Dominic Stone
Fish have muscles, and their anatomy is often shaped by the characteristics of water, the medium in which they live. Fish have a complex muscular system that works in tandem with their skeleton to enable precise control of their swimming movements. The fish's body is divided into a head, trunk, and tail, with the trunk and tail playing a crucial role in locomotion. Fish possess the same three types of muscles as other vertebrates: skeletal, smooth, and cardiac or heart muscle. The skeletal muscle, which makes up most of the fish's mass, is striated and aids in movement. Smooth muscle, found in the digestive tract and organs, is involuntary and helps with functions like peristalsis. Cardiac muscle, found exclusively in the heart, is striated and involuntary, responsible for pumping blood. Additionally, fish have layered muscles, which facilitate their side-to-side movement in water, and their fins are supported and moved by these muscles as well.
| Characteristics | Values |
|---|---|
| Fish have muscles | Yes |
| Types of muscles | Skeletal, smooth, and cardiac or heart muscle |
| Skeletal muscle | Striated and comprises most of a fish's mass |
| Smooth muscle | No skeletal, involuntary, associated with the gut and organs, and part of the circulatory system |
| Cardiac or heart muscle | Non-skeletal, striated, and found only in the heart |
| Muscle composition | Red and white fibres |
| Red muscle fibres | Highly vascularized, contract slowly, sustain contraction, and have aerobic metabolism |
| White muscle fibres | Less vascularized, contract rapidly and less sustainably, and have anaerobic metabolism |
| Pink muscle fibres | Fast contracting, intermediate resistance to fatigue, and intermediate speed of fibre shortening |
| Muscle movement | Layered, unlike other vertebrates |
| Muscle function | Locomotion, swimming, and controlling fins |
| Muscle development | Closely related to the bone to which it is attached and varies with age, exercise, and fish nutritional status |
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What You'll Learn
- Fish have layered muscles, unlike other vertebrates that have bundled muscles
- Fish have three types of muscles: skeletal, smooth, and cardiac
- Skeletal muscle includes cephalic, trunk, tail, and appendicular musculature
- The fish heart has three or four chambers, depending on what is defined as a chamber
- Fish fins are supported by muscles and help the fish to swim, glide, and crawl
Fish have layered muscles, unlike other vertebrates that have bundled muscles
Fish have a complex muscular system that works in harmony with their skeleton, allowing them to move with precision and agility underwater. The muscular structure of fish is notably different from that of other vertebrates. While most vertebrates have bundled muscles, fish possess layered muscles, resembling the layers of an onion or the rings of a tree.
This unique structure of layered muscles is well-suited to the side-to-side undulating movement that fish make when swimming. As fish swim, the muscle blocks on one side contract while those on the opposite side relax, resulting in the fish's body flexing alternately from side to side. This sequential contraction and relaxation of muscle blocks, known as myotomes or myomers, enable the trunk and tail to bend, generating propulsion forces that propel the fish forward through the water.
The layered structure of fish muscles provides several advantages for swimming. Firstly, it allows for a more streamlined body shape, reducing drag and enabling the fish to move through the water with less resistance. Secondly, the layering facilitates the horizontal contraction and relaxation of muscles, which is essential for the side-to-side movement that fish exhibit when swimming. In contrast, bundled muscles are bulkier and better suited for vertical movements, such as closing a jaw or moving a limb, which is why most land vertebrates have evolved with this muscle structure.
The skeleton of a fish provides the necessary support and attachment points for its muscles. Fish skeletons can be composed of either cartilage (in cartilaginous fish) or bone (in bony fish). The endoskeleton of a fish consists of two main components: the axial skeleton, which includes the skull and vertebral column, and the appendicular skeleton, which supports the fins. The fins themselves are composed of bony spines or rays and are supported and controlled by the muscles, allowing the fish to swim, glide, or crawl.
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Fish have three types of muscles: skeletal, smooth, and cardiac
Fish have muscles that work in synchronization with their skeleton, which is formed by bones and cartilage. The fish body is divided into a head, trunk, and tail, and the main skeletal element is the vertebral column. The fins are the most distinctive features of fish, and they are supported and moved by muscles. The skeleton and musculature of a fish allow it to precisely control its swimming movements, making it highly adapted to life underwater.
The two main types of skeletal muscle in fish are red and white. Red muscle is highly vascularized, allowing it to contract slowly and sustain contraction, and it has aerobic metabolism. In contrast, white muscles are less vascularized, contract rapidly but less sustainably, and have anaerobic metabolism. Most of the myotomic muscle is made up of white fibres, while red fibres are located in fine longitudinal bands under the skin.
Some groups of fish also have a third type of muscle called pink muscle, which is arranged in a mosaic pattern between the red and white muscles. Pink muscle fibres contract rapidly, have intermediate resistance to fatigue, and exhibit an intermediate speed of fibre shortening. Additionally, some teleosts have electric organs derived from muscle fibres that have lost their ability to contract but can still generate and accumulate an electrical potential difference.
The heart of a fish, a part of the cardiac muscle system, is often described as two-chambered, consisting of one atrium and one ventricle. However, due to the presence of entry and exit compartments, it can also be described as three- or four-chambered, depending on what is considered a chamber. Fish have a closed circulatory system, similar to humans, where blood is contained within a network of blood vessels.
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Skeletal muscle includes cephalic, trunk, tail, and appendicular musculature
Fish have muscles that work in synchronisation with their skeleton, by means of tendons and ligaments. The fish skeleton is formed by bones and cartilage. The body of a fish is divided into a head, trunk and tail, and the fish's musculature reflects this.
The trunk and tail muscles generate propulsion forces propelling the fish forward through the water. As the muscle blocks on one side contract, those opposite relax, flexing the entire body from side to side. This movement is called lateral undulation and is the most efficient form of propulsion for fish.
There are two main types of skeletal muscle in fish: red and white. Red muscle is highly vascularised, contracts slowly, and has aerobic metabolism. White muscles, on the other hand, are less vascularised, contract rapidly and less sustainably, and have anaerobic metabolism. In some groups of fish, there is also a third type of muscle: pink. This is arranged in a mosaic pattern and is characterised by fast contraction with intermediate resistance to fatigue.
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The fish heart has three or four chambers, depending on what is defined as a chamber
Fish have a complex muscular system that works in synchronisation with their skeleton, tendons, and ligaments. The skeleton is formed by bones and cartilage, and the fish's body is divided into a head, trunk, and tail. The trunk and tail muscles play the most important part in locomotion and are stronger than the appendicular musculature, controlling the fins. The fins are supported and moved by the muscles, which compose the main part of the trunk.
The fish heart typically has two chambers: one atrium to receive blood and one ventricle to pump it. However, the presence of entry and exit compartments that may be called "chambers" means that the fish heart can also be described as having three or four chambers. The atrium and ventricle are sometimes considered the "true chambers", while the others are referred to as "accessory chambers".
The circulatory system of fishes is closed, meaning that blood is contained in a circuit of blood vessels and never leaves these vessels. Deoxygenated blood is carried from the veins to the heart from different parts of the body. The blood is then pumped from the heart to the gills, where it is oxygenated, before being circulated through the rest of the body. This is in contrast to mammals, including humans, which have a four-chambered heart and bidirectional double circulation.
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Fish fins are supported by muscles and help the fish to swim, glide, and crawl
Fish have a complex muscular organisation that works in sync with their skeleton, allowing them to make precise swimming movements. The skeleton of a fish is made of either cartilage or bone, depending on the species. The endoskeleton, or the support structure inside the fish's body, is made up of the axial skeleton (skull and vertebral column) and the appendicular skeleton, which supports the fins.
Fish fins are the most distinctive features of fish. They are either composed of bony spines or rays protruding from the body, with skin covering them. Fins have no direct connection with the spine, except for the caudal fins, and are supported only by muscles. Their principal function is to help the fish swim, but they can also be used for gliding or crawling.
Fins located in different places on the fish serve different purposes, such as moving forward, turning, and keeping an upright position. For example, pectoral fins have been observed to aid in stabilisation at slower speeds, while being held close to the body at high speeds to improve streamlining and reduce drag. Some fish, like the flying fish, have evolved abnormally large pectoral fins that act as airfoils and provide lift when the fish launches itself out of the water.
The skeletal muscle of the trunk and tail plays a crucial role in locomotion and is stronger than the appendicular musculature, which controls the fins. Appendicular muscles are derived from trunk myotomes and play a secondary role in locomotion, especially in species that move through lateral undulation. The muscle blocks on one side contract while those opposite relax, resulting in the fish flexing its body alternately from side to side to generate propulsion forces.
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Frequently asked questions
Yes, fish have muscles. In fact, fish have the same three kinds of muscles as other vertebrates: skeletal, smooth, and cardiac or heart muscle. Fish muscles are layered, unlike the bundled muscles of most other vertebrates.
Fish have three types of muscles: skeletal, smooth, and cardiac or heart muscle. Skeletal muscle comprises most of a fish's mass, excluding the skeleton. Smooth muscle is involuntary and associated with the gut, as well as other organs and the circulatory system. Cardiac or heart muscle is a thick, dark red involuntary muscle that is striated and found only in the heart.
Fish muscles serve various purposes. Skeletal muscles are important for locomotion and swimming, with the trunk and tail muscles playing a crucial role in generating propulsion forces to move the fish forward through the water. Smooth muscles line the digestive tract and are involved in peristalsis, while also being associated with the swim bladder and reproductive and excretory tracts. Cardiac or heart muscle is responsible for the contraction of the heart, pumping blood through the circulatory system.
