Having already mentally selected several fish I had seen while scuba diving, this initially felt like a bit of a let down, but realising that I could actually create a whole new environment, without bias.

With this new blank canvas approach, the tendency was to accelerate in and fill the tank.

As this was a wall mounted tank, I had to slow down as this required that the wall be re-enforced to take the weight of 30kg of water and equipment. So I began planning from scratch...

Dividing the tank into layers, we have the top portion (like open water), the middle portion (just above the rocks), and the bottom portion (bottom dwellers). (I'm sure aquarium experts would give them better names).

With the particular tank, we could not have interstitial sediment dwellers  (i.e. living in the sand), as the tank did not support sediment, but instead used a special course gravel which could not fall down through the aluminium mesh and block or damage the heaters and filtration equipment.

Dimensions are important in this tank. Animals that are too small (or have small offspring) may risk falling through the gravel and the metal mesh, and onto the heater. Animals that are too big will have limited or no space in which to swim, and animals that start small and grow well could be fine at first, and then become restricted and struggle to move.

With the tank only being a few inches depth, smaller fish bigger than 0.5cm, but smaller than 7-8cm length when fully grown, seem to be be the obvious conclusion for my tank.

Had it been a marine tank, one of my choices would have been the Percula Clownfish or the Ocellaris Clownfish (their near identical cousins), made somewhat more popular through the Pixar film, Finding Nemo, who live best in mated pairs, with them being fairly active, colourful, and fun to watch, and moving in and out of the rocks and anemone in the middle layer just above the bottom. Regal Tang and Powder blue Tang, both stunningly beautiful fish were further choices for fish liking the middle and open water layer, and hermit crabs and starfish liking the gravel layer.

Fresh water fish and marine fish look and behave differently.

For a start, freshwater fish don't drink. They just absorb it, and work hard to not take pass it back out. Marine fish have to take in sea water and process it. As a result, their physiology and shapes are different. Their colours are radically different. Freshwater fish, from rivers and lakes are lucky in that nutrients are more readily available. Most are black or muddy coloured in part or full to help them hide or blend in to their environments. Tropical marine fish are famous for their variety of colours and shapes, used to attract their partners in a fiercely competitive environment.

Some freshwater tropical fish appear more ornamental. Larger tails, with more flowing fins such as on the Betta Splendens, more commonly known as the Siamese fighting fish.

Light in freshwater is different than in sea water. We do not associate the rich blue water colours with lakes, but instead see this as a darker more black, brown and white. (This is due more to effect of the masses of materials in suspension in freshwater lakes and rivers, rather than the salinity)

So the varieties for freshwater, even the diverse tropical Amazonian river species, did not appear to be as colourful or varied.

The next step was to make some big choices...

To be continued...