minecraft-assets/data/minecraft/loot_tables/entities/salmon.json

{
    "pools": [
        {
            "rolls": 1,
            "entries": [
                {
                    "type": "item",
                    "name": "minecraft:salmon",
                    "weight": 1,
                    "functions": [
                        {
                            "function": "furnace_smelt",
                            "conditions": [
                                {
                                    "condition": "entity_properties",
                                    "entity": "this",
                                    "properties": {
                                        "on_fire": true
                                    }
                                }
                            ]
                        }
                    ]
                }
            ]
        }
    ]
}