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Short Notes on Nature Singapore

13 March 2016 | Freshwater Snails | Physa acuta | Mini-aquarium |

photo In December last year, I added another small fish tank to keep 8 Molly Fish brought back from Qian Hu Fish Farm. Based on the experience with the first fish tank started in February last year, I limit the aquatic plants to only Java Fern (Microsorum pteropus) and the floating Frogbit (Hydrocharis morsus-ranae). The Molly Fish settled down quickly and within a month, started to produce baby fishes. To house these baby fishes, I brought in a third tank though this one is only half the size of the first 2 tanks.

With the new Java Fern, freshwater water snails started to appear in the new tanks within a few days. There were at least 2 new species on top of the 2 snails (Amerianna carinata and Gyraulus convexiusculus) seen when the first tank was set up. One of new snail had shells that was covered with light brown spots and I had identified it as Physa acuta. It can grow up to a length of about 10 millimetres (mm), a size that was at least 3 times that of the Amerianna carinata. The tiny flat circular Gyraulus convexiusculus that had extinct in the first tank also reappeared in the new tanks. photo photo photo

photo Though Physa acuta probably had been crawling in our local waterways, streams, ponds and lakes for many years, the first specific report on it only surfaced in 2013 but it was named as Stenophysa spathidophallus. The same named was used in the local pocket guide to snails and non-marine molluscs published by the Science Centre in 2012. In a more recent publication in June 2015, it was clarified that the naming of this snail as Stenophysa spathidophallus was incorrect. The snail should be the globally-invasive Physa acuta. The other new snail looked quite similar to Physa acuta but is more rounded and smaller. It should be Bithynia tentaculata.

So far, this is the fifth post on my mini-aquarium since I started it in February 2015. The other 4 posts over the last one year were listed by date below:
| 22 March 2015 | 24 May 2015 | 19 July 2015 | 8 November 2015 |

I had no intention to set up a conventional aquarium with many of the fancy gadgets. What I am interested is to keep it as natural as possible and to use it to observe nature in freshwater environment. Since it is a small and closed ecosystem, I do have to intervene at times to perform some basic maintenance such as changing part of the water once a week, address serious water pollution issue such as sudden peak in algae growth and control the snail population.

As indicated in my post on 21 February, I had place 2 Phasey Bean plants (Macroptilium lathyroides) into the tank with the Molly Fish. A week later, I found a Chinese water chestnut (Eleocharis dulcis) and decided to push the corm (swollen underground stem) into the sand of the tank. As of today, both the Phasey Bean plants and the Chinese water chestnut are doing well. Hopefully, I will get flowers from the Chinese water chestnut eventually.

Update: 8 May 2016

There was another snail (Pseudosuccinea columella) in my tank that looked very similar to Physa acuta. In fact, two of the Physa acuta pictures shown above were Pseudosuccinea columella, the ones where the snails had broad and shorter tentacles. Read more in my later post on 8 May 2016.

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