Make mine a Mexican!


We love a biotope here at PFK, so when we spotted David Nørholm’s spectacular firemouth set-up, we had to speak to the man behind it to learn more. 


Name: David Nørholm

Age: 36

Location: Mariager, Denmark

Occupation: Schoolteacher

Time in the hobby: 7 years

Current number of tanks: 2

Favourite ever fish: Altolamprologus calvus

Favourite ever plant: Nephrolepis exaltata (It’s emerged, I know) 

What would your dream tank be? A tank large enough to hold a small Caiman (crocodile).

PFK: Hi David, huge thanks for taking time out to tell us about your magnificent tank. What sort of set-up are we looking at here? 

DN: It’s an honour to share my aquarium in this great magazine! Well, first and foremost this is a biotope aquarium, and a biotope aquarium is a relatively close replica of an aquatic habitat — it’s a way of imitating nature and trying to get as close to it as possible. This obviously affects the selection of fish, plants, substrate, hardscape, and so on. It is a little slice of nature, if you will, where the fish and the habitat is in focus. 

How long has it been up and running for?

This setup has been running for almost a year now, with some changes to the scape underway.

Which part of the world is this biotope tank a replica of? Is it a specific river or pond? 

Both yes and no, actually. The basic idea was to replicate a river from Mexico, since both the firemouths, Thorichthys meeki, and the giant sailfin mollies, Poecilia velifera, that live in this tank are native to this area. I chose the Usumacinta River as the inspiration since both species should live there sympatrically — however, it’s debated whether they both live there or not. Some literature states that they don’t, and some local information states that they do. Nevertheless, the look and scape of the tank is still based on the river. 

How did you go about planning this tank? Where did you source your inspiration and biotope details? Did you sketch ideas down in picture form first, or did you just go for it? 

The researching process for a biotope setup is always both tricky and fun. It can be difficult to find useful information from a location and area, and it can be even more difficult to find pictures or video showing the specific habitat. For this setup I mostly relied on books and reports from experts in the area. 

For many of my biotope projects I use a couple of websites. I often visit, where you can find reports and research documents from many specific river systems in the Americas. For this setup I read a publication called ‘Rivers of Mexico’ from researchgate. 

In addition to this I also use the website, where you can look up specific plants and see if they live in a certain area. is the same system, just for fish instead of plants. Furthermore, I used the book ‘A Selection of Freshwater fish Biotopes in Mexico’ by Kai Qvist and Rune Evjeberg. 

With the geographical location in place, it was kind of easy to do the aquascaping. I was very much inspired by Lee Nuttall and his beautiful Central American biotope aquascapes. I try to be meticulous in the aquascaping process, since my goal is not only to make the aquarium as biotope correct as possible, but also to have it as aesthetically attractive as can be. Lee’s tanks are a great inspiration! 

Firemouth cichlids display to each other. 

How did you go about sourcing the right type of hardscape? Are these the types of rocks and wood that you’d find in the Rio Usumacinta? I notice that the rocks are all rounded, is there a reason for that? 

The hardscape material is based on various photos and video from the area. Most Central American rivers do basically look the same; a great number of rounded rocks, driftwood and sometimes leaf litter covering the bottom. Often these rivers have only sporadic (if any) plant growth. 

As far as my research went, the Usumacinta River and its sidearms are a classic Mexican and Central American river, with rounded rocks, so I replicated that. When it came to wood, I used three different types, which is actually a bit unorthodox since many aquascapers will tell you that you should stick to only one type. But I consider it more realistic to find various types of wood, roots, and twigs in a real river, since there are obviously many types of trees surrounding it. 

Tell me about the types of fish you’re keeping here. Are they naturally found together? Are there any other species you could have added as well? 

A couple of years ago I stumbled across a video of some sailfin mollies from a Mexican cenote. I was blown away by the beauty of this fish. I knew the sailfin molly by the name and the look, but I had never seen the wild type of it before — I had only seen the widespread, commercially bred types. As a sidenote it is still a mystery to me, why this fish is so popular in the line bred variants of  black, white, orange or even that terrible balloon type, and almost never sold in its beautiful yellow-blue wild type colours. After seeing this video, I instantly knew that I needed to keep them at some point. 

Firemouths are highly interactive.

A couple of years down the line, and some other projects later, I was starting to prepare for a Central American biotope, and I knew it was time to try the wild-type sailfin molly. The only problem was to find some suitable tankmates. As an aquarist my main interest is cichlids, so I wanted to find some cichlids to keep alongside the mollies. The requirements for the cichlid species were that it need to be able to cohabit with the mollies in the aquarium, and it needed to coexist with them in nature as well. 

Read the rest of the feature in the July issue, available to read instantly on our digital edition HERE  or purchase the print edition HERE.


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