We have a 37gal tank habitated for about a month now. The lucky occupants are 6 tiger barbs (2 each of 3 color variations), 1 gold gourami, and 1 rainbow shark. I have it lightly planted with real and artifical plants. The barbs are each about 1" and the gourami and shark are about 1.5-2" lnog I would guess. I do want to leave room for these guys to grow. But was hoping to add a touch more variety. So I was curious how long it takes these 3 species to grow to full size. Right now I have about 10" of fish and would expect about 28" when they are fully grown. My goal in the end is to either find another species to get for the tank that will work forever, or a fish that has a short life span and will work now while there is plenty of space, and die of old age before the tank gets crowded.

I wouldn't add more fish. Many fish grow quickly, usually the most in the first year or two and when all your fish are fully grown I think you will be more than maxed out.

One option is a large, durable livebearer like a molly. Mollies have a lifespan of 1.5-2 years and with tiger barbs and gouramis, you wouldn't have to worry about future generations surviving. I believe that you do have some room to flex within. I would encourage adding some more types of small barbs. Odessa and Rosy barbs have a semi-aggressive temprament but stay about 2-3 inches. If you had a school of three to five, they would look quite nice.

Sorry, I just realized I read your first post wrong, somehow I added more fish to your list, sorry about that. My only concern is that your tank is a bit small for the rainbow shark as they need space to swim. In terms of bio load I think you could add at least a couple more fish without a problem, perhaps a school of corys for the bottom.

Thank you for the replies. So far the rainbow shark has plenty of space to swim, though he spends alot of time hunkered down in his cave. We do realize he will out grow this tank sooner or later though. I had thought about corys, but wasn't sure they could survive the aggression of the shark.

I read somewhere that they make good tank mates, but I just googled rainbow sharks and they really don't seem like they should work together. It might partly depend on the personality of your shark but only larger tank mates seem to be recommended.

In my experiences a Rainbow/Red Tail/Albino Shark will not bother cory's.

If it were my tank I would add a Dwarf Cichlid or two. Mikrogeophagus ramirezi (German Blue Ram) are very colorful and stay small. Average life span of the species is two years.

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I really like rams too, I thought they lived for more like 3 or 4 years though.

Hmm, the Rams are an interesting idea. They would definetly add some variety for our twin toddlers to look at. However, will they be able to deal with the tiger barbs?