Cleaner Fish Do Clean!
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Summary
'Cleaner fish' are well known to biologists and tourists on the reef. Just what they do is controversial. Through close observation of the population dynamics of parasites and the use of caged fish on coral reefs, we showed that cleaner fish do indeed have a dramatic effect on the numbers of fish parasites which likely benefit their fish clients.
Project description
For the past 13 years, we have been studying cleaning behaviours on the Great Barrier Reef. Fish cleaning behaviour involves cleaner fish pecking away at the bodies of fish (clients). Often, clients 'pose' motionless, spreading out their fins to give cleaners access. Some even allow cleaners to enter their mouths and gills - this is especially dramatic when the clients are large fish that normally eat other fish! Although cleaning interactions are extremely common, until recently there has been much controversy on why client fish seek the services of cleaners and whether parasites motivate this behaviour.
We found that a single cleaner fish can clean more than 2,300 fish a day from over 130 species and that amazingly, each cleaner eats about 1,200 parasites daily. Interestingly, cleaners preferentially eat gnathiid isopod larvae, parasites similar to ticks on land. These, we found, are one of the most common parasites of coral reef fish, but because they are so mobile they had been missed in most previous parasite surveys of fish. By following fish in the field, we determined that most fish are cleaned daily, with some fish seeking cleaners around 150 times a day.
Recently, we placed fish in cages on coral reefs. This revealed that fish are attacked by gnathiids at a very rapid rate, but at a higher rate in the late afternoon and at night. Fish are therefore attacked by many of these parasites each day. However, we also found that gnathiid abundance on wild fish declined between dawn and sunset. Was this decline due to the actions of cleaners?
To test this, we placed caged fish on reefs with cleaners and on reefs with all cleaners removed and found that without cleaners, parasite numbers increased five-fold between dawn and sunset. This suggests that cleaners cause the daily decline of parasites we observed on wild fish. This is the first study to show that cleaners affect the abundance of parasites on fish and supports the idea that interactions between cleaner fish and clients are mutually beneficial. We also found that parasite infection, not tactile stimulation as it had been previously assumed, motivated fish to seek cleaner fish.
In 2002, in a series of experiments, we showed that cleaning behaviour can be used as a model system to understand the role that partner recognition, partner choice, and partner control play in cooperation among animals. We found that cleaner fish recognize familiar client fish, that clients which had been cheated by cleaners (i.e. bitten) chose to leave such cheaters, and clients which had been cheated controlled their cheating partners by punishing them with vigorous chases.
In 2003 we discovered that cleaner fish affect the abundance and diversity of reef fish. We found that in the absence of cleaner fish (all cleaner fish removed from reefs) fish abundance and diversity was one-fourth and one-half, respectively, compared to that on reefs with cleaner fish. But only mobile fishes were affected with resident fishes not affected at all. Thus many fish appear to choose reefs based on the presence of cleaner fish.
All the above information is published. Please see publications list for more details.
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