The Impact of Cotton Mouth in Fish

Deadly

• Like many fish diseases, cotton mouth is unsightly, but its impact goes far beyond cosmetic damages. The disease will result in the death of your fish if left unchecked. Before killing your fish, cotton mouth often leads to nasty lesions that spread across your fish's body, while cottony spots usually appear on and erode your fish's mouth. The disease often infects and eats away at your fish's gills. The subsequent wounds enable fungi and other types of bacteria that are present in your tank to enter the wounds and cause fungal and additional bacterial infections, which can lead to other symptoms and hasten your fish's death. If your fish's gills become infected, he'll find it difficult to breathe and will eventually suffocate.

Contagious

• Cotton mouth is extremely contagious. If one of your fish comes down with the infection, bank on the disease also affecting your other fish. Because of its communicability, one fish who suffers from cotton mouth can lead to the death of all your fish in the tank. The disease can wipe out a large number of fish in just a few days. On the plus side, cotton mouth affects only fish; it does not affect snails, shrimp or other aquatic life.

Prevention

• While columnaris bacteria are normally present in a freshwater tank environment, a fish's immune system typically swats away the bacteria. But when a fish suffers from stress, his immune system becomes less effective, enabling the bacteria to set up shop, resulting in cotton mouth. Preventing the disease calls for preventing your fish from becoming stressed. Test your water once monthly to ensure your water parameters, such as ammonia, nitrates and nitrites, are within a safe range. (Pet stores and many retail stores sell water tests.) If your water parameters are not within a safe range, change between 20 and 40 percent of your water daily until they return to normal. Otherwise, changing out 20 percent of your tank's water weekly usually keeps water parameters in check. Research every fish thoroughly to avoid overfeeding, underfeeding, overstocking and grouping together incompatible fish. Too much commotion near the tank, such as a child tapping on the glass, and wildly fluctuating temperatures can also lead to stress. If you have tropical fish, a heater keeps temperatures consistent, while a chiller may be required for a cold-water tank.

Symptoms and Treatment

• If cotton mouth plagues your fish, you'll see patches that vary in color, from yellowish-brown to gray to white, spread across your fish's body. The patches often resemble a cottony growth. In just hours the patches can develop into lesions and appear to be eating through your fish. Affected fish often gasp for air because the disease erodes their gills. Cotton mouth is sometimes confused with an infection of Ichthyophthirius multifiliis, more commonly known as ich, but ich results in cottony dots much smaller than the patches cotton mouth causes, and those dots do not eat away at your fish. Cotton mouth is treatable, but the prospects for successful treatment drop quickly if you don't catch the disease soon after it infects your fish. Blue Ridge Fish Hatchery suggests using an aquarium antibiotic. Columnaris bacteria are gram-negative, so ensure the antibiotic is effective against gram-negative bacteria, and always follow the manufacturer's dosing recommendations.