Seawater tolerance in Atlantic salmon, Salmo salar L., brown trout, Salmo trutta L., and S. salar × S. trutta hybrids smolt

Abstract

High levels of hybridization between Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) have been reported in the Gyrodactylus salaris infected Rivers Vefsna and Driva in Norway. The survival and behaviour during the sea phase of such hybrids is unknown. The reported work documents ionoregulatory status after 24 h seawater challenge tests (24hSW) and gill Na+/K+-ATPase (NKA) activity of migrating wild smolts of Atlantic salmon, brown trout and hybrids at two sampling dates during the 2006 smolt run in River Driva. Salmon, trout and hybrids contributed to 27, 52 and 21% of the catches, respectively. The large contribution of hybrids suggests both a high hybridization rate and a high survival rate from fry to smolt. Both salmon and hybrids had a well-developed seawater tolerance at the time of downstream migration, revealed by small ionoregulatory effects and no or low mortality rates during the 24hSW tests. The trout were not fully adapted to seawater, and high mortality rates were observed (71 and 92%) during the 24hSW tests. The NKA activity was not significantly different between salmon and hybrids. Most of the hybrids were physiologically capable of direct entry to full strength seawater. The incomplete seawater tolerance in trout compared to salmon corresponds well with differences in life-history patterns between these two species. The life history strategy of the hybrids during the sea phase is not known, and further investigations on the marine behaviour and survival is needed to evaluate the role of hybrids in the risk of spreading G. salaris to nearby river systems.

Diel migration pattern of Atlantic salmon (Salmo salar) and sea trout (Salmo trutta) smolts: an assessment of environmental cues

“…The improved growth opportunities are accompanied by enhanced energy costs associated with smolting and increased swimming activity, and increased risk of predation (Mather, 1998). The smolting process is similar in principle in different salmonid species, but species may differ in degree of hyperosmotic capacity obtained (Urke et al, 2010, Urke, Kristensen, Arnekleiv, et al, 2013, corresponding to the salinity of their marine feeding habitats (e.g., Urke, Kristensen, Arnekleiv, et al, 2013). As most smolt predators are visual predators, the diel timing of the migration may affect the survival probability.…”

A rapid qPCR method for genetic sex identification of Salmo salar and Salmo trutta including simultaneous elucidation of interspecies hybrid paternity by high‐resolution melt analysis

“…e . Gyrodactylus salaris (Urke et al , ) and directionality of hybridization seems to vary geographically (Alvarez & Garcia‐Vazquez, ).…”

A General Model of Distant Hybridization Reveals the Conditions for Extinction in Atlantic Salmon and Brown Trout

“…However, hybrids are increasingly frequent [24], in particular because escaped individuals raised in farms exhibit a relaxed species mate choice [42]. In addition, overfishing and diseases have significantly reduced salmon populations locally [24].…”

“…However, hybrids are increasingly frequent [24], in particular because escaped individuals raised in farms exhibit a relaxed species mate choice [42]. In addition, overfishing and diseases have significantly reduced salmon populations locally [24]. In such conditions, the rare species has more difficulties in finding a conspecific partner and becomes less demanding when looking for a mate, a situation known as the “ desperation hypothesis ” [43].…”

“…Once in the wild, these fishes show a relaxed mate choice with frequent interspecific crosses, leading to hybrid frequency exceeding 10% [23]. Levels of up to 29% or even 60% were reported in some Norwegian rivers [24], where the hybridization rate seems to be higher in rivers hosting small and threatened populations of Atlantic salmon than in rivers with large populations [25]. This human increased hybridization rate between Atlantic salmon and brown trout may threaten local populations of parental species.…”