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Thin is 'in' for Reef Species, Like the Filefish

Why being 'laterally compressed' can make all the difference to a fish.

A few years ago, we had the good fortune to be snorkeling over a shallow reef in the Bahamas and came across a scrawled filefish. An adult, about two feet long.

As they tend to do, this filefish hung vertically on the reef, pretending to be coral. It would turn its eyes to look at us, then look away. Look at us, then look away. You could almost hear it saying, “I’m not here. You don’t see me.”

We’ve been suckers for filefish ever since.

They’re just a fun-looking fish. Their bodies sport an irregular splash of dark spots but also electric-blue dots and dashes, all against a field of tan, gray or olive, which the fish can lighten or darken as needed for camouflage. Indeed, some snorkelers in our group probably did swim by that filefish without seeing it.

We also love their shape, particularly their oversized broom tail and their long snout, which ends in a toothy puckered mouth. And this is a pretty big fish for coral reefs, growing up to 3 feet long. How can a fish that big escape predators on a reef? Well, of course, they’ll hang vertically amidst the reef in hopes that no one sees them. But their bodies also are – as scientists would say of most reef species – flattened or compressed laterally. In other words, when viewed head-on, filefish are thin. Really thin.

So let’s talk about fish shapes for a paragraph. Fish that swim only out in the open water – pelagic fish – are built for speed. They’re streamlined to move through the water as efficiently as possible. Reef fish, however, work in tighter spaces. They’ve adapted to be thin, and that helps them to dart and turn quickly. For them, maneuverability may be more important than straight-line speed.

Also, being really thin lets them hide in cracks and crevices.

Scrawled filefish have another special safety adaptation: the first spine on their dorsal (or top) fin is long and can be made to lock straight up. A smaller spine on its belly can do the same thing. If a filefish is hiding in a crevice, it can use those spines to hold it in place, even if a predator is trying to yank it out.

Scrawled filefish (Aluterus scriptus) are found in tropical waters around much of the globe. They graze on plants (algae, seagrass) and bottom invertebrates (such as hydrozoans, gorgonians and anemones).

They’re not native to Long Island Sound but they may sometimes catch a ride up here in the summer aboard the Gulf Stream current. That’s why The Maritime Aquarium displays a scrawled filefish in our “Tropical Travelers” exhibit. 

This post is contributed by a community member. The views expressed in this blog are those of the author and do not necessarily reflect those of Patch Media Corporation. Everyone is welcome to submit a post to Patch. If you'd like to post a blog, go here to get started.

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