New weeds arise in lakes

By Lillian Nsubuga Two new weeds have been cited in Lake Bissina and Lake Opeta in North Eastern Uganda. According to Dr Timothy Twongo, Principle Research Officer at the Fisheries Resources Research Institute (FIRRI), one of the weeds, Najjas horidda, has been around much longer than the second weed, Hydrilla pectinatus. "The fishermen say they have seen Najjas horridda in the lakes since the early 1980s, but it was only brought to our attention in the last two years," Dr Twongo said. Najjas horridda has also been cited in some parts of Lake Victoria. Dr Twongo also said that Hydrilla emerged as a weed only recently, and is growing so fast that it is beginning to overshadow Najjas horidda. Unlike the water hyacinth, these weeds grow and live under the water surface, which makes them more difficult to detect. Fishermen are said to complain about increased difficulty in catching fish because when they throw their nets, their nets get clogged with weed. FIRRI is carrying out research on the factors that favour the growth of Najjas horridda and Hydrilla, but scientists already suspect increased nutrients in the lake have a lot to do with this growth. Twongo said FIRRI is yet to deduce the effect these weeds are having on the feeding habits of fish, or on their reproduction and movement under the water. However, Hydrilla has already been confirmed to be far more dangerous than Najjas horridda. "It is a very bad weed which has been battled in North America for years with little success," said Dr Twongo. Government has not yet started implementing any control measures against the weeds, as this is only possible after conclusive research results on their growth and reproductive habits are derived. The presence of Najjas horridda and Hydrilla in Uganda lakes could spell more disaster for the country's fish industry. This is especially true because Government has still failed to eradicate the water hyacinth from Lake Victoria and Lake Kyoga. Dr Twongo told journalists during a meeting with scientists at FIRRI offices in Jinja that the weevils have failed to control the water hyacinth that is found on River Nile and River Kagera. "We are researching on what is making the water hyacinth in the riverine areas difficult to control," said Dr. Twongo. Failure to control the water hyacinth in the rivers has made it impossible to eradicate the weed from Lakes Victoria and Kyoga, as it gets blown into the lakes by strong winds. ends