First Documented Case of Anadromy in a Population of Introduced Rainbow Trout in Patagonia, Argentina

PASCUAL, M.A.; BENTZEN, P.; RIVA ROSSI, C.M.; MACKEY, G.; KINNISON, M.; WALKER, R.

TRANSACTIONS OF THE AMERICAN FISHERIES SOCIETY

The American Fisheries Society

Lugar: Bethesda, MD, United States; Año: 2001 vol. 130 p. 53 - 67

1548-8659

he examination of population-specific adaptations of introduced salmonids to the wide range of environments found in Patagonia (southern South America) can help unveil some of the genetic and environmental contributions to life history variation. The rainbow trout Oncorhynchus mykiss introduced into Argentina originated from a few parental stocks. Although some of these stocks were anadromous, all of the dozens of established populations described until now have been freshwater resident. In this paper we provide the first documentation of the presence of an anadromous run of rainbow trout in the Santa Cruz River, the second largest river of Argentinean Patagonia. Microsatellite analysis revealed that anadromous and resident fish from the Santa Cruz River are genetically indistinguishable, probably representing alternative life histories within the same population. Both wild types are very different from the fish of Danish origin that were reared in a local hatchery, suggesting that they are descended more directly from California stocks or that they have been affected by strong drift or selection. Marine growth and freshwater residence are comparable to those of California steelhead. River entrance peaks in early fall. Population age structure and scale pattern analysis indicate that fish enter the river at age 3 but that most do not spawn until their next river entry as 4-year-olds. An unusual aspect of Santa Cruz anadromous fish is that they are long-lived and highly iteroparous. For instance, 20% of the fish analyzed had experienced as many as five spawning events.