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One Daily Temperature Unit (DTU) = 1° Fahrenheit above freezing (32° F). For example, if the water temperature is 56° F, it would contribute 24 DTU (56°-32°).
Total Temperature Units (TTU) = cumulative total of DTU. For example, if the tank temperature measured 40° F for five days the TTU would = 40 ((40°F-32°F)*5 days).
Atlantic salmon eggs development can be measured in stages. Eye -up occurs at 350-375 TTUs, Hatching at 700-800 TTUs, First Feeding at 1000 TTUs, and Stocking at 1000-1001 TTUs
Starting TTUs (obtain from the hatchery):
| Date | Tank Temperature (° F) | Daily Temperature Units (DTU) | Total Temperature Units (TTU) | Data Collector |
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To Predict when salmon fry will reach each phase of development and when to stock into the stream divide the desired stage from above by the DTU.
U.S. Fish and Wildlife Service