Most recent regrettable fish purchase was shrimp in my community tank. They multiplied like maniacs and there were males constantly frantically swimming around at top speed looking for females...not conducive to fish tank meditation. I literally gave a couple hundred of them away over 10 months, started with about 12. Took forever to get rid of them. They were also hard on some of the plants, scratching holes in them. If you could just buy a few all males or all sterile females, they'd be great.