I have a male hystrix ray, currently about a 5.5" disk, give or take, in a 6 ft. 150. Male hystrix get a max disk of about 12"... one of the smallest rays you can get in the hobby. I got mine at about a 4.5" disk in March. His is doing really great. I give him shrimp on occasion, but he now greedily gobbles up sinking pellets. I got my ray from a guy on MFK who breeds hystrix (like with many other fish, the source is important... you start with a quality fish, your success rate improves). I do weekly water changes of about 30%, skimming off the sand on the bottom. I only have angels and rainbow fish in with my ray at the moment. I bought my ray after asking a million questions on MFK, and wanted a ray that could do well in a 150 if possible, and male hystrix was almost the unanimous suggestion. Of course, I'm not adding any monster fish to the tank, so the ray will have the heaviest bio-load. I am running an Eheim canister and 3 AC110s on this tank.
-Rich
