Fresh Water Fishes of Sri Lanka
Jayantha JAYAWARDENE
FRESHWATER FAUNA: 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.
(1) Indigenous fresh water species - these are fish that live in
freshwater right through their life. This category has 44 endemic
species.
(2) Those species that live in brackish water lagoons and deltas in
the coastal areas. They also, in some instances, live in fresh water
habitats.
For example, some eels are born in the sea but soon after come and
spend most of their lives in fresh water. They go back to the sea later,
where they breed and later die.
(3) The species that live in marine water throughout. However, in
rare instances some of these species have been recorded in fresh water
as well. They may be brought in by the influence of the tides.
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.
1. A conservation assessment of the freshwater fauna is overdue, but
for most species up to date information on populations and trends simply
does not exist to facilitate one. A comprehensive assessment of the
populations of all freshwater fish species based on fresh sampling is
therefore an urgent necessity.
2. While fisheries managers maintain detailed catch records at
several stations in Sri Lanka, taxonomic data are not acquired. The
maintenance of records of the catch of each species, especially the
indigenous-species by-catch, could provide a means to make trend
analyses that could inform future conservation decisions.
3. All pesticides approved for release in Sri Lanka should be
assessed for impact on non-target organisms and the environment in
general, and the labelling of such products should include information
on environmental safeguards.
4. All future releases of exotic fishes should be preceded by an
environmental impact assessment involving specific safeguards against
invasiveness.
5. A positive list of organisms that may be imported by the
ornamental fish industry needs to be developed and enforced.
The necessary legal provisions for this already exist in the Fauna
and Flora Protection Ordinance.
6. Legal and institutional reforms need to be made to engage local
communities in the in situ conservation of point-endemic freshwater
fishes; and to engage the ornamental fish industry in ex situ
conservation, especially the development of methodologies to breed
"difficult" threatened species (e.g. Puntius asoka) in captivity.
7. International agencies, particularly the FAO and ADB should be
informed of the negative consequences of their fisheries development
projects in Sri Lanka and urged to engage in supporting the research and
capacity-building necessary to manage the fishery sustainably into the
future.
8. Incentives and regulatory measures need to be introduced to phase
out, over a defined time scale (say 2-3 years), the harvesting of fishes
from the wild by the ornamental fishery, while encouraging the culture
of such species as for which there is commercial demand.
9. Finally, although its consequences will have minimal conservation
benefit at this stage, the Department of Wildlife Conservation should
take steps to eradicate the last population of rainbow trout in Sri
Lanka.
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.
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