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The Reef Bully: Confession of a Misunderstood Fish

The Reef Bully: Confession of a Misunderstood Fish

  By Gdiggers – Own work, CC BY-SA 3.0,

Have you ever asked yourself: “why is my fish such a jerk?”

You are not alone. 

However, it’s costly and tedious to be a bully on the reef. Rather than lazing around in a corner, enjoy the sunlight, gentle wave, and the beautiful corals, the bully has to patrol the rocks endlessly, flaring the fins, and put up impressive colour display, chase, nip and fight some harmless new comers. The opportunity cost for reef bullies are extremely high, they have less time to feed; they use up more energy swimming; and they also expose themselves more to the potential predators.

Then why would they do that?

Let us consider the fundamental drive of life – to reproduce, and perhaps we can make sense of these “unreasonable” creatures.

Purpose of Life

In order to produce the next generation, reef fishes needs to be able to navigate through many challenges. It needs to avoid predators so that it won’t meet an untimely demise. It need to find sufficient food source to allow it to grow and become mature. It need to have an opportunity to spawn with another fish. Both parent fishes needs to be healthy enough to produce viable offspring. All these are life-and-death situations for reef fishes.

Predator Evasion

Let’s take about predator evasion first. On the coral reef, a fish can’t call 995 and expect some law enforcement to save them from a hungry grouper. Some fishes arms themselves with spines (like porcupine fish) or toxins (such as rabbitfishes), but most of the fishes are basically swimming McNuggets. For these fishes, the only possible defence is to run and hide. This need becomes more pressing as the fishes prepare to go to sleep, becoming completely defenceless and mostly unawares. Therefore a place to hide is critical for any reef fish. Losing the right to this shelter is tantamount to a death sentence to a hungry mouth. Wouldn’t the fish be very worked up if someone threatens to evict them? It’s a fight for live.


The next item on the checklist is food. The reef is teeming with life, but for fishes, food is nevertheless in short supply. Herbivorous fish, such as clown tang, has to take 17000 bites per day to eat enough algae for its growth needs. If there is competitors which feeds in the same area, the grazing pressure increases, and there is a risk of insufficient food for everyone. Therefore, reef fishes defends their feeding turf very aggressively, especially from those fishes which shares similar food source with them.

 By Paul Asman and Jill Lenoble – lined surgeonfish Acanthurus lineatus (striped surgeonfish)Uploaded by Amada44, CC BY 2.0,


Lastly, let’s look at the ultimate goal of the fishes, to reproduce and keep its genes in the gene pool. The right of breeding is hard earned in many reef fishes, clownfishes, anthias, wrasses among others. Many of these fishes are hermaphrodites. The ability to change sex maximizes the possibility of having spawning population in a particular site, it also allows selection to take place so that only the fittest individuals are able to reproduce. Therefore, the alpha and beta of the group have to constantly harass and suppress the smaller ones, minimizing the possibility that one of them will grow faster and bigger, and usurp their position.

 By Nhobgood – Own work, CC BY-SA 3.0,

In the Aquarium

So, a fish have to behave aggressively not because they are born a jerk. They do it because it’s the only way for them to survive and reproduce. These behaviour are written in the genes from centuries of evolution, and it’s not about to change when the fish is moved into an aquarium.

As a conscientious aquarist, we can’t change what the nature intends, but we can try the level best to mitigate some of these stressors, and hope for the best.

  • Allow for correctly sized and shaped hiding place for every fish in the aqua scape. A cave will do very little to make a cleaner wrasse comfortable, while chromis would much prefer a colony of acropora rather than a pile of rocks.
  • Provide sufficient food for the fishes, both in terms of grazing/hunting opportunities, as well as feeding of prepared food. Abundance of food will not remove the drive to defend a grazing ground, but it can potentially reduce such behaviour.
  • Understand and provide proper social structure for the fishes we keep. For example, lyretail anthias lives in harems, where a dominant male keeps a group of females in check. The constant harassment prevents the females from changing to male. If the harem structure is absent, when an aquarist keeps a pair, for example. The harassment will be focused on a single female, which will have a higher chance of succumbing.
  • Finally, understand that fishes are individuals. They can have their own quirks. As pet owners, we need to accept them for what they are, and do what we can to care for them. We must also understand that as fishes grow and mature, they needs may change, and be prepared to cater to the new needs.

Jia En

I'm a skeptical reefer. I believe progress in reefing comes from questioning, observing, and experimenting.
I enjoy discussion on everything reef related. I hope what I wrote can be a start to interesting discussion.