Is salmon’s readiness for sea an indicator of how they’ll perform?

When I was working in Tasmania, every year around spring time, fish farmers will be gearing up to move their fish from the freshwater ponds to the sea. How do you know when they’re ready? Visually, they will start to lose their parr marks, turning a wholly more silver colour.

When this happens, a random sample of fish are placed in seawater ponds for a seawater ‘challenge’ trial. These fish are then taken to the lab and we would take blood samples from salmon to check whether they were ready to go to sea. We would test their blood for any elevations in serum sodium or chloride levels. If they are able maintain these parameters within their normal reference ranges, then it means that the fish are ready to be trucked to sea cages. If not, then the fish are held back till they are ready.

But this paper states that even if fish are ready, they’re not all necessarily going to do well. Read the paper below to find out more.

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Aquaculture
Volume 363, Number 8 (September 2012)
	Gill Na+,K+-ATPase of Atlantic salmon smolts in freshwater is not a predictor of long-term growth in seawater
	Authors:	Gayle B. Zydlewski, Joseph Zydlewski
	Author Affiliations:	no affiliations available
	Source:	Aquaculture, Volume 363, Number 8 (September 2012)
	Page Numbers:	121 – 126
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: Unknown Location: Publisher’s Site Authentication: Publisher’s Site
	Abstract:	Gill Na+,K+-ATPase activity is a widely used measure of osmoregulatory preparedness in salmonid smolts. The degree to which this measure may predict long term performance is uncertain. In order to assess the relationship of this enzyme to long term growth and ion homeostasis, a cohort of Atlantic salmon hatchery smolts was used in a controlled environment with no salinity perturbations. In May 2006, gill Na+,K+-ATPase activity from 940 individually PIT tagged, Penobscot River smolts (USFWS, Green Lake National Fish Hatchery, Maine, United States) was measured immediately prior to isothermal transfer from freshwater to 32ppt seawater. From the observed range of activities, individuals were classified as having “low”, “middle”, or “high” enzyme activity levels. Individual size (fork length and mass) was recorded on days 0, 1, 3, and 14 and monthly for four months. Growth rates over four time periods were calculated for individual fish maintained until the end of the experiment. Gill Na+,K+-ATPase activities were also measured from a subset of sampled fish. All groups effectively osmoregulated as evidenced by minor perturbations in plasma osmolyte levels. Apart from initial weight loss on transfer, fish grew throughout the experiment, however, there were no differences (fish size, growth rate, and gill Na+,K+-ATPase activity in seawater) among groups with initially different gill Na+,K+-ATPase activities (prior to seawater entry). While gill Na+,K+-ATPase activity may be predictive of performance during the acute phase of acclimation (first few days), typical variation in this enzyme, expressed in freshwater at the peak of smolting, does not appear to be predictive of long-term growth in seawater.
	Citation:	Gayle B. Zydlewski, Joseph Zydlewski . Gill Na+,K+-ATPase of Atlantic salmon smolts in freshwater is not a predictor of long-term growth in seawater. Aquaculture, Volume 363, Number 8 (September 2012), pp. 121-126, <http://ejournals.ebsco.com/direct.asp?ArticleID=4E8696AA9BDF92F34569&gt;
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=4E8696AA9BDF92F34569