When will they hatch?
You can predict when salmon will hatch by keeping track of the water temperature. Salmon eggs prefer temperatures from 45oC to 58oC. The higher the temperature, the faster the embryos inside the eggs will develop. One of our hatcheries is kept colder then the other. Can you predict in which hatchery the eggs would hatch first?
People who raise salmonids in hatcheries know when each batch of eggs will hatch because they know how much thermal energy the eggs must get to develop fully. The thermal energy comes from the heat in the water and can be measured as temperature units, or T.U.
Beginning on the day the eggs are fertilized, the temperature units for every day are added. When the sum of the daily temperature units reaches the required total, the eggs will hatch. The required total for salmon is between 750-850 TU.
To
find the daily temperature units (D.T.U.), you must know the average temperature
of the water for that day. Subtract 32 from the average temperature.
T-32
= D.T.U.
At the Hatchery:
Date eggs fertilized- 10/15/09 Date eggs arrived in classroom- 11/13/09
Total days eggs spent at hatchery-28
Average hatchery water temperature-50oF 
Average T-32 = Temperature Units per day: 50oF
- 32 = 18T.U. per day
18T.U. X 30
days = 504 T.U. This is the number of temperature
units our eggs received while they were living
at the hatchery.
In the Classroom:
Total T.U. required for hatching- 825--925 T.U.
Temperature Units at hatchery- 504 T.U.
Temperature Units still needed- 321--495 T.U.
| The average daily temperature in the classroom "mini-hatchery" has been- |
| ~57oF |
This means that approximately 25 D.T.U. will accumulate each day.
In how many days will the fish hatch? To determine when the eggs will hatch we use division.
|
In how many days will the fish hatch? To determine when the eggs will hatch we use division. |
321--495 T.U. ÷ 25 = 12.84-19.8 days from the date the arrived in our classroom! |
 |
We were right!
Our eggs began to hatch on November 24th! 13 days after we received them!
