CRITTER: How and why the hilu piliko’a fish fight

When you go out diving or snorkeling next time, relax and observe the fish on the reef and see if there seems to be any order involved in their movements. If we were on land in a large city we might notice that there are people who are walking down a sidewalk but not on the road where the cars are and there are people going in and out of stores but not sitting up on top of the store. For a city to operate smoothly there must be an orderly movement of people and it is exactly the same way out on the reef with the fish!

Some fish species have a very distinct territory on the reef and they do not go outside of their territory. They let in certain other fish species into their territory and chase off certain species. Much like a store owner on the side of a street in a human city. The small gregory fish farms its own algae forest on the reef for its own food and it will aggressively chase off other algae eating fish even if the fish is ten times its size. Sometimes the gregory will invite its neighbor in to share some of its garden, much like we would defend our own vegetable garden from a hungry cow but share our veggies with a neighborhood friend.

Certain predator fish don’t have territories like the omilu but they don’t spend long in a territory of a smaller fish. They just zoom in and out of territories trying to grab a smaller fish for dinner much like us humans going shopping at several different stores but not spending much time in each store. Some big algae eating fish like the uhu have a large algae garden for their territory and they keep out their neighbor by patrolling every few hours and chasing off any invading neighbor. There are other fish like moray eel that are like shoplifters where they sneak into a store through the back door, steal some food then take off running!

Once you notice all of the controlled fish movements out on the reef you will see it is much like watching people in a big city where there are many rules governing where you can go and where you cannot go without disrupting the order of the city. Sometimes in a large city fights break out where people disagree about the rules. It is the same out on the coral reef. When people get in a fight they usually don’t get eaten by another animal species but they may harm each other but it is different out on the reef. Certain fish species will fight for their territory but they don’t hurt each other during the fight but they may cause their neighbor to get eaten.

Hilu piliko’a is the common black sided hawkfish that is very territorial and will chase away other hawkfish from its coral home that is usually about the size of a bedroom in your house. Most small fish can’t get into a long fight because they would get eaten by a larger predator fish. Much like us humans wont get into a fight in the middle of a freeway as we might both get run over by a large truck. The hawkfish has developed a way to get into a fight to protect its territory in a unique way. The fish that is the strongest will bite the intruding fish in the mouth and lock jaws much like they are kissing. The stronger fish backs up into a crack in the reef and holds its rival so it can’t move and is exposed out in the open. The stronger fish will then wiggle its tail making a noise that will attract a larger predator fish. When the big fish responds the hawkfish basically feeds its neighbor to the large predator much like we call it when someone gets “thrown under the bus”!

A healthy coral reef is a very complicated city with many rules much like a large city of people on land. In order to protect a large complicated community out on the reef one needs to understand all of the rules the city is operating under. If you go into a city like Honolulu and remove all of the traffic lights the city would turn into one big mess very quickly. It is the exact same thing out on the coral reef. If we wish to save our coral reefs and marine life here in Hawaii we need to understand the rules of the reef first.

•••

Terry Lilley is a marine biologist living in Hanalei Kaua‘i and 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 www.reefguardianshawaii.org.