|Better Farming Series 38 - Better Freshwater Fish Farming: Raising Fish in Pens and Cages (FAO, 1990, 83 p.)|
124. You can build a cage and put it in a stream, a river, a lake or a reservoir.
Stream or river
125. In addition, as you have already been told, you can put a cage in a fish pond.
Note If you have a fish pond and decide to put in some cages, you will raise many more fish. For example, a pond of 20 by 20 metres (400 square metres) will hold 800 fish. If you also put in 3 cages of 1 cubic metre each, you can raise 450 to 600 more fish. So, in this case you can raise as many as 1400 fish in the same pond.
1 x 1 x 1 m
= 450 to 600 fish
800 + 600 = 1 400 fish in all
126. The water should be deep enough so that when the cage is in place it will be at least 50 centimetres from the bottom.
127. A cage should be in a place where the flow of water is gentle and not fast. In addition, it should be protected from the wind.
128. The water should be clean You should not put a cage too near an inlet where the water may be muddy or full of rubbish.
129. A cage can be any shape. It can be round, square or long.
130. A cage can be small or large depending on the number of fish that you want to raise. However, when you first begin, start by building a small cage. You will need fewer materials. It will be easier to take care of.
131. You can begin with a cage that has about 1 cubic metre (1 metre by 1 metre by 1 metre) of space for the fish. Later, when you have learned more, you can build bigger ones.
132. The best material to cover a cage is ordinary fish net. If you cannot get fish net you can use either plastic mesh, woven material made from split bamboo or wooden strips.
133. The openings in the material that you use to cover a cage must be small enough to keep the smaller fish from getting out.
134. However, if the openings are too small they may become filled with dirt or with the very small plants that grow in the water.
135. So, be sure to use material with openings of 1.5 by 1.5 centimetres. This is the right size to keep in the smaller fish and also to let fresh water through.
136. You can build a simple cage by driving four or more posts into the bottom under the water and hanging a fish net inside.
Simple post cage
137. You can also build a simple cage by putting a square float on the water and hanging a piece of fish net inside.
Simple floating cage
138. If you want a better floating cage, you can build a frame with floats and close it with fish net, woven material or plastic mesh.
Better floating cage
139. You can use either bamboo or wood for the posts, floats or frame. However, if you are using wood, choose one that does not rot quickly when it is in the water.
140. The drawings on pages 50 to 66 show you how to build these cages. You will also be shown how to close the tops of cages and how to fix cages in the water.
A simple post cage
you can build a simple post cage using bamboo or wooden posts
and fish net
find a place where the water is at least 1.50 metres deep even during the dry season
Simple post cage
drive 4 posts into the bottom to form a square 1.25 m x 1.25
the posts should be about 50 cm above the water
Four posts cage
tie a rope around the top of the posts to hold the fish net at least 25 cm above the water
Use a rope
hang a piece of fish net over the rope inside the posts and make sure that it is at least 1 m under the water at the deepest part tie the net to the rope all the way around the cage using strong cord
Lie the net to a rope
you can put in the fish now (but first see Items 141 to 145)
Put the fish
if you have enough fish net stretch a piece over the top of the cage and tie it to the rope using strong cord
when you feed the fish, do not remove the cover
however, you may have to open part of the cover from time to time to take out any dead fish
A simple floating cage
you can build a simple floating cage using any wood that floats
well, such as bamboo or banana stalks, and covered with either fish net, woven
material or plastic mesh
tie 4 pieces of wood together using strong cord or rope to form a float 1 m square
hang the float about 1.50 m above the ground so you can work on it easily
Hang the float
cut 1 long piece of material for the sides of sides of the cage and one square piece of material for the bottom
Sides of cage
depending on the material that you are going to use, tie or wire the long side piece arround the outside of the cage
then, tie or wire the square bottom piece to the lower edges of the sides in the same way
Make the cage
if you have used fish net or woven material, tie a length of rope to the bottom of each corner to be used for weights when the cage is in the water
Tie the rope
carefully pull the cage into the water
Put the cage into the water
make sure that there are at least 50 cm of water under the cage and tie it firmly in place
Tie the cage
to do this, tie a piece of rope to one comer at the float and anchor the other end to a stake in the bottom
Anchor the cage
if you have used fish net or woven material, tie a weight to the rope on each comer
note: if the that sinks below the water, tie on more pieces of wood until it floats on the surface
now you can put in the fish (but first see Items 141 to 145)
Put the fish in cage
after the fish are in, you can cover the cage with fish net
Cover the cage
if your cage is built of woven material or plastic mesh you can use this material for a cage cover
depending on the material that you have used for the cover tie or wire it in place just as you did the sides and the bottom of the cage
Tie the top of cage
however, you may have to open part of the cover from time to time to take out any dead fish
A better floating cage
you can build a better floating cage by making a light frame from bamboo or straight pieces of wood cut from trees and covered with either fish net, woven material or plastic mesh
tie 4 pieces of wood together using strong cord or rope to make one side of the frame, which should be about 1 m by 1.25 m
Use a bamboo frame
make another side the same as the first
Make another frame
using 4 more pieces of wood, tie the two sides together 1 m apart
Use 4 more pieces of wood
cut 1 long piece of material for the sides of the cage and 1 square piece of material for the bottom
Cut the material
depending on the material that you are going to use, tie or wire the long side piece around the inside of the float
Put the material
then, turn the cage on its side and tie on the bottom piece in the same way
Turn the cage on
for floats you can use bamboo, banana stalks, wooden blocks or, if you can get them, plastic containers, pieces of styrene plastic or used tyre inner tubes.
Materials for floats
bamboo floats, styrene plastic floats, tyre tube floats
carefully put the cage into the water
Put the cage into water
make sure that there is at least 50 cm of water below the cage
and tie it firmly in place
to do this, tie a piece of rope to one corner at the float and anchor the other end to a stake in the bottom
the cage should float so that 25 cm of it is above the water and 1 m of it is below the water
Let the cage float
note: if the cage does not float 25 cm above the water tie on more floats until it does
now you can put in the fish
(but first see Items 141 to 145)
Put the fish in the cage
after the fish are in, you can cover the cage with a fish
if your cage is built of woven material or plastic mesh you can use this for a cage cover
when you feed the fish do not remove the cover however, you may
have to open part of the cover from time to time to take out any dead
you can build an even better floating cage using pieces of squared, rough- cut wood.
you can build this kind of cage with a door that can be locked and with a special opening for feeding the fish
Use rough- cut wood
with a locked door it is more difficult for people to steal your fish however, you may need more floats for a cage with a heavy wooden door
141. When your cage is finished and in place in the water, you are ready to stock it with baby fish.
142. You have already been told that small fish can be hurt easily. So, you must be very careful when you handle them or carry them from place to place. Items 61 to 65 in this booklet will tell you how.
143. If you are raising Tilapia nilotica you will need to put in 150 to 200 baby fish for each cubic metre of cage.
Use tilapia nilotica
144. The baby fish that you use should be at least 8 to 10 centimetres long or weigh about 15 to 20 grams each.
Note If you need any help or want to raise a different fish, your extension agent or fishery officer will be able to give you good advice.
145. Put the fish in your cage just as you were told to do in a pen. Items 68 to 72 in this booklet will tell you how.
146. You have already been told that there may be very little natural food in a cage. So, you must be sure to give your fish plenty of very rich food.
147. Here are some rich foods that fish like to eat. You can give them
· grain mill sweepings
· rice bran
· beer wastes
· cottonseed or groundnut cake.
Food for fish
148. Prepare all of the food for one day's feeding at the same time and give the fish part of the food at two or three different times during the day.
149. Always try to feed your fish at the same time each day.
Feed the fish at the same time
150. The bigger your fish grow the more food they will need. For each cubic foot of cage feed them
· 150 to 200 grams of food every
day during the first month
· 200 to 350 grams of food every day during the second and third months
· 350 to 450 grams of food every day from the fourth month until the time you are ready to harvest.
Note 100 grams of rice bran is about one handful. Use a small tin to measure this amount.
Measure the rice bran
51. It is not easy to know exactly how much to feed your fish. You must watch them carefully to learn how much food they need.
152. Put the food for your fish near the centre of the cage so that they can eat it before it floats away through the holes in the sides.
Put the food in centre of cage
153. Put in the food little by little so that you can watch the fish and see that they are eating.
154. If you see that the fish do not eat all of their food, give them a little less.
155. If you see that the fish eat all of their food quickly, give them a little more.
156. Remember, that if you give your fish too much food to eat it will collect on the bottom and make the water around the cage bad.
157. So, check the cage often. If you see too much uneaten food on the bottom, you will know that you are feeding too much. When this happens, move the cage to a clean place.
Move the cage in clean place
158. You must always watch the fish to see that they are healthy and swimming strongly.
159. If the fish in your cage are not well, they will stop eating.
160. If this happens, stop feeding your fish for a day or two.
161. When you begin to feed them again, at first give them small amounts of food and then slowly more and more. When your fish begin to eat as before, you will know that they are well again.
162. If you find any dead fish floating in your cage, take them out right away.
Take away the dead fish
163. Then, stop feeding your fish and watch them carefully for the next few days.
164. If no more fish die, you can begin to feed them after a day or two.
165. If fish continue to die, take them out as soon as you can and ask your extension agent or fishery officer for help.
166. You have already been told that a cage can easily be damaged. If this happens you may lose fish.
167. So, it is very important to check your cage every day to be sure that there are no holes where your fish can get out.
168. If you find any places where the fish can get out, repair them right away.
Note If your cage is in shallow water you may be able to repair any holes in it as you were shown on page 33. However, if the water is deep it may be easier to completely cover the damaged side of the cage with a new piece of material.
Repair the cage
169. In addition, you must be sure that the openings in the cage material are free from dirt and plants so that fresh water can flow into the cage.
170. You can clean the material of a cage using a brush or a broom. However, do it very gently so that you do not damage the cage material.
Clean the cage material
171. Also, do not forget to check for uneaten food on the bottom under the cage from time to time.
172. If you have put your cage on posts in the water, make sure that the posts are firmly in place so that the cage cannot float away.
Hammer in posts
173. If you have a floating cage, make sure that the floats and that the cage is firmly tied in place so that it cannot float away.
Check float and anchor cage
174. If you have used baby fish 8 to 10 centimeters long or weighing about 15 to 20 grams and have fed them well, they will be ready for harvest in about five months. At this time the fish will weigh 100 to 150 grams each.
175. If you want to harvest only some of your fish, use a small hand net and collect what you want without moving the cage.
collect what fish you want without moving the cage
176. If you want to harvest all of your fish and your cage is small enough, pull it into shallow water and begin to collect the fish using a small hand net.
collect some of the fish after moving the cage to shallow water
177. When you have collected most of the fish, you can lift the cage out of the water and collect the rest.
then, collect the rest of the fish after moving the cage out of the water
178. If your cage is too big to lift out of the water, pull it into shallow water as far as you can and collect the remaining fish.
if your cage is too big you may have to collect all of the fish in shallow water
Note If you do not need all of your fish, harvest only what you need and leave the rest in the cage. Fish can be left in a cage as long as you continue to feed them.
179. After you have harvested, clean and repair your cage as quickly as you can so that you can begin again.
180. If your cage is small and you took it out of the water when you harvested the fish, clean and repair it before you put it back into the water.
clean and repair a small cage out of the water
181. If your cage is too big to take out of the water, you will have to clean it and repair it in the water.
clean and repair a big cage in the water
The faster you can do this, the sooner you will be able to raise another crop of fish.
182. You can hold the baby fish you catch in a small pen or in another cage for small fish (see Item 114 and Item 184) until you have finished the cleaning and repairing.
Hold baby fish in a small pen
183. When you are ready to begin again, put in 150 to 200 baby fish 8 to 10 centimetres long for each cubic metre of cage. However, be sure to choose your biggest and best baby fish to put back in your cage.
184. You can raise baby fish in a cage. To do this build a cage just like one of the ones shown on pages 50 to 66.
185. However, the material you use to cover the cage should have smaller openings to keep in the baby fish. So be sure to use material with openings of 0.5 by 0.5 centimetres.
186. Materials with such small openings will get dirty more quickly. So, you must be sure to clean it often enough so that fresh water can flow into the cage.
187. You can put up to 1 000 baby fish 1 to 2 centimetres long in a cage of 1 cubic metre. However, do not put in more than you need to use or sell.
If you have more baby fish than you can use or sell you can dry them in the sun. After you have dried the baby fish, grind or pound them and mix them with crushed cottonseed, groundnut cake or rice bran to feed to your big fish, your poultry or your pigs. You can also use the dried baby fish to fertilize your farm garden.
188. Feed your baby fish two or three times each day just as you do with your big fish. You can give them
· rice bran
· cottonseed or groundnut cake.
Food for fish
189. Feed your baby fish carefully. Break their food into very small pieces and sprinkle it little by little on the surface of the water. Watch very carefully that they eat well and stop giving them food as soon as they stop eating.
190. With a cage, it is important to give the baby fish only what they will eat and no more. Uneaten food under a cage is very bad for baby fish.
191. In 30 to 40 days the baby fish will grow to 8 to 10 centimetres long and you can put them in a pond or another cage.
192. To do this take them out carefully using a smooth plastic containers.