Minecraft wiki entry for Elder_Guardian, associated text: 0–2 prismarine shards – always. Affected by Looting: 1 more drop per level, for a maximum of 5.
1 wet sponge – when killed by the player. Not affected by Looting.
One of the following:
1⁄2 chance: a raw cod (cooked cod if killed by fire‌[JE only]). Affected by Looting: 0–1 more drops per level, for a maximum of 4.
1⁄3 chance: prismarine crystals. Affected by Looting: 0–1 more drops per level, for a maximum of 4.
1⁄6 chance: no drop.
2.5% chance: a random fish. Affected by Looting: 1% more chance per level, for a maximum of 5.5% with Looting III. This drop uses the same chances that fishing uses, resulting in a 60% chance for raw cod, a 25% chance for raw salmon, a 13% chance for pufferfish, and a 2% chance for tropical fish.
10 – when killed by a player or tamed wolf.