after reading this I kind of dont want to catch them.I think we may or may be able to tell from a closeup photo of the back of the pectoral spine - someone having this experience should advise because I've never tried it so I simply don't know.
On the other hand, you can tell by feeling the back of the spine. If you don't want to pester your pets, you could catch another one from the same body of water and check out its pectoral spines. Carefully. Let the fish exhaust itself from flipping and fighting because you don't want to get stubbed. It's not lethal but hurts pretty bad. Or wear a heavy leather glove on one hand, immobilise the pec spine, and feel with the other.
I wonder if the teeth serve the same purpose as used by Doradids in a scissor fashion - if your finger gets between the spine and the body, Doradids press hard the spine against the body, which also bears thorns, and the finger gets punctured in several places. If the fish tosses and rolls too, the puncture wounds get ripped also.
btw what kind of smileys does this forum have?kakashi? dragon ball?this one is awesomeballkick?? what