The Effect of Temperature on Crayfish Food Assimilation
M. Jansen, K. Nichols, T. Peeples, H. Tydings
Introduction:
Crayfish are a species of freshwater decapod crustaceans that can be found in both
the Northern and Southern Hemisphere and are divided into three main families based
upon their geographical distribution. The first family of crayfish is known as the
Parastacidae and can be found in southern hemisphere in places such as Australia, New
Zealand and South America. The second family of crayfish is the Astacidae and is
located in the northern hemisphere and can be found in western North America, Europe
and western Asia. The third and largest family is the Cambaridae and is located in eastern
Asia and eastern North America. This family has over 300 different species and is the one
that is located in the freshwater bodies of water in Southwest Virginia (Groves, 1985;
Holdich, 1988)
Crayfish are generally described as having the appearance of miniature lobsters.
Their body is divided into two main parts consisting of the abdomen and the
cephalothorax consisting of the fused thorax and head. On the head the eyes are located
on stalks known as the rostrum and there are two antennas that the crayfish use as sensory
organs. Each crayfish has four pairs of walking legs and a pair of claws, or chelae, that
they used to either protect themselves from predators and other crayfish or as a method of
capturing food. Crayfish are covered with a hard exoskeleton composed of chitin that
provides them with protection from potential predators. As crayfish grown larger they
routinely shed their exoskeleton and grow a new one. Crayfish will go through multiple
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molts within their lifespan, though they tend to decrease in number as the animal gets
older. Due to the weight that is created by the exoskeleton, crayfish do not normally
swim and instead move around on their four pairs of legs. If a crayfish becomes startled
however, it can shoot backwards through the water by beating its tail. The life span of a
crayfish is estimated to be between 2-5 years, although some scientists speculate that they
could live for longer. The average size for a crayfish is around 7.5cm, though some
crayfish in the family Parastacidae can get as big as 40cm Often times crayfish during
their lifetime will lose one of their walking legs or claws and these appendages can be
regenerated if the crayfish is not too old (Groves, 1985; Holdich, 1988; Huxley, 1973).
Crayfish are classified as omnivores and are characterized by a willingness to eat
almost anything. In the wild they will consume a wide variety of foods including snails,
larvae, fish and freshwater vegetation. In captivity, crayfish will consume a variety of
commercial fish foods like fish flakes or shrimp pellets and also vegetables such as
carrots. In both the wild and captivity crayfish will practice cannibalism and will
consume other crayfish that are or unable to protect themselves due to being too small,
old, or injured. However, in general crayfish that are younger tend to prefer meat while
those that are older eat more plants (Groves, 1985; Hobbs, 1972; Huxley, 1973)
Freshwater crayfish live a wide variety of different habitats including streams,
lakes, marshes and swamps. Crayfish require habitats that have a high level of oxygen
and a slightly basic pH. Crayfish prefer a habitat with a temperature of around 18-25˚C,
although they can survive in temperatures outside of this range.They also need to live in a
habitat that has hard water since they require the calcium ions to help them regrow their
exoskeletons when they molt. While in the freshwater habitat, crayfish prefer to remain
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hidden, either through tunneling into the mud or hiding under rocks or pieces of
driftwood. Crayfish typically only leave their hiding place to mate, eat or molt and
usually do so at night because they are nocturnal. If a crayfish is living in a habitat that
they find unsuitable they will attempt to travel to a new habitat with better conditions.
This behavior can also be seen in captivity, where crayfish will escape from their
enclosures if they do not like the conditions (Groves, 1985; Hobbs, 1972).
Crayfish play a fundamental role in freshwater ecosystems as both a part of the
food web and as an indicator of the health of the body of water. Within the habitat,
crayfish are fundamental to maintaining the environment’s balance. They serve as
predators for many other animals such as fish and smaller invertebrates and also are a
source of food for some larger animals like mammals and birds. Vegetation levels within
a habitat are also controlled by crayfish as they graze. Besides being an important part of
the environment, crayfish also can serve as an organism to measure for changing
conditions within an ecosystem. Due to the fact that they only thrive in habitats that have
clean water, they are good indicators to tell if an ecosystem has become polluted,
especially with heavy metals. Their preference for certain temperatures of water also can
be used to determine if the temperature of a habitat is changing drastically enough to
reduce their numbers. Thus, crayfish are important due to not only their important role in
their ecosystem but also as a gauge for the overall condition of a habitat (Groves, 1985;
Huxley, 1973; Price, 1982).
Industrialization, deforestation, pollution, carbon dioxide emissions, and burning
of fossil fuels are just a few of the many acts done to contribute to the temperature
changing phenomenon known as global warming. Global warming, the gradual
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temperature increase of the earth’s atmosphere, has been greatly altering the climates of
the world for centuries. This increase of temperatures can be linked back to the start of
the Industrial Revolution, and the growth does not show any signs of slowing down in the
immediate future.
In 2001, the Intergovernmental Panel on Climate Change concluded there was a
sixty six percent chance that humans were likely the cause of global warming (Roach,
2007). There is new and stronger evidence that most of the warming observed over the
last 50 years is attributable to human activities. Fossil fuel burning and land clearing has
released a large amount of carbon dioxide into the atmosphere. These emissions act like
a blanket around the earth, keeping it warm and heating up the ocean, land, and
atmosphere. As a result, “current levels of carbon dioxide in the atmosphere are higher
than at any time during the last 650,000 years (IPCC 2001).
According to livescience.com, “the scientific consensus on climatic changes
related to global warming is that the average temperature of the Earth has risen between
0.4 and 0.8 °C over the past 100 years.” Although the earth has natural fluxes of
increasing and decreasing temperatures, this amount of rise is extreme and an effect of
this change is already evident across the world. Roach quoted that “arctic ice is rapidly
disappearing…polar bears and indigenous cultures are already suffering from the sea-ice
loss. Glaciers and mountain snows are rapidly melting. Coral reefs suffered the worst
bleaching—or die-off in response to stress—ever recorded in 1998. An upsurge in the
amount of extreme weather events, such as wildfires, heat waves, and strong tropical
storms, is also attributed in part to climate change.” These are just a few of the obvious
consequences that have already occurred due to global warming.
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One critical focus of global warming is the effect on ecosystems and biodiversity
of both terrestrial and aquatic organisms. Ecosystems are very vulnerable to climate
change, which in turn can have a positive or negative effect depending on the species.
According to the Environmental Protection Agency, “the Intergovernmental Panel on
Climate Change… concluded that 20 percent to 30 percent of species assessed may be at
risk of extinction from climate change impacts within this century…” This percentage
shows that even a small change in the temperature of the earth’s atmosphere can have
catastrophic effects on many species. Many species have been able to naturally adapt to
rising temperature changes thus far. However, as the temperatures continue to rise; their
resilience is going to be exceeded by combinations such as change in climate and land
alterations.
The rise in global temperatures could have a profound impact on crayfish and the
freshwater ecosystems they inhabit. One study conducted by Hammond, et al. (2006)
indicated a relationship between crayfish growth and temperature. They observed a
positive correlation between increased temperature and increased growth. This growth
could be related to increased activity and rate of feeding. Although the study focused
specifically on Paranephrops zealandicus, a species of crayfish found in New Zealand,
the trend likely holds true to other species as well.
The objective of this experiment is to determine if the correlating trend of
temperature and growth applies to crayfish species found in Southwest Virginia by
measuring the rate of food assimilation at various temperatures. This rate will be used as
an indicator of potential growth. We hypothesize that if temperature is increased then
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assimilation will also increase because metabolic and enzymatic processes increase with
temperature.
Methods:
Six ten gallon aquariums were cleaned and then filled with ten liters of tap water;
each aquarium was equipped with an aerator and three three-inch sections of PVC pipe to
serve as a shelter for the crayfish. One aquarium served as the holding tank and was kept
at room temperature which was approximately 18ºC. Four tanks were equipped with
heaters and set to 18 ºC, 20 ºC, 22 ºC and 24ºC respectively. The sixth tank served as the
control and was placed in a refrigerator at approximately 5ºC to create a chilled
environment closer to that which the crayfish were collected from. The tank preparation
was modified from a procedure by Hammond, et al. (2006).
D-frame kick nets were used to collect crayfish of a similar size (1.5 to 2 inches)
from Sinking Creek. The crayfish were transported in a bucket of water collected from
the creek at the time of capture. The bucket was left at room temperature with an aerator
so the crayfish would gradually warm and acclimate to the warmer temperature and
confined conditions. After twenty-four hours the crayfish were transferred to the holding
tank.
Each tank was randomly assigned three crayfish and the remainders were kept in
the holding tank. Afterwards each tank was given 0.5 grams of shrimp pellets. The tanks
were then covered to reduce evaporation and prevent escape. The crayfish were fed 0.5
grams of shrimp pellets daily for the next two days. Seventy-two hours after starting the
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experiment the crayfish were returned to the holding tank. Any crayfish that died were
replaced with a random crayfish from the holding tank before feedings.
Tap water was then added to each tank until each tank’s total volume was ten
liters. The water was stirred to homogenize and a one liter sample was collected from
each tank. More crayfish were collected from Sinking Creek and assimilated using the
same methods as the first time. They were then placed in the holding tank with the
remaining crayfish and then the experiment was repeated.
After the second run was complete each one liter sample was filtered with a
vacuum filter. In the second run, half of each one liter sample was used due to time
constraints. Multiple filters were used for each sample as the filters became clogged.
Each filtrate was dehydrated in an oven and then the filtrates from each sample were
summed and weighed. To find the total dry weight of material in each tank the dry
weights of the filtrates from each tank in the first run was multiplied by ten and the
weights of the filtrates from each tank in the second run were multiplied by twenty. This
amount is representative of the amount of food remaining plus the amount of fecal waste.
The total for each tank was compared to the total dry weight of food given to that tank.
The difference between the two weights indicated the amount of food assimilated by the
crayfish.
Results:
Run 1:
The average temperature of each tank was similar to the approximated
temperatures (see Table 1). The average amount of food given per day was also similar to
the approximated value of 0.5 grams (see Table 2). The amount of food assimilated for
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the tanks in the refrigerator, at 18 ºC, 20 ºC, 22 ºC, and 24 ºC were 0.576 grams, 0.638
grams, 0.592 grams, 0.734 grams, and 0.731 grams respectively. A simple linear
regression is provided below.
It should be noted that two crayfish died in the 22 ºC tank, while one died in the
24 ºC tank. Three crayfish escaped from the 18 ºC tank and one crayfish escaped from
both the 22 ºC and 24 ºC tanks. All dead and escaped crayfish were promptly replaced.
Table 1: Recorded Temperatures (ºC)
Tank
Day 1
Day 2
Day 3
Average
Refrigerator
7.5
7.5
5
6.67
18 ºC
17.7
17.7
20.1
18.50
20 ºC
20.4
20.4
20.5
20.43
22 ºC
22.4
22.4
22.5
22.43
24 ºC
25.5
25.5
25.5
25.50
18 ºC
0.4995
0.5025
0.5217
0.508
20 ºC
0.4979
0.4981
0.5033
0.500
22 ºC
0.4938
0.4979
0.5088
0.500
24 ºC
0.4981
0.5191
0.4991
0.505
Table 2: Food Added (grams)
Tank
Day 1
Day 2
Day 3
Average
Refrigerator
0.5086
0.4924
0.5034
0.501
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Food Assimilation at Various Temperatures (Run 1)
0.8
Food Assimilated (grams)
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.00
5.00
10.00
15.00
20.00
25.00
30.00
Average Temperature (ºC)
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Run 2:
As in Run 1, the average temperature and average amount of food given were
similar to the approximated values (see Table 3 and Table 4). The amount of food
assimilated for the tanks in the refrigerator, at 18 ºC, 20 ºC, 22 ºC, and 24 ºC were 0.846
grams, 1.068 grams, 1.166 grams, 1.116 grams, and 0.696 grams respectively. A simple
linear regression is provided below.
One crayfish died in the 24 ºC tank and none escaped. The dead crayfish was
replaced per the procedure.
Table 3: Recorded Temperatures (ºC)
Tank
Day 1
Day 2
Day 3
Average
Refrigerator
4.9
5.0
5.4
5.15
18 ºC
18.7
19.2
18.5
18.80
20 ºC
20.7
20.4
20.5
20.53
22 ºC
22.1
22.1
22.1
22.10
24 ºC
24.4
25
26.1
25.17
18 ºC
0.5094
0.4962
0.5099
0.505
20 ºC
0.5043
0.4921
0.4991
0.499
22 ºC
0.5069
0.4967
0.5076
0.504
24 ºC
0.4953
0.4992
0.4983
0.498
Table 4: Food Added (grams)
Tank
Day 1
Day 2
Day 3
Average
Refrigerator
0.49
0.5061
0.5
0.499
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Food Assimilation at Various Temperatures (Run 2)
1.4
Food Assimilated (grams)
1.2
1
0.8
0.6
0.4
0.2
0
0.00
5.00
10.00
15.00
20.00
25.00
30.00
Average Temperature (ºC)
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Literature Cited:
Groves, Roy, E. The Crayfish: it nature and nurture. Surrey: Fishing News Books
Ltd, 1985
Hammond, K., J. Hollows, C. Townsend, and P. Lokman. 2006. Effects of temperature
and water calcium concentrations on growth, survival, and molting of
freshwater crayfish, Paranephrops zealandicus. Aquaculture 251:271-279.
Hobbs, Horton, H. Crayfish (Astacidae) of North and Middle America. Washington D.C.:
U.S. Government Printing Office, 1972.
Holdich, D.M. and Lowery, R.S. Freshwater crayfish : biology, management, and
exploitation. Portland: Timber Press, 1988.
Huxley, T.H. The Crayfish: AN Introduction to the Study of Zoology. Cambridge: The
MIT Press, 1973.
Price, J.O. The Life history and ecology of the crayfish Orconectes Neglectus
Chaenodactylus in North Sylamore creek, Arkansas. Ann Arbor: University
Microfilms International, 1982.
‘
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“All About Global Warming” Live Science Online[Internet]. [cited 2008 April 22].
Available from http://www.livescience.com/globalwarming/
Intergovernmental Panel on Climate Change. 2001. Climate change 2001: The scientific
basis. Cambridge, UK: Cambridge University Press. Available from
http://www.ucsusa.org/global_warming/science/Fingerprints.html
Roach, John. 2007. Global Warming "Very Likely" Caused by Humans, World Climate
Experts Say. National Geographic Online[Internet]. [cited 2008 April 22]. Available from
http://news.nationalgeographic.com/news/2007/02/070202-global-warming_2.html
U.S. Environmental Protection Agency. “Ecosystems and Biodiversity.” [Internet].
[cited 2008 April 22]. Available from
http://www.epa.gov/climatechange/effects/eco.html
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