Osmoregulation in Atlantic salmon Salmo salar smolts transferred to seawater at different temperatures.

In order to investigate how changes in gill Na(+) , K(+) -ATPase (NKA) α1a and α1b subunits, Na(+) , K(+) , 2Cl(-) co-transporter (NKCC1) and the apical cystic fibrosis trans-membrane conductance regulator-I (CFTR-I) transcripts in wild strain of Atlantic salmon, Salmo salar, smolts are affected by temperature during spring, hatchery-reared parr (mean ± s.e. fork length = 14·1 ± 0·5; mean ± s.e. body mass = 28·5 ± 4·5 g) originating from broodstock from the Vosso river (western Norway) were acclimated to three temperature regimes (4·1, 8·1 and 12·9° C) in May and reared under gradually increasing salinity between May and June. Changes in plasma Na(+) , haematocrit (Hct) and PCO2 were monitored in order to assess and compare key physiological changes with the transcriptional changes in key ion transporters. The temperatures reflect the natural temperature range in the River Vosso during late spring. Overall, higher gill NKA α1b mRNA levels, gill NKCC1a levels and CFTR-I levels were observed in the 4·1° C group compared to the 11·9° C group. This coincided with a 2-3 week period with decreased Hct and PCO2 and may indicate a critical window when smolts suffer from reduced physical performance during migration. Further research is needed to confirm the potential interaction between ecological and physiological conditions on mortality of hatchery-reared smolts from River Vosso during their natural migration.

Effects of hypo- and hyperoxia on transcription levels of five stress genes and the glutathione system in liver of Atlantic cod Gadus morhua.

The transcript levels of three genes coding for antioxidants, Cu/Zn superoxide dismutase (SOD), catalase and phospholipid hydroperoxide glutathione peroxidase (GSH-Px), and those of two stress proteins, metallothionein (MT) and CYP1A, were examined with real-time quantitative (q) RT-PCR in hepatic tissue of Atlantic cod exposed to 46% (hypoxia), 76% (normoxia) and 145% (hyperoxia) O(2) saturation (tank outlet). To evaluate the oxidative stress state, the levels of total glutathione (tGSH), reduced glutathione (GSH) and oxidized glutathione (GSSG) and subsequently the oxidative stress index (OSI), were determined in the same tissue samples. The transcript level of GSH-Px was significantly upregulated in fish exposed to hyperoxia, and significantly downregulated in fish exposed to hypoxia, compared to the normoxia group. Significant downregulation was also found for SOD and CYP1A transcriptional levels in fish exposed to hypoxia. The transcript levels of catalase and MT did not change in liver of cod exposed to suboptimal oxygen levels. No significant differences were seen between the groups for tGSH, GSH, GSSG or OSI. Prolonged exposure to unfavourable oxygen saturation levels did not alter the OSI, indicating that the antioxidant glutathione system is maintained at an unchanged level in liver of the examined cod.