| Summary: | Low intensity (1-1.5 body lengths per second, b1.s-1 ), short or long term exercise training significantly reduced the growth rate of underyearling (0+) chinook salmon, Oncorhynchus tshawytscha, at all stages of development from 'zip-up' fry to post-smolt (at 13-15 °c). Decreased growth with training was observed in both hatchery and wild chinook, and in 0+ sockeye salmon, O. nerka. Trained fish had lower weight specific (SGR) and linear growth rates (LGR), condition factor (CF), and exhibited lower gill Na+ -K+ -ATPase activity. SGR was greatest in pre-smolt fingerlings (i.e. fry), and then declined, whereas LGR was maximal during the period of parr-smolt transformation. Growth rate of chinook was accelerated in the warmer water of the laboratory (13-15 °c) compared to that experienced at a commercial hatchery (7-11 °c). It is evident therefore that exercise training does not appear to offer a viable commercial option for enhancing the growth of 0+ chinook, whereas 'warm water' rearing provided a measurable improvement of growth performance.
Hypo-osmoregulatory ability, assessed by 48 hour seawater challenge tests and gill Na+-K+-ATPase activity, of untrained chinook was determined over their first growing season, and was greatest during October-December. The smallest 'smolts' to survive in seawater were 2.5 g (65 mm). Fresh- and seawater growth rates were equivalent, provided the fish were transferred in a 'smolt condition'. Stunting and parr-reversion were rarely observed. Although plasma osmolality, and plasma concentrations of sodium and chloride were significantly greater in seawater resident fish, haematocrit was unaffected by salinity. Gill Na+ -K+ -ATPase activity increased two to four fold in seawater resident fish, and did not demonstrate the seasonal decline observed in post-smolts held in freshwater. After two to four months in seawater, visceral water content of seawater resident fish was higher than in freshwater reared fish of a similar size.
Swimming ability (i.e. critical swimming speed or Ucrit, cm.s-1) of chinook increased with fork length, and was unaffected by parr-smolt transformation. Ucrit measurements of individual fish were repeatable. Low intensity exercise training did not enhance the swimming performance of chinook in subsequent Ucrit tests. Whereas the swimming ability of 'wild' (i.e. naturally spawned) and hatchery reared, 0+ chinook did not differ, 0+ sockeye Ucrit were significantly slower than those of 0+ chinook. Ucrit tests tended to disrupt osmoregulation, causing decreased plasma chloride concentration in freshwater reared fish, and increased plasma chloride concentration in seawater resident fish.
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