There is much more interesting in nature than a person is not interested in due to time constraints or lack of curiosity. For example, the body temperature of 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 subject.
What do ichthyologists say?
The modern classification of the animal world classifies fish as cold-blooded. This means that the body temperature of the fish depends on the temperature indicators of the environment. In warm-blooded representatives of the fauna, the thermometer always shows the same value, with small variations, usually caused by ill health. When cold weather sets in, such animals “warm up” - grow thicker fur or accumulate subcutaneous fat by the frosty months (for example, seals do this).
In fish, body temperature almost always corresponds to water temperature. 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 seriously hurts.
Causes of instability
It is not difficult to explain the unstable body temperature of a fish. Water is an environment with a very high heat capacity. Accordingly, all the heat that the body produces is immediately absorbed by it. Aquatic mammals belonging to warm-blooded have developed complex and particularly powerful personal thermal insulation during evolution. The fish "went" in a different way. Their body adapts to environmental conditions, without wasting energy on meaningless heating of water.
Low efficiency
True, such an arrangement of the body is absolutely impossible to be called perfect: when the degrees of the fish drop, their body temperature becomes insufficient for activity, they become lethargic and sleepy. And if the frosts are too strong, these aquatic vertebrates die, unable to counter anything to the vagaries of the weather.
Muscle warmth
However, the official position of biologists who attribute all fish without exception to cold-blooded is not entirely correct. There are chordates that are part of this group, which are able to maintain a constant temperature, albeit not throughout the body. These include striped tuna. Back in 1835, the British doctor John Davy was struck by the fact that the body temperature in the water of fish of this species exceeds the readings 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. Researchers later found that the source of heat for these fish was intensively working muscles. And his loss in cold water is hindered by a special arrangement of the circulatory system. Owing to partial warm-bloodedness, tuna gains a significant advantage over fellow biological groups - it is able to gain convincing speed when moving, despite its size (tuna often grow to meter, and sometimes even longer).
The herring sharks, which include the "horror of the depths", the white shark, also have the same feature. The muscles of the main mover, the tail, are “warming” for her.
Brain warm
Marlins, swordfish, and sailboats evolved somewhat differently. In their respect, nature acted differently, providing a "heating" of the brain and eye area. If the rest of the body obeys the rules of cold-blooded existence, then these important organs are not dependent on the cooling of the environment. According to ichthyologists, this factor greatly increased the chances of these breeds for survival.
Not so little
If the question of body temperature in fish is scrupulous, it turns out that partial warm-bloodedness is not so rare. Such aquatic inhabitants are about 0.1 percent of the total number of breeds. That is, about 2-2.5 thousand species.
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. An important contribution is made to warm-bloodedness and the way of breathing. In fish, progress in this regard is due to the work of muscles and some features with the regulation of blood flow.
The collapse of authority
On the question of what body temperature in fish can be considered normal, new data have recently appeared. And they can make biologists with ichthyologists radically rethink their ideas about these creatures. As it turned out, there are unique fish in nature - animals with a body temperature that remains constant throughout the body. This fact was established by scientists from the American National Oceanic and Atmospheric Administration. They studied Lampris guttatus; this creature is known in the same way as the ordinary smell, or sunfish. Unlike partially warm-blooded tuna, sharks and mackerel, the smell is stable throughout the body and constantly, not only during movement. Moreover, his personal indicator is quite significant: solar fish are warmer than the environment by as much as five degrees. And not only on the outer integument or in the skeletal muscle. The smell is warm-blooded and at the level of internal organs like the heart, digestive tract and brain.
