renewable-resources/data/minecraft/loot_table/gameplay/fishing/fish.json

{
  "type": "minecraft:generic",
  "pools": [
    {
      "rolls": 1,
      "entries": [
        { "type": "minecraft:item", "name": "minecraft:cod",           "weight": 60 },
        { "type": "minecraft:item", "name": "minecraft:salmon",        "weight": 25 },
        { "type": "minecraft:item", "name": "minecraft:tropical_fish", "weight": 10 },
        { "type": "minecraft:item", "name": "minecraft:pufferfish",    "weight": 5 }
      ]
    }
  ]
}