I've heard it before but I'm finding out the hard way that fish teeth and/or spines can and will puncture the inflatable tubes of a RIB. In my case I can't be sure if it was the teeth or the dorsal spines, but I had two tiny punctures about 1/2" apart.
On my boat the tubes are PVC. Punctures are not difficult to repair, but good prep work is a must for a solid repair and can be time consuming, and a boat full of patches is not a pretty sight. Essentially a patch is glued on to repair a puncture. I found some good glue at a local RIB repair shop, $40 for a small can with a tube of curing agent. Used carefully this glue will last for a few small repairs. The white PVC material is surprisingly expensive.
I'm also posting this as a heads up for anyone coming on my boat to handle fish carefully. Most fish have strong sharp spines on their dorsal fins. It is best if they're dispatched in the water and go directly from the water into the cooler. One of the disadvantages of a RIB I suppose.