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CRITTER: Meet the gregory fish, the undersea farmer

This 3-inch-long, gray-colored gregory with yellow eyes is the most aggressive fish on the Hawaiian coral reef. The gregory (a damselfish) are highly territorial, and they keep all other fish away from their home by attacking bigger fish, including scuba divers. These small fish dictate where on the reef larger fish can feed, and they have little fear of larger fish that could easily eat them.

The gregory has its own all-purpose territory that is about 2- to 4-foot wide, where it has a hole to hide in and a nesting site along with its own filamentous algae farm. The gregory will defend its farm and chase away other algae-eating fish, including an entire school of much larger surgeonfish.

The gregory grows a certain type of algae for food, and removes any other algae species it does not want to eat, very similar to us humans on land having our own vegetable garden and removing the weeds. This small fish creates its own space on the reef, grows its own food, and will even chase away another gregory fish unless it is mating season.

Algae-eating fish like the manini are very important to the health of the coral reef because they eat algae, which gives room for coral to grow.

But huge schools of manini stay away from the gregory’s private farm. The small gregory determines where on the reef the other algae-eating fish can feed, which then determines where the predator fish can feed. It is just amazing that this 3-inch fish can determine the feeding pattern on an entire coral reef.

When out diving you can find the gregory in shallow, calm water, and if you look close you can see its home garden. But if you get too close, the fish will attack your mask to keep you away from its private farm. The coral reef is a very complex ecosystem, and the marine life creates many boundaries and territories that dictate where the fish feed and live. If one was to remove a gregory from the coral reef, that could change the entire reef ecosystem.

You can see the gregory in action in my Hawaiian coral reef educational series on my website at and Youtube channel at Underwater2web.


Terry Lilley is a marine biologist living in Hanalei. He is co-founder of Reef Guardians Hawai‘i, a nonprofit on a mission to provide education and resources to protect the coral reef. To donate to Reef Guardians Hawai‘i go to
Source: The Garden Island

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