I suppose this could be young barracuda, but there are a number of fish that will nip especially if people are trying to hand feed them on the beach. I have had my mated pair of clownfish in my reef tank at home nip my fingers when feeding time comes around, but not to the point of drawing blood. All marine fish have small teeth though some fish like Parrotfish actually have a beak that they use for scrapping algae from rocks. If the bites actually drew blood and the wounds are 'V-shaped' then smaller barracuda fry could be the culprit (though larger barracuda attacks upon people are very, very rare).