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How To Tell If Aquarium Fish Are Stressed: And How To Help

How To Tell If Aquarium Fish Are Stressed: And How To Help 1

Stress can cause a fight or flight response in your fish. This could likely be the reason for why they do not seem healthy. Stress is a vicious circle, stress can lead to other problems, and in turn, those other problems can make the stress worse. This is true for humans and for fish.

It is easy to think your fish live in peace in your tank. What care would they have other than making sure they eat when I give them food?

There isn’t a fish out there that will not become stressed. Some fish are just more prone to stressing out that others. Some can handle stress for longer time periods, and other can die just by looking at them.

There will be times when your fishes stress will be completely obvious. Other times you will not know that there is a problem unless you regularly observe your tank. With time you will become more experienced by watching your fish. You will be more ready to spot anything out of the ordinary.

Things to watch for could be sluggish movements, they could be also swimming frantically. They could either not have an appetite or may be bloated. Other things of concern could be disease, toxins, or insufficient oxygen.

Most fish will turn pale or others a dark almost-black coloration. The fish could also lose any markings that they would normally have. This can be a key indicator to act. The sooner you notice a problem, the quicker you can act!

Consistency is key. Some stress can be good for your fish, it keeps them conditioned and healthy. Continued or chronic stress over long periods can be harmful and can take your fish with minimal signs.

If you notice a stressed fish, the best thing to do is get it separated from the problematic environment. Place them in a small quarantine tank. This will allow them to recover in clean water and without other tank mates that can complicate things.

Having a quarantine tank is also a good idea when you get new fish. You want to make this acclimation process as comfortable as possible for your fish. You can prevent your tanks inhabitants from harassing the new fish before they have time to acclimate. This acclimation also allows you to watch for disease so that you are not introducing it into your aquarium.

The environment where you keep the fish tank must be in a place that doesn’t cause unnecessary stress on your fish. If you have children make sure you watch them make sure they are not banging on the glass or making loud noises. This banging can cause high levels of stress. This goes the same for a hobbyist to be constantly messing with the tank, like uprooting plants or rearranging the decor.

Just like humans, animals get stressed too. Fish are no exception to this fact. Realizing that your fish are stressed and taking action is the best thing that you can do.

Act quickly! It is ultimately up to you to fix the problem. These problems are more than likely caused by outside influences on the tank. Remember we put fish in these environments and it is up to us to regulate it.


There will be times when you can easily tell the stressors in your tank. Other times you will not be able to figure it out. A fish could have problems and you may never know it until it is too late. They will just hang on and give no indication that there is something wrong. I will try to explain some signs that could be easily recognized.

Visible signs of stress should be your first indicator. Your fish can exhibit any of these follow symptoms:

  • Sluggishness
  • Erratic Swimming
  • Gasping for Air
  • Appetite
  • Hiding
  • Cloudiness
  • Wounds
  • Clamped Fin
  • Other Unorthodox Behaviour

Sluggishness – You can notice this one pretty easily. If you observe your fish and get an idea of their normal activity this should tell you if they are moving slower than normal.

Erratic Swimming – Just like with being sluggish, your fish can also swim in a frantic manner.

Gasping For Air – Caused by high toxins and or low oxygen in the water, do not confuse this with normal behavior. Some fish will routinely go to the surface for air even though they have gills, they are known as lung breathing fish. Constantly resting at the surface can be the key indicator of low oxygen or high toxins. The oxygen level is higher at the top of the tank compared to the bottom.

Appetite – Will not eat, or attempts to but doesn’t have the energy to do so. This lake of an appetite may not be their fault. Feeding time can be stressful for your fish. Some may need to have food placed in different places in the tank so that they have a chance to eat. You may not win this battle but at least you can try.

Hiding – While many fish will hide among the wood, rocks, and plants in your tank. This isn’t normal for all fish though. A good rule would be if the fish is a bottom feeder they will likely need some cover. If you have a fish that doesn’t normally hide or is secludes themselves more, then you might need to be concerned. This could be a result of bullying by other fish.

Cloudiness – Your fish or shrimp can appear cloudy. Their eyes may be glazed over. If you see this, make sure you are quarantining the fish. Only quarantine if only one fish is afflicted, if all inhabitants are infected then there is no need to separate. Find the cause and fix it.

Wounds – This could also be from bullying. If the aggressive fish doesn’t give up, they could terrorize their tankmates to the point of physically hurting them. This could be a wound, gash, or nipped fins. I recommend quarantining either fish so that the problem doesn’t continue.

Clamped Fin – If you notice your fish isn’t using their pectoral fins (the front side fins), then that could mean they are under great stress. Clamped find Isn’t related to a disease or anything but specifically

Other Unorthodox Behavior – This list consists of a few from the top, and others to watch for include:

  • Staying at the surface
  • Erratic swimming
  • Going to the surface constantly for air
  • Doesn’t swim, stuck in vegetation
  • Do not move or flee when other fish pick on it
  • Swimming upside down
  • Rubbing up against objects and substrate in the tank


How To Tell If Aquarium Fish Are Stressed: And How To Help 2

Disease – This one can be hard to figure out sometimes. Most of the time the fish will not exhibit symptoms until right before death. It is also hard to keep an eye on your tank to catch every occurrence that could pop up. I know I keep repeating it but the best bet is to just keep a clean tank, and do not introduce other fish that could be diseased already.

Diseases like Ich will show up as little white spots on your fish. You can usually find it around the mouth and fins but can take over the whole body. For this reason, a cycled tank is important. It will help with giving the fish a protective slime coat, which is a slimy layer all over their bodies. Slime coat is greatly reduced when a fish is stressed.

Fish can carry diseases that can be dormant or so minimal that the fish can cope it. Sometimes stress on the fish can cause these parasites to become more of a nuisance. Keep your fish tank clean and your fish will be healthier, allowing them to fight off anything that resides in the aquarium.

Fungus – This can appear white just like Ich but more like a fuzz. Unlike Ich, Fungus will cover larger areas, Ich remains as spots. Usually first appears on the fins, but can cover the whole skin.

Bacterial Infection – Your fish could appear to have blood red or dark maroon colored spots on fins.

Other ailments to watch out for would be Dropsy, Fin Rot, Gas Bubble, Anchor Worms, Gill Mites, and Fish Lice.

New Tank Syndrome – This one cannot be stressed enough for new aquarium keepers. You always want to start your fish tank ahead of time so it is fully cycled. This cycling allows beneficial bacteria to establish itself. If you do not do this then many problems can occur that will stress your fish, starting with Ich, guaranteed.

pH – Going along with a cycled tank you want to make sure that the water conditions are optimal for your fish. Poor water conditions lead to disease and stress. You want to make sure you do a water test. Testing for Ammonia, Nitrates/Nitrites, and the pH.

Some fluctuation in these attributes is normal, but any sudden spike will be a cause for concern and could lead to sudden death in your fish. If you feel this is the case, you should always do a water test. Then be ready to do a partial water change. Make sure it is a partial change and not larger volume, the larger the water change causes more damage to your fish than not doing a change, to begin with. You may have to do a few more within the next week to get it to balance out.

The hardness or softness of your water can affect your fish as well. Certain ones like the cichlids require some special water conditioners. Make sure that pH swings do not have more than a sudden 2 pH change. Many fish could handle small changes especially if it is less than 2 points incremental. This is something to watch out for when doing water changes. It is specific for each fish, but do not go outside of the range of 6-8.2 pH.

Oxygen – The oxygenation of your water is important. If you feel it is low then go ahead and add an air pump and airstone. Insufficient oxygen can be from too much biowaste creating contaminants.

Salinity – Too much salt in a freshwater aquarium can be bad. A small amount of salt in a freshwater aquarium can be beneficial. It has sanitizing properties but can easily kill your tanks inhabitants if not used sparingly. The salinity can be measured by the osmotic gradient, which shows the balance of the salt and the water column.

Temperature – Changes in temperature can play a big part in your fishes happiness. Make sure that you are always keeping a constant temperature. Any sudden swings in temperature can definitely stress your fish out. When doing water changes, replenish with similar temperature water. This could also be from a heater going bad. Check your temps each day when you feed. If needed, keep an extra heater on hand in case you need to swap it out.

Light Intensity – This would not normally be a problem in a planted tank. If you do not have plants to shade the water, then you need to make sure that you are not adding too much light to the tank. If you feel it is too intense then find a way to lower the light level or raise the light itself away from the water surface.

Dirty Filter – Check the filter to make sure it isn’t clogged with excessive debris. This will cause the water flow to become stagnant. The extra biowaste will also produce deadly gasses that can harm your fish. Make sure to empty out the filter and clean the medium to wash out these bad contaminants.

Note: Be careful not to introduce chemicals or harsh minerals. These can be from rocks or bad parasites in wood.

Tankmate Compatibility – Issues with tankmate compatibility is common, fish will bully their tank mates. Not only can they be territorial, but it is amplified by the fact that they are confined to such a small space. This can also happen right after adding new fish. They are automatically going to start trying to find their place in the fish tank. Sex of the fish can also be an issue, especially during breeding. The spawning fish couple will be territorial and that can be stressful for the other fish.

Population Density – This cannot be overlooked. If you overstock your tank, it will fail. There will be considerable biowaste if the population is too dense. Not only this but some fish require more space. If they are put in a small tank, then they will be aggressive to their tank mates.

No Hiding Places – To provide your fish with a natural habitat that they will feel comfortable, you want to make sure to provide hiding places. Many bottom feeders will appreciate a log or cave to hide in. Using these hiding places also helps keep the other fish calmer since they cannot see the other fish in their territory.

Travel – Fish are not pets that can be taken with you when you travel. They come from a completely different environment. It should go without saying that travel can be stressful for fish. In order to reach your tank, your fish will most likely come from a hatchery, shipped to a local fish store, purchased by you, and brought home. That can all happen in a short amount of time. The fish can go through the whole range of tank parameters just gettings to your house. Most fish deaths will occur during the acclimation process. Proper acclimation is key.


Cycle your tank if it is new before adding any fish. If you fail to do this, then you will likely lose all of them.

Condition water when doing changes, this should go without saying. Local fish stores will sell a solution that will help make chlorine inert so it doesn’t harm your fish.

Note: Household cleaning products. Never use anything not made for a fish tank anywhere near the aquarium. Bleach or ammonia-based products can harm your fish. Always be careful of harsh chemicals, many disinfectants contain copper which can kill your shrimp and snails.

Check out this video from expertvillage on YouTube, this video is filmed in front of a large peaceful looking tank. The creator definitely has some good points on how to recognize and then keep your fish from becoming stressed.


Keep your tank clean! This is the number one thing I stress all across my site, cleanliness is next to godliness, remember that. Quarantine. Spend the extra time, helps reduce chronic stressors.

I always perform regular water tests. This helps give you a baseline to know when things go wrong. Remember the important ones are ammonia, nitrates/nitrites, and pH.

Observing your fish is also important to get a baseline of their behavior. This way you can tell if your fish is acting weird.

Stress can be tough on the fish, even though the fish may appear fine, it could eventually pass. Some stress can be beneficial though helping condition the fish. You cannot eliminate all stress, that is this hobby.

The most important thing to do when you notice something is wrong is to act quickly! You have the ability to act, the fish don’t. Now you have more information so you can help them!

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