Does a Naturalistic Environment Reduce Stress in Aquarium Fish?

The blue-throat triggerfish (Xanthichthys auromarginatus) in my aquarium exhibited repetitive behavior prior to transitioning the system to a reef

The blue-throat triggerfish (X. auromarginatus) in my aquarium exhibited repetitive behavior prior to transitioning the system to a reef

For today’s post, I’d like to elicit your thoughts on an interesting phenomenon I’ve observed in my aquarium, specifically involving an aggravating repetitive behavior exhibited until fairly recently by my pair of blue-throat triggerfish (Xanthichthys auromarginatus).

Allow me to set the stage: I introduced the blue-throats to my 125-gallon about a year and a half ago when it was still a FOWLR system. Their tankmates at the time included a one-spot foxface (Siganus unimaculatus), yellow tang (Zebrasoma flavescens), tomato clownfish (Amphiprion frenatus), and sixline wrasse (Pseudocheilinus hexataenia).

The repetitive behavior I’m referring to—and both the male and female exhibited it—was repeatedly swimming around the base of a powerhead mounted at the far left end of the tank (as I usually face it—you can actually view the tank from either side and one end) about 5 inches below the surface. They would swim in a circle 10, 15, even 20 times or more, briefly break away and swim about half the length of the tank, and then come right back to the powerhead to swim another set of “laps.”

Both triggers fed with gusto and would swim up to greet me whenever I approached the tank, no doubt assuming more food was forthcoming, and sometimes they would stop the lap swimming and explore more of the tank for brief periods. But they would always revert to that same maddening behavior.

I tried moving the powerhead next to my overflow box and closer to the surface so it would be harder to swim in a loop around it, but the triggers just wiggled their way through the narrowed pathway anyway. Afraid they’d get injured or flip out of the tank, I moved the powerhead back to its original location.

Perseverative behavior like this in any animal (such as frenetic pacing in zoo mammals) often indicates stress. But what was the cause? The tank is sufficiently large and they had open swimming space all around the perimeter of the tank and through a channel running between two peaks of rockwork, so it wasn’t the case that they were constrained and couldn’t expend energy. The other fish pretty much ignored them completely, so tankmate aggression wasn’t the problem either. Neither trigger exhibited signs of disease nor subsequently became ill. Of course, I’m always pretty fanatical about maintaining excellent water quality and feeding a well-balanced diet, so it’s safe to scratch those factors off the list as well.

Now, about a year ago, I began to transition my 125-gallon from a FOWLR system to a reef system. I first added just a handful of corals from the 75-gallon reef tank I was shutting down at the time, and I later got a nice assortment of gorgonians and corals (not to mention a beautiful Atlantic blue tang) from Caribbean Chris, who was tearing down his tank in anticipation of his move to Florida.

Then a funny thing happened. I can’t say precisely when, but at some point during or after the addition of sessile invertebrates to the 125-gallon, the triggers’ repetitive behavior stopped—and I mean stopped completely. In fact, it’s safe to say they don’t even give that powerhead they were so fixated upon a second glance anymore. Today they regularly cruise the entire tank and exhibit no signs of nervous energy. This behavioral change was pretty stark, and once again I find myself questioning the cause.

I have a theory on this, which is loosely based on the idea that the closer to natural the aquarium environment is, the better for the fish from a psychological standpoint, but I’m more interested in hearing what you have to say on the subject. If you have an opinion or similar experience to share, please do so in the comment section below.


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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. Dave Malet says

    My only question is why did you mess with the set up if you thought they would spawn.Wouldn’t you want to try to see if they would and tweak whatever you needed to do to make that happen.

    • Jeff Kurtz says

      HI Dave! I wasn’t necessarily trying to encourage spawning, but your question raises a good point. Perhaps the behavior was related to courtship? In my mind, I’d more or less ruled that out because their “lap swimming” seemed less directed than that–more frenetic, sort of like freshwater livebearers repeatedly swimming up and down in a corner of their tank. Still, you might be on to something.

  2. Jeff I also have a theory, not a very good theory but a theory none the less. It is also a theory that most, OK all people will dismiss as science fiction but after enough years you begin to think (and look a little like) a fish. Something that is never discussed is the lateral line system of a fish. (I go into this in my book) We can’t even start to imagine how the system works but it is somewhat like sonar. Most submarines don’t have windows (or screen doors) but the crew knows exactly where they are. Submarines also don’t crash into things and neither do fish, even in pitch darkness. The lateral line is why you can’t catch a fish with a net unless you trap it against something. The fish knows what’s behind and next to it all the time. In a somewhat bare tank the fish constantly gets signals from the glass even though they can’t see it. I am sure it totally confuses the fish. (I think that is also what causes HLLE) When we make the tank more natural and add corals, it diffuses the rigid signals the fish pick up and allows it to navigate easier. I personally don’t have a lateral line so I am speculating a little. But if you dive, you will see dozens of fish all dive into a coral head. The fish doesn’t even know they will fit, but they always do. They never get stuck or even scratched. That is all because of their lateral line that we are just minutely starting to understand.
    Even without a lateral line, I can feel my wife behind me right now waiting for me to help her with something.

  3. I have a pair of crosshatch triggers for over 2 years and the female does this behavior and not the male. i think it may have to do with courtship since ive only seen this happen at certain times during the year. Seems to be playful like behavior and doesnt bother or injure the fish. it has nothing to do with tank size at least in my opinion, mine is 10ft long by 3 1/2 feet deep and 3 feet in height. These are healthy thriving Crosshatches with voracious appetites. Ps this is a reef tank with sps and lps.

    • Jeff Kurtz says

      Thanks for sharing this, Ben! It is interesting that this happens only at certain times of year, and I think you’re definitely safe in assuming the size of your tank isn’t the issue (I’m envious!). Since you’re seeing it in crosshatches, maybe it’s just a Xanthichthys thing! He he!

  4. Hi Jeff,
    We have three blue-throat triggers that do exactly what you are describing; so exactly its spooky. They live in our 180 (6’x24x24) reef tank which has a fair amount of lps as well as some sps (over 30 good sized colonies). On the one end, all three triggers swim laps around the two mp40s constantly; they never really venture to the single mp40 at the other end unless its feeding time. I have noticed the laps are typically initiated by the female, the two males do laps around the pump but seem to prefer back and forth for 3-4′ on the back wall. The two of them started really developing color about a year ago but never bother one another. They all started as juveniles so we couldnt really tell the gender otherwise we wouldn’t have picked 2 males and a female. Ive been reading your articles for a while, but cant say I recall a picture of your tank. I sometimes wonder if the behavior we see from our triggers is caused by the tank being fairly low energy, i.e. bubble coral and other lps that dont seem to like a lot of flow. I say this because the triggers seem to stay in the highest flow area of the tank. I’m not sure if your original flow pattern would support this as being a possible cause for the behavior, or perhaps they just like track and field. Thanks for all of the great articles by the way!

    • Jeff Kurtz says

      It’s my pleasure, Kyle, and thank you for your kind words! The previous level of water flow in the tank was fairly robust, but I did increase it somewhat during the reef conversion, so that certainly could be a factor!

  5. I’d be curious to know if a captive bred fish would display the same kind of nervous behavior in a non-natural environment. It would be interesting to see if a fish raised in captivity would still have instincts to know what a natural environment should look like.

    • Jeff Kurtz says

      That’s a great question, Eric. Who knows, maybe a captive-bred fish would be more unsettled by the sort of environment that we would consider natural.

  6. No real doubt in my mind about this when the naturalistic aquarium contains a functioning ecosystem with a diverse community of microorganisms and invertebrates such as may be found especially on fresh live rock and sand. In the more complete ecological functioning of such a system, life stages such as the cysts of Cryptocaryon irritans (marine Ich) and the dinospores of Cryptocaryon irritans (marine velvet) are controlled by a myriad of tiny predators that treat these diseases as tasty snacks. This is a big reason why we don’t see much fish disease in the natural setting, despite the fact that various remedies and treatments and not available on the reef.
    Diseases are the result of unbalanced biology, a fully functioning ecosystem is know to be much more stable. We all need to learn to promote and love, not fear, biodiversity!

  7. I love (and agree with) Tim’s last sentence.

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