Why do sea lice never attack fry or parr?

Sea lice prefer to attach to larger, more mature fish, as fry and parr are typically too small and have less surface area for the lice to latch onto. Additionally, younger fish often have a more robust immune response, which can help them fend off parasites. The habitat and behavior of fry and parr also make them less susceptible to sea lice infestations compared to larger, slower-moving fish.