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What Does a Fish in Shock Look Like and How to Save It

Aquarium fish are sensitive creatures accustomed to living in specific conditions. A sudden, large change in the environment can send them reeling.

If the change in water parameters is slow and over an extended period of time — hours or days as opposed to seconds or minutes — the fish’s health may still deteriorate, but then we’ll be talking about fish in stress rather than shock.

The key differentiator here is a sudden change. Prolonged exposure to unfavorable living conditions will likely be fatal, but when the fish is shocked, the reaction time to save it is much shorter.

But what does a fish in shock look like and how does it behave?

Fish in shock look and act strangely. Depending on the exact cause for shock, fish may be lethargic or dart around, gasp for air at the surface, or breathe rapidly. Changes in temperature or pH are the main reasons for shock, and temperature fluctuations are by far the more dangerous of the two.

We’ll discuss the symptoms, causes, and prevention in greater detail further down in the article.

Before that, here’s a table with the most common symptoms a fish in shock exhibits, depending on the cause:

CauseWater Too ColdWater Too HotpH change
SymptomsLethargyErratic breathingLethargy
Lying at the bottomDarting aroundWhitening
ComaThrashingNo appetite
ComaErratic breathing

There is some overlap in the symptoms, so let’s break them down in greater detail.

Symptoms of Hot Temperature Shock

These are the most common symptoms of a fish in too hot water:

  • Difficulties breathing, either too rapid or gasping for air at the surface
  • Darting frantically around, looking for an escape
  • Thrashing
  • Coma

Fish are cold-blooded creatures that cannot tolerate drastic temperature changes.

If the water heats up quickly, they will start breathing rapidly. Many will approach the surface often to gasp for air, as warmer water contains less oxygen.

Some fish will swim around frantically. Higher temperature increases their energy flow, but it will ultimately kill them.

Dropping them into considerably warmer water might send them directly into a coma.

Again, if the warmth grows gradually, tropical fish have a fighting chance, as I know from sad experience.

Once as a kid, I was out all day. Little did I know that the heater’s thermostat had given up on life. The heater had started working in the morning, heating up the water throughout the day. 

My father heard a crack and rushed into the room to witness some 5 inches of the water column spilling out. The front glass panel had been unable to handle the heat. The thermometer was close to 50 C.

My five danios were dead. Surprisingly, mostly everyone else was alive. The marble gourami couple was fine. The corydoras shoal had lost a single member, and my medium-sized red-tailed black shark was agitated, but as the temperature dropped it calmed down. The plecos and cardinal neons seemed unphased.

Many fish break harder than glass. But the real moral is that they can adapt to excessive heat (please, don’t EVER test that).

However, if someone were to drop a fish from 25 C water into the hell that my tank became on that winter day, it would have definitely experienced severe temperature shock that would have killed it, in all likelihood.

Symptoms of Cold Temperature Shock

These are the most common cold temperature shock in fish:

  • Lethargic
  • Stop swimming altogether, lying at the bottom
  • Enter coma by floating sideways or upside down

If a fish is dropped in considerably colder water, it will struggle to adapt.

Its bodily functions will slow down and it will become lethargic and slow. Next, it will either lie down at the bottom or directly enter into a state of coma. The latter looks particularly scary, as the fish will look very much dead. It will float upside down or sideways and won’t be moving at all.

It may recover if you gradually raise the temperature, but you have to act quickly.

Imagine being in a cozy room, with fire booming in the hearth, a warm drink in hand. Then imagine stepping outside, in the snowy frozen winter realm. Even if well-dressed, the first few seconds will be shocking. Now, imagine stepping out of the heat into the frozen outside naked.

That’s what it would be for a fish to enter considerably colder water.

The thing is that we generate our own heat. However strong and unpleasant such an experience might be, we can handle such extremities.

Cold-blooded creatures can’t.

Symptoms of pH Shock

Fish in pH shock often exhibit the following symptoms:

  • Lethargy interrupted by sudden dashes
  • Whitening of color
  • Lack of appetite
  • Troublesome breathing
  • Hiding

Fish in pH shock can manifest an array of symptoms, but most commonly you will see them lying on the bottom or standing still in one place. Instead of swimming normally around, the afflicted aquatic animals will be largely immobile, with drooping dorsal fins.

The occasional jerky dash followed by another period of relative immobility is a typical continuation of the pattern.

You can test their reactions by dropping a small amount of food. If they aren’t interested, that is a strong secondary indicator that something’s wrong with the water’s pH. (Of course, testing the water is a quick way to ascertain any abnormalities.) Lack of appetite is practically unheard of in healthy fish.

Darker fish also can look paler as their bodies produce extra slime. Lightly-colored species also do that, but it is usually harder to distinguish the difference in color.

Common Causes for Shock in Fish

The most common scenario for exposing fish to shocking conditions is transportation. By default, moving them from one tank to another means different water parameters.

Be that from the local fish store to your quarantine tank or from the fry tank to the main one, the water will be different. Obviously, the former is likelier to produce a more pronounced difference in pH and KH (carbonate hardness).

The other common reason for dramatic shifts in water conditions is regular aquarium maintenance. Regular water changes replace 25%-50% of the water column, and the pH is bound to fluctuate.

Even if you refresh the water column directly with tap water, the ecosystem of your tank sets its own pH parameters. Driftwood, for example, makes the water more acidic, while quartz increases the pH.

But in many places tap water is inadequate without proper treatment. The water often needs a conditioner to remove nitrates and chlorine, purify ammonia, or alter parameters like pH.

More importantly, when adding new water to the tank, you must ensure it is of the same temperature. Temperature shocks are much more common and dangerous than pH fluctuations. If you replace 50% of the water column during maintenance and the new water is considerably colder or hotter, the fish will suffer.

This is one of the dangers associated with tap water. Should you fill the tank directly from the tap, make sure that the temperature doesn’t change suddenly. Sometimes the flow from the tap changes due to a small change in water pressure in the pipes, altering its temperature.

Here’s how to prevent such mishaps from happening.

Shock Prevention when Transporting Fish

Shock can easily occur when fish are introduced to a new aquarium.

To give them time to adjust to the water conditions of the new tank, mainly to its pH levels and temperature, do these two things:

  1. Avoid buying tropical fish on particularly cold winter days. Taking them out of the store to the car may be a short walk for you, but the difference inside the shop and outside might be more than 25 degrees. The chilly winter air will suck out the warmth of the fish bag in no time. Likewise, when you enter the car it might take a few minutes to warm up, which may be a few minutes too many.
  2. Transport fish in clean plastic bags. Before releasing them into the new environment, submerge their container in the new water and leave it there for 20 minutes. This way, the temperature in the bag and the tank will equalize.
  3. Use the temperature adjustment period to add a bit of water from the tank into the transporting bag. Every five minutes or so pour tank water into the bag. A clean syringe is excellent for this purpose. When the 20 minutes are up, a third-to-a-half of the water in the bag should have come from the aquarium. This also helps with the temperature, but its main utility is to equalize the pH.

Now, if the pH between the original and recipient tanks is over two points, such a short adjustment period might not suffice.

It is imperative to test the water of the shops you buy fish from. Most places have largely consistent water parameters, so testing it after the first couple of buys will give you a good idea of what to expect.

Definitely write the info down!

Use Quarantine Tank, Even for Short Periods

If the difference between the shop water and yours is large, it is best to use a quarantine tank. Having one is generally a great idea, but not everyone has the possibility to maintain one. For pH adjustments, you can use a bucket or a large jar.

Besides being an attainable solution, a smaller quarantine vessel allows you to adjust the pH levels faster and with fewer expenses.

Still, don’t go too fast! Add aquarium water to the vessel of choice slowly, so that the pH levels equalize over the course of a day, if possible.

Be mindful of the temperature in the quarantine vessel, as it may drop quickly on a cold day unless a heater is supplied.

Too Long Transportation

If, for whatever reason, you keep fish in a bag or another small closed container for long, say, two hours or more, the pH may drop dramatically when you open the container.

Exposing suddenly the water surface to air will release the accumulated CO2 and the resulting chemical reaction that will drop the pH very quickly.

Make sure to aerate the container regularly, to avoid this. Besides, exposing the water surface to oxygen is essential to prevent the fish from suffocating.

Shock Prevention During Maintenance

Regular water changes could be hazardous if you don’t follow a good routine. Again, temperature differences are the bigger threat here.

If you change the same amount of water week in, week out, adjusting the pH quickly becomes straightforward. Measure how much conditioner you need to reach the target levels and apply the same dose every time.

But with temperature, things are not so simple, especially if you live in a place with varied weather conditions throughout the year. Sometimes the new water may be considerably colder than others due to changes in the ambiance.

Warming Up the New Water

If you have a large enough container to pour in all the new water and let it age for 24 hours, you should place a thermometer there. Then, you can take a few liters out and warm them on a stove before pouring the heated water back into the container to reach the tank temperature.

An easier and more precise approach is to place a heater in the container and let it warm the new water. Of course, you need to own a second heater, but such an investment is justified. Besides helping with water changes, it can serve in a quarantine tank.

In case you are pouring new water directly from the tap, use a digital thermometer. Calibrate it by measuring the tank temperature first and comparing the readings with those of the aquarium thermometer.

Some cheap digital thermometers don’t give precise readings, but as long as they are consistent, you are good.

The biggest danger when pouring directly from the tap is a sudden change in the water pressure. That’s a relatively common occurrence in large residential buildings with many inhabitants. If several households start using hot water at the same time, your supply may dwindle for a few minutes, dropping the temperature too much.

People who use their own water boilers also are not immune to disasters, as water boilers might run out of warm water or malfunction.

That’s why it is imperative to observe what is flowing out of the tap at all times.

Now, using your hand to compare the temperature of the new water and that of the tank also works, even though it is imprecise. You don’t need the degrees between the two to match perfectly but to be close enough.

Sill, a thermometer is highly recommended.

Cooling Down the New Water

If you have cold-loving species, adding fresh water to their tank usually requires no heating up. Just let the water sit in its container for 24 hours and it will be the same temperature as the room. Still, you should measure the temperature of the new water to ensure there are no major differences.

All it takes to end up with dead fish is for a single maintenance session to go wrong.

The bigger issue with cold species is hot weather.

If the room temperature raises a lot, the aquarium will follow suit. Excessive temperatures might affect tropical species too. The best solution in such conditions, especially if they are stretched over weeks and months, is to install an AC unit into the room. Alternatively, put the tank in a basement with a cooler ambiance.

Sudden pH Changes due to CO2 Dosing

pH can drop rapidly if you dose your tank with CO2. Without going into too much detail here, part of the CO2 molecule reacts with the H2O water molecule to become H2CO3 or carbonic acid.

pH below the neutral point of 7 signifies acidic water. You can imagine how this chemical reaction alters the water parameters.

The general understanding is that pH fluctuations can be mitigated by higher KH, but this is a rather simplistic view that doesn’t correlate to reality so straightforwardly.

A workaround for pH drops caused by CO2 is to have a constant, small supply of CO2 that will increase the overall acidity but will maintain it at one level. Otherwise, dose the water with smaller amounts of CO2 in more frequent intervals.

Remember, it is not the change in environment but the speed with which it is introduced that causes shock.

Also, it is crucial to measure pH levels before and after you use CO2. Depending on the dose and the size of your tank, the drop may be insignificant.

Treatment of Fish in Shock

The main issue with shock is that it strikes quickly and often wreaks devastation before you can react. Quick counter-measures are essential to save fish lives.

Treatment of Temperature Shock

  • Move the fish to a body of water with adequate temperature
  • Adjust the temperature
  • Increase the oxygen flow
  • Turn off the aquarium light

If the water temperature is way off, change it gradually but quickly toward the desired point. If it’s too hot, add cold water so that it cools off by three degrees per hour. I’d advise staying away from ice cubes as they can lower the temperature more rapidly than you want.

Respectively, if it is too cold, add hot water to raise the temperature levels by three degrees per hour.

If the fish room is equipped with an air conditioning unit, direct the airflow toward the tank and adjust the temperature accordingly. Naturally, introducing a tank heater in cold water is a great option too, as they don’t heat things up too quickly.

If you’ve moved a fish from one tank to another and it starts exhibiting shock symptoms, you can return it back to the original tank.

If viable, I’d mix the original water with the one from the recipient tank in a 2:1 proportion in a separate container. It can be a bucket or large jar, as long as they are clean and have absolutely no traces of soap or other detergents. This approach reduces the chances of secondary shock, as another abrupt change in the conditions will be rough.

That being said, it is much better to return the suffering creature to its original water than leave it in the inadequate environment.

Increasing the oxygen flow helps fish in hot water, as warmth reduces the oxygen levels.

Turning off the lights will help fish with erratic swimming calm down, potentially lowering their body temperature further.

Treatment of pH Shock

  • Move the fish to a body of water with adequate pH levels
  • Adjust pH with a water conditioner
  • Conduct partial water change
  • If too low, stop CO2

In the case of a pH shock, the best solution is to return the fish to its original water source, if possible, just as outlined in the previous section. Mixing the water from the old and new tanks also could help the fish to adjust.

If that’s not possible, use a water conditioner to change the pH levels. Here again, incremental changes are important. Moving the pH levels one point per hour is quite quick. If your fish is extremely distressed, consider increasing the pace to a point-and-a-half.

If your water source and the tank have different pH levels and the one from the water source is better for your fish, changing 20%-40% of the water column is another way to go. How much you should change depends on the swing in pH you want to achieve.

Introduce new water gradually, not all at once, and check how the pH changes. Don’t rush things and observe how the fish reacts.

Do Fish in Shock Suffer Long-term Damage?

It is hard to gauge the impact shock can have on fish in the long term, but it certainly weakens their immune system and saps their vitality in the immediate aftermath. Without proper treatment it is likely to be fatal, but even if you react quickly and save the fish, it might take a few days to recover fully.

Frequent exposure to changing conditions will weaken your aquatic friend severely and will probably lead to its demise.

Keep your water parameters stable, people!

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