minecraft-assets/assets/minecraft/models/item/fishing_rod.json

{
    "parent": "item/handheld_rod",
    "textures": {
        "layer0": "item/fishing_rod"
    },
    "overrides": [
        {
            "predicate": {
                "cast": 1
            },
            "model": "item/fishing_rod_cast"
        }
    ]
}