Concerns raised over black water in Lake Victoria

Fish farmers in Lambwe West location within Homa Bay County are apprehensive after one of them was left counting losses after his entire stock was consumed by unknown disease.

This comes after one Joseph Onyango, a fish farmer in Kisaka Beach lost all his fish early this month under mysterious circumstances.

Onyango, who as usual had gone to inspect two of his cages on that fateful morning was shocked to witness his fish floating in water with mouths wide open indicating that they were suffocating.

The water in the two cages had turned black and emitted a bad smell in the air. “I thought the contamination was due to raw sewerage as the water was unusually dark,” he said.

The fish farmer had in each of two his cages about 12, 000 fish totaling to 24, 000 which in an instant were lost leaving him counting losses since he had envisioned himself reaping big after selling them.

“I was to sell the fish in the first cage by August after maturity which would have given me a return of about Sh. 1.8 million while the fish in the second cage were to be ready for sale by December but everything is lost now,” decried Onyango.

The farmer reported the incident to the fisheries department seeking an explanation behind the death of his fish.

Speaking to Homa Bay County Aquaculture Business Development Officer (ABDP) coordinator Michael Omondi, he said the same incident took place in Siaya and Kisumu before spreading to other areas in the lake.

He explained that the reasons are varied but major one is change in chemical composition of water; “The main factor contributing to mass death of fish is sudden change in chemical composition of water and what happened to fish in Kisaka is called black water, a natural occurrence in water bodies where the level of oxygen is reduced due to chemical activities in water,” he stated.

Omondi said the phenomenon also could be due to failure in proper management of the water environment by fish farmers.

“The phenomenon could be the result of improper management of the water environment by fish farmers. Scientists believe black water occurs when organic matter decomposes at the bottom of the lake before rising to the surface. Decomposition uses oxygen which is drawn from the water leaving fish with less air,” he said.

The decomposition is believed to be from water hyacinth which perennially covers the lake as well as fish feeds.

“Another cause of decomposition that consumes oxygen comes from fish feeds and wastes from fish that drop from cages to the lake bed. Cage fishing is a new concept in Lake Victoria and all its challenges are not known yet. So a precautionary measure is to have an oximeter to check on the oxygen concentration in water,” he said.

He said that fish should eat less when oxygen level is low to prevent depletion of the gas since metabolism requires a lot of oxygen during feeding, which leads to death in case of deficiency of oxygen.

This event is an eye opener to other farmers who wish to venture into the business as they need to put in place precautionary measures before investing into cage fishing to avoid economic setbacks in the event of such incidents.



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