Is the duration of the smolt window related to migration distance in coho salmon Oncorhynchus kisutch?

Abstract

Physiological changes during the parr-smolt transformation were investigated in short distance (Chilliwack River) and long-distance (Salmon River) migrating coho salmon Oncorhynchus kisutch populations in British Columbia, Canada. Biochemical and molecular indicators were used to monitor smolt development for fish reared at 10 °C throughout the spring. Fish grew well and developed the physical appearance of competent smolts. Both populations exhibited increases in gill Na -K -ATPase activity (NKA; an important indicator of seawater tolerance) at the same date and the duration of the increase in enzyme activity did not differ between populations. Gill messenger (m)RNA copies for two isoforms of the NKA α subunit, α1a and α1b, showed significant changes and the pattern was similar between populations. Growth hormone receptor and prolactin receptor mRNA from the gill showed modest changes associated with smolting in the spring for both populations, suggesting that these may not be useful indicators of smolt development in hatchery-reared O. kisutch. Consequently, the duration of the smolt window was not based on the region of origin in the present study.

Advances in our understanding of the parr–smolt transformation of juvenile salmon: a summary of the 10th International Workshop on Salmon Smoltification

“…It is less clear if populations in the same river catchment have evolved differential traits related to smolt development. Elsner & Shrimpton () compared populations of coho salmon Oncorhynchus kistuch (Walbaum 1792) from high and low in the Fraser River catchment by rearing them under common conditions before and during smolt development. They did not find substantial differences in the timing or duration of gill Na + –K + ‐ATPase activity (a common indicator of smolt development), transcription levels of its isoforms or growth hormone and prolactin receptors, suggesting that the onset and duration of the smolt window may not be influenced by location in the same river system.…”

Behavioural changes during the parr–smolt transformation in coho salmon Oncorhynchus kisutch: is it better to be cool?

“…Specific activities were expressed as μmol ADP mg −1 protein h −1 . The T pref trial did not appear to have an effect on gill NKA activity as values for parr and smolt measured did not differ from a companion study where fish were sampled directly after removal from the rearing tanks (Elsner & Shrimpton, ).…”

“…Initial hatchery water temperatures were 4.8 and 3.6°C at Chilliwack River and Spius Creek, respectively. At UNBC, fish from each population (250 Chilliwack River parr and 230 Salmon River parr) were placed into two recirculating systems; each recirculating system was equipped with three square 150 l tanks (Elsner & Shrimpton, ). Approximately 10–40% of the total water volume in each system was removed and replenished with dechlorinated city water each day.…”

“…For the second approach, a two‐way analysis of variance (ANOVA) was conducted using population, stage of development (parr or smolt) and the interaction between the two factors to test for differences in fish L F , K , NKA activity, T pref and U . The same cohorts of fish were sampled throughout the spring in a companion study (Elsner & Shrimpton, ); six fish from each population were sampled as described above immediately after transport on 8 January 2016. Subsequently, six fish from each population were sampled every 10 days from 1 February until 11 April, then every 15 days until 26 May, followed by a final sample date on 15 June, for a total of 13 sampling dates.…”

“…Given that temperature has an important role in smolt development, it is possible that smolts exhibit a T pref that maximises their performance during this critical time. No difference was found in the duration of the smolt window between populations of Fraser River coho salmon O. kisutch (Walbaum 1792) that differ in migration distance from their natal streams to the ocean (Elsner & Shrimpton, ); consequently, changes in T pref in smolts may be important for maintaining seawater tolerance for populations that must make longer smolt migrations to reach the ocean during a time when rivers are warming. To test whether behaviour may regulate physiological function, experiments were conducted to determine T pref in the spring during the parr–smolt transformation.…”