Times of India : http://timesofindia.indiatimes.com/city ... 815856.cms
PUNE: Fishes of foreign origin have led to the decline of the native fish fauna in the city's rivers, according to experts from the city-based Indian Institute of Science Education and Research (IISER).
The experts said the rivers and the associated water bodies in and around the city are dominated by a fish species known as tilapia, which has its origin in Africa. It was introduced in Pune waters, as a result of which at least 10 to 15 species of native fishes have disappeared from Mula-Mutha and the associated rivers. A drastic decline in the number of 20 to 25 other fish species was also found.
Neelesh Dahanukar, an IISER fellow, said tilapia is found in the Mula river, especially in the polluted stretches. Tilapia dominates the Lonavla lake as well. In Indrayani river, 50 to 60% of the catch is tilapia. In Mutha and other associated rivers also tilapia dominates.
Tilapia was introduced as aquaculture (food fish). It breeds throughout the year and thus affects the native fish species through competition for food and nesting space. It also consumes small fishes.
Dahanukar cited an example. There was fish species called nukta or doodondi, which was documented to be available in Pune more than 150 years ago. However, the species is no longer there in Indrayani or Mula-Mutha rivers, possibly because of these introduced species. Its population, found in other parts of the Western Ghats, are also declining drastically. The same fate is shared by many other native fish species.
Tik, another fish species, was fairly common in Mutha river in 1998. In 2008, a survey was done and now, it is locally extinct.
Other than tilapia, several introduced species are found in northern parts of the Western Ghats, which are contributing to the decline in native fish fauna, as the introduced species threaten the native population through competition for resources and predation.
Guppy and gambusia fish species, both from South America, were introduced for mosquito control. But it affects other larvivorous native fishes through competition for food. Green Swordtail, a fish from North and Central America, was introduced to Mutha river by accidental introduction from aquarium trade. It also affects native larvivorous fishes through competition for food. Another such introduced species is African catfish, which escaped captive breeding and now breeding in rivers. It is a predatory fish and a voracious feeder.
Experts point out that there should be public awareness about the threat of introduced species, and control measures should be taken up on breeding and check on their population.
Apart from the introduced species, other reasons for the decline of the fish population in Pune waters are pollution and exploitation of natural resources.