16. Producing fish in cages

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Locating fish cages
Building a cage
Building a simple post cage
Building a simple floating cage
Building a better floating cage
Putting baby fish in the cage
Feeding fish in cages
Taking care of your fish in a cage
Taking care of the cage
Harvesting fish in cages
Starting again

Locating fish cages

435 You can build a cage and put it in a stream, a river, a lake or a reservoir. You can also put it in a pond and it will help you produce more fish there.

Figure 216

436 The water should be deep enough so that when the cage is in place it will be at least 50 centimetres from the bottom.

437 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.

Building a cage

438 A cage can be of any shape. It can be round, square or long.

Figure 217

Figure 218

439 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 and it will be easier to take care of.

440 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.

441 The best material to cover a cage is ordinary fish netting. If you cannot get fish netting, you can use either plastic mesh or woven material made from split bamboo or wooden strips.

442 The openings in the material that you use to cover a cage must be small enough to keep the smaller fish from getting out.

443 However, if the openings are too small they may become filled with dirt.

Figure 219

444 Material with openings of 1.5 by 1.5 centimetres is suitable to keep in the smaller fish and also to let fresh water through.

445 You can build a simple cage by driving four or more posts into the bottom under the water and hanging a fish net inside.

Figure 220

Figure 221

446 You can also build a simple cage by putting a square float on the water and hanging a piece of fish net inside.

447 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.

448 You can use either bamboo or wood for the posts, floats or frame. However, if you are using wood, choose a kind that does not rot quickly when it is in the water.

Building a simple post cage

449 You can build a simple post cage using bamboo or wooden posts and fishing net.

Figure 222

Figure 223

450 Find a place where the water is at least 1.5 metres deep even during the dry season.

451 Drive four posts into the bottom to form a square of 1.25 by 1.25 metres The top of the posts should reach about 50 centimetres above the water.

Figure 224

Figure 225

452 Tie a rope around the top of the posts to hold the fish net. The rope and the net should be at least 25 centimetres above the water.

453 Hang a piece of fish net over the rope inside the posts and make sure that it is at least 1 metre under the water at the deepest part.

454 Tie the net to the rope all the way around the cage using strong cord.

Figure 226

Figure 227

Building a simple floating cage

455 You can build a simple floating cage using any wood that floats well, such as bamboo. It can be covered with fishing net, woven material or plastic mesh.

456 Tie four pieces of wood together using strong cord or rope to form a float 1 metre square.

457 Hang the float about 1.5 metres above the ground so you can work on it easily.

Figure 228

Figure 229

458 Cut one long piece of material for the sides of the cage and one square piece of material for the bottom.

459 Depending on the material that you are going to use, tie or wire the long side piece around the outside of the cage.

460 Then tie or wire the square bottom piece to the lower edges of the sides in the same way.

Figure 230

Figure 231

461 If you have used fishing net or woven material, tie a length of rope to the bottom of each corner to be used to attach weights when the cage is in the water.

462 Carefully put the cage into the water.

Figure 232

Figure 233

463 Fix the cage firmly in place. Tie a piece of rope to one corner of the float and anchor the other end to a stake in the bottom.

464 Now, if you have used fish net or woven material, tie a weight to the rope at each corner; the weight should not touch the bottom.

Figure 234

Figure 235

Building a better floating cage

465 You can build a better floating cage by making a light frame of bamboo or straight pieces of wood cut from trees and covering it with either fishing net or plastic mesh.

466 Tie four pieces of wood together using strong cord or rope to make one side of the frame; it should be about 1 by 1.25 metres

467 Now make another side of the frame the same as the first.

Figure 236

Figure 237

468 Using four more pieces of wood, tie the two sides together 1 metre apart as shown below.

469 Cut one long piece of material for the sides of the cage and one square piece of material for the bottom.

Figure 238

Figure 239

470 Depending on the material that you are going to use, tie or wire the long side piece around the outside of the cage.

471 Then turn the cage on its side and tie on the bottom piece in the same way.

Figure 240

Figure 241

472 For floats you can use bamboo, banana stalks, wooden blocks or, if you can get them, plastic containers, pieces of polystyrene foam or used tyre inner tubes.

473 Tie on the floats 25 centimetres below the top of the cage.

Figure 242

Figure 243

Figure 244

Figure 245

Figure 246

474 Carefully put the cane into the water.

475 Make sure that there is a depth of at least 50 centimetres of water below the cage, and tie the cage firmly in place.

476 To do this, tie a piece of rope to one corner of the float and anchor the other end to a stake in the bottom.

477 The cage should float so that 25 centimetres of it is above the water and 1 metre of it is below the water.

Note: If the cage does not float 25 centimetres above the water, tie on more floats until it does.

Figure 247

Figure 248

478 You can build an even better floating cage like the one shown below using pieces of squared, rough-cut wood.

479 This kind of cage can also be built with a door that can be locked and with a special opening for feeding the fish.

480 A locked door makes it more difficult for people to steal your fish; however, you may need more floats for a cage with a heavy wooden door.

Figure 249

Putting baby fish in the cage

481 When your cage is ready in the water you can put baby fish in it.

482 If you are raising Tilapia nilotica you will need to put in 150 to 200 baby fish for each cubic metre of cage.

Figure 250

Figure 251

483 After the fish are in you can cover the cage with a fishing net. This will protect your fish from fish-eating birds. To do this, stretch a piece of net over the top of the cage and tie it to the top rope.

484 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.

Feeding fish in cages

485 In a cage, there is usually very little natural food available to the fish, especially if you put the cage in a stream, lake or reservoir.

486 Movement of water may also carry the food you give to the fish out of the cage before the fish can eat it all.

487 Feeding your fish well becomes very important when raising fish in cages.

Figure 252

488 Use rich food, for example cottonseed or groundnut cake and wheat or rice bran, mixed with fresh slaughterhouse wastes such as blood and rumen contents.

489 Mix dry food with some water to make it stick together in the form of a moist mash.

490 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.

491 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.

492 Put in the food little by little so that you can watch the fish and see that they are eating.

493 If you see that the fish do not eat all of their food, give them a little less.

Figure 253

494 If you see that the fish eat all of their food quickly, give them a little more.

495 Remember that if you give your fish too much food it will collect on the bottom and make the water around the cage bad.

496 So, check under the cage. If you see too much uneaten food, you will know that you are feeding the fish too much. When this happens, move the cage to another place.

497 Follow the recommendations given earlier for ponds and pens: feed your fish at least once a day feed them at about the same time of the day, preferably early in the morning or late in the afternoon.

Taking care of your fish in a cage

498 You must always watch the fish to see that they are healthy and swimming strongly.

499 If the fish in your cage are not well, they will stop eating.

500 If this happens, stop feeding your fish for a day or two.

Figure 254

501 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.

502 If you find any dead fish floating in your cage, take them out right away.

503 Then, stop feeding your fish and watch them carefully for the next few days.

504 If no more fish die, you can begin to feed them after a day or two.

505 If fish continue to die, take them out as soon as you can and ask your extension agent or fishery officer for help.

Figure 255

Taking care of the cage

506 A cage can easily be damaged. If this happens you may lose fish. It is very important to check the cage every day to be sure that there are no holes where your fish can get out.

507 If you find any places where the fish can get out repair them right away.

508 In addition, you must be sure that the openings in the cage material remain free of dirt and plants so that fresh water can flow into the cage.

509 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.

Figure 256

510 Also, do not forget to check for uneaten food on the bottom under the cage from time to time.

511 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.

Figure 257

Figure 258

512 If you have a floating cage, make sure that the floats are tied firmly to the cage and that the cage is firmly tied in place so that it cannot float away.

Harvesting fish in cages

513 If you have used baby fish 8 to 10 centimetres long or weighing about 15 to 20 grams and have fed them well, they will be ready for harvesting in about five months. At this time the fish will weigh 100 to 150 grams each.

514 If you want to harvest only some of your fish, use a small hand-net and collect what you want without moving the cage.

Figure 259

Figure 260

515 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.

Figure 261

Figure 262

516 When you have collected most of the fish, you can lift the cage out of the water and collect the rest.

517 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.

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.

Figure 263

Figure 264

Starting again

518 After you have harvested your fish, clean and repair your cage as quickly as you can so that you can begin again.

519 You can hold the baby fish that you have caught in a small pen or in another cage for small fish until you have finished the cleaning and repairing.

520 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 the biggest and best baby fish to put back in your cage.

Figure 265

Summary
YOU HAVE LEARNED HOW TO PRODUCE FISH IN CAGES

To locate your fish cages best, look for

To begin, prefer small cages such as 1 x 1 x 1.2 m

Build simple cages with locally available materials:

Stock your cages with 8 to 10 cm fish, 15 to 20 g each

To produce tilapias, stock each cage with 150 to 200 fish per m

Feed your fish well:

Maintain your cages in perfect condition:

Harvest your fish after 6 to 7 months:


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