Five External Stressors of Marine Aquarium Fish

Be aware that external vibrations can affect your aquarium and its inhabitants

Be aware that external vibrations can affect your aquarium and its inhabitants

Most marine aquarium hobbyists want to provide as naturalistic and stress-free an environment as possible for the fish and other livestock in their care, so they’re careful to maximize water quality, offer nutritious foods, promote compatibility among tankmates, aquascape appropriately, and so on. In other words, they put a lot of thought into what’s going on inside the aquarium. But what about what’s happening outside the tank?

In some cases, very conscientiously maintained aquariums can still contain stressed-out fish because of various external influences that may not even occur to the hobbyist—especially if the tank houses species that are naturally skittish to begin with. Here are four of them off the top of my head:

1) Vibrations

Try this little experiment: Stand on the opposite side of the room from your aquarium and shout, whistle, or clap your hands loudly while observing your fish. Next, stomp your foot on the floor, still keeping an eye on your piscine pets. Very likely, the shout, whistle, or clap had little to no effect on the behavior of your fish but the stomp sent them dashing for cover.

The explanation for this is, higher-pitched sounds produced in the air don’t do a very good job of crossing the air/water interface and, therefore, will tend to go unnoticed by fish. On the other hand, low-frequency vibrations that travel along solid surfaces will definitely be transferred to the aquarium and felt by the fish.

While many fish seem to grow accustomed to constant low-level vibrations, such as that produced by a submersible return pump, they’re apt to be stressed by sudden, intermittent vibrations—such as the aforementioned stomp, slamming doors, the thumping bass of stereo speakers, or the infernal revving of your neighbor’s ’72 Chevy Malibu engine.

2) Unnatural room lighting

In nature, fish are subjected to a predictable day/night cycle with very gradually shifting light levels. Suddenly turning on the room lights after the fish have been in total darkness or constantly turning lights on and off can be extremely startling and stressful to fish. Ideally, your aquarium should be situated in a room where this is unlikely to be an issue. Otherwise, you’ll need to be mindful of this stressor and, perhaps, simply leave the room lights on until you’re ready to call it a night yourself.

3) Unpredictable movement

A certain degree of human activity in the vicinity of an aquarium is unavoidable, but excessive motion—especially sudden, erratic movement—is to be avoided. Remember, as far as aquarium fish are concerned, something unfamiliar moving near the tank could be a predator fixing to eat them or a competitor out to take their resources, so they’ll stay in fight-or-flight mode when there’s too much activity nearby.

4) Fluctuating room temperatures

Today’s submersible aquarium heaters make it pretty easy to set and maintain a desired water temperature, but if the air temperature in the room fluctuates wildly, unacceptable changes may occur in the tank as well. This is most commonly an issue during the warmer seasons in homes lacking central air conditioning. If you encounter this problem, installing either an aquarium chiller or window air-conditioning unit might be in order.

5) Young children

As any parent with an aquarium knows, young children can be guilty of causing many of the stressors mentioned above—stomping around, repeatedly turning lights on and off, slamming doors, tapping on the aquarium glass, chasing fish from one end of the tank to the other, and so forth. Since we don’t want to make our aquariums completely off limits to kids—and since most states forbid the sale of children (as it turns out)—the best option is to establish aquarium “ground rules” for youngsters (no running, fighting, throwing of toys, tormenting of fish, etc.) and supervise them very closely whenever they’re in the vicinity of the tank.


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About Jeff Kurtz

Jeff Kurtz is the Co-founder/Editor of Saltwater Smarts, former Senior Consulting Editor for Tropical Fish Hobbyist Magazine, and the aquarist formerly known as “The Salt Creep.” He has been an aquarium hobbyist for over 30 years and is an avid scuba diver.


  1. Paul Baldassano says

    I would like to comment on the room lighting as this is a very important, but rarely discussed topic. Many marine fish and most corals depend on the cycles of the moon to inform them when it is the right time to spawn. With artificial lighting they get no cues thus, no spawning occurs. We don’t know how much this affects fish or corals but I am sure it is a huge stressor for them.

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