PFK in Sri Lanka: The incredible lake


Jeremy Gay visits a large lake in Rekawa on the south coast of Sri Lanka.

When I spent two weeks in Sri Lanka with the Marine Conservation Society recently, I experienced my own unforgettable journey of discovery.

Early in our trip we were taken to a large lake at the village of Rekawa on the south coast. It covered several acres and looked a real haven for wildlife, having plenty of birdlife, plenty of plant life, and, we hoped, plenty of aquatic life too.

Exciting lake
Even the look of the lake excited me, as we don’t really see anything as exotic as this in the UK. About 40% of its entire area was thickly planted, mostly with floating Salvinia natans, several varieties of water lilies, Water hyacinth, tall reeds and thousands of square metres of what looked to be Ceratophyllum demersum.

The plants seemed key to the health of the lake, as close inspection of a net revealed simply thousands of tiny aquatic invertebrates, insect larvae and larger inverts like shrimp and crabs. These would feed in and around the abundant mass of plants, which, in turn, went on to feed the lake’s fish.

I wasn’t disappointed with numbers of fish either, as I could see a few on the surface next to the bank. From above, they looked to be small killies, and where there is an abundance of one species there are usually many more too – at least in the tropics.

Our first glimpse of the lake was towards evening when we were actually in the area to visit a fish growing-on facility ran by the Turtle Conservation Project and because it was getting dark I didn’t get to dip my net. Yet on the Thursday morning of the first week Peter Richardson of the Marine Conservation Society and I were desperate to do some fishing so left early to see what we could catch.

I’m always cautious when entering unfamiliar waters because I don’t know how deep they get and how quickly, and I have a healthy fear of what I can’t see underwater. Peter was first in and I followed, and we found that in some places the lake felt as warm as bathwater and, in the margins where we were fishing, it averaged just 45cm/18” in depth.

As I said the plant life was incredibly thick, with Ceratophyllum completely filling the water in places and water lily leaves and floating Salvinia growing on top of that. Water tests were surprising, revealing an average temperature of 28°C/82°F, a pH of around 8, and general hardness that was through the roof. So this was a hard, alkaline, warm, habitat.

First fish
Despite feeling pretty horrible to walk through and accumulating floating rafts of plants around our legs as we did, this gave us an advantage in that the killifish-like fish at the surface didn’t really scatter when we came near. We could just scoop them up.

They were the first fish placed in our holding tank on the bank and we could make out females and some particularly nice males. Peter was excited as he had set up a Sri Lanka biotope before and I could appreciate that, although quite subtly coloured, these small panchax-looking fish, averaging only 2.5cm/1”, were thriving in the habitat and I was glad we had at least managed to catch something.

 

A later check in the reference book hinted that they might be Aplocheilus werneri, a fish that occurs where we were in southern Sri Lanka. However, the fish in the photograph looked far larger and more colourful than the one I had caught and, after reading that they grew to 9cm/3.5” and liked water between 22-26°C/72-79°F, I wasn’t so sure that those I caught were not a sub species or a regional variant. Mine were tiny and living in very warm water. Were they A. werneri at all? I think they were A. dayi.

Contemplation that night made me wonder if there weren’t any large adult fish because of the many hundreds of birds that frequented the lake. It didn’t seem to be from lack of food…

We only had one net so Peter took a stab into the raft of floating plants and immediately brought up a 5cm/2” snakehead that had been resting there. I was really pleased as I thought it looked like a snakehead habitat and this was the first large, predatory freshwater species that we had caught.

I couldn’t identify the species as it was quite mottled, and typically shaped,though a local fisherman told me that it got to about 25cm/10” in length, which isn’t too bad and does make it suitable for captivity. Ralf Britz later confirmed it was Channa punctata, a species that is quite cheap and easy to get hold of in the UK.

The only problem with any snakehead is that they hate confinement, refuse to be tamed and are great jumpers — and ours jumped out of the tank when I wasn’t looking. We got lots more, but all fish were put back anyway. We were there to discover and appreciate them, not to collect them for ourselves.

Key to keeping
I think the key to Channa punctata in captivity, and maybe many others, is to heavily plant the tank with feathery leaved plants and use floating plants on the surface too, as these were resting just under the surface among the plants. It may help to stop them from jumping out too!

Next were the barbs. The first we caught were tiny and silver, and there in abundance. We caught them fairly easily and a close inspection revealed a hint of yellow colour on some males, but all with a small black spot in the dorsal fin. They were Puntius vittatus, though again the book’s temperature reference was too low. Were they taking measurements in wintertime and me in the summer?

P. vittatus are really too plain for most peoples’ tastes. I liked their small average size though, again at around 25cm/1” in length. Through the shoals of thousands of panchax we started to spot a few vertically-banded barbs, small at first and the larger at 5cm/2” in length or more.

The black bands were clearly defined and looked like what the locals called “filamentosa”. The Sri Lankan filamentosa is actually Puntius singhala.

They proved incredibly agile and hard to catch and we caught just one juvenile, making identification even more difficult. The juveniles would certainly stand out in any aquarium!

But you can’t be in ponds, lakes and ditches in somewhere like Sri Lanka without catching a few anabantids and before long we started to catch some tiny fish that looked like small Paradise fish. The closest geographical match in the book was the Black spike-tailed Paradise fish (Pseudosphromenus cupanus.)  

Either way they were tiny and gratefully received. We didn’t see any of these in the lake and every one was caught just by shooting the net through a load of floating plants and checking it.

Introduced species
As beautiful as this lake was it did have issues in terms of fish and the main one involved introduced species. It was full with Oreochromis niloticus of all sizes, known just as 'tilapia,' and they were introduced to Sri Lanka as a food fish.

They are very popular as such, only inevitably they escaped and are now in most natural waters in the country. As we visited a tilapia and Koi growing-on farm just feet from the lake’s edge I voiced my concern about having alien species so close to a natural water because of the risk of escapees.

The guy feeding the captive tilapia pond said he had caught them from the lake in the first place, so it looked like they were there to stay. Thushan, our local expert and guide, said there were also Catla catla in the lake as food, which I caught as small fry later that day (above). They are not really aquarium fish, looking a bit like carp and growing large.

Wonderful plants
If into either natural or cultivated plants, either terrestrial or aquatic, you would have loved this lake. Every plant in Sri Lanka looks like something out of the Eden Project anyway and the plants here were no exception. As I mentioned, I think plant life in the lake plays a major part in its ecology, as well as looking aesthetically wonderful.

Floaters, lilies and vast beds of Ceratophyllum dominated, though there was also Hydrilla, Potamogeton looking in wonderful contrast to the Ceratophyllum with its red leaves, what looked like Aponogetum and lots of lily-like plants.

All the plants grew in deep, soft mud, warmer than the water above as the sun shone onto it. Where there were patches of sand, no plants grew. The huge patches of aquatic plants looked superb in the clear patches of water and were undoubtedly a huge factor in this lake’s habitat. Whether it will continue as the population of tilapia grows I couldn’t say.

Set up a Rekawa lake biotope
A lake biotope tank would be easy to set up at home and, due to the small fish species we caught, doesn’t have to be too large either.

Choose an aquarium at least 60cm/ 24” long with gentle filtration and quite bright lighting for the plants. All plants in the lake are hardy and quite easy to grow in the aquarium without much special care, though CO2 could be added for better growth.

The substrate in most places was dark brown mud, littered with dead plant leaves, stalks and detritus. In open water where no plants grew, there were patches of fine sand. To replicate this and feed the plants at the same time, either use a complete soil-based aquarium substrate like Tetra Complete, Sera Floradepot or Dennerle Deponit — or make your own out of pond soil.

To stop it getting stirred up place a layer of sand on top, again dark if possible, and heating cables could be used to replicate that warm mud I waded through across the lake shallows.
There were few hard aquascaping features in the lake, just the odd log or branch or two, so some narrow bogwood is all that’s needed. I felt or saw no rocks.

Plants were a massive feature in the shallows, so plant heavily with Ceratophyllum demersum and place Salvinia natans floating above it. For larger aquariums of 120 x 45cm/47 x 18” or more, large tropical water lilies could be added along with Water hyacinth. Potamogeton spp aren’t that readily available for the aquarium, so check with a plant specialist as to their availability. Use bright daylight spectrum lighting set for ten hours per day.

Use a heater set to 28°C/82°F to regulate temperature and, to be particularly biotope correct, use hard alkaline water with a pH of 8. Add Aplocheilus dayi, Puntius vittatus and Pseudosphromenus cupanus.

For the larger, oddball version of this biotope leave out all the small fish and add Channa punctata instead — or for the alien, but also biotope correct look, add Oreochromis niloticus.

The Marine Conservation Society
The Marine Conservation Society (MCS) are a UK charity caring for our seas, shores and wildlife. MCS have supported the Turtle Conservation Project (TCP) in Sri Lanka since 2002.

MCS and TCP arranged Jeremy’s trip as part of a collaborative project developing alternative income within Rekawa village, which is supported by the BBC Wildlife Fund.

MCS also campaign for better protection of endangered marine creatures; promote sustainable seafood choices to protect fish stocks for the future; campaign for pollution-free seas and litter-free coastlines; and involve thousands of volunteers in work to survey and protect our marine life. You can join MCS for as little as £3 per month.

Visit Sri Lanka
If you want to explore the aquatic wildlife of Sri Lanka, visit www.birdandwildlifeteam.com

This item first appeared in the May 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.