Regulate specific gravity? Fish regulate the specific gravity of their body with the help of the deflation and inhalation of the swim bladder to match the specific gravity of the surrounding water, which allows the fish to stay in all layers of the water without any effort.
Deep water - shallow water: the pressure of the water decreases, the gas in the swim bladder expands and the specific gravity of the body decreases.
Shallow water-Deep water: the water pressure increases, the volume of the swim bladder compresses, gas is expelled, and the specific gravity of the fish's body increases.
Gas regulation in swim bladder:
Throat bladders: inhale or exhaust gas directly through the swim bladder tube.
Closed swim bladder: by red gland and oval window. The red gland is the gas secretion area and the oval window is the gas absorption area. Closed swim bladder species inflate slower than throat swim bladder species.
Respiration? The swim bladders of lungfish, polydactyls, finfish and bowfin fish act as lungs.
Lungfish: at the beginning of the summer dry season in the burrow, the body secretion of mucus to form a mucus shell - "cocoon", the top of the shell has a small hole, which can be used to breathe into the air, at this time the lungfish is in a state of summer hibernation, completely swim bladder respiration, and so up to a few months. This can be up to several months, and the African lungfish can even sleep for 3 years. When the rainy season comes, the "cocoon" dissolves and the lungfish returns to the water. Regulating the gas in the swim bladder is more useful in slow rise and fall, while it becomes an obstacle for rapid rise or fall.
The swim bladder is a specific gravity regulator, but it is not a motor organ for lifting and sinking. It only helps to raise and lower the fish, and the movement of the fish mainly depends on the movement of fins and muscles.
The swim bladder has both vagal and sympathetic regulation:
The vagus nerve controls the secretion of gases
The sympathetic nerve controls the uptake of gases.3
. Sensory functions? When fish are subjected to pressure changes, the gas in the swim bladder compresses or expands, and the swim bladder can act as a manometer or microphone in the water.
Some fish have swim bladders with varying degrees of connection to the inner ear, giving them a more sensitive sense of hearing and the ability to feel pressure.
Mimic sardines: the anterior end of the swim bladder has two thin tubes leading into the head to connect with the inner ear
Anchovies: the anterior end of the swim bladder has a thin tube that bifurcates forward to become the left and right branches that lead into the head to connect with the inner ear
Saw scales and deep-sea hake: there is a pair of blind sacs at the anterior end of the swim bladder, which are connected to the inner ear
Carp family fishes: the Weber's apparatus connects the swim bladder to the inner ear
Wherever the Weber's apparatus with Weber's apparatus or thin tubes and blind sacs connected to the inner ear have better hearing than fish without this connection, can perceive sounds of higher frequency and lower intensity, and are more alert in their actions.4
. Vocalization
The swim bladder plays an important role in the production of sound.
It is capable of producing ****ing sounds from nearby organs. The sound is produced by the friction of the spatulae and posterior spatulae in the shoulder girdle of the family Lepidopteridae, which can amplify the sound through the swim bladder.
Carp and eel: the swim bladder tube makes a sound when it is deflated.
Some fishes have special articulating muscles, for example, the swim bladder of large and small yellowtail has two long stripes of dark-colored muscle called bulge muscle, which is connected to the swim bladder by ligaments. When the drum muscle is contracted, it can make the swim bladder emit a cooing sound. Experienced fishermen can determine the size and distance of the fish group according to the strength of the sound, and even distinguish between male and female.