Pacific Tenpounder

Pacific ladyfish
Pacific LadyfishElopaffi.jpg, Elops affinis
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Elopiformes
Family: Elopidae
Genus: Elops
Species: E. affinis
Binomial name
Elops affinis
Regan, 1909

The Pacific Tenpounder or Pacific ladyfish (Elops affinis) is one of five other species within the Elops genus. Elops is the only genus within the family Elopidae, making Elopidae a monotypic family. The Pacific Tenpounder is the only species that prefers brackish water with a salt content of only 15ppt or less. The other four species prefer much saltier water. The Pacific Tenpounder can be found throughout the entire southwest, including areas in the Pacific Ocean.[1][2][3][4][5][6][7]

Contents

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Description

The Pacific Tenpounders have very round bodies with terminal mouths, and profound gill formations known as pseudobranchiae. Tenpounders have a larger number of dorsal fin rays than most Arizona fish, with numbers ranging from 27 to 35. Anal fin rays usually range from 13 to 19, and they have 12 to 16 pelvic rays. This species is very different from most chordates in that it has no conus arteriosus, a tendinous band of tissue from which the pulmonary artery arises. Because of this absence, tenpounders have a much smaller pulmonary artery. The tenpounder’s lateral lines are unbranched, and lateral line scales are usually within ranges of 95 to 120. All scales are silvery and cycloid, along with the overall color of the fish; however there can be yellow pigment in the eyes. Some aids to identification include noticing the prominent auxiliary and inguinal processes.

Distribution and Habitat in Arizona

This species is restricted primarily to the Southwest regions of the United States, as the distribution maps will indicate. Most records come from the Colorado River Delta and the Gulf of California, as they spawn here and then travel southwest into Arizona. They were also common in the Salton Sea in California, however their numbers have been slowly declining. During flooding events, tenpounders enter the Lower Colorado River from the Gulf. They can be found in Yuma Colorado River portions, and there are sporadic records as far south as certain Mexico dams. Pacific Tenpounders are primarily a marine form, meaning they require a higher salinity water content then most freshwater fish. Because of this, they have evolved efficient swimming techniques allowing them to penetrate lagoons and estuaries with higher salinities.

Reproduction

This species prefers to use a wide range of water salinities when spawning. Under normal conditions, the Pacific Tenpounder will be located in brackish water, however they travel deep into oceanic, salty waters for breeding. They will place their eggs far from shore in more planktonic regions to provide them with nutrients as juveniles. The larvae look interestingly like eels at birth, however a forked tail can distinguish them. Their young will usually feed on the crustaceans located in the brackish or coastal waters. This may explain the reasoning behind their instinct to flow from the Gulf of California into the Lower Colorado during flood conditions.

Biology

Tenpounders are pelagic, marine forms preferring either brackish or fresh water unless they are breeding. They prefer specific water depths of no more than 8 meters. Little is known about the ecology of this species, however they are known to be highly carnivorous, feeding on smaller fish and crustaceans. This behavior is very similar to the tenpounder’s close relative, the Atlantic ladyfish. Maximum size is relatively larger than most Arizona fish, reaching lengths of 1 meter. There is a negative correlation between size and appearance in the Colorado River. As they become larger in size, they prefer more brackish waters for unknown reasons. Larval and juvenile stages of fish have large records of distribution near Rocky Point, in the Sea of Cortez tidal inlets. Their spawning areas are usually closer to coastal areas, because they desire saltier waters for their young.

References

  1. ^ Battaso, R.H. and J.N. Young, 1999. Evidence for freshwater spawning by stripped mullet and return of Pacific Tenpounder in the lower Colorado River. California Fish & Game, 85 (2): pp 75-76.
  2. ^ Eschmeyer, W.N., et. al. 1983, A Field Guide to Pacific Coast Fishes of North America, Houghton Miffin Company, Boston, USA. 336.
  3. ^ Forey, P.L. 1973. A revision of the elopiform fishes, fossil and recent. Bulletin of the British Museum of Natural History (Geology) Supplement 10. pp. 222.
  4. ^ Froese, R. and D. Pauly, Editors. 2002. FishBase World Wide Web electronic publication, www.fishbase.org, 24 September 2002.
  5. ^ Minckley, W.L. 1973. Fishes of Arizona. Arizona Game and Fish Department, Phoenix. pp. 46-47.
  6. ^ Nelson, J.S. 1984. Fishes of the World. Wiley-Interscience Publication, John Wiley and Sons, pp. 523.
  7. ^ Nelson, J.S. 1994. Fishes of the World. John Wiley and Sons, Inc. New York. pp. 99, 100.