Pictured below are the bony structures of the Synodontis catfish. Checkout the long bony first ray of the dorsal fin. It’s like a lance and can penetrate any soft tissue readily.
Checkout the serrated first ray of the pectoral fins! Looks like a spear that only goes in one direction!
All these bony structures can be locked in place and provides the gentle fish a defence mechanism. This is the reason many predators leave them well alone; and this is why we must take care when handling them.