In nature, there are many interesting things that a person, due to limited time or lack of curiosity, is not interested in. For example, the body temperature of a fish is a nuance that we studied in biology at school. And he was instantly forgotten, leaving the walls of the alma mater. The only exceptions are those who have chosen biology as their specialization. Well, maybe even the fishermen can say a few words on this topic.
What do ichthyologists say?
The modern classification of the animal world classifies fish as cold-blooded. This means that the body temperature of fish depends on the temperature of the environment. In warm-blooded fauna, the thermometer always shows the same value, with slight variations, usually caused by ill he alth. When cold weather sets in, such animals “warm up” - they grow thicker fur or accumulate subcutaneous fat by the frosty months (this is what, for example, seals do).
At the fishbody temperature almost always corresponds to the temperature of the water. With active movement, it can increase, but slightly: by 0.2-0.3 degrees Celsius. If the temperature of this aquatic animal exceeds the "warmth" of the sea or river by two degrees, then it is seriously ill.
Causes of instability
Explaining the unstable body temperature of a fish is easy. Water is a medium with a very high heat capacity. Accordingly, all the heat that the body produces is immediately absorbed by it. Aquatic mammals, related to warm-blooded animals, have developed complex and especially powerful personal thermal insulation during the course of evolution. The fish "went" the other way. Their body adapts to environmental conditions, not wasting energy on senseless heating of water.
Low efficiency
True, such a device of the body cannot be called perfect: when the degrees fall, the fish, whose body temperature becomes insufficient for activity, become lethargic and sleepy. And if the frosts are too strong, these aquatic vertebrates die, unable to resist the vagaries of the weather.
Muscular warm-bloodedness
However, the official position of biologists, who classify all fish without exception as cold-blooded, is not entirely correct. There are chordates in this group that are able to maintain a constant temperature, albeit not throughout the body. These include skipjack tuna. Back in 1835, the British physician John Davy was amazed by the fact that the body temperature in the water of this species of fishexceeds the reading of a thermometer lowered into the habitat by as much as 10 degrees Celsius.
Moreover, tuna is found in waters with different temperature indicators, ignoring only the Arctic expanses. Later, researchers found that the source of heat for these fish is intensely working muscles. And its losses in cold water are prevented by a special arrangement of the circulatory system. Due to partial warm-bloodedness, tuna acquires a serious advantage over its biological group brethren - it is able to gain convincing speed when moving, despite its size (tunas often grow to a meter, and sometimes more, in length).
The herring sharks, which include the "horror of the depths", the white shark, also have the same feature. It is mainly the muscles of the main mover - the tail that "warm up" in it.
Brain warm
Marlins, swordfish and sailboats evolved somewhat differently. In their regard, nature acted differently, providing “heating” for the brain and eye area. If the rest of the body obeys the rules of cold-blooded existence, then these important organs do not depend on the cooling of the environment. According to ichthyologists, this factor greatly increased the chances of these breeds to survive.
Not so little
If you scrupulously approach the issue of body temperature in fish, it turns out that partial warm-bloodedness is not such a rarity. Such aquatic inhabitants are about 0.1 percent of the total number of breeds. That is, approximately2-2, 5 thousand kinds.
It is clear that their thermoregulation is fundamentally different from that characteristic of warm-blooded mammals and birds. More highly organized creatures have a radically different structure of the heart in particular and blood circulation in general. It makes an important contribution to warm-bloodedness and the way of breathing. In fish, progress in this regard is due to the work of the muscles and some features with the regulation of blood flow.
Collapse of authorities
In the question of what body temperature in fish can be considered the norm, not so long ago, new data appeared. And they can force biologists and ichthyologists to radically reconsider their ideas about these creatures. As it turned out, in nature there are unique fish - animals with a body temperature that remains constant throughout the body. This fact was established by scientists from the US National Oceanic and Atmospheric Administration. They studied Lampris guttatus; this creature is also known as the common opah, or sunfish. Unlike partially warm-blooded tuna, sharks and mackerel, opah maintains a stable temperature throughout the body and constantly, not only while moving. Moreover, his personal indicator is quite significant: the sunfish is warmer than the environment by as much as five degrees. And not only on the outer covers or in the skeletal muscles. Opah is warm-blooded and at the level of internal organs like the heart, digestive tract and brain.
For reference
Sunfish lives at a depth of 200-400meters, is a predator. The main diet of the opah consists of squid and medium-sized fish. Very fast, and the speed of the sunfish is ensured by an extremely efficient metabolism.
Who knows, maybe in the future other cold-blooded fish will be found, which in fact are not.
