A certain degree of behavioral variability is often seen among individual specimens of the same fish species. But what exactly do I mean by this and why does it matter to marine aquarium hobbyists?

The type of “behavioral variability” I’m referring to here is not, for example, an obligate corallivore butterflyfish (e.g. Chaetodon larvatus) suddenly deciding it prefers to eat algae, or a clownfish observing a parrotfish cloaked in its nighttime mucus cocoon and thinking, “Hmm, very clever. I might give that a try myself. To heck with hiding in this anemone!” (Of course, I’m being ridiculous here. Everyone knows clownfishes don’t speak English. They speak Tagalog.)

Rather, I’m referring to different individuals within a given species exhibiting varying degrees of a particular behavior or characteristic, such as the level of inter- or intraspecific aggression shown to tankmates or the tendency to nip at corals or other sessile invertebrates.

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