What is the Brook Trout Gill Bug, and how do I treat my fish?

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Answered by: Chyanne, An Expert in the Fish Facts and Profiles Category
Pennsylvania has a long history of fishing in our wonderful freshwater streams. The natural limestone in the state protects the freshwater inhabitants from the harmful effects of acid rain. These slightly basic streams also make wonderful habitats for the brook trout,that is Pennsylvania's state fish. Unfortunately, this fish's health and its populations are suffering from a much different offender then acid rain.

All About The Brook Trout Gill Bug?

The gill bug is a parasitic copepod that starts out as a sack of fertilized eggs on the floor of an infected stream. It then has a 24 hour free swimming period where it must find a host, which are our poor brook trouts. At this point, it must attach to the tip of the gill filament and inserts a hook that is twice as long as the bugs own body, which is approximately 2cm. Here it will live out the rest of its adult life creating its own sac of eggs. Where eventually, it will detach them into the water. Since, the bug's hook is so deeply embedded into its host, it will not fall off but rather stay attached until the fish dies or the gill itself is removed.

Is The Brook Trout Gill Bug Harmful?

It depends on the size of the trout but generally speaking, yes gill bugs do harm brook trout. If the trout is smaller than 10 in the bug will get caught on the gill rakers and the fish will simply ingest the bug. If a gill bug does attach, it causes redirection of blood flow and death of the surrounding gill tissue. You can physically see this is happening when the gill tip near the bug turns white instead of pink. If the infestation is too serious, it will cause suffocation and the fish will die.

Is There A Cure?

No, unfortunately as of today, August 25, 2016, there is no known cure or this treatment that is approved by the FDA for gill bugs on the brook trout. A lot of these fish live in the wild and are difficult to obtain. There are no practical ways to safely treat these fish, however, hatchery fish are easy to obtain and are used to stock streams. It is important to consider the fact that it is easy to treat them in a controlled setting. Hatcheries are a source of disease propagation. Taking action in a hatchery would be a great way to prevent spreading into clean streams.

Potassium Permanganate, however, may be giving hope to our little brook trout yet. It is found in many freshwater clarifiers and has shown interesting results on other fish illnesses. It tends to kill water parasites by oxidizing the exoskeleton of the bug, which only happens if used in slight excess. As a side effect, it has successfully treated ich, which is a common aquaria pest. Since, many fish have a protective slime layer they are not affected by this chemical as easily. This purple water clarifier may be relabeled soon, at pet stores near you.

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