Currently not working on this, will revisit later.
BlastFishing is a highly customizable plugin that adds fishing with TNT in Minecraft. Simply drop it into your plugins folder and you're ready to go!
Submerge the TNT into water in order to begin fishing!
BlastFishing allows you to customize its loot table, as well as the number of items that spawn in. Want a small chance to earn a diamond when TNT fishing? BlastFishing makes it easy!
Plugin on Spigot (1.12.x):
https://www.spigotmc.org/resources/blastfishing-fishing-with-tnt-customizable.54541/