Animal Diversity Web

Geographic Range

Marbled trout, Salmo marmoratus, are endemic to the Adriatic Basin of northern Italy and the western Balkans, which includes the Isonzo, Adige, Po, Neretva, Brenta, Adriatic, and Tagliamento River basins. Their geographic distribution is considered restricted (Lorenzoni et al., 2012).

• Biogeographic Regions
• palearctic
  • native

Habitat

Marbled trout are freshwater fish typically found in the headwaters of rivers and in small mountain streams with gravelly beds (Chiesa et al., 2016; Marchi et al., 2016). They, like most other trout, seek out holes in the riverbed near the bank to hide in. They prefer cold, fast-flowing waters (Cuvier et al. 1829). While these fish are almost exclusively found in freshwater, there has been a report of marbled trout being captured by a commercial fisherman in the Adriatic Sea (Soldo, 2012).

• Habitat Regions
• temperate
• freshwater

• Aquatic Biomes
• rivers and streams

Physical Description

Marbled trout resemble their close relative, brown trout (Salmo trutta), though they differ in several ways. Marbled trout have an elongate and circular body, with the head making up roughly 25% of the total body length. These fish can grow up to a meter long and up to 30 kilograms, making it the second largest salmonid in Europe (Crivelli et al., 2000). The coloration ranges from gray to green, with dark lines forming a marbled pattern, hence its name (Muhamedagic et al., 2008). Some specimens also have red dots along the body (Cuvier et al., 1829). To the right of the esophagus lies a single-lobed liver that is thick anteriorly and grows thinner until it reaches the gall bladder, which is relatively large in size. A large swim bladder that connects to the esophagus takes up the entirety of the upper back (Cuvier et al., 1829).

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry

Development

No information found for this species

Reproduction

Trout nesting sites, called redds, are aggressively protected by males (Crisp, 2000). (Crisp, 2008)

Marbled trout typically spawn on sandy or gravelly river bottoms from November to January by digging into the substratum and burying the eggs (Muhamedagic et al., 2008). Spawning in most salmonids usually occurs earlier in higher altitudes than in lower altitudes due to longer egg incubation, which is caused by lower water temperature. Eggs hatch several months after spawning (Klemetsen et al., 2003). Females reach sexual maturity at around 3.5 years of age; males at 4 years. Marbled trout hybridize readily with brown trout (Marchi et al., 2016).

• Key Reproductive Features
• seasonal breeding
• sexual
• fertilization
  • external

• Breeding season

  Spawning occurs between November and January.

• Average age at sexual or reproductive maturity (female)

  3.5 years

• Average age at sexual or reproductive maturity (male)

  4 years

Like other trout, marbled trout lay abundant eggs in protected areas and then abandon them. Their parental investment includes investing energy resources into the eggs so that they can successfully finish development.

• Parental Investment
• no parental involvement
• pre-fertilization
  • provisioning
• pre-hatching/birth
  • provisioning
    • female

Lifespan/Longevity

Marbled trout, like their close relatives, brown trout (Salmo trutta), can live over 20 years, but typically live to about 8 years (Klemetsen et al., 2003).

Behavior

The behavior of S. marmoratus is similar to that of other freshwater salmonids. They are predatory fish that rely on sit-and-wait and drift-feeding techniques (Watz et al., 2013). The fish prefer to hide and wait for prey in small holes near river banks (Cuvier et al., 1829). Marble Trout will aggressively compete with one another for resources and territory, forming dominance hierarchies within populations (Klemetsen et al., 2003).

• Key Behaviors
• natatorial
• motile

Communication and Perception

There is little available information on communication and perception in marbled trout.

• Perception Channels
• visual
• tactile
• vibrations
• chemical

Food Habits

Marbled trout are predatory fish that prey on fish, insects, and small crustaceans with their large, powerful jaws (Muhamdagic et al., 2008.) Juveniles feed heavily on chironomid larvae (Klemetsen et al., 2003). As with most other salmonids, marbled trout utilize drift-feeding to secure their prey. The temperature of their habitat affects their feeding habits, with the fish feeding nocturnally at low temperatures and feeding more during the day with higher temperatures (Watz et al., 2013).

• Primary Diet
• carnivore
  • piscivore
  • insectivore
  • eats non-insect arthropods

• Animal Foods
• fish
• insects
• aquatic crustaceans

Predation

Salmo species are preyed upon by birds, mammals (including humans), and other fishes. Insects will sometimes feed on trout eggs (Klemetsen et al., 2003). Adult Marble Trout are not typically preyed upon by other fishes, as they can grow very large (Muhamedagic et al., 2008).

Ecosystem Roles

Marbled trout act as top predators in their habitats, impacting populations of invertebrates and smaller fishes (Klemetsen et al., 2003). They also compete with introduced brown trout (Salmo trutta) and native fishes, such as Dentex trout (Salmo dendex) and softmouth trout (Salmothymus obtusirostris oxyrhyncus), for food resources and territory (Muhamedagic et al., 2008).

Economic Importance for Humans: Positive

As with most other salmonids, marbled trout are popular sportfish among anglers due to the taste of their meat and their fighting abilities (Klemetsen et al., 2003).

• Positive Impacts
• food

Economic Importance for Humans: Negative

There are no known negative impacts of marbled trout on humans.

Conservation Status

Marbled trout have been the focus of many conservation efforts. Their geographic range is becoming more and more restricted due to habitat alteration from the construction of dams and hybridization with introduced brown trout (Salmo trutta) (Muhamedagic et al., 2008, Meldgaard et al., 2007). Introgression through hybridization with S. trutta has seriously threatened the genetic identity of S. marmoratus, with only eight pure populations remaining in isolated streams (Crivelli et al., 2000, Meldgaard et al., 2007).

• IUCN Red List

  Least Concern

Contributors

Seth Spinner (author), Louisiana State University, Prosanta Chakrabarty (editor), Louisiana State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

Chiesa, S., L. Filonzi, C. Ferrari, M. Vaghi, F. Bilo, A. Piccinini, G. Zuccon, R. Wilson, J. Ulheim, F. Marzano. 2016. Combinations of distant molecular markers allow to genetically characterize marble trout (Salmo marmoratus) breeders and stocks suitable for reintroduction plans. Fisheries Research, 176: 55-64.

Crisp, T. 2008. Trout and Salmon: Ecology, Conservation, and Rehabilitation. Malden, MA, USA: Fishing News Books.

Crivelli, A., G. Poizat, P. Berrebi, D. Jesensek, J. Rubin. 2000. Conservation Biology Applied to Fish: The Example of a Project For Rehabilitating the Marble Trout (Salmo marmoratus) in Slovenia. Cybium, 24: 211-230.

Cuvier, G., G. Buffon, M. Valenciennes. 1829. Histoire naturelle des poissons.

Klemetsen, A., P. Amundsen, J. Dempson, B. Jonsson, N. Jonsson, M. O'Connell, E. Mortensen. 2003. Atlantic salmon Salmo salar L., brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.): a review of aspects of their life histories. Ecology of Freshwater Fishes, 12: 1-39.

Lorenzoni, M., D. Giannetto, G. Maio, E. Pizzul, L. Pompei, P. Turin, S. Vincenzi, A. Crivelli. 2012. Empirical standard mass equation for Salmo marmoratus. Journal of Fish Biology, 81: 2086-2091.

Marchi, H., M. Bertoli, A. Mosco, P. Giulianini, E. Pizzul. 2016. Analysis of the reproductive cycle of female wild marble trout Salmo marmoratus in a prealpine brook of the Soca River basin (Northeast Italy). Ichthyological Research, 64: 221-231.

Meldgaard, T., A. Crivelli, D. Jesensek, G. Poizat, J. Rubin, P. Berrebi. 2007. Hybridization mechanisms between the endangered marble trout (Salmo marmoratus) and the brown trout (Salmo trutta) as revealed by in-stream experiments. Biological Conservation, 136: 602-611.

Muhamedagic, S., H. Gjoen, M. Vegra. 2008. Salmonids of the Neretva river basin – present state and suggested sustainable selection programme to protect and strengthen salmonid populations. EIFAC FAO Fisheries and Aquaculture Report, 871: 224-231.

Soldo, A. 2012. First marine record of marble trout Salmo marmoratus. Journal of Fish Biology, 82: 700-702.

Watz, J., J. Piccolo, E. Bergman, L. Greenberg. 2013. Day and night drift-feeding by juvenile Salmonids at low water temperatures. Environmental Biology of Fishes, 97: 505-513.