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March 19, 2015

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Little fish found to kill smaller ones by posing as family

March 19, 2015
Courtesy of the University of Basel
and World Science staff

A lit­tle fish in the Aus­tral­ian Great Bar­ri­er Reef preys on smaller fish by mas­quer­ad­ing as an adult of their own spe­cies, a study has found.

The dusky dot­ty­back’s dis­guise—ac­com­plished by chang­ing col­ors—al­so helps pro­tect it from its own preda­tors, ac­cord­ing to the stu­dy, pub­lished in the lat­est is­sue of the jour­nal Cur­rent Bi­ol­o­gy.

A dottyback (in the back) eyes its young dam­sel­fish prey. (Cour­tesy Chris­toph­er E. Mir­bach)


Trop­i­cal cor­al reefs like the Great Bar­ri­er are among the world’s most col­or­ful habi­tats. But that still puz­zles sci­en­tists: Why do these reefs host so many col­or­ful or­gan­isms such as cor­als, crus­taceans and fish?

An­i­mals com­monly use de­cep­tion to in­crease ac­cess to food, re­pro­duc­tive op­por­tun­i­ties or pro­tection, not­ed the study lead­ers, ev­o­lu­tion­ary bi­ol­o­gists Fabio Cor­tesi and Wal­ter Salz­burger from the Uni­vers­ity of Ba­sel in Switz­er­land. But an im­pos­tor risks be­ing busted if it uses the fraud too of­ten or out of con­text. 

The re­search­ers no­ticed that the dusky dot­ty­backs (scien­ti­fic name Pseu­dochromis fus­cus) change their col­or to mim­ic dif­fer­ent harm­less fish spe­cies in their sur­round­ings. But they can al­so change back again, “mak­ing it dif­fi­cult for their prey to learn about the threat,” said Cor­tesi. 

“This strat­e­gy is very si­m­i­lar to the clas­sic ex­am­ple of the wolf in sheep’s cloth­ing. How­ev­er, while the wolf may be found out even­tu­al­ly, dot­ty­backs are able to change” again.

Chang­ing col­or al­so pro­tects them from their own preda­tors, the in­ves­ti­ga­tors said. They trained big­ger cor­al trout to strike at im­ages of dot­ty­backs in front of dif­fer­ent back­grounds. The ex­pe­ri­ment found cor­al trout struck less of­ten at dot­ty­back im­ages col­or-matched to the nat­u­ral back­ground of fish the dot­ty­back mim­icked. 

It’s “an in­tri­cate form of mim­icry that not only gives them a pred­a­to­ry ad­van­tage but al­so pro­tects them from their own preda­tors,” Cortesi said.

Cor­al reef in­hab­i­tants show an al­most inconceiva­ble va­ri­e­ty in col­or and shapes, many of which serve as warn­ings or in­crease pro­tection from preda­tors, he added. Stone­fish hide by mim­icking their sur­round­ings, sea slugs use viv­id col­ors to warn preda­tors about their dis­taste­ful­ness and cut­tle­fish can change in a mat­ter of sec­onds to ei­ther court po­ten­tial sex­u­al part­ners or to hide.


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A little fish in the Australian Great Barrier Reef preys on smaller fish by masquerading as an adult of their own species, a study has found. The dusky dottyback’s disguise—accomplished by changing colors—also helps protect it from its own predators, according to the study, published in the latest issue of the journal Current Biology. Tropical coral reefs like the Great Barrier are among the world’s most colorful habitats. But that still puzzles scientists: Why do these reefs host so many colorful organisms such as corals, crustaceans and fish? Animals commonly use deception to increase access to food, reproductive opportunities or protection, noted the study leaders, evolutionary biologists Fabio Cortesi and Walter Salzburger from the University of Basel in Switzerland. But an impostor risks being busted if it uses the fraud too often or out of context. The researchers noticed that the dusky dottybacks (Pseudochromis fuscus) change their color to mimic different harmless fish species in their surroundings. But they can also change back again, “making it difficult for their prey to learn about the threat,” said Fabio Cortesi. “This strategy is very similar to the classic example of the wolf in sheep’s clothing. However, while the wolf may be found out eventually, dottybacks are able to change” again. Changing color also protects them from their own predators, the investigators said. They trained bigger coral trout to strike at images of dottybacks in front of different backgrounds. The experiment showed that coral trout struck significantly less often at the dottyback images that were color-matched to the natural background of those fish mimicked by the dottyback. It’s “an intricate form of mimicry that not only gives them a predatory advantage but also protects them from their own predators,” Cortesi said. Coral reef inhabitants show an almost inconceivable variety in color and shapes, many of which serve as warnings or increase protection from predators, he added. Stonefish hide by mimicking their surroundings, sea slugs use vivid colors to warn predators about their distastefulness and cuttlefish can change in a matter of seconds to either court potential sexual partners or to hide.