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Fish Outgrow Aquariums. Corals, Too. What to Do About It?

Leather Coral Outgrowing Aquarium

First, congratulations! This is most likely a pretty healthy tank. Fish outgrow aquariums, as do corals, when a healthy tank thrives for a long enough time.

Doesn’t a fish just grow to the size of its tank?

Generally speaking, while a number of fish do grow to a certain size based on the tank, it’s not because that’s the way it’s supposed to work, naturally. When this happens, something has occurred to stunt its growth, and regardless of what we humans think is happening, it’s pretty stressful for the fish.


So what happens when it outgrows an aquarium?

I generally classify this into two categories: Maturity and Size.


Fish maturity in the aquarium:

Fish enter aquarium communities at all sorts of ages, and over time, they mature, just like we do. When fish mature, their adult  personalities begin to come out, and some start to become aggressive with their tankmates.

It is for this reason that we get more requests to remove Maroon Clownfish from aquariums. They have taken control of the aquarium, and new additions are risky, at best, because of their aggression.

One customer had a Trigger fish which had been living peacefully in the aquarium’s community for a couple years, and then one night, it attacked its other tankmates until only a few fish were left (which is one of the reasons that I am often a bit skeptical when I hear someone say “it’s working fine in my aquarium.”).

The fish has grown too big for the aquarium

I usually see this manifest in one of three ways.

With fish, I have seen them outcompete the other fish for food, and the others begin to slowly starve or suffer from malnutrition.

The other behavior I have seen is that they just have such a demand for space that they shoo the other fish away, and the tank gets stressed and sick with their behavior.

Another way, which is often overlooked, involves corals and clams in tanks which are doing really well with plenty of growth.

Corals and clams demand a lot of calcium, and they pull it from the water. As they grow, so does their demand, until they need more than the tank can provide them, even with a calcium reactor. Eventually, something (or somethings) starve from the lack of calcium.


So what do you do when a fish or coral outgrows the aquarium?

In my opinion, the most humane way to handle this is to remove the animal which has outgrown the aquarium. There is not a large market for large fish, but your community may have places or people who accept them. Also, some large corals react poorly when being moved from their home.

ReefTechs operates a fish and coral rescue in which unwanted animals can be removed from their situations and rehomed into tanks which can support them. Ask your ReefTechs Technician for details or to make arrangements.

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