SAN FRANCISCO -- Chimps do it, birds do it, and now it turns out that fish do it, too -- they all use tools of one kind or another to catch whatever they need to eat.
Giacomo Bernardi, an evolutionary biologist at the University of California, Santa Cruz, reports that on a recent diving expedition to Australia's Great Barrier Reef he discovered and filmed a wrasse -- also known as an orange dotted tusk fish -- using an underwater rock as an anvil to smash a clam's shell and allow it to devour the flesh inside.
It was, Bernardi said, a remarkable example of how evolution has endowed these fish with the ability to "think forward" and to reason how to obtain hidden sources of food.
All wrasses "are very keen on finding prey, very curious and highly competitive," Bernardi said Wednesday. "Their brains show that they have a very advanced sense of smell and advanced vision."
They also have a fairly advanced ability to put their reasoning to good use, he added.
All that is evidenced in the video Bernardi made, where a large male wrasse of the species Choerodon anchorago uses his pectoral fin to uncover a clam hidden in the sand, then carries the clam, shell and all, in its mouth to a craggy rock wall nearby. There it bashes the clamshell against the rock, and swims away with the clam meat in its mouth, ready to swallow.
Wrasses of many species swim in all the world's oceans. At least two other species have also been reported to use the tool technique, Bernardi said, and evolutionary studies have shown how far back in time they developed their varied feeding methods.
Peter Cowman and colleagues at James Cook University in Australia have used modern genome analysis to trace the history of wrasses since the time when two ancestral lineages diversified nearly 63 million years ago.
During a "wave of innovation" about 23 million years ago, varied wrasse tribes developed different "specialized feeding modes," Cowman said. So by 7.5 million years ago, it appears, some specialized wrasse species had evolved to the point of using rocks to obtain food.
Wrasses aren't the only tool users in the animal kingdom.
Charles Darwin discovered a tribe of finches in the Galapagos Islands that used cactus spines in their beaks to dig out grubs hidden inside the thick leaves of cactus plants.
Jane Goodall, the famed anthropologist and primatologist, found more than 50 years ago that chimpanzees were tool users. She gained that insight in Africa when she watched a chimp she nicknamed David Greybeard and his family stripping the leaves from twigs and poking the twigs into termite mounds to retrieve the succulent insects.
Evolutionary biologist Giacomo Bernardi's video of the tool-using wrasse can be seen at links.sfgate.com/ZLDF
About the wrasse
Range: Wrasses are found all over the world.
Size: More than 600 species of wrasse are known, and most are less than 8 inches, but the Bullhead wrasse can be up to 8 feet long.
Gender: Most wrasses are born as females, while many change sex to male as they reach adulthood.
Social relationships: In many wrasse species, the largest or dominant female changes her sex to become the dominant male when the dominant male in a group dies.
Symbiotic relationships: Many small species are known as "cleaner fish" and swim around the bodies and fins or into the open mouths of other fish to feed on parasites and debris.
Uses: Some colorful species are kept in aquariums as a hobby, while others, known as the Atlantic tautog, are excellent eating.
Source: Chronicle reporting.
(Email science writer David Perlman at firstname.lastname@example.org.)
(Distributed by Scripps Howard News Service, www.scrippsnews.com.)