This chance is increased by 1% per Looting level, for a maximum of 5.5% with Looting III.

When killed by the player Guardians have a 2.5% chance of dropping a random fish as an extra drop in addition to the normal fish drop. An additional 0-1 drops are added per level of Looting for a maximum of 4 prismarine crystals with Looting III. 40% chance of dropping prismarine crystals.An additional 0-1 drops are added per level of Looting for a maximum of 4 cod with Looting III. 40% chance of dropping a raw cod ( cooked cod if killed by fire‌ ).Looting increases the maximum prismarine shard drop by one per level, for a maximum of 5. When killed, guardians always drop 0-2 prismarine shards. Guardians spawn in between Y=39 (floor of the ocean monument) to Y=61 (1 block higher than the topmost block of the monument). Like all structure spawns, guardians belong to the cave cap. If their sky access is obstructed by a solid block, the guardians spawn significantly faster. They spawn on the northwest corner of the spawning spot block, meaning they can spawn inside of a portal and get instantly sent to the nether. The x-coordinate of each spawning spot is X+2, X+13, X+29, X+45, or X+55, where X is the western edge of the monument. In Bedrock Edition, guardians are structure spawns, spawning on 25 pre-determined spawning spots. Guardians will spawn even if the monument has been destroyed by the player. Specifically, spawning fails 95% of the time if the spawning water block is below sea level (Y=63 by default), all blocks between the spawning water block and sea level are liquid or fully transparent, and the block at sea level has a view of the sky. In Java Edition guardians spawn less often in ocean open to the sky than they do in covered areas (such as inside or underneath the monument). Specifically, they can spawn only if the spawning block and the block below the spawning block are both water (regardless of stationary water or flowing water). Guardians spawn naturally in ocean monuments.

Michigan data guardian