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In vertebrates, the gallbladder, also known as the cholecyst, is a small hollow organ where bile is stored and concentrated before it is released into the small intestine. In humans, the pear-shaped gallbladder lies beneath the liver , although the structure and position of the gallbladder can vary significantly among animal species.
Fish typically have quite small brains relative to body size compared with other vertebrates, typically one-fifteenth the brain mass of a similarly sized bird or mammal. [59] However, some fish have relatively large brains, most notably mormyrids and sharks, which have brains about as massive relative to body weight as birds and marsupials. [60]
The combination of gases in the bladder varies. In shallow water fish, the ratios closely approximate that of the atmosphere, while deep sea fish tend to have higher percentages of oxygen. For instance, the eel Synaphobranchus has been observed to have 75.1% oxygen, 20.5% nitrogen, 3.1% carbon dioxide, and 0.4% argon in its swim bladder.
Pharyngeal teeth are teeth in the pharyngeal arch of the throat of cyprinids, suckers, and a number of other fish species otherwise lacking teeth. [ 1 ] Many popular aquarium fish such as goldfish and loaches have these structures.
The scales are small. As with many deep-living fish, the lateral line system in grenadiers is well-developed; it is further aided by numerous chemoreceptors located on the head and lips and chemosensory barbels underneath the chin. Benthic species have swim bladders with unique muscles attached to them. The animals are thought to use these ...
Many fish also have chemoreceptors that are responsible for extraordinary senses of taste and smell. Although they have ears, many fish may not hear very well. Most fish have sensitive receptors that form the lateral line system, which detects gentle currents and vibrations, and senses the motion of nearby fish and prey. [53]
They do, however, have a number of unique features in common. Firstly, their cerebellum is greatly enlarged, enabling them to interpret complex bio-electrical signals, [2] and to the large size of the valve. [3] [4] Secondly, an auditory vesicle (a small bladder) is present inside the labyrinth of the left and right inner ears.
Bony fish have fin spines called lepidotrichia or "rays" (due to how the spines spread open). They typically have swim bladders, which allow the fish to alter the relative density of its body and thus the buoyancy, so it can sink or float without having to use the fins to swim up and down. [14]