Histrix are good beginner rays but good luck finding one. You can get any of the peru brown rays to start with. The humerosa, yepesi sp, and motoros. Most rays labelled histrix are some varient of the above mentioned. With a tank your size, you will have no problems with any of the rays species. A couple can get to large for your tank but a ray that size will cost you about $5 a day to feed so you will probably get rid of it before that LOL! Stay away from tigers, flowers, or the small eyed rays as they can require a lot more attention in the beginning.