Describing pelagic fishes is easy: They swim, feed and just hang out in the open ocean, a pretty consistent pattern across many ocean-going species. Describing benthic fishes is something else. They live at the bottom of the ocean but they go about their lives in a bunch of differing ways – above, on and sometimes in the seafloor. Some may engage in all three approaches. IF TOLSTOY HAD WRITTEN ABOUT MARINE LIFE, he might have
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If your idea of how fish feed on the reef is ferocious hunters swooping in to grab other fishy prey, you’re very unlikely to see that on most dives. But the 28,000 species of bony fishes in the world’s oceans make their livings in a myriad of ways – and they’re doing it all around you. IF YOU’RE SURPRISED AT HOW LITTLE FISH-ON-FISH FEEDING ACTION YOU ACTUALLY SEE WHILE YOU’RE UNDERWATER, a major reason is
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This is a video sidebar to a longer feature on “How Fish Feed.” Two minutes in length, it shows four types of fish bottomfeeding techniques to find and capture small crustaceans, mollusks and other invertebrates buried in the sand flats surrounding reefs. WHEN YOU’RE TALKING ABOUT LOAN SHARKS AND SHADY LAWYERS, “bottom-feeding” is a disparaging term. But for lots of fish and other reef denizens, it’s a productive way of life. We may see a
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FISH GOTTA SWIM…THEY ALSO GOTTA BREATHE. Or, more properly, they need to continuously restock their blood supply with oxygen from the surrounding water column to maintain the functions of living. Key to how fish breathe is the constant streaming of water past thin, permeable membranes in their gills that enable the diffusion of oxygen from the water into the blood stream. Fish maintain that flow of water by either of two methods – ram ventilation
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The terms Osteichthyes and Chondrichthyes may seem a trifle wonkish, as opposed to street talk like “bony fish,” “sharks” and “rays,” but you will encounter them from time to time and should at least be aware of them. • Osteichthyes (os-tee-ik’-thee-eez, from the Greek for “bone” and “fish”) is the taxonomic class of bony fishes, those with hard, rigid skeletons based on calcium, phosphate and other minerals, smooth scales, covered gills and flexible fins. With
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HOW FISH SLEEP DEPENDS ON THE SPECIES. Nocturnal fishes, like cardinalfishes and those closely packed platoons of grunts and gray snappers you see just hanging around by coralheads and pier pilings during day dives, are likely resting rather than actually sleeping. Some species, like parrotfish, clearly sleep at night, although they seem like they can be awakened with minor disturbances (I base this on my own clumsiness around them on night dives). FISH BASICS ON
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ONE THING IS CLEAR – FISH HAVE BETTER BUOYANCY THAN YOU. And, they don’t have to press any buttons. Many bony fishes have built-in versions of the buoyancy-compensators that divers use to control their position in the water versus changing ambient pressures. In these fishes’ case, it’s an internal gas-filled sac called a swim bladder that automatically works to counteract the ambient pressures applied by the waters surrounding it and keep the fish at neutral
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ANIMALS IN THE OCEAN ARE ALWAYS LOOKING FOR FOOD (and trying to avoid being food). Some times it involves more than one animal. On Bonaire, one year, I encountered several instances of group fish hunting. Sort of. There’s a known phenomenon called Nuclear Hunting in which a small eel (like a goldentail moray) and one or more other fishes (like rock hinds) meet up, identify a nearby coral head as a target site and race toward
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WHETHER FOR HEALTH OR PLEASURE, FISH SOMETIMES ENGAGE IN A PHENOMENON CALLED “FLASHING,” otherwise known as rubbingtheir bodies along the sea bottom. Ned Deloach, in his estimable Reef Fish Behavior, describes it as an effort to deal with the irritation of parasites by scrapping them off, an alternative to the much more commonly seen symbiotic cleaning by small fishes and crustaceans. Discussions about the cleaning dynamic sometimes suggest that, in addition to health benefits, the fish
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