I stayed in Cayo Santa Maria for 7 days a couple years ago. Beautiful beaches, and the hotels are all fairly nice and new. It's an area created for tourists, and you wont find anything that's authentic Cuba.
The most prized catch from shore in the area is barracuda. But there are lots of small feeder fish that you can catch. No idea exactly what they're called. I heard of a couple shark being caught too.
The resorts and locals have the worst fishing gear you have ever seen. Your only option is to bring your own gear. I don't fly fish, but I'm sure you can do well on a fly. Spoons and spinners should work too. I did see hotel workers floating fish guts and doing well for the small feeder fish. First light is best in the crystal clear water. If you do catch a fish, let the locals eat it.
You can also take guided fishing excursions, but it's quite expensive, 225 CUC from what I remember. And if you get a chance to do a jet boat tour through the mangroves, do it, it's awesome.
The mission of the hotel workers is to take every dollar from your picket before you leave. Few tips I can offer. Make friends with one bartender, and one beach staff member. Tip them well the first day, 5-10$ each. And tip your chamber maids the first night too. And don't buy anything from the hotel staff. They try to sell you fake cigars, booze, cigarettes, etc.