At one point, I had a huge plecostomus living with my Malayan box turtle. The pleco eventually died of old age (turtle's doing great).
When I mentioned this to someone, remaking on the pleco's tendency to clean the turtle's shell, I was immediately chastised, and told that the pleco's tail can blind a turtle, so they should not be housed together.
Has anyone actually had this happen? Seriously? Because it seemed utterly ridiculous to me. Considering all the other sharp objects turtles live around in the wild, and the pokey bits of driftwood in the habitat, a pleco's tail seems like the least of my concerns.
