This eight-inch-long fish with huge eyes and forked tail are common out on the Hawaiian reef, but divers and snorkelers rarely see them. They are usually found in caves and only venture out at night to feed on small shrimp and crabs. If you are out diving, look into a cave in the lava reef with a dive light and you will almost always see these fish darting around, much like a squirrel does up in a tree. There are about 12 species of squirrel fish here in Hawai‘i, and they all look similar, with a variation of colors from yellow, orange to red.
‘Ala‘ihi have large eyes and red colors so they can see well at night. The red wavelength of sunlight is rapidly absorbed by seawater, so a red fish actually looks black underwater, which allows this fish to better hide from predators.
The deeper you go down into the sea, you have more red fish because the sun from above does not reflect off of the red fish and ‘ala‘ihi thinks it is black, not red! For a fish to be black would be very difficult because the black color is a blend of many different genes, but the red color is controlled by a single gene so it is much easier to develop.
At night the squirrel fish will come out of its cave to feed on the sea floor. Other red fish like the aweoweo and ‘u‘u also feed at night, but in more open water areas away from the sea floor. There may be 50 red fish out feeding at night on the edge of the reef at different depths, but when a shark cruises by looking for a meal he may not see any of these fish because they are solid black to the shark and blend into the dark night. Sharks have developed different ways of finding their food items, so when they are down deep they use their electromagnetic sensors on their snout to pick up the vibration of the red fish.
When the shark feeds in shallow water the shark will often use its eyesight to find food.
You can see ‘ala‘ihi in action on the underwater educational web page at underwater2web.com in the movie “The World’s Guide To Hawaiian Reef Fish.}
Terry Lilley is a marine biologist living in Hanalei 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.