HABITAT - Volta River Biotope

creating a

Volta River Biotope

by Melanie Newfield

For my first ‘biotope’ tank, which I wrote about in a previous issue, I confined myself only to species which were native to Thailand. But as I learned more about the different fish I had in that tank, I realised that, even though they were all found in one country, their distributions didn’t necessarily overlap. So, for my next attempt at a biotope, I decided to confine myself to species which all occurred in the same river catchment.

I was, at the time, setting up my third Fluval flex tank for Norman’s lampeye killifish (Poropanchax normani). It was going to be a species tank – just the Norman’s lampeyes – so I didn’t need to worry about finding other fish that came from the same area. But the

plants were going to be a real challenge – the two plants that do best in my tanks are Java fern and ambulia – Asian species and definitely not native to West Africa. If I wanted to do a biotope for Norman’s lampeye, I was going to need to find something else to grow in their tank.

I vaguely remembered that one of the two species known as Indian fern or water sprite (Ceratopteris cornuta) was not, in fact, Indian, but African, so I started looking to see if that species was found within the range of Norman’s lampeye. To do this, I went to a website called the Global Biodiversity Information Facility – more commonly known simply as GBIF. This website collates information on species distributions from a number of different sources and allows you to look at them on a map. It’s not perfect – it doesn’t have good data for every species, and if you are using the site for serious research you need to do a fair bit of data checking – but the records for Norman’s lampeye were pretty good. Among the areas where their ranges overlapped, one particular area stood out as having the most records for both species. This was the lower part of Volta River catchment, which runs through Ghana. The large number of records didn’t necessarily mean there was more Indian fern or Norman’s lampeye there than anywhere else – just that people were noticing and reporting them there. Among the nations of West Africa, Ghana is particularly known for its democracy and political stability. It may be that this stability allows for more time and effort on activities like biodiversity surveys. I hoped that the good records of for those two species would mean that there were also good records for other species. If you know the name of the species you are interested in, GBIF is a good place to find out where it occurs. But if you are looking for something quite specific at a particular site – in this case, aquatic plants which were available in New Zealand – it’s not useful. So to find other species, I searched for reports on aquatic plants in Ghana or the Volta River. One of the first sources that I found was a report on aquatic plants for the area around Lake Volta, a hydro-electric lake on the river. The focus of the report was introduced species, some of which can affect the production of hydro-electricity. However it did also mention some of the native species. The report confirmed that Ceratopteris cornuta was present in the catchment. It also mentioned another fern, Bolbitis heudelodtii, known as Congo fern. I already had a small amount of this in another tank. In addition, the report mentioned two genera I knew were present in New Zealand – Vallisneria and Anubias. However it didn’t say where species in their genera were present there. Vallisneria species are tricky things to identify at the best of times. They have separate male and female plants, and you need both to identify them. In New Zealand, most populations are one or the other, and only propagate by runners. Botanists have gone to some trouble to try and identify the species present in New Zealand, and various names have been used. What’s generally agreed is that there is a rampant, giant version of the plant choking the water’s edge in Lake Pupuke on Auckland’s North Shore, which is prohibited from sale. There is also a less aggressive version known as twisted vallisneria, or Vallisneria spiralis. This form is permitted. I was not going to be able to determine whether the form which we are allowed to keep in New Zealand was the same as in the Volta River, but I decided it didn’t matter. My only option, if I wanted Vallisneria, was the twisted val. I decided to use that.

The Anubias was going to be a bit more tricky. There are a lot more Anubias species

than there are Vallisneria. I could take the pragmatic approach that I used for Vallisneria, but I decided to see whether I could find the correct species. So I went back to GBIF and tried entering the name ‘Anubias’, then I looked at the records from the Volta River. There were a few different species, and one, Anubias afzelii, was listed on overseas aquarium plant sites and on the New Zealand Plant Biosecurity Index. The Plant Biosecurity Index gives the requirements for importing plant species in New Zealand, and if a species is listed it means that it is likely that it has been cultivated in New Zealand at some point. Here, I turned to social media to help me. I posted a request to the New Zealand Aquatic Plants facebook group explaining my plan for my tank and asking whether anyone had Anubias afzelii available. I also mentioned the other species I intended to plant in there. As a result, I was able to get the Anubias I wanted, as well as twisted val and more of the Bolbitis.

Both Congo fern and Anubias afzelii grow attached to wood and stones but they have slightly different requirements. Congo fern grows fully submerged, but the Anubias tends to grow near the waterline and I was told that it does best when it’s sometimes submerged and sometimes not. So I attached the Anubias on one end of the piece of bogwood I was putting in the tank with the Congo fern at the other. I placed the driftwood on an angle in the tank, where the Congo fern would stay submerged but where the Anubias would be out of the water every time I did a water change. For my tank substrate, I used Dalton’s aquatic mix with a fine gravel over the top. I usually use sand to cap the aquatic mix, but I used the gravel as I wasn’t planning to have any bottom-dwelling fish in the tank. The only species planted in the substrate was the Vallisneria. I added a couple of small plants of Indian fern as floating plants. Indian fern is far too big for a 55 litre tank – in fact it regularly outgrows my 400 litre tank. As plants mature, they also change their emergent leaf form. My usual strategy with either species of Indian fern, either the African species or the species found throughout Asia (Ceratopteris thalictroides), is to pull out the plants which have got too big or grown into the emergent form and replace them with new plants. Both species propagate themselves easily in my tanks so it’s no effort at all.

When it comes to replicating the correct water quality for biotope tanks, I’m usually a bit stuck. I have odd tap water – it has a pH of 8.2 but both GH and KH are in the “moderately soft” range. I’ve repeated the tests many times with the same result. If I put a lot of new bogwood into a tank, I can get the pH down to just under 7, but then it gradually rises again as I change the water. I’ve heard various opinions on whether or not I should do anything with my water, but the balance of advice seemed to be not to worry. So, apart from adding a bit of wood and leaf litter to the tanks, I leave the water chemistry be. Once the tanks are well-established, they maintain a consistent pH of 7.8. Fortunately, Norman’s lampeye is generally described as a species with a wide tolerance of water conditions. They were reported to like a little hardness in the water, so I added a small amount of crushed shell. I periodically add dead leaves to the tank as well, since any stream running through forest will end up with leaves.

Once I had my Volta River tank up and running, it quickly became one of my favourites. Although Norman’s lampeye are often described as quite a shy, skittish fish, mine quickly became very confident. The plants grew well and I’ve spotted eggs in the tank, but so far I’ve made no effort to remove the eggs and raise the fry.