According to the study, coral reef fish suffering from parasite infestation cannot think straight, which renders them vulnerable to accidents or predators.
These sick fish will seek out nearby cleaner fish like the blue-streaked cleaner wrasse. The latter eat dead skin and harmful parasites on their "clients," facilitating their recovery from the infestation.
Based on these findings, the study suggests that both parasites and cleaning organisms can indirectly affect the decision-making abilities of other animals.
Parasites cause poor performance during tests for fish, human kids
"We collected wild damselfish with or without access to cleaner wrasse and tested their ability to solve a feeding test in the lab," reported Dr. Sandra Binning, a Canadian marine biologist who authored the study.
Dr. Binning and her colleagues infected some of the captured damselfish with parasites. They then compared the problem-solving performance of healthy specimens with those of infected fish.
"We found that infection with parasites, especially in high numbers, really affects the ability of fish to learn," she reported.
The results are akin to a sick person who attempted to perform any activity that needed thought and concentration.
"When we're sick, our body diverts resources away from our brain towards fighting off the infection. This makes it harder for us to think and learn," Dr. Binning observed.
She cited human studies such as schoolchildren with stomach worms who scored lower than healthy kids.
"Treating these kids with anti-parasite medication improves their performance," she said.
Aquarium fish might be able to enjoy access to medication courtesy of their human owners. But their wild counterparts don't have that luxury.
What they can do is visit the nearest cleaner fish, which can remove their parasites and restore them to good health. The study showed that a fish performed much better during learning tests if it could get cleaning services.
"Cleaner wrasse act like the vets of the sea. Clients visit cleaners to get their parasites removed, and this helps boost their ability to think and solve the test," explained Dr. Binning.
She and her team found out that fish that enjoyed cleaner wrasse services showed lower levels of stress. Furthermore, the presence of a cleaner population draws other fish to the coral reef they live in, increasing the local population and improving biodiversity.
Every cleaner wrasse in an aquarium is one less vet for coral reefs
The appealing behavior and vivid coloration of cleaner wrasse are intended to draw the attention of client fish who need their services. Those qualities also make them very popular fish for aquariums and marine parks.
Since it is extremely difficult to breed them in captivity, all specimens are caught in the wild. Most of them do not survive for long in private aquariums, which fuels the hunt for replacements.
Binning is worried that loss of local cleaners could affect the health of the coral reef communities. (Related: Study shows that a loss of biodiversity can put an entire ecosystem at risk of extinction.)
"It's important that we understand the impacts of reduced access to cleaners on client fishes," she warned.
Arguing that thousands of fish might depend on the services provided by a few cleaner wrasse, Binning urges collectors to consider long-term effects when setting limits on their catches and managing fish populations in marine parks.
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