Colomesus tocantinensis AMARAL, BRITO, SILVA & CARVALHO, 2013

Etymology

Colomesus: from the Ancient Greek χωλóς (cholós), meaning ‘physically defective, crippled’, and μέσος ‎(mésos), meaning ‘middle’, presumably in reference to the frontal bones being narrowed, not connected to the orbit, and with the elongated postfrontals connected to the prefrontals (see Gill 1884, also note misspelling of χωλóς as Κολoς).

tocantinensis: named for the type locality, the rio Tocantins in Brazil.

Classification

Order: Tetraodontiformes Family: Tetraodontidae

Distribution

Known only from the type locality at present.

Type locality is ‘Tocantins River, near Porto Nacional, State of Tocantins, Brazil’.

Maximum Standard Length

The largest specimen in the type series measured 34.9 mm, but it should grow larger.

Reproduction

Unknown, but the closely-related C. asellus exhibits a spawning strategy comparable to that of marine puffers and in contrast to the majority of freshwater tetraodontids, with high fecundity, relatively small eggs, and no parental care. Limited studies in the central Amazon basin suggest that spawning occurs in main river channels or close to banks at the mouths of floodplain lakes and tributaries during periods of high water. The pelagic larvae are washed into nursery zones in floodplain lakes where they complete their development, returning to river channels when flood waters recede.

NotesTop ↑

This species may not yet have appeared in the aquarium trade.

It is distinguished from congeners by the following combination of characters: anal-fin with 6-7 basal pterygiophores and 9 rays (vs. 10-11 rays in C. asellus and C. psittacus); dorsal-fin with 10 basal pterygiophores and 10 rays  (vs. 11 in C. asellus and C. psittacus); transverse series of dermal flaps on chin absent (vs. present in C. asellus); opercle notched ventrally, appearing as an inverted V (vs. triangular in C. asellus and C. psittacus); base colour in dorsal portion of body light yellow to pale (vs. golden yellow in C. asellus); presence of 5 transverse dark bands dorsally on the body (vs. 6 in C. psittacus).

Tetraodontids are commonly referred to as ‘puffers’ due to the ability of many species to inflate their body to an enormous size when stressed or threatened. This is achieved by drawing water into a specialised ventral diverticulum of the stomach, although air can also be used if the fish is removed from the water. As a result of these morphological adaptations puffers swim via a unique combination of pectoral and median fin undulations referred to as ‘diodontiform’ swimming. They are also able to produce sounds by grinding the jaw/pharyngeal teeth or vibrating the swim bladder. Puffers are secondary freshwater fishes, with the majority of members exclusively inhabiting marine environments.

Other defining characters of tetraodontids include a tough skin usually covered with small spines, a beak-like dental plate divided by a median suture, a reduced gill opening anterior to the pectoral-fin base, no pelvic fins or spinous fin rays, typically short-based dorsal and anal fins, and no ribs.

Puffer flesh is toxic and can cause clinical poisoning and human mortality, although it is regarded as a delicacy in certain countries. The predominant toxin, usually either tetrodotoxin or saxitoxin, is dependant on species, geographic area, and time of year. The toxins are not produced by the fishes themselves, but by bacteria living in symbiotic association, or they are acquired via the food chain. Colomesus species accumulate saxitoxin, although it is unclear whether eating their flesh represents a danger to humans.

References

1. Amaral, C. R. L., P. M. Brito, D. A. Silva and E. F. Carvalho, 2013 - PLoS ONE 8(9): 1-15
   A new cryptic species of South American freshwater pufferfish of the genus Colomesus (Tetraodontidae), based on both morphology and DNA data.
2. Araujo-Lima, C. A. R. M., D. Savastano, and L. Cardeliquio Jordão, 1994 - Revue d'Hydrobiologie Tropicale 27(1): 33-38
   Drift of Colomesus asellus (Teleostei: Tetraodontidae) larvae in the Amazon river.
3. Gill, T. N., 1884 - Proceedings of the United States National Museum 7(26-27): 411-427
   Synopsis of the plectognath fishes.
4. Helfman, G., B. B. Collette, D. E. Facey, and B. W. Bowen, 2009 - Wiley-Blackwell: 1-736
   The Diversity of Fishes: Biology, Evolution, and Ecology, 2nd Edition.
5. Nelson, J. S., 2006 - John Wiley & Sons, Hoboken, N. J.: i-xix + 1-601
   Fishes of the World. 4th edition.
6. Oliveira, J. S., S. C. Rego Fernandes, C. A. Schwartz, C. Bloch Jr., J. A. Taquita Melo, O. R. Pires Jr., and J. C. de Freitas, 2006 - Toxicon 48(1): 55-63
   Toxicity and toxin identification in Colomesus asellus, an Amazonian (Brazil) freshwater puffer fish.