Most sportfishing trips are available out of San Juan del Sur [1], an increasing number of Pacific beach towns, and along the Río San Juan [2]. There are also opportunities on the Atlantic coast, especially off the Corn Islands. Bonefishing in the flats around Little Corn Island is exciting, but you’ll have to have some idea of what you are doing, as experienced guides are limited.
There are freshwater fish to be caught in Lake Apanás and El Dorado in Jinotega, and of course, in Lake Cocibolca and down the Río San Juan.
Saltwater sportfishing on the Pacific coast is focused primarily on hurel (jacks), pargo (snapper), pez gallo (roosterfish), bonito, pez vela (sailfish), and dorado (mahimahi). All commonly reach sizes in excess of 50 pounds.
Off the Corn Islands, you’ll find kingfish, amberjack, red snapper, and barracuda. In the lakes, the giant freshwater bull sharks and sawfish are all but gone, but mammoth catch-and-release sábalos (tarpon), bigger than your mother and carrying up to 50 pounds of meat, are still abundant, as are robalos, guapote, and the basin’s newest invasive resident, tilapia.
Links:
[1] http://www.moon.com/destinations/nicaragua/southwest-coast
[2] http://www.moon.com/destinations/nicaragua/rio-san-juan/down-the-rio-san-juan