Identifying Disease In Aquarium Fish

Tropical fish may seem uncomplicated creatures that are happy to swim around as long as the water conditions aren’t too bad, but in fact they can get pretty sick. While an ornamental fish won’t tell you that he is sick, his behaviour will make it clear. And hopefully learning to identify the signs of disease in marine and freshwater fish means you will be able to provide treatment.

How To Tell If Your Fish Is Sick

It is true that fish aren’t the most communicative creatures, however they do have ways to tell you when things are not alright. Sick fish will look and behave unusually, which means if you are used to looking at your fish you will be able to spot the first signs of disease quickly, and act accordingly. Not all changes in behaviour imply that your fish is sick (you could even have a very healthy breeding pair in your aquarium!) but the following are some things to look for:

  • Clamped fins: The fins are held close to the body, or the tail is not fanning out
  • Gasping in the surface for air, or breathing heavily
  • Rubbing or scrapping against the walls or decorations
  • Swimming erratically, loss of equilibrium
  • Hiding or staying away from other fish
  • Not eating: Particularly important if the fish is not new to the fish tank
  • Sluggish swimming, lethargy

Also, any fish that suffers from paleness or sudden color changes, spots on the body or growths should be looked at in more detail. If your fish’s scales look like they are raised or fuzzy, or sores and ulcers are present, your fish is most likely sick. Grey or white discolouration usually means some sort of opportunistic bacterial infection is attacking your fish.

Keeping an eye on the behaviour and appearance of your fish is an important part of keeping a healthy tropical tank, and the easiest way to do this is at mealtimes. When you feed your fish they should be highly active and enthusiastic, and it gives you a perfect chance to check how they look. Feeding time is also a perfect time to evaluate whether some of your fish could be bullied by more vivacious tank mates.

I Think My Fish Is Sick, What To Do?

The first thing to do if you believe your fish is sick is identifying whether it is a tank-wide problem, or something only affecting a particular fish. Check out the water parameters with a good freshwater aquarium testing kit, and make a water change if necessary. Bad water conditions don’t usually make all your fish sick at the same time; some will be more sensitive and stress our more than others. For example, Discus are much less hardy than other more beginner friendly fish. So just because not all your fish are refusing to eat it doesn’t matter the water is fine. Always test the water before doing anything else.

Most fish sickness are related to stress. Bad living conditions cause fish stress. Aggressive tank mates cause fish stress. A dirty tank causes fish stress. Low quality food causes stress and weakens your fish. If a fish is stressed out, it will get sick, as parasites and bacteria overpower its weakened immune system. A fish that is seemingly very sick can recover overnight when the circumstances around him that were causing stress are removed.

As a fish keeper, you have a duty to keep your fish healthy and happy providing them with the right living conditions and a safe environment. This will keep your fish and your aquarium looking great, and save you a lot of money in fish medicines and fish stock. And it only takes a short while once per week to perform tank maintenance.

Quarantine Tanks

A quarantine tank is a regular fish tank, usually smaller than your main one, dedicated exclusively to keep fish in isolation when they have just been purchased or when they look sick. Having a quarantine tank will allow you to ensure new fish stock is not sick (happens more often than one would think, even when buying from reputable fish stores) and in case a fish is sick it allows you to provide treatment without affecting the water quality of the main tank.

Quarantine tanks (or hospital tanks) are the perfect place for new acquisitions to recover from the stress of moving to their new surroundings, and can be used to effectively treat fish with medicines or changes in water temperature without affecting other fish in your main tank. It is not designed as a long term residence, so you can keep it barebones in order to make it easier to clean it up. Water quality should be kept at its absolute best, and some people swear by using RO water with aquarium salts on their hospital tanks.

If your fish is still sick and the water parameters look normal, move it to the hospital tank and check him out in more detail to try and identify the disease that may be affecting him. This is usually much easier when the fish can’t hide among the decoration of a regular tank. Take a look at your fish symptoms to try and identify the most likely culprit, or take a picture and take it to your local fish store (or trusted aquarist forum) for a second opinion.

Fish Medications

Cichlid affected by common Ick who may need white spot medication
Cichlid affected by common Ick who may need white spot medication

There are many different medications to treat fish internal and external infections and parasites. The reason why they should only be used as a last resort is that some of them can be toxic to the rest of inhabitants of your aquarium (hence the usefulness of a hospital tank) and most will degrade the water quality significantly.

Medications aren’t easy on fish, so it’s better to only use them when you know for sure what is affecting it. Otherwise you run the risk of weakening your fish further, and worsen the problem by exposing it to secondary opportunistic infections. Just remember how you felt after your last course of strong antibiotics… meds aren’t easy on anybody.

A hospital tank should be run without a carbon filter, as the carbon filter would remove the medications from the water right as you add them.

Before using any medication on your fish, it is worth trying less aggressive remedies such as aquarium salt. Aquarium salt is designed for freshwater aquariums, it is not ocean salt, and it is not suitable for all types of fish but can be very helpful to help heal guppies and other life bearers.

Read the usage instructions before using any medication, and follow the instructions to the letter. Pay particular attention to any contraindications, as some are highly poisonous to some fish and invertebrates. For example, copper can kill snails and other invertebrates, and species such as loaches and other scaleless fish may need a reduced dose due to increased absorbency through the skin.

Every aquarist has its own tricks for when their fish get sick. If this article has helped you identify whether disease is affecting your tank, share with others what you did to fix it.

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