Samoa Guide, 13. The alogo surgeonfish

Like a lot of other reef fish, the alogo is a territorial animal, which means that it dwells at a particular patch of reef and protects that site from all other fish. The territory of each alogo measures about 5 x 5 feet. There it feeds on the thin film of plant material (algae) that covers the reeftop and appears as a greenish grassy turf. Because of their territorial nature, the alogo space themselves evenly across the reeftop, and as they munch away on the algae-covered rocks, they remind me of a herd of miniature
cows feeding in a distant pasture.

Many other species of coral reef fish are also algae eaters, and two general patterns of feeding have evolved among these species. One is for a species to become territorial and fiercely guard its own algal patch, the other is to be non-territorial and roam around the reef looking for an unguarded patch of algae to eat. To an underwater observer, this dual approach to feeding is readily visible -- most of the reef is picked clean of all edible algae and looks like bare rock, except where a territorial fish guards its lush algal plot.

The feisty alogo defends its plot from all competitors, so the turf algae grows well there and provides all the food the alogo needs. Protection of this garden doesn't come cheaply, however. The alogo must defend its territory every minute of the day from other fish that lurk nearby, waiting for a chance to sneak in and chow down.

That's where the alogo's sharp blade comes in handy (see photo). The alogo will threaten to viciously sideswipe an intruder with this weapon. Most other fish heed the alogo's warning and backoff quickly. It's mostly a bluffing game played repeatedly through the day, and rarely does nyone
get hurt.

Other aspects of the alogo's behavior are fascinating. Every evening at dusk, all the alogo migrate off the reeftop to deeper waters where they will spend the night sleeping in crevices to escape being eaten by predators like sharks (malie) and jacks (malauli, ulua). At dawn, they return by the same route. Their migrations to and from the reeftop look like rush-hour traffic on an underwater highway.

The alogo is a popular Samoan food fish and it is one the most important species of reef fish caught, accounting in some years for up to 30% (by weight) of all reef fish caught in the nearshore subsistence fishery. Most are caught by spear fishermen, particularly at night when the fish are sleeping in reef crevices. Daytime spear fishermen have a much harder time catching them, because the alogo tend to stay just out of spearing range.

At first glance, the reef seems to be an exotic panorama of mass confusion, complete with bizarre shapes of fish painted in psychedelic colors. It's like looking into an overstocked aquarium. But as you frequent the reef more often, you begin to notice some structure to the confusion. Each species is generally found only in certain habitats such as shallow reef flats, sandy bottom areas, or deeper waters.
Many individual fish even take up permanent residence at a particular site rather than roam around. One particular fish I watched stayed at the same coral block for 3 years (it had a unique markings on its body, so I could easily identify it). That coral block was home.

The alogo grows about 8 inches long and weighs half a pound. It is a very attractive fish, with bold yellow, blue, and black horizontal lines on its sides, although its basic color pattern can be swiftly altered depending on the alogo's mood. For example, when the alogo becomes aggressive and chases another fish, its face and fins darken and it looks angry (to me at least).

The alogo lives in the foamy surge zone where the waves crash against the reef. This is not an easy place to live, but the alogo is adept at it. When a really rough wave hits, the alogo darts down into a hole or over the reef edge into the safety of deeper water.

Such stay-at-home behavior is actually quite common among coral reef fishes. One abundant species on our reefs that does this is the alogo, also known as the blue-lined surgeonfish (Acanthurus lineatus) because of its knife-like blade located near its tail. The blade is usually not visible because it is folded away into a groove in the fish's skin. It is a bit poisonous, and careless handling of the fish may cause a puncture and painful swelling in your hand.

American Samoa's coral reefs are truly a wonder of nature. Our sea is home to a very diverse and
colorful assemblage of plants and animals. Some 890 species of fish occur here, which is about twice
the number of marine fish species found in Hawaii.