Lockable and portable ponds widen options for the fish farmer

Friday March 18 2016
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Dr Joseph Muga with his lockable ponds in Nairobi. PHOTO|LEOPOLD OBI|NATION


On the left side of the guesthouse overlooking the Safaricom Stadium Kasarani at the Sports View Hotel sits a tiny farm that hosts sukuma wiki (collard green) and indigenous vegetables.

The garden is also home to two structures that look like huge basins standing about 10 inches from the ground, both constructed of wood.

The ‘basins’ are ponds, the creation of Dr Joseph Muga, who is revolutionising the small-scale fish industry with the structures.

Dr Muga, a soil scientist, says he stumbled upon the idea of rearing fish in wooden ponds after scouring the internet for a technology that farmers can use to keep fish.

“I started searching for an alternative to earthen ponds several years ago after floods swept away fish in my eight earthen ponds in my home in Butula, Busia. I restocked but thieves later gave me a hard time,” recalls Dr Muga, who picked the wooden ponds idea, and modified it, making the ponds lockable.

Later, he made a portable version of the lockable ponds.


“The ponds vary in size depending on a client’s taste. Like that at Kasarani measures 3 by 4 metres and carries 900 fingerlings.”

Besides wood, the ponds are made of a strong black polythene material that holds the water to avoid spillage and wire mesh for the cover.

Maintaining wooden pond

Dr Muga says the polythene can stay for up to five years if properly maintained.

“If the polythene is exposed to the sun, it becomes weaker and begins to leak. In that case, it could serve for only six months. So the farmer should always ensure his pond has water all the time.”

The ponds have an inlet, which brings in fresh water, and an outlet that can be directed to the vegetable garden.

“Fish droppings are like manure from cows, therefore, they are good for providing nutrients to the crops,” says Dr Muga, who also runs an NGO called Rural Development through Social Appropriation of Technologies International.

One can keep in the wooden ponds both fingerlings and big fish. The movable pond, according to Dr Muga, suits urban farmers. The pond is similar to the lockable one only that it can easily be dismantled and moved from one point to another.

“The movable pond is bolted on a wooden reinforcement, therefore, if the farmer wants to use the space for any activity, he simply transfers the fish into a container, drains the water and unbolts the pond. The farmer can later assemble it once he’s done,” he explains, noting the pond is ideal where a farmer has limited space and goes for about Sh60,000.

Process of cleaning a fish pond

Wheels can be fitted on the pond to make portability faster and easier.

One can keep both tilapia and catfish, but a farmer must be cautious not to stock too many fingerlings in a pond because the fish must have adequate space.

“The process of cleaning the ponds is called flashing. Clean water runs into the pond through the inlet pipe while dirty water is automatically forced out via the outlet pipe. Flashing happens every time water is allowed into the pond, this could three times a week,” says Dr Muga, as he advices farmers to feed fish more on dried vegetables because they float over the water pond. 

Rearing fish in earthen ponds, according to the soil scientist, is susceptible to climate change factors such as torrential rains which affect the fish.

“With wooden ponds, such shortcomings are eliminated because they are above the ground.”

Ultra violet treatment

Prof Charles Ngugi, a fisheries expert, says the technology is good for those who have limited land.

However, he warns that smaller ponds are susceptible to fungal diseases because the fish will be brushing themselves on each other if the stocking density is high.

The government’s recommended stocking rate is four fish per square metre for all kinds of species.

According to him, the polythene liner can stay for over five years if it is treated against ultra violet (UV) rays damage.

“UV treatment is done by manufacturers themselves and not the farmer, therefore, it’s for the farmer to choose whether to use UV treated liner or not. UV treated liner are costly though,” Prof Ngugi explains.

He advises farmers to change pond water once in two weeks. “Once the water becomes too green, the farmer should change it because that indicates high presence of algae, which competes with the fish for oxygen uptake.”

If the algae stays for long, ammonia builds up resulting to death of fish. “The benefit of rearing fish in the wooden ponds is that the smaller number of fish are grown in a smaller unit thus ensuring high profit return.”