Depression in Fish

The photos included in this article are not depicting depressed fish, but rather they are just some good fish photos from the Reef2Reef archives showing different species that we commonly see in saltwater tanks. ©2019, All Rights Reserved.

We often set up aquariums for the joy that they bring us, the soothing feelings we get watching colorful fish flit around beautiful coral displays and the deep satisfaction the aquarist gets from having built and cultivated something impressive. With all the happiness that can be created by an aquarium have your thoughts ever drifted to the emotions of the little finny friends that occupy that gorgeous tank?


Powder blue tang photo by @ChristopherKriens.

While fish are not often thought of as very emotive animals they are actually quite emotionally complex possessing very similar neurochemistry to humans and are often used in trials for psychiatric drugs. This means that yes, fish can get depressed just like their owners. But how do you recognize depression in fish and what can a concerned aquarist do about it?

As fish cannot sit down with a therapist and discuss their concerns and worries we can identify depression in fish by observing their behaviour. One of the most notable indicators which should be easy for most aquarists to identify is the degree to which a fish explores his or her tank. Depressed fish tend to linger in one spot, usually near the bottom and will rarely move around the entire tank. The key element here is inactivity as depressed fish will just let the currents of the water move them around, allowing themselves to sink to the bottom and not swimming to the top for mealtimes.


Starry blenny photos by @MJC.

There are some fish species that stay in one small territory as part of their normal behavior. That's not what we're talking about here. We're talking about the fish that would and should normally swim around but chooses not to.

One test that aquarists can perform in order to see if their fish is depressed is to introduce it to some new surroundings, as most fish are naturally curious they will, when in a healthy state of mind, immediately begin to explore the new environment or feature whereas a depressed fish will often allow itself to sink to the bottom and remain there.


Royal gramma photo by @Joey Bekius.

What causes a fish to become depressed? According to Victoria Braithwaite, a professor of Biology and Penn State University, some of the most likely causes are a lack of stimulation or insufficient oxygen in the water. Another cause can be chronic stress, which can come from and be enhanced by a variety of sources.

Some of the most common stressors to occur in an aquarium environment include overcrowding, inability to avoid aggressive fish, a struggle for food and changes in lighting and currents. Thankfully, unlike humans, genetic causes of depression are rare in fish, usually only occurring in selectively bred fish used for laboratory research so you shouldn’t need to worry about having to flood your tank with Prozac or put your fish on medication to deal with their depression.

In situations where you aren’t dealing with a genetic mutation that requires chemical correction of the issue there are steps an aquarist can take to improve the livelihood of your fish and mitigate the effects of stress and depression. As fish can become bored with their surroundings one of the simpler solutions to ichthyoid depression involves enriching their environment, doing things like adding some new marine flora or some interesting decorations and ensuring that more nervous fish have plenty of places to hide and plenty of room to get some safe space. It might also be prudent to check your filtration system to ensure water quality.


Purplelined wrasse photo by @Acorral
Remember that the warmer your water is, and the saltier it is, the lower the oxygen saturation. The solubility of oxygen decreases as temperature increases, and dissolved oxygen decreases exponentially as salt levels increase. (1)

For increasing oxygen in the tank, sometimes something as simple as opening a window in the room where the tank is helps the oxygen uptake in the water. More surface agitation will help with gas exchange, and that's easy to accomplish with changing the direction of a powerhead or adding another one or adding a small air pump and bubbler or adding a skimmer.

You could also observe your depressed fish and determine if it is being harassed by any other fish and take steps to separate them or give them space apart from each other. Another simple solution is making sure that when feeding your fish you spread the food around, reducing competition for food among tank denizens. In extreme cases where your fish are being crowded your options are a lot more limited: get a bigger tank, get a new tank, or get rid of some fish.


Harlequin tusk fish photo by @OrionN

We recognize that discussing the emotional lives of your fish is a new concept and one that will likely bring about some debate and disbelief. However, the fact that fish are intelligent and have emotional lives is what the recent peer-reviewed research is concluding, so as aquarists, it's something we need to be aware of. In humans, untreated depression shortens life expectancy, so it's not a big step to suggest that untreated depression may shorten life expectancy in other species as well.

It probably doesn’t come as a surprise to experienced aquarists that fish are more emotionally complex than many people give them credit for. Fish have been observed exhibiting complex emotions such as joy, relaxation and playfulness and as we’ve already noted, depression and stress. Hopefully with our discussion above we’ve given you some solid strategies to minimize the stressful and depressing elements in your fish's lives and to bring out the best emotions in them, so you and your fish can both enjoy each others company to the fullest.

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· (1) Fondriest Environmental, Inc. “Dissolved Oxygen.” Fundamentals of Environmental Measurements. 19 Nov. 2013. Web. < >.











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Author Profile: Peter Steckley

Peter Steckley is a freelance science writer based in Calgary, Alberta, Canada. When he's not studying reef aquariums or testing out new recipes on his family, he's usually reading or enjoying the latest video game releases.
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