Countdown to Hatching!
Summary Students explore the role of temperature
in salmon egg development by recording daily water
temp and calculating Accumulated Temperature
Units (ATUs) to predict hatch date.
Objectives
Students will:
 Make predictions of hatch date based on evidence.
 Track an environmental factor (water temperature) throughout egg development.
 Understand that temperature affects salmon survival throughout their life cycle.
Making Connections
Duration
35 min for first day
calculations and hatch
date predictions
5 min daily to record tank
water temp
NGSS
LS1B: Growth and
development of
organisms
Materials
Floating thermometer
Daily and Accumulated
Temperature Log
Many students know that salmon face extraordinary challenges in their lives,
beginning at the egg stage. Salmon eggs in rivers and streams are subject to
predators, smothering by silt, and fluctuations in water quality. Because of these
challenges, only 10% of salmon eggs survive to hatch. Temperature is one of the
most critical factors for salmon survival throughout its life cycle. Students may
not realize how important water temperature is to the survival of salmon, from
the egg stage all the way to adult salmon returning to spawn. This activity
introduces the effects of temperature on salmon in the first stage of their life
cycle as developing eggs, and can serve as a reference point for future discussions
about temperature requirements of adult salmon in streams, the role of shade
from trees in maintaining water temperatures cold enough for salmon to survive,
and community stream restoration and tree planting efforts.
Background
Temperature controls the developmental rate of many organisms. Many living
things require a certain amount of heat to develop from one point in their life
cycles to another. Because fish are cold-blooded, the temperature of the water they live in controls when
their eyes develop, when they begin to move inside the egg, and when they will hatch. Of all the factors that
control salmonid egg development (i.e. temperature, dissolved oxygen, water quality, and light), temperature
is probably the most critical. By recording the temperature of the water each day at a hatchery, fish culturists
can estimate when the eggs will hatch, as well as other important milestones in fish development.
Procedure
Warm Up: Use the questions below to help guide a group discussion and introduce the activity.
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Does anyone have a guess about when our salmon eggs will hatch? What makes you say that? Do you
have any evidence to back up that prediction? Scientists use evidence to develop their predictions.
Do you think the hatchery has any idea when their fish eggs will hatch? How do they know? Did they
call a psychic to tell them what day to expect the eggs to hatch? Hatchery staff record careful
observations about egg development and the conditions of the rearing environment.
What factors might influence our salmon eggs as they’re developing in the tank? How is this different
for salmon eggs developing in rivers or streams? Temperature greatly influences the rate of egg
development. Eggs in rivers are exposed to predation, silt, and greater fluctuations in water quality
and temperature.
Can you think of any differences between how embryos of salmon and humans develop? Fish are coldblooded and the surrounding water temperature determines how quickly the eggs develop. Humans
are warm-blooded and develop internally, so the temperature stays relatively constant during
development.
What species of salmon is in our tank? Are there other species of salmon? Would our Coho eggs
develop at the same rate as Chinook salmon? What if we put them in the same tank, under the same
conditions? Envirionmental factors such as temperature aren’t the only thing that control the rate of
egg development. Genetics also play an important role. Coho are genetically different from Chinook
salmon, so they develop at different rates, even under identical conditions.
Activity:
Recording Daily and Accumulated Temperature Units: Have students record the tank water temperature
twice daily, using the form provided (Table 1. Daily and Accumulated Temperature Units). It is important to
record temperatures daily to calculate ATUs. For weekend temperatures simply estimate using averages of
Friday and Monday information.
Daily temperature units (also called thermal units and degree days) are
calculated by taking the day’s average temperature and subtracting 32.
Each day’s temperature units are added to the previous day’s to represent
the accumulated temperature unit.
For Example: Let’s say you record an average daily temperature of 47F the first day eggs are in your tank, and
your SITC coordinator told you the eggs you received already had an ATU of 400. Record a daily temperature
unit of 15 (47 - 32 = 15) for the first day, and an ATU of 415 (400 + 15 = 415).
Days
at
School
1
Date
1-22-15
1-23-15
AM
Temp
PM
Temp
Average
Temp
Daily Temp Units
(Avg temp - 32 F)
Accum.
Temp Units
Notes
46
48
47
15
400
415
@pickup from hatchery
Eggs in tank at school!
Predicting Hatch Date
Using the information provided about ATUs required for salmonids to reach important developmental stages
(Attached, Table 3), have students predict how many calendar days it will take for their eggs to hatch. Coho
generally require ~800 ATUs before hatching. Students will also need to know the ATUs the eggs received at
the hatchery and the target daily temperature for raising Coho eggs (47F). Record the students’ predicted
hatch date(s) very visibly on the outside of the tank, so the rest of the school knows when to expect the
salmon. Offer a prize if the students’ prediction is accurate, or prepare a birthday serenade for the baby
alevin (Happy Hatch-Day To You!). Have fun with it, and help students get egg-cited to meet their new salmon
friends!
Wrap Up: Follow up on any questions from the warm-up that students struggled with. You can also ask:
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Can you think of anything that might happen over the next few weeks that would make you want to
change your prediction? What would happen if our power went out and the chiller stopped working?
Do you think all the other classrooms that have salmon tanks will sing Happy Hatch-day on the same
date as our class? Why or why not?
Do you think temperature only affects salmon when they are in the developing egg stage of their life
cycle? How might temperature affect adult salmon?
Extensions
Beyond the Hatch Date
Predict the date your fish will be “swum up” or emerged from the gravel (~1600 ATUs), when they will be
ready for tease feeding (~1380 ATUs), and when they will be ready to be fed 2% of their body weight (~1470
ATUs). Compare your class data with another school.
Hatchery Mix-Up
Instead of predicting the hatch date for the Coho eggs, tell the students there was a mix-up at the hatchery.
We’re not sure if we received Coho or Chinook eggs! Have students determine which species they have after
the eggs hatch, by comparing their calculated ATUs with the developmental information in Table 3.
Adapted from:
Salmon Egg Incubation in Alaska http://www.adfg.alaska.gov/static/viewing/pdfs/sic_atu_log_sheet.pdf
http://www.pac.dfo-mpo.gc.ca/education/documents/sicinter-secinter/sic_intermediate_unithandouts_5.pdf
http://www.ipm.ucdavis.edu/WEATHER/ddconcepts.html
When will they hatch? Worksheet from Meredith Gannon
(Sacajawea Elem)
School-wide prediction calendar from Jayne Salisbury
(Pioneer Elem)
Table 1. Daily and Accumulated Temperature Units (DTUs and ATUs)
Days
at
School
Date
1-16-15
1-17-15
1-18-15
1-19-15
1-20-15
1-21-15
1-22-15
1-23-15
1-24-15
AM
PM Average
Temp Temp
Temp
47F
48F
47F
47F
48F
49F
48F
49F
48F
47F
48F
48F
48F
47.5F
47.5F
Daily Temp Units
(Avg temp - 32 F)
48 – 32 = 16
48 – 32 = 16
48 – 32 = 16
47.5 – 32 = 15.5
47.5 – 32 = 15.5
Accum.
Temp
Units
631
647
663
679
694.5
710
Notes
@pickup from
Lewis River Hatchery
@ Columbia Springs
@ Columbia Springs
@ Columbia Springs
@ Columbia Springs
@ Columbia Springs
Table 1. Daily and Accumulated Temperature Units (DTUs and ATUs)
Days at
School
Date
AM
Temp
PM
Temp
Average
Temp
Daily Temp Units
(Avg temp - 32 F)
Accum.
Temp
Units
Notes
Table 2. Accumulated temperature units (ATUs) required to reach
important embryonic developmental stages in commonly cultured
salmonids in Alaska.
ATUs in °C
CHINOOK SALMON
To eyed stage
To hatch
To emergence
CHUM SALMON
To eyed stage
To hatch
To emergence
COHO SALMON
To eyed stage
To hatch
To emergence
PINK SALMON
To eyed stage
To hatch
To emergence
SOCKEYE SALMON
To eyed stage
To hatch
To emergence
ARCTIC CHAR
To eyed stage
To hatch
To emergence
RAINBOW TROUT
To eyed stage
To hatch
To emergence
STEELHEAD
To eyed stage
To hatch
To emergence
ATUs in °F
280
480-540
900-1000
504
864-972
1620-1800
300-350
475-525
900-1000
540-630
855-945
1620-1800
220
400-500
700-800
396
720-900
1260-1440
350-400
550-650
900-950
630-720
990-1170
1620-1710
230
500-550
900-1000
414
900-990
1620-1800
200
475
700
360
855
1260
210-240
300-320
500-580
378-432
540-576
900-1044
250-270
360
600
450-486
648
1080
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.
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 accumulated temperature units, or
ATUs.
Beginning on the day the eggs are fertilized, the temperature units for every day are added.
When the sum of the daily temperature units (DTUs) reaches the required total, the eggs will
hatch. The required total for coho salmon is between 720-900 ATU.
Predict when our salmon eggs will hatch:
Our salmon eggs were fertilized at the hatchery on Dec. 3, 2014. They spent the time at the fish
hatchery in 44 degree water. As of Jan.20, the eggs had 695 temperature units. They need
between 720 and 900 temperature units to hatch.
1. How many accumulated temperature units do our salmon need to hatch?
______ - 631 = ________
________- 631 = ___________
The salmon need between ______ and ______ temperature units.
2. Water Temperature – 32 = DTUs (Our water temperature is 47 degrees)
_______ - 32 = ________
3. Our fish get _____ temperature units each day. They need between ______ and ______
more temperature units.
_____ ÷ ______ = ____more days
_____ ÷ ______ = ____more days
4. Count from Jan. 20 on the calendar. Our fish should hatch between
__________ ________ and _________________.
Salmon in Schools
PREDICT the date our salmon will hatch! Our salmon should hatch between
January 26, 2015 and February 7, 2015.
Write your teacher’s name and room number on the day you PREDICT
the salmon will hatch. The classroom that comes closest to predicting the correct date will win a very
LARGE box of YUMMY FISH CRACKERS!
January 2015
Sunday
Monday
Tuesday
Wednesday Thursday Friday
21
22
23
Pick-up
Date
Saturday
24
25
26
27
28
31
29
30
February 2015
Sunday
1
Monday
2
Tuesday
3
Wednesday Thursday Friday
4
5
6
Saturday
7
8
9
10
11
13
14
Salisbury
Room 9
Valentines
Day!
12