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

Abstract

The 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.

Anadromy and residency in steelhead and rainbow trout (Oncorhynchus mykiss): a review of the processes and patterns

“…Similar observations of residents producing anadromous offspring have been documented in other populations (Zimmerman et al 2009;Zimmerman and Reeves 2000), in addition to female steelhead producing resident offspring . Interchange between forms was also observed in the Santa Cruz River, Argentina, where steelhead apparently evolved from resident trout (Pascual et al 2001;Riva-Rossi et al 2007). Perhaps not surprisingly, molecular analysis has seldom revealed genetic divergence between anadromous and resident individuals where fish displaying these life histories patterns are sympatric (Docker and Heath 2003;McPhee et al 2007;Olsen et al 2006), consistent with evidence for considerable interbreeding between life histories from parentage analysis (Christie et al 2011;Seamons et al 2004) and direct observation (McMillan et al 2007).…”

Fishes of southern South America: a story driven by temperature

“…However, landlocked G. maculatus has retained the ability to display several alternative life history patterns in relation to migration and the choice of reproduction sites (Chapman et al 2006;Barriga et al 2007;Boy et al 2007). The salmonid species introduced into Patagonia (Pascual and Ciancio 2007) seem to follow the same pattern, with a 'spontaneous' establishment of anadromous populations of O. mykiss and chinook salmon Oncorhynchus tshawytscha (Pascual et al 2001;Ciancio et al 2005;Soto et al 2007; D. Fernández et al, personal communication).…”

“…However, the progressive southward disappearance of the 'otunos' Diplomystes cuyanus, D. viedmensis, and D. mesembrinus, the 'bagre' Trichomycterus areolatus, H. macraei, the Patagonian 'pejerrey' Odontesthes hatcheri and, finally, the 'perca' Percichthys trucha is noticeable. The lowest diversity occurs on Tierra del Fuego Island, the southernmost (54°S) area of the world with freshwater fish fauna, where only salmonids (Becker et al 2007;Pascual and Ciancio 2007) and four native species of the Galaxiidae family are found (Cussac et al 2004;Liotta 2006;Milano et al 2006). …”

Seasonal age distributions and maturity stage in a naturalized rainbow trout (Oncorhynchus mykissWalbaum) population in southern Chile reveal an ad-fluvial life history

“…This technique has been used in rainbow trout populations of New Zealand (e.g., Graynoth, 1996) and the Argentinean Patagonia (e.g., Pascual et al, 2001;Riva-Rossi et al, 2007). Scales were removed from an area below the posterior margin of the dorsal fin and approximately five scale rows above the lateral line (Pascual et al, 2001;Riva-Rossi et al, 2007).…”