This is a configurable fishing mod. How it works is, whenever you would normally fish up a salmon item, it spawns a live salmon instead!
Guess what?
It entirely supports data packs! In fact, the entire mod uses a datapack for the item->entity conversions!
Place your jsons in a fishing folder and reload your datapacks to instantly fish new entities!
The json format is as follows:
{
  "input": {
    "item": "minecraft:tropical_fish"
  },
  "result": {
    "id": "minecraft:tropical_fish"
  }
}
That takes the minecraft:tropical_fish item and turns it into a minecraft:tropical_fish entity!
We can even do NBT for the entities as well!
{
  "input": {
    "item": "minecraft:tropical_fish"
  },
  "result": {
    "id": "minecraft:tropical_fish",
    "nbt": {
      "Variant": 117834241
    }
  }
}
That will result in a very specific tropical fish each time!
Also, if you want to override one of the vanilla ones, create your datapack with the namespace fishingreal and override either cod.json, pufferfish.json, salmon.json, or tropical_fish.json
