A total of 82 species of fish from 30 families have been identified in the Golfo Dulce. The waters off of the small towns of Puerto Jiménez, Golfito and Zancudo abound with sail sand marlins. Inshore, one can find jacks, runners, mackerel, amberjack, roosterfish and large snapper. The Golfo Dulce, with its profusion of small coves and rocky islats and shoreline, is also excellent for small barracuda, snapper and corvina (sea bass). Snook there sometimes weigh in at over 40 pounds. Inside the Zancudo peninsula, and farther north, at the mouth of the Esquinas river you can also find great places for snook.
Please read here for the first preliminary analysis of the fish species of the area:
http://link.springer.com/article/10.1007%2Fs11273-010-9183-1#/page-1