Curiosities about fish

Fish also sleep, but their sleep can be of two different types. There is waking rest, which corresponds to a kind of wakefulness where the brain is rested but the senses are active, and actual sleep, understood as the suspension of activities. Since they have no eyelids, it is not possible to understand the state of a fish at first sight

In other species, however, sleep is well recognisable, such as for some species of madreporic reef fish, which at night wrap themselves in a thick layer of mucus (with the function of neutralizing odors and flavours, making them invisible to predators) from which they will emerge in the morning. next one; or like others, who sleep leaning on their side. We must not then associate darkness and night with sleep, since there are many nocturnal species, especially predators, which rest during the day and wander around the seabed or rocks at night to feed on sleeping fish

BUT DO FISH DRINK?

The body of living beings is composed of a certain percentage of water; thus that of fish, which live immersed in a fluid (water) in which a few mg of mineral salts per liter are dissolved.

According to the phenomenon known as osmosis, when two solutions with different concentrations are separated by a semi-permeable membrane, the solvent of the less concentrated solution moves towards the other, thus tending to balance the concentration of the two. This also happens in the body of fish, since the skin is nothing more than a semi-permeable membrane. Living in different types of water, however, freshwater and saltwater fish will dispose of water differently.

Saltwater fish live immersed in a solution with a higher concentration than that present in their body; due to this, they are subject to continuous loss of fluids from the skin and especially from the gills. To replace the lost fluids they must drink a lot: the kidneys will filter the salt water and produce very little urine, very concentrated, which will allow the expulsion of the salt.

Conversely, freshwater fish live immersed in a less concentrated solution than the body's: they do not need to drink as it tends to penetrate the skin, diluting the liquids and forcing the fish to expel large quantities of water through urine.

WHAT DO THEY EAT?

Among fish there are species herbivorous, carnivorous, necrophagous and omnivorous. Among herbivores there are species filters, which feed on phytoplankton that filter through structures present in the gills, called gill rakers,

THE scrapers they feed on algae and encrusting ones, ei grazers which feed directly on algae and seagrasses. Carnivores instead use different hunting systems.

Planktophages they filter the water with their gills to feed on zooplankton and other small organisms;

The hunters on the prowl they camouflage themselves on the bottom and wait for prey to approach them;

THE hunters on the lookout they hunt their prey by remaining hidden inside ravines and other hiding places;

The hunters in pursuit they are strong swimmers and actively hunt their prey;

The benthophages they feed on species that live on and in the seabed;

The shredders they have teeth suitable for breaking the exoskeleton of crustaceans, madrepores and echinoderms

The scavengers they feed on dead or injured animals and search for their prey relying on the reception of olfactory, chemical or pressure stimuli.

The omnivores they do not have a well-defined diet and feed on everything edible, whether animal or vegetable.

HOW LONG DO THEY GROW AND LIVE?

Fish are organisms with indeterminate growth, that is, their growth never stops. The greatest growth rate occurs before sexual maturity is reached. Once the gonads are formed, in fact, much of the energy is used for the production of gametes, considerably slowing down the growth rate