def a red tailed shark and i agree with gourami swami and buggy - maybe the colors on your monitor are messed up if you see a yellow tail... some have an orange hue more than red tho - here are some pics to show this and to confirm this is indeed the fish you are referring to:
http://www.dkimages.com/discover/Hom...k-Shark-1.html
http://commons.wikimedia.org/wiki/Im...lack_shark.jpg
it would do well with other aggressive fish so that he can't bully them such as tiger barbs but the list of fish you have in your sig (esp the 2 otocinclus & rainbows) might suffer a bit however, I have known tetras to hold their own vs this species so it would be a hit-n-miss in your tank. These red tailed sharks can get up to 6inches long and are sort of deep bodied at this size so consider that as well - they seem to be less aggressive in an aquarium size of 40+ - and are happiest with plenty of hiding spaces like caves or logs - something they can call their own. They are bottom feeders due to their mouths being underslung so brine shrimp pellets and sinking wafers and an occasional vegetable like zucchini is a nice varied diet.