The Free On-line Aquaculture Dictionary

Challenge tests to determine smoltification

Test 1 - High salinity challenge test
This test involves placing a random sample of 10 fish into a tank with seawater at 40 parts per thousand. An equal number of control fish are kept under identical conditions in fresh water. After 4 days, smolts which are ready for transfer will show a 90 - 100% survival. The test should preferably be run alongside the test 2, below;
Test 2 - 24 hour tolerance test
As part of the physiological changes which occur when a fish adapts from a freshwater to seawater environment, there is an increase in the blood plasma sodium and chloride levels. This is a temporary phenomena and fish which are able to adapt to the environment will show reduced levels again after 24 hours. A fish which after 24 hours in a marine environment has less than 170mM/litre is deemed to have adapted. After immersion for 24 hours in the seawater, the fish are anaesthetised and a >0.35ml blood sample taken. This is placed in a heparinised tube (which prevents the blood clotting) and centrifuged for 10 minutes at 4000 rpm. Sodium levels are then measured in a flame photometer.