This study examines the effects of temperature on the physiology and
viability of a native catfish (Ictalurus punctatus), an introduced fish
(Oreochromis niloticus, tilapia), and a native freshwater aquatic plant
(Lemna spp, duckweed). The goal of this work is to relate how global
climate change, largely raised temperatures, will affect living organisms
and its distribution. As a result of increased temperatures, many drastic
repercussions can and will occur. Living organisms that are conducive to
warmer temperature will encroach the temperate zone and thus
displacing the native species there in response to global climate change.
Concomitantly, a rise in temperature will also cause elevated metabolic
rates, which will translate to an increase in food consumption. At the
same time, temperature increase may result in the demise of native
temperate primary producers, as such threatening the food web. In
this study, we test the effects of increase temperature on catfish and
tilapia and measured their respiration rates as a surrogate for
metabolism. In the plant experiment, we assessed the viability of
duckweed that were exposed to ambient and a higher temperature
slightly above their physiological range. Our results showed a higher
scope change in respiration rates in the tilapia from 22oC to 34oC, while
the change in the catfish was blunted. In the duckweed experiment, a
two degrees increase from its physiological upper thermal limit result in
increased mortality. We conclude that a small sliver of the effects, such
as increased water temperatures, can elicit on a multitude of change in
a community.
Impact of Global Temperature
Rise on Exotic Species
Natalie Bentley, Madori Spiker, Christopher Peterson, and Christina Li
Cluster 3: Living Oceans and Global Climate Change
Oreochromis Niloticus (Tilapia)
Lemnoideae (Duckweed)
Tilapia consume aquatic
plants like duckweed.
Optimal temperature range:
Nile tilapia’s upper limit is
Range of Survival: 6-33°C
Due to anthropogenic global climate change, rising temperatures are
inevitable. Therefore, it is important to study the consequences of
increasing water temperature on wildlife. Due to an increase in food
demand, plants and animals that are deemed productive have been
introduced by humans throughout the world. An excellent example of
this is the tilapia (Oreochromis niloticus), a native fish from Africa and
is now introduced to all continents except the Antarctica. Tilapias
have in recent time become a staple fish product in the United States
and are farmed extensively here with 2.5 million tons being projected
in 2010. Therefore, the likelihood of encountering this exotic species
in our waterways is not too far-fetch. In this study, we compared the
respiratory physiology of tilapia and a native catfish at their upper
thermal limit (Fig 1). In addition, we also examined the viability of a
native aquatic plant over the same thermal range. The rationale of
this work is to understand how global climate change can upset the
ecology of a community.
Figure 2
Duckweed: The mortalities were substantial when the plants were subjected to 35°C, albeit it is not significantly different from control.
In the control group, only a few dead cells were found at 22 °C. The result shows that a change of 2°C in the upper thermal limit of the
duckweeds greatly decrease viability, underscoring the sensitivity to temperature in primary production.
Water temperature increase will not have an effect on catfish and
tilapia respiration rates nor on duckweed mortality.
Effects of Temperature on
Duckweed Mortality
Duckweed: Three dishes of duckweed in
water were placed at ambient temperature
(control group, n=50 plants per dish) while
another six were placed on a warming pad set
to 35oC (experimental group, n=50 plants per
dish). The plants were left at normal daynight cycle for five days before enumeration
(Fig 2).
Figure 1
Fish study: A large insulated thermal container was used to house
the experimental fish (catfish, n=2 and tilapia, n=2), which were
instrumented with a pressure transducer (Millar Instruments) in
the buccal cavity for respiration rate measurements (Fig 1).
Measurements were made at ambient temperature (22oC ) and
subsequently raised by an aquarium heater to 34oC . An analogdigital convertor (DataQ, Ohio) was used for transforming the
analog pressure signals from the Millar amplifier into digital bits
onto a computer for post analysis.
The most important finding of this study is that a small change in
temperature fluctuation translates to large physiological change which
can influence the composition of the community. In the case of the
duckweed, a rise of 2 °C drastically affects the viability of the plants
and thereby can cause a dramatic reduction in the food base. The fish
study shows that a rise in temperature increases the ventilation rates
– vis-à-vis increase metabolism - of tropical tilapia while temperate
catfish stayed somewhat blunted. Global climate change will be
conducive in extending the range of this exotic fish north of
continental United States, which has seen its share of tropical invasive
species. For example, the marine tropical lionfish are now common
off Florida, Asian carps have invaded several of the major rivers,
snakeheads are found in the astern seaboard, Asiatic swamp eels
inhabit the Everglades. Tilapias which are grown by the millions can
easily saturate our freshwater communities. Even if the native species
can adapt to the temperature rise, they may not be able to compete
with this artificially selected fish that were bred to feed and grow
Fish: The increase in ventilation rate for the catfish was only 10 ventilations per minute from ambient to 34°C while in the tilapia the
change was more than times as high (35 ventilations per minute). However, the catfish displayed a higher initial rate of ventilation than
that of tilapia (78 ventilation/min vs 48 vent/min, respectively). , but the increase of ventilation in response to temperature rise was
less than that of the tilapia otherwise. Overall, at the end of the experiment, before each of the species unfortunately died, the
ventilation rate of the two species was about the same.
Results are presented as mean+sem. Group differences
for the duckweed experiments were analyzed by
Student’s t-test while the fish experiments were
determined by one-way ANOVA. The null hypothesis
was rejected when p>0.05.
Ictalurus Punctatus (Catfish)
Optimal temperature range :
Catfish acclimated to 25°C has
“upper lethal temperature” of
Carnivorous but can consume
aquatic plants as well
Statistical Analysis
Temperature plays a large role in defining the range and distribution
of organisms. These three experiments showed that a rise in water
temperature as in global climate change can have considerable
impacts on plants and fish alike. Our data show that increases in
temperature can have substantial effects on the overall success of
fish and on the mortality rates of plants. If global warming continues
to worsen, and anthropogenic activity continues to exacerbate our
fragile environments we will most certainly see a threat in our food
We’d like to thank Dr. Ngai Lai, Chase Hightower and members of
Cluster 3 for assisting us with our experiments.

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