a lining is used (see page 5). If the water is still there, then you may have a suitable site but will need water from an outside source to fill the pond.


Measuring the natural foods 

The amount of natural food in the pond can be measured by placing your arm in the water until your elbow is at the water surface. If the water is so green that you cannot see your fingers, then there is a lot of food in the water. If your fingers are clearly seen, then you need to increase the natural food by using manure, compost or chemical fertilisers. If the water is so green that you cannot see any of your arm, there may be too many nutrients in the water. Stop adding fertiliser or compost until the water becomes clearer.


Can your fish breathe?  

Check your pond each day, early in the morning. If the fish are all at the surface gasping for air, then this means that the oxygen level is dangerously low. The next morning, the fish may all be dead! Action is needed.


Keep a variety of fish 

Mix the different kinds of fish in the pond (but not predatory ones) so that all the different foods will be used.



A good pond has…

  • green water, 1–2 metres deep
  • no large overhanging trees
  • grass growing on the banks, cut short to avoid giving cover for snakes
  • no floating plants (unless needed for fish breeding)
  • screened or netted inlet and outlet pipes
  • a fence to keep out otters
  • a compost basket in the corner
  • a controlled, mixed population of fish


Bob Hansford worked in Bangladesh for six years with Tearfund. He trained local farmers in fish farming techniques. He is now with the Asia Desk at Tearfund.