Fish Anatomy, Physiology, and Common Species
Fish Anatomy and Physiology
Muscles
Formed by two dorsal and two ventral muscles. Fibered packages are called myotomes, which are separated by a membrane called the myoseptum.
The color of the muscle will be more reddish in more active fish, as in swimming, due to the need for more irrigation. According to the irrigation, muscles can be classified as more or less fatty.
- Fatty fish: > 5% fat content (e.g., oily fish with external metallic coloring, such as teal)
- Medium-fat fish: 2-5% fat content
- Lean fish: < 2% fat content (e.g., white fish with very white muscle)
The skeleton of cartilaginous fish lacks a thoracic box.
Lateral Line
The lateral line runs from the end of the operculum or gill line or cranium to the caudal region.
In cartilaginous fish, ampullae of Lorenzini are formed in the prolongation of the head, receiving electrical stimuli.
Digestive System
In bony fishes, the mouth is terminal, meaning it is at the front or top of the head. This changes in cartilaginous fish, where it is at the bottom, below what we might call the snout.
The teeth in bony fishes are fused to the jaw. In cartilaginous fish, they are not fused, having several rows of teeth. If one falls out, the next one progresses, taking the place of the one that has fallen.
After the mouth comes the larynx, esophagus, and stomach. The liver in cartilaginous fish is very large, which does not happen in bony fish. In the gut, there are ceca for the digestion of foods. There may be one or more; monkfish, for example, have only one cecum, and mackerel have about 200.
In cartilaginous fish, there is a spiral valve in the last stretch of the bowel.
The anus is where waste is expelled from digestion. In cartilaginous fish, there is a chamber where the exit of the digestive tract meets the excretory and reproductive tracts. This chamber is called the cloaca.
The swim bladder is found in the digestive tract and is a chamber that fills with air to regulate the buoyancy of the fish. When the fish fills it with air, it floats, and when it empties it, it sinks. This system is only present in some bony fish that need to change levels or stay at a certain water level. Bony fish lacking this system are those that live on the bottom; they are benthic fish.
Cartilaginous fish lack a swim bladder. They are capable of floating due to their large liver and the disposition of their pectoral fins. They are always moving, as their skeleton is lighter.
Respiratory System
Water enters through the mouth and gills, which use the oxygen in the water because of the thin sheets that are in the gills.
In bony fish, there is only one branchial chamber. All the gills are well communicated with the outside, which is protected by the operculum, a bone that closes it.
In cartilaginous fish, there is a chamber for each gill, one on the right and one on the left, called gill slits.
The operation is as follows: Water enters the mouth, passes through the gills, and exits through the gill slits, capturing the oxygen dissolved in water. In cartilaginous fish, the spiracle contributes to respiration.
Planktivorous fish that feed on plankton are filter feeders, filtering water and holding ingested plankton in communication with the gut and bronchi, separating the plankton, which goes to the gut, and oxygen, which goes to the gills.
Circulatory System
Circulation of blood through blood vessels: veins, arteries, and capillaries.
The heart pumps blood and has two chambers: an atrium and a ventricle.
The blood carries CO2, passes through the atrium to the ventricle, and from there to the gills, where gas exchange occurs. It then sends oxygenated blood throughout the body.
The circulatory circuit is simple, and there is no mixture of blood.
Types of Fish
Salmon
Teleost fish in the clupeoid group. They have an adipose fin.
Types of salmon: Salmon, smelts, capelin.
Atlantic salmon: After one or two years in the river, they go down to the sea, where they remain at large for three years. Before going to sea, they undergo morphological and physiological changes. Growth in the sea is faster, and after a year of residence, they double in size. Upon reaching sexual maturity at two to three years of their marine life, they return to rivers to reproduce, beginning a long migration. In Spain, the return to the river begins in January and lasts until the summer when they spawn. During the ascent, they live on stored fat. Upon reaching the top of the rivers, they lose all their strength, but their sexual organs are already eligible to make the start. They die after spawning.
Gadoids and Merlucids
Teleost fish, demersal, living near the bottom, although generally separated from it at night. They are migrants from grazing areas to spawning areas, which takes advantage of large concentrations to fish them. The pelagic eggs and larvae complete their development on the surface of the water.