Don’t Overestimate Piscine Individualism!

Undulate triggerfish (Balistapus undulatus) are well-known for their belligerent nature

Undulate triggerfish (Balistapus undulatus) are well-known for their belligerent nature

LFS staffer to customer eyeing sohal tang as potential purchase: “Hmm, I don’t think that fish would be a good choice for your tank. It can get very aggressive, and most of the fish you have in there now are pretty shy and passive.

Customer to staffer: “Yeah, I know sohals have a reputation for aggressiveness, but it’ll be the last fish introduced to the tank. Besides, you have to remember that individuals of a species are going to vary to some degree in their behavior. I’m willing to take my chances.”

This is one of those circumstances (albeit a totally fabricated one) in which a hobbyist willingly ignores good advice and overrides common sense because, come hell or high water, he or she just really wants a particular specimen. And, in this context, referencing the variable behavior among individuals within a species is merely another manifestation of self-delusion.

Don’t get me wrong, there most definitely can be considerable behavioral variation within a species. For example, I’ve kept several yellow tangs over the years, and these individuals have ranged in their level of assertiveness toward perceived competitors anywhere from pushover to outright bully. But the lesson I learned from that wasn’t, “Hey, some of these guys are surprisingly peaceful, so you can pretty much keep them with anything.” Just the opposite, it was more like, “Hey, some of these guys are downright belligerent, so it’s best to err on the side of caution and avoid keeping them with any species that might tick them off.”

With respect to Acanthurus sohal, the species cited in the spurious conversation above, it’s true enough that some individuals are going to be less aggressive than others. But even a relatively peaceful sohal could still be pretty feisty once it reaches maturity. And let’s face it, just how different are any two undulate triggerfish specimens really going to be from another when it comes to their characteristic explosive aggression? I’d say not different enough to ever warrant keeping one with other fish in a home aquarium.

Also keep in mind that individuals of certain aggressive species are sometimes prone to “Jekyll-and-Hyde” behavior. That is, they may behave peacefully toward tankmates for a time but then suddenly turn on them violently.

So what’s the practical message you should take away from this? It’s always best to stock fish with the assumption that all the individuals purchased will exhibit the least desirable traits commonly associated with their species. That way, you’ll never be caught off guard by a fish suddenly “going rogue,” but you may pleasantly surprised by an individual proving to be more peaceful than expected.


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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.

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