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Fish - The oldest and most numerous (about 22 thousand species) group of chordates that inhabit the sea and freshwater bodies. Their whole organization bears the imprint of adaptation to life in a liquid medium (water is 1,300 times denser than air).

During the evolution of the fish acquired streamlined torpedo shapeflattened in the lateral or dorso-ventral (near-bottom fish) directions. The front part of the head (rostrum) has a wedge-shaped shape, which reduces drag. In most fish, the longitudinal axis of the body is elongated. The parts of the body (head, torso, tail) smoothly transform into each other, which creates a laminar (without twists) flow of water around the swimming fish. The dorsal surface of the body of the fish is usually convex and wide, the abdominal - flat and narrow. Located at a certain angle to the body, the pectoral fins and the rostrum, as well as the abdominal and tail fins, create lift, like an airplane wing. The skull of the fish is still connected to the spine. The spine has only two departments - the trunk and caudal. Biconcave vertebrae are connected with the help of articular surfaces, ensuring the strength of the axial skeleton and its mobility mainly in the horizontal plane.

Also formed set of devices that increase the buoyancy of fish. Thus, bone fish have a special hydrostatic organ - the swim bladder, which is a hollow, filled with a mixture of gases, an outgrowth of the initial part of the esophagus. A dense network of blood capillaries is developed in its wall, which allows it to absorb gas from the bladder or to release a gas mixture into the bladder. As a result of a change in the volume of the bubble, the buoyancy of the fish also changes.

In cartilaginous fish swim bladder is absent. The buoyancy of their body is achieved by accumulation of fat in the liver, less often in other organs. Therefore, in some species of sharks it makes up to 25% of the total body mass, whereas in bony fish it is only 1-8%.

Leather fish covered with placoid or bone scales, rich in glands, richly secreting mucus, which reduces the friction of the body against water and performs a protective function.

Musculature fish is represented by homogeneous segments separated by connective tissue layers. Differentiation touched only the muscles that control the movements of the eyes, gill covers of the lower jaws and fins.

Respiratory - Gills - located on the gill arches. Gas exchange is carried out in numerous gill capillaries, the blood in which flows towards the water washing the gills, thus achieving a high degree of extraction of dissolved oxygen from the water.

In fish two-chamber heart (with venous blood), consisting of the atrium and ventricle, one circle of circulation. Organs and tissues are supplied with arterial blood rich in oxygen. Fish are poikilothermic animals, whose vital activity depends on water temperature.

Most of the fish, especially freshwater, are ammoniothelial animals. Their ribbon-like trunk buds remove the final product of nitrogen metabolism - ammonia, the concentration of which is strongly diluted with water entering the body, which reduces its toxicity. A significant part of ammonia is excreted directly through the gill lobes.

Sense organs Fish are adapted to function in the aquatic environment. Due to the low transparency of natural waters, the organ of vision is not adapted to far vision. The flat cornea and an almost spherical lens allow the fish to see only closely spaced objects (up to 10–15 m). The sense of smell in fish is well developed, allows you to stay in the pack and discover food. The significance of the sense of smell and the “chemical memory” of migratory fish is great, with the help of which they find spawning grounds.

Organ of hearing and balance represented only by the inner ear. The high speed of propagation of sound vibrations in water and the high sound conductivity of the tissues of the body of fish make it possible to perceive sounds quite well with the relatively simple structure of the organ of hearing.

Plays an extremely important role in fish life lateral line organ. It is represented by longitudinal channels lying on the sides of the body in the skin and communicating with the external environment through numerous linearly located holes. At the bottom of the channels opposite the holes there are sensitive cells, equipped with cilia. They perceive changes in water pressure. With the help of the lateral line, the fish are oriented in the streams of water, perceive the approach or removal of a predator, prey or partner in the pack, avoid collisions with underwater objects.

Most fish external fertilization, which is typical for primary water chord animals.

Lionfish Habitat and behavior.

Lionfish lives in the Indian and Pacific Ocean off the coast of Japan, Australia and China. They prefer to stay near coral reefs. During the daytime, the lionfish are mostly not mobile, they find shelter in caves, corals or among stones, and rest before hunting. Lionfish, unlike most fish, can not only float horizontally, they are able to assume any position, even roll over or lie on their side. In case of danger, the fish unfolds and spreads its poisonous fins. There is information that the lionfish are capable of collective, organized hunting, having straightened their fins, several lionfish try to surround their prey. They feed on lionfish fish of a suitable size, shrimps, and mollusks.

Lionfish has a bright color, it cautions the other inhabitants of the sea from attack and tells them that the fish is poisonous. The poison is contained in special grooves of spiny rays located on the dorsal and anal fins. The poisonous effect of the winged venom depends on the number of punctured rays, the more their number, the more poison enters the victim's body. When injections of human lionfish, pain shock occurs, but for fish in most cases, the injection will cause a fatal outcome, there are however fish species in the sea for which the lionfish can become prey, cannibalism is also observed among the lionfish.

Are the lionfish poisonous?

The scorpionfish family (scorpions) got its name because of the poisonous rays of the dorsal and anal fins of fish. These rays are arranged like medical needles. When the beam rests on the victim's flesh, the poison from the sac, located in the dorsal musculature of the fish, rises through the channel inside the beam and hits it.
Prick fin on a person acts like a bee sting. Severe pain can last over 3 hours. With more intoxication with zebra venom, weakness, nausea, vomiting, fever with delusions, difficulty breathing, abdominal pain and even loss of consciousness can occur. The strength of the poison attack depends on the size of the fish. Lethal outcomes at pricks of lionfish are very rare, and are associated, rather, with a weakness of the human cardiovascular system. However, special care must be taken when handling the lionfish.

First aid for poisonous injections

If you have been pricked by a lionfish, it is necessary, without waiting for pain reactions, to place the bite in heat. If it is a limb, then you can put it in a bowl with hot water (45º C) for 30-40 minutes or until the pain goes away. The affected areas of the body can also be heated with a hair dryer, being careful not to get a thermal burn. Heat denatures toxic proteins, preventing the spread of toxins in tissues. If possible, it will not be superfluous to contact a medical institution for the provision of qualified assistance.

How to avoid contact with poisonous fish?

First of all, it is necessary to know as much as possible about their habits and the potential threat that they may pose. Naturally, while there is glass between you and the fish, there is no threat. However, when manipulating inside the aquarium and not taking precautions, the likelihood of damage is still present, especially if slaves perceive your hands as a direct threat. In this case, the sea zebra can put forward poisonous spikes and go on the attack. But, as a rule, in spacious aquariums, these fish hide among the scenery until the danger has passed. In order not to fall into the danger zone of scorpions, you need to know where it is at the moment. Therefore, during the start of the manipulations inside the aquarium, it is necessary to track where these fish will go and to be most careful in these places. If these precautions are observed, then the probability of encountering these fish is negligible, since the fish themselves do not attack if they do not feel the imminent danger.

Sea zebra menu

Studies have shown that members of the genus Dendrochirus should consume more crustaceans, and large and active fish of the genus Pterois are more demanding on the presence of fish in their diet, but crabs and shrimps are also important for their normal diet. Observations of marine zebras have also shown that crustaceans are vital for the development and growth of juveniles.
Most zebras start eating at dusk or at night. For example, a spotfin emerges from its hiding place in the afternoon and begins to hunt crabs and shrimp at the end of the day. Volitans lionfish and some of its close relatives are not as secretive as long-distance relatives, and can hunt all day long.

Some zebra fish, in order to increase their chances of prey, can make a collective hunt. Groups of volitans lionfish lead a flock of baitfish away from reef shelters, divide it, and launch an attack.
Watching a zebra fish hunt in an aquarium can be very interesting, but it doesn’t get good nutrition from a zebra from live fish. They need ghost shrimp, crabs, freshwater crayfish, guppies, cardinals, mollies. Unfortunately, many marine aquarium owners feed their zebras with goldfish, which leads to beriberi. Goldfish meat contributes to the breakdown of thiamine (vitamin B1). As a result, the fish become lethargic, their nervous system is inhibited, which in turn often leads to death cases. For a variety of diets of zebra fish, there are frozen foods that contain the inside of shrimp, rich in healthy substances.
Zebra fish eagerly eat only live food, but with aquarium content they should be accustomed to frozen foods. To do this, amateurs go to all sorts of tricks, such as creating zones of turbulence, falling into which pieces of frozen food begin to move.

Feeding frequency

In the natural habitat, the lionfish can eat from one to ten organisms of small and medium size. In the aquarium, it is advisable to feed the zebra two or three times a week, depending on the water temperature. The cooler the water, the less feed must be given. When systematically overfeeding in fish, liver obesity occurs, leading to its dysfunction, suppression of the immune system, bruising and anemia. Variety of diet - very important for the health of zebras. These slaves have a good appetite and are even able to kill themselves with overeating. Perhaps such voracity stimulates them to actively search for food in nature, but in the aquarium, their well-being depends only on the owner's consciousness.

What are the most capricious types of lionfish?

Fu Manchu lionfish (Dendrochirus biocellatus) is considered the most fascinating species. This fish leads a rather secretive lifestyle and is difficult to feed, especially in a spacious aquarium with a lot of food competitors. This species is best kept in a small separate aquarium of 100-150 liters. This capricious zebra is also difficult to translate into frozen food.

Compatibility of zebras with other species

The livability of zebras with other fish mainly depends on their size. Large species are not interested in zebra fish as an object of prey. In turn, the zebras themselves can fall prey to predators such as large bulls and some representatives of wrasses. Often there are zebras aggressive to their relatives. For example, twinspot and shortfin lionfish can continuously chase each other to exhaustion. And, if the dominant individual is not removed from the aquarium, the victim will soon die from hunger and stress. A large aquarium partially solves the problems of good-neighborly relations between zebras. Zebra do not die from the venom of the opponent's thorns, but they may weaken for a while. Intoxication is manifested by rapid breathing and stiffness of movement. In nature, individuals often have one eye, most likely lost as a result of the injection of an aggressive fellow.

Can you keep zebra fish in a reef aquarium?

Lionfish will certainly become a bright addition to the reef aquarium. They do not harm sedentary invertebrates, such as corals and sponges, but they pose a threat to ornamental crustaceans. Fishes do not touch large hermit crabs, however small crabs can become their prey. Similarly, zebras can attack fishes that correspond to the size of their mouths.
Author: M.Tamilin specifically for nemo.by