Sotalia fluviatilisgray dolphin(Also: tucuxi)

Geographic Range

Tucuxis, also known as gray dolphins and Guianian River dolphins, are neotropical dolphins that live exclusively in the Amazon and Orinoco basins and are thought to be endemic to this region of South America. The closest living relatives of Tucuxis are Costeros, dolphins that live in the shallow waters along the Atlantic Coast of South America. However, Tucuxis are sympatric with Amazon River dolphins of the family Iniidae. (Beneditto and Ramos, 2004; Caballero, et al., 2007; Cunha, et al., 2005; Ding, et al., 2001; Flores and da Silva, 2009; Martin, et al., 2004; Nowak, 1999; Oliveira, 2005; Secchi, 2010)


Tucuxis are found throughout the Amazon and Orinoco River basins and are commonly found near low current confluences and river junctions where food is abundant and less energy has to be expended during foraging bouts. They avoid mud banks and flooded forest areas. The mouth of the Amazon River occurs at its junction with the Atlantic ocean, thus making the first 2 km of the river relatively saline. Although some Tucuxi can be found within this area, they prefer the freshwater habitat found further inland. (Beneditto and Ramos, 2004; Caballero, et al., 2007; Martin, et al., 2004)

Physical Description

Sotalia fluviatilis and Sotalia guianensis are very similar in appearance and were once classified as a single species. However, phylogenetic evidence indicates that they diverged approximately 1.5 to 2 million years ago during the Pliocene or early Pleistocene. Despite their many similarities, three major differences help distinguish between these 2 species. First, S. fluviatilis largely prefers fresh water habitat, whereas S. guianensis prefers saline coastal habitat. Second S. fluviatilis is much smaller in size than S. guianensis. Finally, the haplotype and nucleotide sequences of S. fluviatilis are as diversified from S. guianensis as they are from other delphinids. In general, S. fluviatilis is smaller and has a shorter beak than most other members of the family Delphinidae. It ranges from blue to pearl-grey along the dorsal surface and from white to pale-pink along the ventral surface. Most individuals have a white tipped beak. The dorsal fin has a prominent triangular shape that sometimes hooks toward the caudal fin. Adults have between 28 and 35 teeth. Sotalia fluviatilis is not sexually dimorphic and ranges from 86 to 206 cm long and weighs 55 kg on average. (Beneditto and Ramos, 2004; Caballero, et al., 2007; Cunha, et al., 2005; Ding, et al., 2001; Emmons, 1990; Nowak, 1999; da Silva, et al., 2007)

  • Sexual Dimorphism
  • sexes alike
  • Average mass
    55 kg
    121.15 lb
  • Average mass
    46666.7 g
    1644.64 oz
  • Range length
    86 to 206 cm
    33.86 to 81.10 in
  • Average length
    152 cm
    59.84 in


There is no information available regarding the mating system of Tucuxis.

Tucuxis breed during late summer and early fall. Gestation ranges from 10 to 11.6 months and results in one calf, which is born during the fall low-water season. Newborn calves range in size from 71 to 106 cm in length. Both sexes become sexually mature by six years of age, at which point males are around 180 cm long and females are around 160 cm long. Despite their differences in length at reproductive maturity, fully grown males and females are usually equal in length and weight. (Beneditto and Ramos, 2004; Flores and da Silva, 2009)

  • Breeding season
    Tucuxis breed from August to October.
  • Average number of offspring
  • Average number of offspring
  • Range gestation period
    10 to 11.6 months
  • Average age at sexual or reproductive maturity (female)
    6 years
  • Average age at sexual or reproductive maturity (male)
    6 years

Little is known of parental care in Tucuxis; however, mothers are known to whistle at their calves once they have found food. As mammal, mothers likely nurse their young until weaning is complete. (Pivari and Rosso, 2005)

  • Parental Investment
  • female parental care
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female


Evidence suggests that wild Tucuxis can live for up to 35 years. There is no information available indicating the average lifespan of captive individuals. They are susceptible to capture stress and often tangle and suffocate themselves within netting. In addition, Tucuxi do not respond well to extended periods of transportation. (Flores and da Silva, 2009)

  • Average lifespan
    Status: wild
    35 years


Tucuxis are slow swimmers compared to other dolphins, but are mostly active and avoid resting. They can perform many acrobatic maneuvers such as flips, summersaults, leaps, and rolls and often perform these movements in sync with other dolphins. They can leap as high as 120 cm out of the water and rise for air every 5 to 85 seconds. In a similar to fashion to certain ungulate species, males appear to herd females while traveling. They travel in small groups of 1 to 6 individuals but have been witnessed in groups as large as 40. Larger groups can coordinate hunting strategies. Whistling is used as a means of communication between conspecifics. Calves are often present in larger groups, which is thought to provide them with ample opportunity to learn a variety of social behaviors. (Emmons, 1990; Flores and da Silva, 2009; Nowak, 1999; Oliveira, 2005; Pivari and Rosso, 2005)

Home Range

There is no information on the average home range size of Tucuxis. (Flores and da Silva, 2009)

Communication and Perception

Like most dolphins, Tucuxis use a variety of whistles and clicks to communicate with conspecifics. Among delphinids, evidence suggests that species' size has a linear effect on whistle pitch, with smaller species having higher pitched whistles and larger species having lower pitched whistles. Tucuxis align with this relationship, and as one of the smallest extant dolphin species, they are known to have some of the highest pitched whistles when compared to other dolphins (e.g., 16% of whistles exceed 24Hz). Whistle frequency tends to ascend rather than descend during a single whistle. Whistling increases while foraging, and is thought to attract conspecifics to where food is abundant; suggesting a co-operative rather than competitive attitude between conspecifics. Like other delphinids, Tucuxis use echolocation to help them find prey. (Pivari and Rosso, 2005; Pivari and Rosso, 2005; Azevedo and Van Sluys, 2005; Mass and Supin, 1999; Pivari and Rosso, 2005)

Tecuxis use their vision to perceive the local environment, and despite living in a freshwater environment, have a number of ocular features that are similar to those of many marine dolphins. Tucuxis have two high density ganglion areas, a feature which is common among delphinids and helps them process visual information more efficiently than Amazon River dolphins, which have only one. Being originally adapted for life in a saline environment, however, may negatively affect their ability to see objects in freshwater at high resolution. Evidence suggests that although their clarity of vision is less than that of true river dolphins, it is better than that of marine dolphins. What they lack in eye sight, however, they make up for in their ability to echolocate prey and potential predators. (Azevedo and Van Sluys, 2005; Mass and Supin, 1999; Pivari and Rosso, 2005)

Food Habits

Tecuxis are carnivorous, and primary prey includes marine ray-finned fishes, along with squids and octopuses. Confluence areas result in favorable pH levels for plankton growth, which attracts many species of ray-finned fish. As a result, Tucuxis are often seen travelling to confluences, likely in search of prey. (Beneditto and Ramos, 2004; Emmons, 1990; Martin, et al., 2004)

  • Animal Foods
  • fish
  • mollusks


Other than illegal hunting by humans, Tucuxis have no known predators. (Flores and da Silva, 2009)

Ecosystem Roles

Although barnacles are commonly found Tucuxis, they are not considered parasitic, as they have no known negative impact on their host. Limited information exists regarding parasites of Tucuxis; however, stomach flukes and two species of nematode (Anisakis typica and Halocercus brasiliensis) are known to infect the gastrointestinal tissues of this species at various stages throughout their complex life cycle. (Beneditto and Ramos, 2004; Kane, et al., 2008)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

Indigenous South Americans hold Tucuxis in high regard as protectors that carry the drowned to shore for burial. Despite Brazilian law protecting them, Tucuxis are illegally hunted for their meat (bait), oil (emulsion to protect boats from water), and various body parts that are used in traditional medicines or religious ceremonies. (Alves and Rosa, 2008; Nowak, 1999)

Economic Importance for Humans: Negative

There are no known adverse effects of Tucuxis on humans.

Conservation Status

Tucuxis are classified as "data deficient" on the IUCN Red List of Threatened Species. Currently, population trends are unknown and thus potential conservation and management needs cannot be determined. They are the only species of fresh-water delphinid currently known. Although there has never been a commercial fishery for this species, a significant number of deaths occur due to by-catch and incidental mortality in fishing gear. Other potentially important threats include damming, overfishing of prey, boat strikes, chemical pollution and noise pollution. Without further research on the demographics of this species throughout its geographic range, the significance of these threats cannot be established and potential conservation and management actions cannot be prioritized. (Cunha, et al., 2005; Pivari and Rosso, 2005; Secchi, 2010; Trujillo Gonzalez, 1994)


Michael Dobbin (author), University of Alberta, Augustana Campus, Doris Audet (editor), University of Alberta, Augustana Campus, John Berini (editor), Animal Diversity Web Staff.



living in the southern part of the New World. In other words, Central and South America.

World Map


uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

brackish water

areas with salty water, usually in coastal marshes and estuaries.


an animal that mainly eats meat


uses smells or other chemicals to communicate

  1. active during the day, 2. lasting for one day.

a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease


The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.


animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.


an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

female parental care

parental care is carried out by females


mainly lives in water that is not salty.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


eats mollusks, members of Phylum Mollusca


having the capacity to move from one place to another.


specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.


an animal that mainly eats fish

seasonal breeding

breeding is confined to a particular season


remains in the same area


reproduction that includes combining the genetic contribution of two individuals, a male and a female


associates with others of its species; forms social groups.


uses touch to communicate


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


uses sight to communicate


reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.


Alves, R., I. Rosa. 2008. Use of Tucuxi Dolphin Sotalia fluviatilis for Medicinal and Magic/Religious Purposes in North of Brazil. Human Ecology, 36/3: 443-447.

Azevedo, A., M. Van Sluys. 2005. Whistles of tucuxi dolphins (Sotalia fluviatilis) in Brazil: Comparisons among populations. Acoustical Society of America, 117/3: 1456–1464.

Beneditto, A., R. Ramos. 2004. Biology of the marine tucuxi dolphin (Sotalia £uviatilis) in south-eastern Brazil. Journal of the Marine Biological Association of the United Kingdom, Vol. 84, no. 6,: 1245-1250..

Caballero, S., F. Trujillo, J. Vianna, H. Barrios-Garrido, M. Montiel, S. Beltran-Pedreros, M. Marmontel, M. Santos, M. Rossi-Santos, F. Santos, C. Baker. 2007. Taxonomic status of the genus sotalia: Species level ranking for "Tucuxi" (Sotalia fluviatilis) and "Costero" (Sotalia guianensis) dolphins. Marine Mammal Science, 23/2: 358-386.

Cunha, H., V. da Silva, J. Lailson-Brito, M. Santos, P. Flores, A. Martin, A. Azevedo, A. Fragoso, R. Zanelatto, A. Sole-Cava. 2005. Riverine and marine ecotypes of Sotalia dolphins are different species. Marine Biology, 148/2: 449-457.

Ding, W., B. Wursig, S. Leatherwood. 2001. Whistles of boto, Inia geoffrensis, and tucuxi, Sotalia fluviatilis. Acoustical Society of America, 109/1: 407-411.

Emmons, L. 1990. Neotropical Rainforest Mammals: A Field Guide. Chicago and London: The University of Chicago Press.

Flores, P., V. da Silva. 2009. Tucuxi and Guiana Dolphin. Pp. 1188-1192 in J Thewissen, ed. Encyclopedia of Marine Mammals, Vol. 1, 2nd Edition. London: Academic.

Kane, E., P. Olson, T. Gerrodette, P. Fiedler. 2008. Prevalence of the commensal barnacle Xenobalanus globicipitis on cetacean species in the eastern tropical Pacific Ocean, and a review of global occurrence. Fishery Bulletin, 106/4: 395-404.

Martin, A., V. da Silva, D. Salmon. 2004. Riverine Habitat Preferences of Botos (Inia geoffrensis) and Tucuxis (Sotalia fluviatilis) in the Central Amazon. Marine Mammal Science, Vol. 20, no. 2: 189-200.

Mass, A., A. Supin. 1999. Retinal topography and visual acuity in the riverine tucuxi (Sotalia fluviatilis). Marine Mammal Science: 351-365.

Nowak, R. 1999. Tucuxi, or River Dolphin. Pp. 920-923 in Mammals of the World, Vol. 2, 6th Edition. Baltimore and London: The Johns Hopkins University Press.

Oliveira, A. 2005. Group characteristics of marine tucuxis (Sotalia fluviatilis) (Cetacea: Delphinidae) in Guanabara Bay, south-eastern Brazil. Journal of the Marine Biological Association of the United Kingdom, 85/1: 209-212.

Pivari, D., S. Rosso. 2005. Whistles of small groups of Sotalia fluviatilis during foraging behavioural in southeastern Brazil. Acoustical Society of America, 118/4: 2725-2731.

Secchi, E. 2010. "Sotalia fluviatilis" (On-line). Accessed November 12, 2010 at

Trujillo Gonzalez, F. 1994. The use of photoidentification to study the Amazon river dolphin, Inia geoffrensis, in the Colombian Amazon. Marine Mammal Science, 10/3: 348-353.

da Silva, V., A. Carter, C. Ambrosio, A. Carvalho, M. Bonatelli, M. Lima, M. Miglino. 2007. Placentation in dolphins from the Amazon River Basin: the Boto, Inia geoffrensis, and the Tucuxi, Sotalia fluviatilis. Reproductive Biology and Endocrinology, 5: 26-26.