There is a "doctor" in the sea, and his "business" is doing well

When thinking of the ferocious sea eels, the sharp-toothed cutlassfish, and the puffy pufferfish, the small animals in the ocean will retreat. However, there is a kind of tiny fish that can boldly swim in the mouths and under the gill covers of these big fish. Even when it encounters danger, these seemingly ferocious animals will protect it. Why is that?

A cleaverfish cleaning the gills of a pufferfish

It turns out that this is a popular "doctor fish" - the cleaver. The cleaver is a species of fish that lives in tropical waters. They like to live in warm shallow reefs in the Indian Ocean and the Pacific Ocean . Their body length is similar to the length of an adult's finger. The back is light brown and the belly is milky white. As shown in the picture above , there is also a gradually widening black stripe on the body of the cleaver extending from the snout to the back of the tail fin, and the light blue area in the back half of the fish body further highlights this black stripe. The rescued fish are mainly identified as doctor fish by the stripes.

However, there are times when they are impersonated: there is a fish called the shield-tooth blenny (wèi) that relies on its longitudinal bands similar to those of the split-lipped fish to mingle among the fish schools, and when the "sick fish" are not paying attention, it uses its sharp teeth to bite the skin of the big fish. Therefore, for health care, the big fish need to remain vigilant and enhance their awareness of discrimination, otherwise they will pay a heavy price.

Shieldtooth Blenny

1. “Shop around” service

How does this doctor treat diseases? The cleaverfish usually has its own "clinic". With its own "clinic", it usually does not go out to see patients. It will wait for "sick fish" to come to the sea near the reef for treatment. It will eat the parasites on the surface of the "sick fish", on the gills, and even in the mouth of the "sick fish". These "sick fish" are very cooperative with the "doctor" and will never swallow the "doctor" by mistake.

The "business" of the cleaver fish is usually good, and there are always patients seeking treatment. When there are too many "sick fish", there will often be a scene of scrambling and crowding. At this time, the cleaver fish, which likes quietness, will hide aside and give up. The "sick fish" will rush to stop it and let it continue to treat everyone.

There are usually two types of people who come to the cleaver fish for treatment: one is the "regular customers" who live nearby, and the other is the "rare customers" who visit temporarily. The cleaver fish often provide better service to the latter because the latter roam around and can "compare prices". If they provide them with good service, they can naturally attract more "repeat customers".

The cleaver fish enters the mouth of a sick fish to treat the disease

How important are cleavers to other fish? Someone once did an experiment like this: All the cleavers in a body of water were removed. Within two days, the area became lifeless. The lively scene of fish swimming in the water was no longer there, and there were only sick fish dying. Later, people put the cleavers back, and not long after, the lively and jubilant scene in the ocean returned.

Cleaver fish for treating oral diseases

2. The superpower of “reversible male and female”

In addition to its superb medical skills, the "doctor fish" also has the ability to "change sex". In the small "society" of the cleaverfish, the largest male fish is the leader, with 3-6 female fish surrounding this "leader". "Sex reversal" occurs 1-2 hours after the leader disappears, and the largest female fish will adopt aggressive behavior like a male fish. After a few hours, this largest female fish can completely replace the leader's position and guard its own territory. After 2-4 days, this new leader will become a male fish.

Sex change of cleaverfish

3. The “Thinker” who “looks in the mirror”

If we find dirt when looking in the mirror, wiping it off seems to be a subconscious action. In the animal kingdom, there are also some smart animals that have the "self" awareness of looking in the mirror. In addition to chimpanzees, elephants, dolphins and crows, the slaty fish is the first fish found to have this ability. Scientists have long used the mirror test to assess whether animals have visual self-cognition and potential self-awareness.

A Japanese research team placed a mirror in a cleft lip fish tank and injected a harmless brown colloid into the parts of the cleft lip fish that needed the help of a mirror to see, such as under the throat skin. After a "mouth fight" (mistaking it for another cleft lip fish) and a "strain test" (moving in front of the mirror to see if the dynamics of the mirror image were consistent with its own), the fish realized that the mirror image was actually itself, and saw the brown spots in the mirror, mistaking them for parasites and trying to rub them off. After the mirror was removed, the fish with dye marks stopped rubbing their bodies. This before-and-after comparison means that the fish can recognize that the reflection in the mirror is its own body.

This self-aware behavior astounded scientists and suggests that wrasses are one of the few animals with an inner life.

After learning about the superpowers of these cleaverfish, do you have a new respect for the doctor fish?