What Is Wrong With My Fish's Gills?

Did the gills become mottled, or blotchy in appearance?

Are the gills of your fish swollen and pale, fish may be brushing and rubbing against objects in its environment?

Did the gills become rotted and eroded, fish may have lost appetite?

Are there any tiny gas bubbles in your fish's eyes, fins, and gills?

Is the damage of your fish's gills extensive, fish may look thin and sickly?

Branchiomycosis affects the fish's gills by causing them to become mottled, or blotchy in appearance due to the dying tissue. For this reason, it is also known as "gill rot." There may also be traces of gray on the surface of the skin. The infection begins in the gills and, if not interrupted, spreads out to the skin. The infected fish will become lethargic and will eventually suffer severe respiratory problems, including hypoxia, which can lead to death. Unfortunately, recognition of branchiomycosis often comes too late, as fish are discovered to have branchiomycosis only after they have died due to hypoxia.

Dactylogyrus is a gill parasite that most commonly infects koi, discus and goldfish, and appears like a small worm under the microscope. Infected fish display such symptoms as swollen and pale gills that make breathing difficult for the infected fish. A fish with dactylogyrus will try to remove the parasite by brushing and rubbing against objects in its environment. After quarantining the infected fish and thoroughly cleaning the fish's environment, the water of the tank, aquarium, or fishpond should be changed and treated with formalin and praziquantel. These medications will kill all parasites, their eggs, and their larvae.

Bacterial Gill Disease attacks fish’s gills, causing them to rot and erode.

Gas bubble disease usually occurs in cold water systems. When the water in the tank, aquarium, or fishpond has an abnormal amount of dissolved gases (i.e., nitrogen, argon, carbon dioxide), fishes can develop gas bubble disease. This occurs when the water is heated up too quickly or because of a faulty pump – pulling air in with the water – in aquariums or tanks; it can also occur if there is heavy algal growth in ponds. Fishes affected with this disease develop tiny gas bubbles in their eyes, fins, and gills. It can then be treated by blowing excess gases out of the water through forceful aeration – stirring up the water – and by fixing any faulty equipment.

Hydrogen sulfide toxicity can be fatal for fishes. Hydrogen sulfide (H2S) is a gas that forms in aquariums or ponds when certain bacteria feed on organic debris in the areas of water that are low or depleted in oxygen. In large amounts, H2S is toxic and is identified by a strong sulfurous smell coming from the water. Fishes with long-term exposure will become thin and sickly, and develop extensive gill damage. Treatment for this particular toxicity involves keeping the water clean of all debris and aerating the water.

Carbon dioxide toxicity occurs when the carbon dioxide concentration in water is more than 20 mg per liter. The pH of the water becomes acidic and thus toxic for fishes. Fishes with carbon dioxide toxicity are unresponsive to stimulus and lethargic. The treatment involves forceful aeration – stirring up the water – to blow out excess carbon dioxide into the atmosphere and increase the water's pH level.