On-farm Monosex Fingerling Production
Adrian Piers: Agriculture,Fisheries and Aquaculture consulting
Phone: +260 965 445464
Note from editor: The use of Methyl Testosterone for sex reversal of fish not yet allowed in Namibia
Tilapia production in ponds for smallholder farmers.
Fish farming results can be improved by using only male fish, especially in ponds. This is because males grow faster than females, and if there are no females they do not waste energy breeding. In mixed sex fish ponds, the other problem is unwanted breeding, and the many small fish that are then eating the food that the big fish should be eating, and this stops them
Advantages of this seed system are also less handling and transport of fish seeds, so there is less mortality and it is much cheaper than buying fingerlings from other suppliers. When harvesting, the fish are much bigger and more even in size.
How to produce your own monosex – male fish.
Even if you only have one fishpond, you can produce your own male fish seeds. This can be
done using a net-cage called a HAPA. If you have many ponds, you can use one just for monosex fish and fingerling production, and even sell these to other fish farmers. Notice these HAPAs are covered with thin nets on top also to stop birds from eating your small fish and to stop the big fish from jumping out. HAPAs look like this (below).
Once you have this in place, you will need to stock it with breeding fish. In HAPAs, the number of fish to stock depends on the size of the HAPA, so for every square meter of surface area you will need three females and one male fish. Breeding fish can be from your own ponds if you have mixed-sex fish, or bought from other fish farmers, or from the Department of Fisheries. Choose good healthy fish, and if you have kept the males and females separate (you can use HAPAs for this too!) for some weeks they will be fat and will breed quickly. Do not use fish thatwere treated with MT as breeders, and you will need to make sure you have the correct numbers of males and females, so check the sex of the fish. You can do this by looking at the sex openings which look like this. After putting the breeders together into the HAPA, after some weeks you will seethe small fish swimming around in the HAPA. Now you need to gently lift the net up and take out the breeding fish, leaving the small fish in the HAPA. Check the mouths of the breeders, if some of them still have eggs in the mouth, drop them back and release the net, then wait a few days and check them again.
Feeding the MT starter feed
To make all the fish male, you will need to feed the small fish, called fry, a feed that contains a chemical called Methyl Testosterone. Some farmers add this to their feed themselves, but you can also buy fish feed that already has this chemical in Zambia. This feed is called MT starter.
Once you have removed the breeders, start feeding the fry the MT starter twice or three times a day. Make sure you do not overfeed! So look and see how much they are eating and there should be no feed remaining after about an hour. You will need to feed them this feed for at least 30 days. At the end of this they should be nearly all males.
After this the small fry can be moved to open ponds, and if the HAPA is already in the pond to be stocked, it can be done simply by pushing the sides of the HAPA down into the water. If they are to be moved to another pond, take care not to hurt the fish when moving them, and not to cause them stress by being too hot or cold, or too many in a container.
If you have another small pond, you can also use that for growing these fish to the next stage, called fingerlings. This normally is for another two months. After that the fish are much stronger and can be transferred to the growout pond for the final stage without being hurt.
When harvesting a growout pond, the best practice is called a TOTAL harvest where you take all
the fish out and sell them. Draining the whole pond is the best way to do this. Then the pond can be dried, repaired and prepared by applying agricultural lime and refilled with water ready for the next crop of fish. Drying out the pond and using lime will kill any remaining fish and sterilize the pond so that you do not have unwanted fish left over or wild fish breeding in the growout pond the next time it is used. This is important otherwise the advantages of having male fish only will be lost. It also helps to prevent diseases, and allows the air and sunlight to release more nutrients that will help to grow more natural food for the fish.
MT starter feed is available from Novatek, and advice on fish farming is available to members of the Aquaculture Development Association of Zambia. Contact details are below.
Mobile: 0978 070076, 0965 445464, 0978 779016, 0966 339833
Sales: 0978 779017/38
Email: firstname.lastname@example.org, email@example.com, firstname.lastname@example.org