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

Abstract

-Rainbow trout is one of the most popular introduced game species around the world. Similar patterns of use for lake and inlet streams have been described for both native and introduced populations. However, for many introduced rainbow trout populations, there is a lack of information about how and when those habitats have been used. Here, we hypothesized that the majority of adult and sexually mature individuals inhabit inlet streams during the reproductive period most likely to spawn whereas juvenile trout occupy these same streams as nursery areas most of the year before emigrating to the lake. We studied rainbow trout age distribution and sexual maturity in a lake and its main inlet streams in southern Chile. We found that stream-dwelling individuals inhabited inlet streams up to age 2 + whereas lake-dwelling trout were older (most of them from ages 4 + to 6 + ). During the reproductive period (May to September) older and sexually mature individuals were in both habitats probably indicating movement to upstream locations to spawn. Rainbow trout of the same ages were larger in the lake than in streams, which may imply better growth in the lenthic environment. Our study offers further evidence of the highly adaptable nature of rainbow trout. Future regulations should consider rainbow trout populations in lakes and streams separately because trout life histories suggest that both environments are important to different ontogenic stages. This study provides key information that may be useful in the management of ad-fluvial populations of rainbow trout in Patagonia.

Trophic interference by Salmo trutta on Aplochiton zebra and Aplochiton taeniatus in southern Patagonian lakes

“…A similar effect has recently been described by who showed that the trophic height of large G. platei individuals declined with increasing S. trutta density. In the case of A. zebra, the significant change in its diet and the reduction of δ 15 N at similar sizes in the presence of S. trutta translate into a significant decrease in K. This index has been inversely correlated with population abundance, for example, in salmonids (Arismendi et al, 2011) suggesting that the final result for A. zebra in the presence of S. trutta can be a reduction of its population size. In parallel, in the same system where A. zebra could be declining, S. trutta shows a clear pattern of enrichment in the values of 15 N and 13 C with size, revealing an ontogenetic change in its diet to more ichthyophagous habits as they grow larger, as reported for S. trutta in other systems (Cucherousset et al, 2007).…”

Skin Spotting Variation Associated with Biometric and Reproductive Parameters in Naturalized Populations of Rainbow Trout, Oncorhynchus mykiss, from Southern Chile

“…This is not unlikely, given that Islam et al (1973) studied cultured strains in Japan, which that are usually subject to intense management in fish farms and, in contrast to a free-living population, are reared under controlled environmental conditions. These conditions are very different to those experienced by the naturalized populations of rainbow trout studied in this work, given that they inhabit a lake in southern Chile (Calafquén Lake), with particular limnic conditions related to special water characteristics (Campos 1984, Arismendi et al 2011). In the case of selection and genetic factors, their effect on spawning time and spottiness would be expected to produce considerable variation among strains.…”

“…In this body of waters, the rainbow trout has importance for recreational fishing purposes. The naturalized populations of rainbow trout inhabiting lakes from southern Chile, called Araucanian lakes, are adapted to particular limnic conditions given that these body waters present special environmental characteristics, such as a) glacial origin with volcanic influence in the soils, b) high deepness, c) thermal stratification, d) high in water transparency, and e) oligotrophic with very low salt/nutrient concentrations (Campos 1984, Arismendi et al 2011. In addition, within these lakes, the naturalized populations of rainbow trout coexist with several native fishes and other introduced salmonids, most of them occupying the same habitat (Soto et al 2006).…”

Reciprocal trophic niche shifts in native and invasive fish: salmonids and galaxiids in Patagonian lakes

“…G. platei completes its life cycle within lakes (Barriga et al, 2002;Habit et al, 2010;data in Correa & Hendry, 2012) whereas trout spawn in streams where their emerging fry grow for several months or years before entering lakes (Forseth et al, 1999;Arismendi, Sanzana & Soto, 2011c). G. platei completes its life cycle within lakes (Barriga et al, 2002;Habit et al, 2010;data in Correa & Hendry, 2012) whereas trout spawn in streams where their emerging fry grow for several months or years before entering lakes (Forseth et al, 1999;Arismendi, Sanzana & Soto, 2011c).…”

“…The outcome of exploitative competition might be affected by ecological differences between G. platei and trout. G. platei completes its life cycle within lakes (Barriga et al, 2002;Habit et al, 2010;data in Correa & Hendry, 2012) whereas trout spawn in streams where their emerging fry grow for several months or years before entering lakes (Forseth et al, 1999;Arismendi, Sanzana & Soto, 2011c). This spatial segregation between G. platei and trout makes G. platei in lakes more vulnerable to predation than salmonids (Mcdowall, 2006;Milano et al, 2006;Macchi et al, 2007).…”