When a diver swimming along a reef encounters a school of snapper fish, they are surprised by the remarkable stillness of the group. It’s as if the fish suddenly become suspended in the water.
As the diver approaches the fish school, they discover that their reaction is very slow and without any sudden movements. The fish divide into small groups, circling around a confined area, making way for the occasional underwater visitor, and then regrouping in the same position. Their movements are so slow and deliberate that it feels like one could touch them.
The explanation for this behavior is quite simple: they are sleeping. Snapper fish gather in groups during the day to rest, and at night, they disperse and search for food individually. Between midnight and dawn, the school reunites in the same location to sleep. Their sleep is not the same as that of humans. Firstly, their lack of eyelids prevents them from closing their eyes. Moreover, for them, sleep is not a state of unconsciousness, as that would be very dangerous, leaving them vulnerable to predators. Their sleep consists of deep muscular relaxation achieved through immobility. Their brain slows down but remains somewhat vigilant to prevent any sudden attack.
An interesting fact is that they are called “snapper” because when a live specimen is captured and brought to the surface, a sound similar to snoring can be heard. The sound is produced by the friction of pharyngeal teeth and is amplified by the swim bladder of the fish, which, being an air-filled space, acts as an amplifier. It is believed that this sound is part of a very primitive communication system, serving as a warning signal to the nearest fish that someone is approaching.
It is likely that they emit different sounds depending on whether they perceive the visit as dangerous or not. The sound is transmitted throughout the group, which reacts slowly or not at all, depending on the circumstances. This is why they gather to sleep, as a hundred eyes see more than two, and they choose the same location each day because it is simply a “meeting point” that they all remember easily. So, it is a matter of moving slowly and trying not to disturb the sleep of these peaceful inhabitants of the depths who work at night.
“One cannot defend what one does not love, and one cannot love what one does not know.”