Physiological characteristics of wild Atlantic salmon post‐smolts during estuarine and coastal migration

Abstract

Changes were measured in some of the major physiological variables associated with seawater adaptability, growth and energetics in wild Atlantic salmon Salmo salar smolts and post-smolts migrating from the river and through the estuary, fjord and coastal areas in the River Orkla and the Trondheimsfjord, Norway during late May to early June. Gill Naþ -ATPase activity increased to levels of 12-16 mmol ADP mg protein À1 h À1 in post-smolts caught in higher salinity zones, probably representing long-term levels of Atlantic salmon post-smolts in oceanic conditions. Muscle moisture was regulated within narrow limits (77Á7-78Á7%) in fish from all zones during both years, suggesting that post-smolts adapt to marine conditions without any long-term disturbance of hydro-mineral balance. Lipid and glycogen content showed a general trend towards depletion from the river, through the fjord and into the ocean. There was, however, no significant change in protein content. The present results confirm that smolts are naturally 'energy deficient' during downstream migration, and suggest that post-smolts also mobilize energy reserves during their early marine phase, while protein is allocated for somatic growth. Plasma growth hormone (GH) levels increased transiently during passage through the estuary and fjord, with lower levels observed in post-smolts caught off-shore, i.e. in fish which were feeding on marine prey and had adapted to the marine environment. These physiological changes may confer substantial selective advantages during the critical early marine phase of anadromous salmonids, and hence are adaptive for long-term survival in sea water.

Modulation of fish growth hormone levels by salinity, temperature, pollutants and aquaculture related stress: a review

“…Similarly, GH treatment was also found to increase saltwater tolerance in coho salmon (Shrimpton et al 1995) rainbow trout (Sangiao-Alvarellos et al 2005) and the euryhaline killifish McCormick 1998a, b, 1999). Rydevik et al (1990) Seawater transfer of smolts GH levels increased transiently following seawater transfer Arnesen et al (2003) Smolt migration from riverestuary-fjord-coast GH levels increased transiently during estuary-fjord migration Stefansson et al (2003) Hatchery release of smolts into river GH levels increased during downstream migration McCormick et al (2003) Coho salmon Seawater transfer GH levels increased following seawater transfer Sweeting andMcKeown (1987) Yamauchi et al (1991) Chum salmon Hasegawa et al (1987) Sockeye salmon Seawater challenge of juveniles GH levels increased within 24 h of salinity challenge Yada et al (1991) Amago salmon Rainbow trout Gradual salinity exposure from FW to 66% SW GH levels increased during salinity challenge Shepherd et al (2005) Mozambique tilapia FW to SW transfer GH levels increased following transfer Vijayan et al (1996) Transfer from FW to ISO or 75% SW GH levels highest in 75% SW at day 4 following transfer Morgan et al (1997) Salinity acclimation at FW, SW and 2 Borski et al (1994) The key action of GH appears to be primarily associated with branchial osmoregulatory function including the activity and distribution of chloride cells (McCormick 2001;Evans 2002). Consistent with a seawater adapting role, GH treatment of freshwater rainbow trout (Perry 1998;Laurent et al 1994;Bindon et al 1994a, b), brown trout , sea trout parr …”

Genetics of Sea Trout, with Particular Reference to Britain and Ireland

“…Thus sea trout and other salmonid smolts typically show an increase in gill Na + , K + -ATPase and H + -ATPase in the period immediately prior to migration to sea, as well as changes in several other enzymes and proteins (Hoar, 1988;McCormick et al, 1998;Stefansson et al, 2003). The converse is the case in sea water with the gain of ions and loss of water occurring.…”

Growth and osmoregulation in Atlantic salmon (Salmo salar ) smolts in response to different feeding frequencies and salinities

“…Smolt development is normally accompanied by decreases in lipid reserves and liver glycogen, even when ¢sh are fed ad libitum (Sheridan 1989;Stefansson, Bj˛rnsson, Sundell, Nyhammer & McCormick 2003). The ¢ndings of Stefansson et al (2003) indicated that smolts also have low energy reserves during the early marine phase. The ¢ndings of Stefansson et al (2003) indicated that smolts also have low energy reserves during the early marine phase.…”