While they could be any number of species, most likely they were either Tarpon or Barracuda. If it was around dusk, then most probably Tarpon. Neither Tarpon or Cuda are anything to be concerned about when swimming. Tarpon are absolutely timid and harmless and have no teeth. Barracuda have a reputation (undeservedly, IMHO) of being aggressive but I've been scuba diving and snorkeling around them and never had a concern. In fact, I head-butted a 4 foot Cuda once when diving off a boat of Creole Rock. He gave me an indignant look then swam off into the blue. The only concern with Cuda is they are attracted to bright, shiny things and may snap at something they perceive as 'prey'. They have some pretty fearsome-looking teeth and could do some damage if they latched on to you. Just respect the ocean and the creatures in it - it's their home and we're just visiting. If you go swimming, leave your 'bling' back on the beach or better yet, at home.

Cuda are not edible in these parts (generally 35 deg N to 35 deg S) due to the high risk of Ciguatera poisoning. Tarpon are generally not good eating, though some people use them for fish stew/soup. They have a lot of small bones and the meat is oily, besides, they will feed on garbage and often live in the most brackish water. Good to catch though! Great sport on light tackle as long as you can get them out in the open.