Additional amounts are produced from decomposing fish food, fish waste and detritus. The effects on fish health Raised levels affect fish health in several different ways. Prolonged exposure to sub-lethal levels can lead to skin and gill hyperplasia . Gill hyperplasia is a condition in which the secondary gill lamellae swell and thicken, restricting the water flow over the gill filaments. This can result in respiratory problems and stress and as well as creating conditions for opportunistic bacteria and parasites to proliferate.
Elevated levels are a common precursor to bacterial gill disease.
Fish response to sub lethal levels are similar to those to any other form of irritation, i.e. flashing and rubbing against solid objects. Without water testing it would be very easy to wrongly conclude the fish had a parasite problem. Gill Hyperplasia click on pictures to enlarge them Fish gill with hyperplasia. The gill filaments are swollen and clumped together, reducing the fish's ability to 'breath'. Elevated levels can also lead to ammonia poisoning by suppressing normal ammonia excrement from the gills.