Fresh Water Fishes of Sri Lanka
This article deals mainly with fish that live in the fresh water rivers, streams, reservoirs, lakes etc in the island. It does not seem to be an accurate record of the number of species of fresh water fish in Sri Lanka.
One reason for this maybe that most times some marine species found in fresh water are also counted and sometimes they are absent at times of a count. However, recent records seem to indicate that there are 111 species recorded from Sri Lanka.
The fish in this country fall into three main categories.
Sri Lanka has over 103 river basins. Covering an area of 59,217 hectares, Sri Lanka has no natural lakes. However there are over 12,000 man made lakes (tanks) in the island. Tanks or man made reservoirs make up the main water bodies in the dry zone.
These tanks have been constructed, from time to time, by our ancient kings to hold the water from the north-east monsoon rains for domestic and agricultural use during the rest of the year. There are also the new reservoirs like Castlereigh, Victoria, Kotmale, Rantambe and Randenigala.
There are rivers that start from the central hill range of the island. These are perennial rivers, since their forested catchment areas ensure a flow of water in the dry weather. The dry zone also has rivers but these are not perennial in that they dry up during the periods of dry weather.
Villus are shallow depressions going not more than about four feet in depth. Some villus dry up and are replenished by the rains or by ground water. Others do not dry up at anytime during the year. The water in some villus are saline.
There are also temporary pools that are shallow depressions filled by rain water or the overflow from nearby rivers. They generally dry up by the end of the dry period. Most of the smaller rivers flow into a lagoon or estuary before the water goes into the sea. Therefore, these waters are sometimes saline due to the tidal inflow from the sea. It is known that some tidal waters go far up rivers.
Wetland swamps in instances where they are inland contain freshwater but the costal swamps like Muthurajawela and Kalametiya are saline. Springs, especially in the hill zone, form pools, which also host some species of fish.
Sri Lanka has 82 species of indigenous freshwater fish belonging to 11 families. Forty-four species or 55% are endemic to the island. Some of these species have yet to be described and recorded scientifically.
Unfortunately, several species are already extinct. This is mainly due to habitat degradation. With the ongoing research, soon there will be a better and fuller understanding of our fresh water fish.
Among the indigenous freshwater fish, 54 species are regularly exported and presently form the mainstay of the ornamental fish export industry. Of the endemic freshwater species, 21 have ornamental value.
Referring to the fish in dry zone reservoirs, Rohan Pethiyagoda says 'that the tanks have not existed continuously for long enough to have developed a ichthyofaunal identity'. Ichthyofaunal is to do with fish fauna. The same species of fish that have come into these tanks from the rivers have not evolved in their new habitats, to form a new species, in that they have not changed any of their features.
On a visit to Nuwara Eliya last week, I was able to see the last habitat of the freshwater shrimp (Lancardis sinhalenesis) called Miridiya Kunissa in Sinhala. Earlier this endemic shrimp was found in a number of habitats in the Nuwara Eliya area, at Ambawela, Moonplains, Bomburuella etc.
Now they are not found in the streams in these areas mainly due to the pollution of the waters, especially with factory effluents and the use of agro-chemicals. It was found even in the Horton Plains but not now.
They are now only found in the stream that runs between the President's Lodge and The Prime Minister's Lodge, bordering the Golf Course, in the heart of Nuwara-Eliya town. This stream remains unpolluted.
The British planters founded the Ceylon Fishing Club. This club catered to its members who were interested in fishing. Only members were allowed to fish in certain streams. These streams were stocked with Rainbow Trout (Oncorhynchus mykis) and Brown Trout (Salmo trutta).
They were introduced to some streams in the Horton Plains and other up country streams by the Fishing Club. Now the Fishing Club is defunct and the hatchery has been closed down. Most of the trout in these streams have been caught or have died out. However, they have bred in the Horton Plains and are found in the fast flowing Belihul Oya and the Agra Oya.
The only record of there being fish at high elevations is from E.F. Kelaart in 1840 where he refers to two species of fish found at an elevation of 1,800 meters. He has not identified these two species. Now there do not seem to be any fish in the Horton Plains other than the trout.
The first exotic species of fish introduced to the low country inland waters, many years ago, was Tilapia Mosambica (Oreochromis mossambicus). This species bred profusely and its increasing availability led to the commercialization of inland fisheries.
Later another species of Tilipia was introduced. Three major species of Chinese carp species and three major Indian carp species, which are now of particular importance in aquaculture, were also introduced.
The Chinese carp are: Grass carp (Ctenopharyngodon idella), Silver carp (Hypophthalmichthys molitrix) and Bighead carp (Aristichthys nobilis). The Indian carp are: Catla (Catla catla), Rohu (Labeo rohita) and Mrigal (Cirrhinus mrigala).
Fish, like Tilipia and Carp were introduced for inland fisheries mainly as a solution to the low availability of protein for the rural people, especially in the dry zone reservoirs.
Another reason for the introduction of fish from outside, referred to as exotic, is to control the mosquitoes that spread malaria. Then there are also a number of species of fish that have escaped from private aquaria or dumped by amateur enthusiasts and those involved in the fish trade.
An exotic species introduced into the Castlereigh Dam, the1950s was, the Green swordtail (Xinphophorus helleri). These species of fish have been introduced into our inland waters deliberately, with altruistic motives, or by accident.
The introduction of invasive species has been the main cause of the extinction of freshwater fishes. Invasive species in their need to survive in a new habitat, are more aggressive and eat up the food resources of the indigenous fish. In some instances they kill the local fish.
Channa Bambaradeniya has reported that some nine alien species of freshwater fishes are now naturalised in Sri Lanka, Many other exotic species are recorded sporadically, and persist as potential invasives.
The Nature Conservation Union (IUCN) has recorded that at present, nine species of freshwater fish in Sri Lanka are considered as globally threatened, while 39 species have been identified as nationally threatened.
Both the freshwater fisheries and the ornamental fish industry are responsible for the introduction of freshwater invasive species to Sri Lanka. The trout in the Horton Plains mentioned earlier are in a stream in a National park and therefore afforded protection by law.
This is a poor reflection on conservation science in Sri Lanka, especially given that the trout occur in the same habitat range as several restricted-range endemics such as the fresh water crabs and the only fresh water shrimp in Sri Lanka.
The fish introduced to the low country water bodies have posed a far more serious threat to the local fish. The aggressive invasive nature of these fish has caused a decline of a number of local fish species.
The fact that Tilapias represent between 70 and 90 percent of the freshwater fish harvest at present shows how they have multiplied and that at the expense of local species of fish. Intensive gill-net fishing now practised, also impacts adversely and directly on the larger species of indigenous fishes.
For example the Shark Cat Fish (Wallago attu), Walaya in Sinhala and the Giant Snake-head (Channa ara), Gangara in Sinhala, are now extremely rare. They may also have impacted on the Orange-finned Labeo (Labeo lankae) and also led to the near extirpation of freshwater turtles in most reservoirs that support a fishery.
Rohan Pethiyagoda observes that 'the problems of conserving freshwater diversity have largely been focused on the fish fauna of Sri Lanka, because Sri Lankan freshwater fishes, since the 1930s, have been part of the national aquarium trade. Many of these species are routinely bred in captivity and found in aquariums throughout the world.
But what first focused the attention on the need to conserve this diversity was the fact that two species, which were not utilized by the aquarium fishery, mysteriously disappeared very suddenly in the 1980s. Both of them enjoyed wide distributions.
They were found on about two thirds of the island of Sri Lanka more in man-modified habitats than in pristine, natural habitats. They were never considered to be in need of conservation attention.
Yet, in just five or six years that we monitored populations of most Sri Lankan freshwater fishes, these two species crashed and disappeared altogether. Unfortunately, both may now be extinct, and only be known from museum specimens.'
Trends in almost all other species are not documented, and with no comprehensive assessment having been made over the past 15 years, it is possible that several other species have disappeared or are on the brink of extinction. Therefore, the foremost priority for the conservation of this fauna is a competent scientific national assessment based on fresh sampling.
Despite its large fresh and brackish water resources, Sri Lanka does not have a tradition of aquaculture and only marine shrimp aquaculture and ornamental fish culture have been developed to any extent.
Sri Lanka has a low number of indigenous freshwater fish plus another 18 exotic species. Among the introduced fish, the Tilipia and Carp species are of particular importance to freshwater aquaculture. The annual harvest of fresh water fish is approximately 30,000 metric tons. All of this is alien fish species. This is an important source of nutrition and employment for rural communities. However, this is less than 0.1% of annual per capita Gross National Product, which suggests that it is not indispensable in economic terms.
Unfortunately, international agencies like the Asian Development Bank and the UN Food and Agriculture Organization have continued indiscriminately to support the introduction of alien species with no consideration of the environmental consequences involved.
An environmental impact assessment has not been made or mandated for the introduction of even one of the dozen or so alien species released in Sri Lanka, and fisheries scientists continue to ignore the potential for negative consequences.
Rohan Pethiyagoda has recently made a number of recommendations that would help stabilise the situation with regard to the fresh water fauna of Sri Lanka. They are.
In Horton Plains National Park, at least so as to demonstrate that it is alive to the risk alien species pose to the indigenous biodiversity of Sri Lanka.
Much has to be done if we are to conserve the freshwater fish diversity in this country. The recommendations made above must be implemented as a first step towards this conservation.
By Jayantha Jayawardene
May 7, 2007