Salmo trutta characteristics, habitat, feeding, behavior

Abraham McLaughlin

Salmo trutta, commonly known as common trout, reo or brown trout, it is a species of fish that belongs to the Actinopterygii class, specifically to the order of the salmoniformes. It is well known worldwide, especially because it has been introduced into ecosystems other than its own, being declared an important invasive species.

This species was first described by the famous Swedish naturalist Carlos Linnaeus. It is found mainly on the European continent and comprises about six subspecies, most of them described by the same specialist.

Common trout. By Helge Busch-Paulick (Grand-Duc @ Wikipedia), CC BY-SA 3.0 de,

The common trout is recognized as a delicacy that is part of the recipes and dishes of different countries throughout the world. In addition, it is an animal that is very interesting, thanks to its behavior, especially during reproduction..

Article index

  • 1 General characteristics
  • 2 Taxonomy
  • 3 Morphology
  • 4 Habitat and distribution
  • 5 Food
    • 5.1 Digestion
  • 6 Playback
    • 6.1 Courtship
    • 6.2 Spawning and fertilization
    • 6.3 Hatching and development
  • 7 Behavior
  • 8 References

General characteristics

Salmo trutta It is an organism classified within the eukaryotes, which means that its cells have a cell nucleus inside which is the DNA forming the chromosomes. Likewise, they are multicellular organisms because they are made up of different types of cells, each with its specific function..

From the embryonic point of view, they are triblastic animals because during their development they present the three germ layers: endoderm, mesoderm and ectoderm. From them all the organs of the adult animal develop. They have bilateral symmetry, which means that they are made up of two exactly equal halves that meet in the longitudinal plane..

It is a dioecious species. There are female individuals and male individuals. They reproduce sexually, without copulation process, with external fertilization.

They are animals that express quite particular behavior and tend to travel long distances, away from their place of birth. Despite this, they return to the same place to mate. In this video you can see this species:


The taxonomic classification of Salmo trutta is the next:

-Domain: Eukarya

-Animalia Kingdom

-Edge: Choradata

-Subphylum: Vertebrata

-Class: Actinopterygii

-Subclass: Neopterygii

-Order: Salmoniformes

-Family: Salmonidae

-Gender: Psalm

-Species: Salmo trutta.


Salmo trutta It is a fish that has an elongated body, whose measurements can reach up to 15 cm. Its body is generally brown in color, but it is not uniform. On the belly it is usually whitish in color, while on the sides it is silver. The flanks and the back have a kind of dark colored spots.

At the level of the head a large mouth is appreciated, which hides a very well endowed jaw. Regarding the fins, it has 2 pelvics, 2 pectorals, 1 dorsal fin, 1 anal fin and 1 caudal fin. As a characteristic element, it has, between the dorsal and caudal fins, another fin known as the adipose fin..

Habitat and distribution

The common trout is a species of fish that is widely distributed in the world geography.

It is possible to find it, naturally, on the European continent, specifically in the Caspian Sea, the Mediterranean Sea, the North Sea and the Black Sea. In addition it is also found in western Asia.

Likewise, this animal is found in other parts of the world, in whose habitats it has been artificially introduced. This has been going on since the late nineteenth century.

Now, with regard to the characteristics of the environment in which the common trout lives, it can be said that it thrives in fresh, very clean and, above all, well oxygenated waters. The trout that have reached maturity are mainly sheltered among the vegetation and roots that are on the shore of certain bodies of water..

It is important to note that Salmo trutta it is a kind of anadromous type. This means that when it is time to reproduce, they move, going up the rivers to spawn (spawn).


Salmo trutta it is a heterotrophic organism, that is, it does not have the ability to synthesize its nutrients. Therefore, it must feed on other living things. In this sense, the common trout is a carnivorous animal, especially ichthyophagus.

The common trout's diet is quite varied, with a wide range of animals on which it feeds. Their nutrition depends on the availability of prey in their habitat at a given time. Because of this, it is known as an opportunistic carnivore..

The diet of Salmo trutta It is made up of aquatic invertebrates, although sometimes it can also feed on terrestrial invertebrates. When the trout reaches an approximate size of 12 cm, it begins to feed on fish. Of course, the common trout feed on prey, the size of which is proportional to the size of this.


The fish ingests the food through the oral cavity. Here the food comes into contact with a substance with a gelatinous texture in which digestive enzymes are dissolved, which initiate the fragmentation of the nutrients..

From there, it passes into the pharynx, which communicates with the esophagus, which is quite short. This communicates with the stomach, where the food comes into contact with digestive enzymes, which further break down and process the nutrients..

Subsequently, the food passes into the intestine, which is the place where the absorption of nutrients takes place. Finally, what is not absorbed and used by the body, is released through the anal orifice.


Salmo trutta It is an animal that reproduces in a sexual way, with external fertilization and indirect development. They are also oviparous.

The time of year greatly influences the reproduction process of this fish. Generally, the process occurs in winter or fall. Most experts set the approximate date between the beginning of October and February.

The first thing that happens when these fish are about to start the reproduction process is that the females dig their nests in the bed to deposit their eggs there..


Once the female has dug her nest, the males, who are ready for reproduction, begin to show a series of behaviors that are related to courtship rituals..

These behaviors include movement patterns during swimming. This behavior has a double function: attracting the attention of females and intimidating other males who also wish to reproduce..

Likewise, according to specialists, another type of behavior related to courtship would be the characteristic tremors of the male. Although others suggest that this last behavior described occurs already when the female has selected the male with whom she is going to mate..

Spawning and fertilization

Once the female has identified the male with whom she is going to mate, she proceeds to deposit the eggs in the nest she dug in the substrate. In this sense, it is possible that the male helps her, stimulating her through tremors that run through her body.

After the female deposits the unfertilized eggs in the nest, the male proceeds to spawn, that is, to release the sperm so that they fertilize the eggs. Here an event occurs that, despite being curious, is not uncommon in the animal kingdom.

The eggs can be fertilized by several males. The larger male will fertilize most of the eggs, and some other males may contribute by fertilizing fewer eggs..

It is important to note that the female does not dig a single nest, but can dig several, some close to each other or far away..

After the eggs are fertilized, the female proceeds to cover them to protect and hide them from possible predators. Despite this, the females of this species do not exercise parental care over the eggs or the young, since after covering them, they leave the place.

The males, on the other hand, can remain on the site, even long after the females are gone, although this has not been shown to be to protect the eggs..

Hatching and development

The incubation period of the eggs is variable and will depend largely on the temperature of the water. The lower the water temperature, the longer it takes for the eggs to hatch.

Once hatching occurs, an individual comes out of the egg that is known as a fingerling and that is a species of larva. This feeds initially on the remains of the egg such as the yolk sac, while it develops. Little by little the individual increases its size and as this happens, its diet also changes..


The behavior of Salmo trutta is determined by several factors, the most significant being reproduction and feeding.

When it comes to breeding, it is well known that trout tend to drift back to their home stream when it is time to mate. This is so because once they have become adults, these animals migrate and move away from their place of origin. They only return to this when they are going to reproduce.

Common trout. Source: Harka, Akos [CC BY (]

It is also important to note that within the populations of Salmo trutta there is a certain social hierarchy. There are the dominant males that are those who were victorious during the fighting to determine which one would fertilize the most eggs. The rest of the individuals in the population are subjected to this.

In this same order of ideas, it is worth mentioning that the males of this species are very territorial. This means that each one has a personal territory, to which they do not allow any other specimen to enter. When that personal territory is threatened, the fish engages in threatening behavior that includes butting, shaking, and biting the opponent..

Food is also a determining factor because it has been shown that, when there is a wide availability of food in an environment, populations are more numerous and the personal territory of each individual is small..

On the contrary, when food sources are scarce, males become more aggressive, defending their individual territory, which increases in size. In this case, the populations of Salmo trutta decrease in size.


  1. Curtis, H., Barnes, S., Schneck, A. and Massarini, A. (2008). Biology. Editorial Médica Panamericana. 7th edition.
  2. González, A., Cortázar, J. and García, D. (2010). Common trout -Salmo trutta Linnaeus, 1758. Virtual Encyclopedia of Spanish Vertebrates.
  3. Hickman, C. P., Roberts, L. S., Larson, A., Ober, W. C., & Garrison, C. (2001). Integrated principles of zoology (Vol. 15). McGraw-Hill
  4. Salmo trutta. Retrieved from:
  5. Sánchez-Hernández, J., Vieira-Lanero, R., Servia, M.J. & Cobo, F. (2011a). First feeding diet of young brown trout fry in a temperate area: disentangling constrains and food selection. Hydrobiology, 663 (1): 109-119.
  6. Sánchez, J. (2009). Feeding biology of common trout (Salmo trutta) in the rivers of Galicia. University of Santiago de Compostela.

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