Can you have this fish in a 36gallon? Like say 5 of them?
no, they need like 150 or more
I think that might be a bit too small of a tank for them as they get 3-4 inches. I would say a 55g min for them to be comfortable. http://www.seriouslyfish.com/species/melanotaenia-boesemani/
agreed with el337 . 48 inch tank minimum.
I have read that they need at least a 4 foot long aquarium to swim.
What about dwarf neon rainbowfish? I read they get to 2.5", I too am curious of their tank space requirements
Those would work!
I've done quite a bit of research on the dwarf rainbows (praecox) and while seriously fish states they can get up to 3.2 inches in my research it seems they rarely get that size in aquaria and 2.5 to a little over that is more the norm. However, I've observed these little guys at my LFS quite a bit while contemplating purchasing some and seriouslyfish states they need a 24 inch tank. I personallywould not put them in anything smaller than a 30 inch tank as these guys are REALLY active and they get larger than the average tetra.
I considered them too but they're very pricey!
I wouldn't keep them in anything less than a six foot tank as they are so active. Mine used every inch of the tank when spawning which they did every morning.