crabs, who goes...
If you chose to do cichlids, specifically african, you could create a masterpiece. Your crab, would prefer a little salt in his water and would readily accept african waters.
Slightly higher pH and a little saltier than most, but the colors and variety available is almost limitless.
You could infact, given the proper lid / cover , have an area at the top when mr crab can sit on the rock out of the water, for a more natural lifestyle.
Buyng juvenile cichlids allows them to grow up with each other and different species, thus producing a more tolerant individual.
"Loading" the tank with as many small ones as possible in the shortest period tends to make the community more compatible, and not as territorial.
- Have the tank cycled first-
Rearranging the rocks and caves frequently or when adding a new fish forces everyone to establish new "homes" thus taking the focus off the new fish. Feeding them first helps as well.
With numbers, fish tend not to be offensive, but rather defensive,which means it' s important to have caves, and more caves, and even more caves. As many hiding places as possible.
This "loading" also slows the growth process, although some fish will get bigger regardless and attempt to dominate. At that point, you must decide who to keep and who gets traded in.
This is part of the regular maintence of a cichlid tank. But the rewards in display and character is barely matched in freshwater.
Unfortunatly, there are a few of the spectacular africans that don't "color" up until maturity, but shouldn't be overlooked.
Outside of the cichlids, gouramis (larger), sharks, danios, kribs, could go with your crab, but know that no matter what u put in, it is always at risk, thus pay close attention to what and when you feed yer crab.
Remember he is a scavenger by nature, so don't make him hunt. Feed him 2 or 3 times per day, fast him once a week, and offer him, shrimp, krill, plankton, zucchini, bloodwords, and many other frozen foods. Ocean Nutrition makes an excellent sinking pellet that stands alone for food.
Hope this helps.