Fish Lice can become a major threat to your koi pond, water garden and are very common in ponds and water gardens in the fall of the year.
Fish lice are big enough to see with the naked eye. Many fish keepers think their fish have freckles until they see the “freckles” move from one location on the body to another. As juveniles fish lice are very small, however, fish lice can grow as large as a fourth inch round in size.
Fish lice will move around the fish’s body injecting it’s stinger into the body, sucking out body fluids. This constant piercing of the skin causes inflammation.
However, the biggest threat is, as the fish lice move from one location to another they leave a hole in the protective slime coat and skin. These “holes” give the opportunistic bacteria such as Aeromonas or Pseudomonas which are one of the biggest causes of deadly ulcers(body sores) to invade your koi and pond fish.
Fish lice are egg layers. They mate on your fish and then lay their eggs on plants and other objects in your pond. Eggs can last through the winter and hatch in the spring as the temperature rises.