And if you want to feel inspired, take a look at what Justin's done for his P. saulosi. Absolutely brillliant.
In a tank that size you are limited, for sure, but there are some very attractive options, too. I presume the footprint of your tank is 36" x 18". If that is the case then you could look at any of the following:
Lake Malawi:
- Species tank of any dwarf Mbuna. P. saulosi would be a great choice thanks to their sexual dimporphism.
- Species tank of P. demasoni. This one would be a lot more tricky than anything else I would recommend, and I think you should build up some experience first. The conspecific aggression displayed by these guys is astounding. For that reason you'd be wanting to start out with about 15 of them in that size tank, and prepare for a mild die-out before they stabilize. Saulosi would be a better choice for you, no doubt.
Lake Tanganyika:
- Shell-dwellers! These guys would be my number one recommendation for a tank your size (or any size, to be fair; they're my favourites). I suggest you have a good read up on them. There are some pretty big differences between the various species. My suggestion would be to read as much as you can, pick one species, and then work out if you can keep anything else with them (if you so choose). For example, my newest tank holds almost 300 litres, and the centre-piece of said tank is going to be a thriving colony of Neolamprologus multifasciatus - probably my favourite fish. I have the option of doing a community of tangs in there but I've decided to just go for the safe option of adding some Cyprichromis leptosoma "Utinta" to fill up the upper-levels with activity and colour.
Once you know which shelly you like, you can stock around their requirements. For instance, some of them (like Multies) exhibit alloparental traits and will breed in a colony, whereas others are strict pair breeders, and must be maintained as such. Some, such as Telmatochromis temporalis, are extremely aggressive and would likely dominate anything you could reasonably fit in your tank (Mbuna included). On the other hand, some are either extremely shy (N. brevis) and/or do not maintain large territories (Multies, N. similis, etc). The less aggressive guys can be kept with other fish from the lake, or even certain other hard-water fish (rainbowfish, livebearers, etc). If I was stocking your tank, I'd be tempted to go with:
6 Multies
6 Paracyprichromis nigripinnis
Start the shell-bed at one side of the tank - it should be at its densest at the side it starts at, then gradually thin-out around the centre of the tank. Leave a good-sized space of open sand which leads to some rockscape for the Paracyps. Be careful not to let your Multies' breeding get out of control, and make sure those rocks aren't too near the shells, or the Multies will eventually claim those, too. You can even keep plants in such an aquarium with relative ease although most don't because it's not 'authentic'. I much prefer the look of a planted tank, as such my shelly tank is going to be quite heavly planted. I'll be sticking a journal up on here in the coming weeks once it's underway.
There are other fish to consider from Lake Tanganyika which could be happily kept in your tank - do some research or fire some questions at me if I've piqued your interest.
Lake Victoria:
- Your only option here is a breeding group of one of the Victorian Haps (such as sp. #44). Aim for one male, three or four females and call it a day.
I'd definitely be looking at shellies, if I were you.