Patriarchal Fish...The Amazing Story of a "Pimp" Fish :) (A very interesting read)
Species: Labroides dimidiatus
Habitat: laying down the law on coral reefs throughout the Indo-Pacific
If someone has committed a serious crime, most people agree that they should be punished more harshly than if they had committed only a minor misdemeanour. That way, people will be deterred from doing anything really heinous, like molesting children or talking at the theatre.
But this idea that the punishment should fit the crime isn't universal. Humans practise it, and some other animals also punish their fellows for bad behaviour, but until now none has ever been seen systematically varying the severity of the punishment.
Now it turns out that one animal does punish just like a human: the bluestreak cleaner wrasse. But their carefully nuanced punishment of "cheats" is really an elaborate plot to oppress their females.
Reef salon
These tropical fish are one of many species of cleaner fish that remove parasites such as lice from much larger fish. The clients get a valuable service and the cleaner fish get food. Local fish may visit the cleaners every day, and even wide-ranging beasts like sharks will occasionally drop in.
Bluestreak cleaner wrasse have small home territories called cleaning stations. Each male maintains a harem of around 16 females dotted around his territory, who help him service his clients.
These clients recognise cleaner wrasse by their small size and the blue stripe running along their sides. The cleaner wrasse stroke their clients to cement the relationship and ensure that they don't attack them.
Mmmm, mucus
But the wrasse have a serious conflict of interest. Although they will eat parasites off their clients, they actually prefer to eat the clients' mucus. As a result, they are tempted to take a bite out of the client – despite the risk oflosing its custom, or even being attacked.
Nichola Raihani of the ZSL Institute of Zoology in London and colleagues reported last year that male bluestreaks punish their females if they bite a client. Deprived of future foraging opportunities, the males chase the females around and try to bite them. In response, the females refrain from further misbehaviour.
Raihani has now found that the males chase offending females for longer when their crime is more serious. She presented captive pairs with artificial "clients" – actually plexiglas plates – that carried two pieces of prawn, which the wrasse love, and either four or eight fish flakes, which they don't like as much. If either fish ate the prawn the plate was taken away, but they could eat as much fish flake as they pleased.
When the female ate a piece of prawn from a plate that had eight fish flakes – thereby depriving the pair of all those fish flakes – the male chased her more than if the plate had only four fish flakes. When a second eight-fish-flake plate was offered, females who had experienced this severe punishment were less likely to eat the prawn.
"Harsher punishment makes them cooperate more," Raihani says. The males must somehow be judging the seriousness of the females' crimes and punishing accordingly, something no other non-human animal has ever been seen doing.
The system may sound just, but it is actually systematic sexual oppression.
Feminism for fish
All bluestreak cleaner wrasse are born female. The largest individual in a given area changes into a male and dominates the remaining females.
That means each male is under constant threat from his attendant females. If one of them manages to grow bigger than him, she can change sex in just two days and potentially take over his territory.
For a female to grow bigger than her male, she needs to eat more than him. So taking chunks out of client fish could work well for her: she gets a particularly nutritious meal, but her partner gets nothing because the client fish leaves in disgust.
Accordingly, Raihani found that males were more likely to dole out harsh punishments if their partners were a similar size to them. Such large females would have been on the cusp of changing sex, so the males controlled their behaviour more strictly.
For bluestreak cleaner wrasse, fish mucus – the illicit eating thereof – is a feminist issue.
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