There has been an ongoing census of the fish community in Lake Tanganyika for the last twenty years. During this census the Japanese scientists have taken note of some rather drastic changes in the fish populations. These findings were published in the most recent issue of the journal “Ecology of Freshwater Fish”.

The conclusions were reached by Yuichi Takeuchi and team, while surveying the density and number of the different fish in Kasenga Point, at the southern end of Lake Tanganyika between 1988 and 2008.

The investigative team, headed by Yuichi Takeuchi, took note of a total of 54 chichlid and six non-cichlid species of fish, over the period of the survey. The most abundant type of fish recorded were the aufwuchs feeders.

Even though there was an abundance of fish and no lack of number of species present, their research indicates that there was a steep decline in the density of the aufwuchs feeders and invertebrate eaters during the course of the study. In a strange turn of events, there was an increase in the density of detritus feeders during this time.

The researches theorize that the change in the fish community could be due to human activities in the area such as deforestation, and agriculture run offs, which would lead to sediment loading in Lake Tanganyika to increase.

While they could not completely rule out natural variation for these changes in the fish community of Lake Tanganyika, there is no doubt that human activity is also making a large impact on the area as well.

Lake Victoria, the world’s second largest lake and the world’s largest tropical lake, has long been plighted by environmental problems caused by pollution and exotic species being introduced to the lake. On of the most well know of these problems was the introduction of Nile perch to the lake; a large predatory fish that all but wiped out the lakes wide variety of native, endemic species.

Moses Kabuusu, Member of Parliament for Kyamuswa country in Kalangala district, has now expressed concerns about another problem developing in the area. According to him the amount of fish in the lake has now become so low that crocodiles are increasingly looking at humans as food. The number of croc attacks on humans has indeed increased in Kalangala, but it is hard to tell whether this is due to less fish being present or if there are other reasons that have increased the number of attacks on humans.

Kabuusu warns people about spending time in the water due to the rampant problem of humans being eaten by crocodiles and adds that it is mostly people swimming in the lake and women getting water in the lake that are being hunted by crocodiles.

He has requested help by the Uganda Wild Authority.

Lake victoria beach.

In a new study on Tanganyika cichlids, three scientists[1] [2] [3] from Uppsala University in Sweden have shown that intricate rearing behaviour varies with brain size in females. The only previously published study showing similar patterns concerned predatory animals.

Tropheus moori – one of the species used in the study. – Picture www.jjphoto.dk

How the vertebrate brain has developed throughout the course of evolution is still not clear, and we are still not certain if brain functions in a specific species develop to match a demanding environment. One way of learning more about this is to compare brain size and structure in closely related species living under dissimilar circumstances.

“It is important to look at differences between males and females since females often distinguish themselves from males, both in behaviour and appearance”, says Niclas Kolm, lead-author of the study.

The study looked for correlations between brain size and ecological factors in a large number of specimens from 39 different species of Tanganyika cichlid. Lake Tanganyika is especially suitable for this type of study since it is inhabited by cichlid groups exhibiting significant dissimilarities in both brain structure and ecology, and whose ancestry is well known. Tanganyika cichlids varies dramatically from species to species when it comes to factors such as body size, diet, habitat, parental care, partner selection, dissimilarities between the sexes, mating behaviour, and brain structure.

The result of the study showed a correlation between brain size and the two factors diet and parental care behaviour. Species where only the female fish cares for egg and fry turned out to have bigger brains than species where both parents engage in parental care. The brain was however only larger in females; there was no difference in brain size between males of the two groups.

The largest brains of all were found in algae-eating cichlids. These fishes live in environments characterized by a high level of social interaction. “This indicates that social environment have played a role in brain development”, says Kolm.

The study was published in the web version of “Proceedings of the Royal Society of London Series B” on September 17. You can find it here (http://journals.royalsociety.org/content/j114062824820l76/).