Mutualism is a type of relationship that exists between two organisms such that both the organisms benefit from the relationship. One of the most amazing case of mutualism that exists in nature is that of cleaner fish and other bigger fish. What makes it amazing is the fact that the bigger fish usually eat up smaller fish as their food. But in the marine water, they live together sharing a mutually beneficial relationship. The cleaner fish cleans the body of the larger fish and removes the parasites, old scales,worn out tissues and other debris etc. In return, they get food and protection from other predators.

Cleaning place:
Cleaning services is usually done at a special place called cleaning stations. It is a sort of meeting place for the cleaner fish and their client. So, such places have usually a large variety of fish species. Many cleaners may work together at a same cleaning station. The cleaners include different species of wrasse, gobies, cichlids, cleaner shrimp etc. while the clients may include large fish like groupers, snappers, puffer fish, ray fish etc. The large fish do not attack or hunt for food in the cleaning stations. Rather when they visit such cleaning stations to be cleaned, they approach it in a passive way to show that they do not mean any harm. There are some territorial fish who prefer not to visit the cleaning stations. So, some of the cleaners visit  them at their  territory and clean them.

Types of cleaners:
Cleaners are of two types:
Obligate feeders: They exclusively depend on cleaning for their main source of food. So normally they do not survive for long outside their natural environment such as in aquarium. Cleaner wrasse and certain species of gobies are obligate feeders.
Facultative feeders:  They do not depend on cleaning for their food. Apart from the parasites from the body of the client fish, they also eat phytoplankton, algae etc. cleaner shrimps are facultative feeder.

How the cleaners and clients communicate:
A cleaner wrasse fish is recognized by the clients from its appearance: a small size body and a horizontal dark blue stripes which runs from its mouth to the end of its tail. It attracts its clients by making a peculiar movement with their body; they swim up and down while moving their tail in zig- zag motion. The movement is recognized by other larger fish. Likewise a cleaner shrimp signals its customer by moving its antennae when a potential customer approaches it. It is said that the movement is more rapid if it notices any large fish coming near it.
When a client fish wants to be cleaned, it approaches the cleaning stations by swimming vertically with its mouth wide open and its fins spread out. Some of them also slightly change their color. During cleaning the client fish lay motionless; occasionally spreading out its fins or opening the gills where it wants to be cleaned. Often the cleaner fish will enter inside the mouth to remove the debris. When a client had enough of cleaning it gives a slight tremor to signal it wants to move.

Cheating during cleaning:
Even the animal world is not free from deceptions. The saber toothed blenny resembles the wrasse fish in its appearance. So, it takes advantage of it and often tries to blend itself among the wrasse fish. It attracts larger fish by mimicking the cleaner fish. But when a client approaches it, instead of cleaning, it would bite a chunk of its flesh and run away. Some cleaner fish themselves sometimes cheat their clients. They prefer to eat the nutritious healthy skins and scales over the parasites and other debris. So sometimes, they also take a bite of healthy skins. So, in order to avoid being cheated, the clients prefer to go to a familiar cleaner.

 Importance of the cleaners:
Cleaner organisms play a very important role in the ecosystem. By their cleaning activities, they maintain a healthy environment. It is also believed that the presence of cleaner fish and shrimps increases the fish abundance and diversity of that place.