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The primitive jawless fish have only a single testis located in the midline of the body, although even this forms from the fusion of paired structures in the embryo. [ 41 ] Under a tough membranous shell, the tunica albuginea , the testis of some teleost fish, contains very fine coiled tubes called seminiferous tubules .
The heart pumps the blood in a single loop throughout the body. In most fish, the heart consists of four parts, including two chambers and an entrance and exit. [ 20 ] The first part is the sinus venosus , a thin-walled sac that collects blood from the fish's veins before allowing it to flow to the second part, the atrium , which is a large ...
The heart receives nerve signals from the vagus nerve and from nerves arising from the sympathetic trunk. These nerves act to influence, but not control, the heart rate. Sympathetic nerves also influence the force of heart contraction. [34] Signals that travel along these nerves arise from two paired cardiovascular centres in the medulla oblongata.
[1] [2] This suprabranchial organ, or labyrinth organ, allows some species the capability of traveling short distances on land (walking catfish). [1] Air-breathing organ of walking catfish. The dorsal fin base is very long and is not preceded by a fin spine. The dorsal fin may or may not be continuous with the caudal fin, which is rounded.
Three distinct types of muscle (L to R): Smooth (non-striated) muscle in internal organs, cardiac or heart muscle, and skeletal muscle. There are three distinct types of muscle: skeletal muscle, cardiac or heart muscle, and smooth (non-striated) muscle. Muscles provide strength, balance, posture, movement, and heat for the body to keep warm. [3]
Electric eel anatomy: first detail shows electric organs, made of stacks of electrocytes. Second detail shows an individual cell with ion channels and pumps through the cell membrane; A nerve cell's terminal buttons are releasing neurotransmitters to trigger electrical activity. Final detail shows coiled protein chains of an ion channel.
[6] [8] The fins are otherwise brown, though the body's mottling may extend into the fins. The anal fin has 14 to 17 rays and a round margin. [8] The flathead catfish grows to a length of 155 cm (61 in) [8] and may weigh up to 55.79 kg (123.0 lb), [9] making it the second-largest North American catfish (after the blue catfish, Ictalurus ...
The skeletal elements of the pterygiophore includes basals and radials. The basals are located at the base of the dorsal fin, and are closest to the body. The radials extend outward from the body to support the rest of the fin. [7] These elements serve as attachment sites for epaxial muscles. [8]