Fin Rot

What is fin rot

Fin rot, a common problem in aquarium fishes, is not a disease by itself, but a symptom of an underlying condition where the fins and tail become worn out or ragged ^[1,3]. Also known as tail rot, it can affect any aquarium fish, though certain tropical freshwater and saltwater species have a greater risk of attaining fin rot than others ^{[1, 2]}.

Which fishes are more likely to get it

Freshwater fishes

• Betta (half moon, crown tail, veil tail)
• Goldfish (pond fish)
• Koi carp (pond fish)
• Angelfish
• Arowana
• Black molly
• Guppy (rainbow fish)
• Neon tetra
• Cory catfish
• Cichlid (Oscar, flowerhorn, African)

Saltwater fishes

• Clownfish

Signs and symptoms to look for in a fish with fin rot

Keep a close eye on the tail and fins of your pet fish to detect any signs of fin rot at the earliest. Infected fins have one or more of the following characteristic symptoms:

• White milky patches on the edges (initial stage) ^[17]
• Tiny holes  ^[5,16]
• Ragged, frayed and tattered appearance ^[5]
• Dark, discolored look and thin texture ^[17]
• A worn out look, becoming as short as a stump along with red streaks and bloody patches (severe stage) ^[1]

Besides the changing texture of the fins, fishes may even appear lethargic, while in severe cases they may have abdominal swelling and body ulcers ^[1,2].

What are the causes of fin or tail rot

Fin rot may occur due to a single underlying condition or a combination of many. Though an aquarium contains a lot of good bacteria, unhealthy living conditions lead to bacterial and fungal infections, resulting in rotten, ragged or patchy fins ^[1,3]. Some of the common causes of fin rot are:

• Bad or unhygienic water conditions that weaken their immune system, making way for any harmful bacteria to affect them adversely ^[3].
• Low temperatures within the aquarium, leading to stress in your fish ^[6].
• A crowded fish tank or nipping and fighting between the aquarium inmates, increasing the chances of bacterial infections.

Sometimes, fishes suffering from fin rot may aggravate their condition further by scratching themselves against decorations or edges of the aquarium, making it possible for more bacteria to enter into their wounds ^{[1, 3]}.

How to prevent fin rot

Correcting the environmental conditions by maintaining proper hygiene is one of the best ways to prevent an onset of fin rot.

• Change about 30% of the tank water on a regular basis ^[3].
• Clean all the decorations and rocks with proper cleaners ^[2].
• Give as much food your fishes can finish as excess amounts may result in leftovers crowding the tank ^[2].
• Maintain the pH value between 7 and 8 in the tank, as an increase may damage or break down the tissues in the fins ^[1,3].
• Prevent overcrowding the tank and keep a check on fin nippers like tiger barbs, black widow, and serpae tetras to make sure they are not hurting each other ^[4].
• Maintain a stable water temperature between 75°F and 80°F ^[10].

Treatment to stop fin rot in betta, goldfish, angelfish, koi carp, arowana and other fishes

Earlier the detection, greater the possibility of curing the problem by treating the underlying cause. The environmental factors that may be responsible for triggering fin rot need to be corrected first ^[7].

How to treat fin rot at home

Regular maintenance of the aquarium

Clean the aquarium water thoroughly by removing any food debris or lumps of dirt from it as well as washing the rocks and decorations using hot water. Changing the water is also essential, but there is no need to change the entire water; replace only 20% to 50% of it to prevent contamination by the scraps of food and feces ^[2,7]

After changing the water, test it to ensure that the pH value, ammonia, and nitrates are all in proper balance as sometimes healthy fishes may acquire fin rot post a water change ^[1]. For the same reason, the problem may occur when you accommodate a fish in a new tank.

Seclude the infected fish

Separate the infected fish to a quarantine tank or a tub having the same water temperature as that in the aquarium. It helps you to closely supervise any progress in the symptoms ^{[4, 5, 8]}, apart from preventing the condition from spreading. Moreover, certain medications may also be harmful to other fishes and some plants thriving in the main aquarium ^[5].

Treat with salt water

Saltwater, because of its antiseptic properties, is an effective way to treat mild fin rot. Isolate the sick fish to a tub or quarantine tank filled with tap water having a temperature similar to the water in the aquarium. Fix a heater in it with the temperature between 77°F and 78°F ^[8].

• Mix about one (mild fin rot) to two and a half teaspoons (moderate fin rot) of salt (aquarium, kosher or rock salt) in a jug or glass [20].
• Once the salt dissolves, add it slowly to the quarantine tank in small quantities over the period of an hour.

Change the water after 24 hours and repeat the same method with fresh water. Make sure to replace 100% of the water before adding more salt. After repeating this salt water bath for about a week, there should be an improvement in the condition. Once you find your fish recovering and its fins growing back to normal, you can move it back into the aquarium.

Apply hydrogen peroxide

Another effective home remedy is to apply hydrogen peroxide on the sick fish.

• Dip a Q-tip into a solution of hydrogen peroxide and dab it gently on the affected area.
• After patting the fins dry, you may apply an anti-bacterial cream, but only after talking to a fish vet ^[13].

Medicines to treat fin rot

If fin rot is not getting better after trying all the initial remedies, consult a vet, who may put it on medications.

Since fin rot is mostly caused by gram-negative bacteria such as Pseudomonas and Aeromonas, gram positive antibiotics may not be effective in treating the condition ^{[6, 22, 23]}.

The common medications used in treating fin rot include erythromycin, maracyn I and II, chloramphenicol, melafix, and tetracycline ^[9]. However, it is always best to consult a vet first who would decide the appropriate medication and its dosage.

Alongside the medicines, you can alternatively add Methylene blue to the aquarium water (one drop for two gallons) and carry this remedy for a week. Make sure to change half of the water every alternative day ^[10].

Can you cure fin rot

With early intervention, fin rot can be cured completely, but a delay in starting the treatment may cause permanent problems, and even prove fatal for the fish.

How long does it take for fin rot to heal

The recovery time depends on the severity of the problem as well as how early the underlying condition causing fin rot is treated. Mild to moderate fin rot would heal within a couple of months with proper care ^[1,12].

Will the fins grow back

When addressed at the earliest, the affected fins do grow back, though it might take some time ^[12]. The new fins would have a thin texture, in the beginning, gradually attaining its original thickness and color ^[18,19].

Is fin rot contagious to other fishes

Though fin rot is not contagious, the sick fish should not be kept in the same tank with the healthy ones since the latter may get stressed by the contaminated water conditions, developing a weak immune system. Hence, they may also develop higher chances of getting fin rot as the condition is caused by opportunistic bacteria that target physically weak fishes ^[5,7].

Is it contagious to humans

There are no reports of humans contracting any bacterial problem from handling sick fishes. Still, it is important to wash your hands properly with disinfectant soap after touching the fishes, or their aquarium contents.

In case of extreme fin rot, medicines may not work, lowering the life expectancy of the fish, sometimes killing them within a few weeks. Some owners even prefer euthanizing their fish when the condition gets too bad, making the fish unable to swim due to lack of fins.