Anoxia-Tolerance in Freshwater Turtles and Crucian Carp

Research Paper Submitted by

RINE CHRISTELLE GALARPE ANFONE

In Partial Fulfillment for

BIOLOGY 52 ANIMAL PHYSIOLOGY

at the

Biology Department

Silliman University, Dumaguete City

Philippines 6200

February 2014

Introduction

Oxygen is an essential element for us to live. May we be vertebrates and invertebrates or even

plants; we require oxygen for various reasons. One of which is our respiration, which involves gas

exchange and transfer of oxygen to cells; then there is cell respiration or metabolism.

However, there are circumstances in which levels of oxygen are very low that is hard to get it.

Examples are when you are at high altitudes or at deep seas. A person will find it hard to breathe.

This is what we call hypoxia. But there are also events that totally deplete oxygen. This might have

been the reason for prehistoric animals to be extinct. We are very vulnerable to this and so are the

other animals.

Professor Goran Nilsson said, "Anoxia related diseases are the major causes of death in the

industrialized world. We have here a situation where evolution has solved the problem of anoxic

survival millions of years ago, something that medical science has struggled with for decades with

limited success." (Society of Experimental Biology, 2006)

Some of the specialized animals that are adapted to anoxia are the Chrysemys picta marginata and

Trachemys scripta elegans which are both freshwater turtles, and the Carassius carassius which is

also a freshwater fish. They developed changes anatomically and physiologically in order to survive

the harsh conditions during winter. They can survive from days up to months.

In the next pages, the reader can find what anoxia means and what its causes are. Also, one can find

the background about the 3 highly adapted species and what their adaptations are.

I. What is Anoxia

A. Definition of Anoxia

Anoxia (etymology: greek “an-” meaning “without” + “ox” from Oxygen + “-ia”) is the total absence

or depletion of oxygen (http://www.thefreedictionary.com/anoxia).

B. Anoxia versus Hypoxia

What is the difference between anoxia and hypoxia which is commonly used by people

interchangeably? Hypoxia refers to the shortage of oxygen (B. Koch,n.d.). In the field of medicine,

hypoxia means the inadequate oxygenation of the tissues usually caused by the lack of oxygen

concentration in the blood (Mandal A., n.d.). Environmentally, the issue of hypoxia refers to the

waters that contain too low concentration of dissolved oxygen, which is a one of the most common

water quality problem worldwide (Committee of Environment and Natural Resources, 2010). Hypoxia

is the condition when dissolved water column oxygen (DO) decreases below minimal concentration

requirement for animal life (20% O2 saturation or 65 ʯmol/L). Extreme hypoxia may lead to suboxia

(<5 ʯmol O2/L) and possibly to anoxia (no oxygen at all) (M. Lehmann, n.d.). Because anoxia means

the absence of oxygen; therefore it is a severe hypoxia (http://www.biology-

online.org/dictionary/Anoxia).

C. Causes of Anoxia/Hypoxia

Medically, hypoxia and anoxia is commonly caused by anemia but there are also environmental

factors (Mandal A., n.d.). In the environment, factors that contribute to an area of hypoxia include

temperature, salinity, vegetation and bacteria. Oxygen levels are very important with water systems

because water holds less oxygen than air. Plants and algae are the main source of oxygen in aquatic

habitats for oxygen is a product of photosynthesis. Natural diffusion of oxygen into water may take

place because the air has more oxygen than water. Water mixing maximizes the air to water contacts

that aids in the addition of oxygen. (“What causes hypoxia?”, n.d.)

Temperature has an effect to dissolved oxygen. Water loses its ability to hold the dissolved oxygen as

temperature of water goes up, therefore, oxygen concentration decreases. As water cools, it gains

back its ability to hold higher amounts of oxygen. Temperature also increases the respiration rates of

organisms because it has an important role in metabolic processes. It is predicted by the Metabolic

Theory of Ecology that respiration rates would increase compared to the photosynthetic rates

because of warming and limited resources like light, oxygen, and carbon dioxide. (Vaquer-Suner &

Duarte, 2010).

Salinity or the amount of dissolved salts in water affects the amount of oxygen in water interestingly.

Salinity and amount of dissolved oxygen in water has an inverse relationship, for 5 gm of salt in 1000

gm of water (5 ppt) will decrease the dissolved oxygen levels about 1 mg/L. Since salt water is denser

than fresh water, two layers of water form: lighter layer of fresh water in top and heavier layer of salt

water on the bottom. This causes inadequate mixing of the water column and not allowing

oxygenated water to deeper waters. However, most ponds and lakes are fresh water so they are

exempted from these salinity considerations. (“What causes hypoxia?”, n.d.)

Plants undergo the process of photosynthesis producing oxygen, so all aquatic plants are important

in maintaining healthy levels of oxygen. Phytoplankton, although microscopic, also undergo

photosynthesis so they also add oxygen to the water. Bacteria, because it respires and uses oxygen

like fishes, has an effect to the amount of dissolved oxygen. (“What causes hypoxia?”, n.d.)

Anthropogenic factors such as agricultural activities (row cropping and livestock operations), urban

runoff, wastewater treatment, and atmospheric deposition are also causes of nutrient-related

impairments which affects the water (Committee of Environment and Natural Resources, 2010).

The climate also has an effect on hypoxia, increasing or decreasing its severity (Committee of

Environment and Natural Resources, 2010).

Table 1. The list shows how climate factors affect hypoxia’s severity (+ means increase and –

means decrease) (Committee of Environment and Natural Resources, 2010).

D. Effect of Anoxia/Hypoxia

It is a serious problem in USA’s great lakes. These areas are called “dead zones” since only few

organisms can survive in these places, mostly bacteria. Some are able to swim away from the area

while some will be trapped, and if the exposure is severe, they may be stressed or worse, die.

Usually, hypoxia’s DO concentration is 2 to 3 mg/L, but sensitive organisms can be affected with just

4.5 mg/L (Committee of Environment and Natural Resources, 2010).

Negative effects of hypoxia (and eventually anoxia) include the loss of suitable and required habitats

for bottom-dwellers and benthic fauna, habitat compression for pelagic fishes, direct mortality, and

increase in predation, decrease in food resources, alteration of trophic energy transfer, changes in

physiology, development, growth and reproduction, and alteration in migration (more on Table 2).

This gives to a reduction in fisheries, including crustaceans. It also disrupts the ecosystem functions

and services like nutrient cycling and bioturbation (Vaquer-Suner & Duarte, 2010).

Table 2. Shown here are the effects of hypoxia in ecosystems. With these kind of effects, it really

shows that hypoxia is extremely dangerous, especially to the aquatic animals. (Committee of

Environment and Natural Resources, 2010)

Fish kills (Figure 1) are very common consequences of both anoxia and hypoxia. This is when large

number of dead and dying fishes floats unto the surface or wash to the shore. (Breitburg, 2002) Lack

of oxygen can asphyxiate most fishes in just hours. Fishes respond to hypoxia by not feeding,

breathing underneath the surface, jumping out the water, swimming disoriented and lying at the

bottom. (Eriss, 2000) High mortality of fishes lacking swim bladders can occur leaving low or no

visible evidence of fishes at the surface. New research is trying to clarify when hypoxia will cause fish

kill despite its ability to avoid it (Committee of Environment and Natural Resources, 2010).

Figure 1. Fish kills results to fishes floating on the surface and is a major effect of hypoxia. (Eriss, 2001)

Another effect of hypoxia is habitat loss since fishes swim away from “dead zones”. Areas used by

aquatic animals for feeding, reproduction, and shelter from predators will be abandoned depending

on the bathymetry of the system, the severity of hypoxia and the behavior and physiological

tolerances of the affected organisms (Breitburg, 2002). This causes reduced growth in commercially

harvested species and loss of biodiversity, habitat, and biomass which affects the economy

(Committee of Environment and Natural Resources, 2010).

However, if we look at it at cellular basis, the main effect of anoxia which is a big problem is the stop

in oxidative phosphorylation which leads to a severely impaired capacity for ATP production. With

this, it is hard to match the ATP demand of the body. Because all cells are in need of a constant

supply of ATP, cells will rapidly lose their ability to regulate key factors like volume and on balance

during anoxia. (Sandvik, 2012)

II. Overview of the Anoxia-Tolerant Marine Animals

A. Freshwater Turtles

In this research paper, two freshwater turtles of the Northern America are being studied, the

Midland Painted Turtle and the Red-eared Slider. Let’s look at what these animals look like and how

they live.

1. Chrysemys picta marginata

The Midland Painted Turtle or the Chrysemys picta marginata is common in Ohio. They have a deep

green colored, sometimes black (“Care sheet – Midland painted turtle”, n.d.) carapace (upper shell)

which is brightly patterned with red and black underside the marginal plates (“Midland painted turtle

(b)”, n.d.). Its shell is smooth and lightly domed (“Care sheet – Midland painted turtle”, n.d.). Their

upper shell generally reaches length of 12 - 14 centimeters; the record for length is 19.5 centimeters.

It has a yellow or dark tan lower shell (plastron) (Crowley, 2013) lined with gray down the center

“Midland painted turtle (a)”, n.d.) or with dark central figure that is normally oval and is less than half

the shell width (Mann, 2003). The marginal scutes are decorated with red bars, blotches and stripes

(“Care sheet – Midland painted turtle”, n.d.). They are in alternating patterns (“Species information:

Midland painted turtle (Chrysemys picta marginata)”). Its shell is made up of 60 bones (“Midland

painted turtle (a)”, n.d.). Light red lines might also appear along the borders of the carapacial scutes.

Its head and throat displays prominent yellow lines from the tip of the nose to the lower part of the

face, and often turns red as it goes down to the neck. Its upper jaw has 'tooth-like' cusps and its eyes

yellow in color with the horizontal bar running through the pupil (“Care sheet – Midland painted

turtle”, n.d.). Their webbed feet to help them move well on water (“Midland painted turtle (a)”, n.d.)

and they can also move quickly and easily due to their size (Knipper, 2002).

Males are smaller and less domed compared to females. Front claws of males are elongated to aid

them in courtship and mating rituals. Their tails are longer than females. (“Care sheet – Midland

painted turtle”, n.d.)

They mostly breed on the months of May-July and incubate for 10-11 weeks (“Midland painted turtle

(b)”, n.d.). Eggs hatch in about 70 to 80 days bones (“Midland painted turtle (a)”, n.d.). The typical

number of offspring is 4-15 (“Midland painted turtle (b)”, n.d.).

They are active during the day (diurnal) (Crowley, 2013). They are omnivores and eat fish, tadpoles,

aquatic inverts and plants. As they grow older, they tend to be more herbivorous enjoying water

lettuce, water hyacinths, duckweeds and many more. (“Care sheet for painted turtles”, 2007)

Figure 2. The Midland painted turtle as described in the paragraphs above: a.) The turtle’s side

view shows the yellow to orange marks on face; b.) the turtle showing off its webbed feet; c.) the

turtle with its upper shell. (“Care sheet – Midland painted turtle”, n.d.)

They are found in the great lakes of Canada to Illinois, Tennessee and Alabama (“Care sheet for

painted turtles”, 2007). They prefer freshwaters that are quiet and shallow (Anonymous, n.d.).

Painted turtles generally bask in groups on log or fallen trees (Knipper, 2002). They are similar in

form with a slider, which is "classic basking" style (“Care sheet – Midland painted turtle”, n.d.).They

hibernate during winter by burrowing into mud, allowing their bodies to be very cold (Knipper, 2002).

They can survive to temperatures up to -9 °C because of they have biological "antifreeze" that

prevents tissues from freezing (Crowley, 2013).

They may live for 30 to 40 years in the wild (Crowley, 2013), but many will not survive for this long.

For those in captivity, their average lifespan is 30 years. (Knipper, 2002)

2. Trachemys scripta elegans

The Trachemys scripta elegans (Figure 3) or commonly known as red-eared sliders are medium-sized

freshwater turtles with a carapace length from 125 to 289 mm (Pendelbury, 2010). Their top shell

(carapace) is rounded and smooth with a black and yellow line pattern. Their bottom shell (plastron)

is smooth and is yellow in color with a unique pattern. The patterns become less obvious as the

carapace becomes darker and the red stripes fade. (“Basic Slider Info”, 2011) They are very

recognizable for their signature red (orange/yellow) stripes that start from the end of the eyes to

their ear area (“Basic Slider Info”, 2011), in fact they were named such because of it (Pendelbury,

2010). Its skin is usually colored olive to brown (Pendelbury, 2010).

The carapace is divided into plates called scutes (osteoderms) which are made of keratin. These are

like scales in the epidermis. Connecting the carapace and the plastron is the bridge, which is a section

of bone between the fore and hind limbs. (“Basic Slider Info”, 2011)

The larger ones with long and thick tails are the males (Pendelbury, 2010). The cloaca (on the

underside of the tail) is the only opening to serve digestive, urinary and reproduction purposes. A

b a c

female’s cloaca is closer to the shell compared to a male which has a longer and thicker tail. Male RES

have long front claws used in courtship and territorial confrontation. These claws are sharp and can

scratch the skin easily. They also have beaks which are made of keratin that cuts flesh and vegetation

easily. Although they don’t have teeth, their throats are flexible to accommodate large portions. But

when they swallow, they need to be in water since they don’t produce saliva. (“Basic Slider Info”,

2011)

Figure 3. The Red-eared slider pictures: a.) shows the whole body; b.) their carapace is rounded; c.)

and its face is lined with red. (Pendelbury, 2010; Somma, Foster. & Fuller, 2013)

They are omnivorous (Pendelbury, 2010) and eat things like tadpoles, small fishes, snails, insects and

plant materials (“Basic Slider Info”, 2011). Their peak breeding activity months are on March to July,

and usually gestate for 85 days. The number of eggs they lay is from 4 to 23 (“Red-eared slider”,

n.d.). The wild RES stays close to their water source unless it is searching for a new source or if a

females needs to lay eggs. Presence of logs or rock formations is needed to give them a basking area,

but stable and dry things that are above the surface are alright. They usually bask together and

sometimes even on top of each other. (“Basic Slider Info”, 2011)

They usually live in rivers, ponds, ditches and swamps. They prefer large bodies of water with many

aquatic plants and soft bottoms. They can also adapt in living in brackish waters and manmade

canals, even park ponds but they usually put themselves in areas with floating vegetation. It is

believed that they feed and grow in the temperature range of 10 °C to 37 °C. An evidence of their

adaptive capabilities is their presence in polluted tropical rivers in Brazil. These rivers give a great

amount of organic residues and food items. (Pendelbury, 2010)

The RES is a habitat generalist. They can live up to 20 years. (“Red-eared slider”, n.d.). Compared to

the other species of turtles, the Trachemys have advantages for they have lower age at maturity,

higher fecundity and larger adult body size. Because turtle compete for food and shelter, the Emys

(considered an endangered species) transferred to low quality basking sites while the Trachemys

have the better ones. The Trachemys are also known to be nematode-carriers. (Pendelbury, 2010)

a b c

The Trachemys' native range is from the Midwestern states to as far as West Virginia and southern

Ohio (east), and eastern New Mexico (west) and the Rio Grande River into northeast Mexico (south).

(Somma, Foster & Fuller, 2013)

B. Crucian Carp

The crucian carp (Figure 4) or Carassius carassius is part of the Actinopterygii or the "ray-finned

fishes" class and under the order Cyprinformes (carps) and family Cyprinidae (Luna, n.d.). It is one of

the four species of Carassius (Facts about crucian carp (Carassius carassius)”, n.d.). Many sources say

that the crucian carp is a wild version of the goldfish. They are sometimes kept as freshwater

aquarium fishes although they are not available commercially. (“Crucian carp – Fish reference

library”, n.d.)

They are usually colored golden-green and are shiny (Luna, n.d.). They have a yellowish to white

belly. They have a very rounded body with small scales patterned evenly and have reddish fins that

are rounded with a convex dorsal fin. (Crucian carp – Carassius carassius”, 2007) They are normally

15cm in length while its maximum length is 64cm (Luna, n.d.). They also rarely weigh above 3.3 lb

(1.5 kg) (Crucian carp – Carassius carassius”, 2007). They usually live up to 3 to 10 years (“Facts about

crucian carp (Carassius carassius)”, n.d.).

They have no barbules around their small mouth for it inclines upward slightly to the front when

shut. Along the lateral line, there are about 32 to 34 scales. Most of the time, the slotting in the

lateral line is either interrupted or incomplete showing disappearance towards its tail end. Their

lower fins are usually brown or reddish. When their tail fin extends vertically, it is almost straight or

slightly forked. They have large and convex dorsal fins and its back is ridged. The crucian carp is softer

to the touch compared to the goldfish. Its body is deep and flattish. (Rolfe, n.d.) Their last simple anal

and dorsal rays are slightly serrated (Luna, n.d.).

Figure 4. The crucian carp: a.)is usually golden-green in color; b.) has no barbules in mouth; and c.)

has large, convex dorsal fins. (Schofield, Nico & Fuller, 2011; Rolfe, n.d.)

a b c

Adults can be found in permanent fresh water bodies such as lakes (“Institute for the study of

invasive species: Carassius carassius”, 2011), shallow ponds and slow-moving rivers (Luna, n.d.). It

usually lives in waters having temperatures from 2 degrees Celsius to 22 degrees Celsius (Luna, n.d.).

They often travel upstream to spawn and lay eggs ((“Institute for the study of invasive species:

Carassius carassius”, 2011). They mainly spawn on water plants in the months of May to June.

Although the egg will hatch within a week, they will still stay attached to the plants for 2 to 3 days

feeding on the yolk sack before swimming off. (“Crucian carp – Carassius carassius”, 2007) They eat

all day, but feeds on plankton, benthic inverts (insect larvae, small crustaceans ((“Crucian carp –

Carassius carassius”, 2007)), plant materials and debris (Luna, n.d.).

It is said that the crucian carp has the ability to live out of the water for hours (Schofield, Nico &

Fuller, 2011). During winter and the dry season, they usually burrow in the mud. They have the ability

to withstand high temperatures in summer and also very low oxygen concentrations and cold under

the ice. (Luna, n.d.) They can be tolerant also to high turbidity like the goldfish. They can survive to

waters with temperatures below 0 °C and may survive with frozen integument for a few days. Their

ability to use anaerobic metabolism allows them to survive in anoxic waters at low temperature.

During winter months when the waters will be anoxic and ice-covered, they may stop for feeding for

months as they will rest in a state of "suspended animation". (Schofield, Nico & Fuller, 2011)

These fishes are native to northern Europe (“Facts about crucian carp (Carassius carassius)”, n.d.).

They can be found the freshwater bodies with poor ichthyofauna in places within 69° N - 35 °N, 10°

W - 169° E and are common in Italy, England and France. They are also present in the basins of the

North, Baltic, White, Barents, Black and Caspian Sea. (Luna, n.d.)

III. Physiology of Anoxia-Tolerance in some Aquatic Animals

People started wondering how these three freshwater animals could survive in cold and

non-oxygenated water. Various scientists then made researches on how these animals adapt

to certain conditions.

A. Chrysemys picta marginata and Trachemys scripta elegans

These turtles which are primarily air breathers evolved their tolerance as a response to overwintering

in anoxic mud on the bottom of rivers and lakes which causes them not to have access to the

atmosphere (Nilsson & Lutz, 2004). Through this, they can use the ability for breath-hold diving and

during hibernation during winter (“Anoxia tolerance”, n.d.).

While most mammals die within minutes from anoxia, these turtles can survive for up to days if in

room temperature and up to months at 3°C. Because they are ectothermic, there is an increased

tolerance to lower concentration of oxygen associated with lower metabolic rates. This tolerance to

anoxia is not just a result of being an ectotherm, but because of specific adaptations in their brain

which is not present in other reptiles. These adaptations allow them to be in a state of deep and

reversible hypometabolism which reduces metabolic rate to 10-15% of basal. With this reduction,

energy demand is now matched to the reduced energy given by anaerobic glycolysis. However, this

reduction in metabolism is a regionally specialized, tightly regulated suite of adaptations that can

permit the functional down regulation of certain brain parts while activity is maintained in other

parts. (Wyneken, Godfrey & Bels, 2008) During anoxia, the turtle brain’s supply of ATP declines

initially, however it returns to aerobic levels and will return to aerobic levels and will be constant for

at least 6 hours after. It survives by avoiding energy failure. (Hochachka, Lutz, Sick, Rosenthal & van

den Thillart, 1993) So, it is like in comatose (Nilsson & Lutz, 2004).

They also sense anoxia using some metabolic indicators. One of which is the fall of ATP and the

increase of the release of adenosine. (Nilsson & Lutz, 2004) The neurotransmitter adenosine might

mediate anoxia tolerance because it can regulate changes that provide compensation when oxidative

phosphorylation is not possible. It is known to modulate brain blood flow, stimulate glycogenolysis

and lower the electrical and synaptic activity through pre- and postsynaptic inhibition. The

extracellular levels of adenosine increased during the transition to anoxia. This increase is temporary

which suggest that adenosine might modulate the early changes during anoxia. This hypothesis is

supported by preliminary findings that agents which block adenosine A1 receptors caused rapid loss

of ion homeostasis during anoxia, which is within 40 minutes. (Hochachka, Lutz, Sick, Rosenthal &

van den Thillart, 1993) These turtles can also detect the molecular oxygen content include

membrane proteins like ionotropic ion channels, particularly voltage-dependent potassium ion

channels (Kv channels, membrane or cytosolic heme proteins, mitochondrial proteins and sensitive

transcription factors like HIF-1 and NF-kappaB. There is also the increase of GABA, which could act

like an endogenous anesthesia reducing metabolism and protecting the anoxic brain (Nilsson & Lutz,

2004). The Gamma-aminobutyric acid or the GABA inhibits synaptic transmission through opening

receptor-gated, postsynaptic Cl- channels and by promoting HCO3- efflux through the opened

channel. The release of GABA may cause reduction of intracellular HCO3- and pH that could depress

metabolism. (Hochachka, Lutz, Sick, Rosenthal & van den Thillart, 1993)

With the shift to anaerobic glycolysis, an end product would be lactate. The turtles deal with lactate

using its extracellular buffering capacity. The presence of Mg2+ and Ca2+ in the shell balances the

negative charge of lactate. The shell also releases carbonate to buffer acidosis and sequester lactate.

The turtle’s liver also contains large amount of glycogen (stored form of energy) needed for extended

use of glycolysis. (Hill, 2013)

Figure 5. The diagram shows the summary of how the turtle survives anoxia through their

adaptations. (Nilsson & Lutz, 2004)

B. Crucian Carp

Scientists at the University of Oslo discovered how the Crucian Carp can live without oxygen for

months. Researchers found out that the crucian carp can change the structure of their gills to avoid

becoming anoxic. Its blood also has a much higher affinity for oxygen than other vertebrates. It can

also make tranquilizers and alcohol when oxygen supply is limited. These allow them to survive for

days or even months without oxygen depending on the temperature, while maintaining physical

activity. (Society of Experimental Biology, 2006) However, they sacrifice some senses which are less

needed like vision and hearing. (Nilsson & Lutz, 2004)

Carps, which are highly vulnerable to predation, have a survival strategy to live in seasonally anoxic

ponds. This protects them from predators that are unable to survive in these waters. Researchers

found that the drop in water temperature makes the carp store huge amounts of glycogen in their

brains. This allows them to switch to anaerobic metabolism which does not require oxygen. This

happens mostly in the months of Febuary to April in the northern hemisphere. According to

researcher Matti Vornanen, these carps use carbohydrates stored as glycogen as energy source

during anoxic conditions. Glycogen is broken down into glucose and ethanol, which gives them

energy to survive. (Thomson, 2006)

According to Nilsson (1990), species in the genus Carassius (including crucian carp) have large

glycogen stores which are 27% of the liver’s mass, and 2-4% in the muscles which comprises about

half the body mass of the fish. His experiment shows that liver glycogen stores can stand to anoxia

15-17 days at 8 degrees Celsius.

Glycogen store from the liver is used to survive these harsh conditions, but researchers discovered

that brain glycogen increased 15-fold during the month of February, when oxygen is most depleted

in ponds. The carp's sodium-potassium pump which keeps their brain cells functioning in extreme

conditions, was still intact but its activity is reduced by 10-fold in lower water temperatures. This

helps them reduce the energy the carp needs for continued brain activity in anoxic conditions. Unlike

turtles and frogs which survive anoxic conditions for long periods in "suspended animation", carps

have evolved physiological mechanisms to cope with hypoxia and even anoxia while remaining

active. (Thomson, 2006)

Prolonged anoxic survival needs balancing of the energy supply and demand, and also managing with

the acidosis connected with the end-product of anaerobic metabolism. Anoxic freshwater turtles

reduce metabolism by 90%, precluding an up-regulation of glycolysis, and they also will buffer lactic

acid accumulation with their shell and bone. Cardiac output is now reduced by 92% and autonomic

cardiovascular control is blunted. Crucian carp however still remain active, up-regulate glycolysis to

maintain their ATP supply, and convert lactate into ethanol to avoid acidosis. " We examined this

hypothesis by measuring Q, heart rate (fH), stroke volume (VS), ventral aortic blood pressure (PVA),

and respiration rate (fR) and by calculating peripheral vascular resistance (R) and cardiac power

output (PO) of crucian carp during 5 days of anoxia at 8 ± 1°C. After an initial adjustment period, Q,

fH, VS, PO, and fR all returned to pre-anoxic levels throughout days 2 to 5 of anoxia,

whereas PVA and R decreased significantly (P < 0.05) by 30% and 40%, respectively, indicating

vasodilation. Furthermore, autonomic controls remained intact during anoxia. Cardiac inhibitory

cholinergic and excitatory β-adrenergic tones were revealed by respective increases and decreases in

both fH and Q after injections of the pharmacological inhibitors of these control processes. Tonic α-

adrenergic vasoconstriction was revealed by decreased PVA and R after pharmacological α-adrenergic

blockade.” (Stecyk , Stenslokken, Farrell & Nilsson, 2004)

Levels of neurotransmitters also changed. Studies by Nilsson (1990) showed that serotonin levels

decreased by 24% after 17 days of anoxia. There are also falls in levels of dopamine with 9% and

norepinephrine with 17% after 7 days. However, kidney norepinephrine and epinephrine levels

decrease at about 92%.

Figure 6. The diagram shows how the crucian carp is able to survive anoxia. (Nilsson & Lutz, 2004)

Conclusion

Through the sources we have collected, the researcher found some similarities and differences. First,

the both live in freshwaters which are mostly on the Northern Hemisphere. Second, the both of them

can are both ectotherms which increases their possibility to tolerate hypoxia and even anoxia. Third,

they have lower body temperatures (Figure 7) compared to other vertebrates and can survive anoxia

in temperatures near 0°C. Fourth, they have large glycogen stores in their liver which can let them

undergo glycolysis for hours. Fifth, they have their own techniques for saving themselves from the

harm of lactic acid which is a product of anaerobic glycolysis. The crucian carp is able to convert

lactate into ethanol; while the turtles are able to buffer lactate using their shell and bones. Then,

there are also changes in neurotransmitter levels (Figure 8) which are hypothesized to help them

tolerate anoxia. However, the crucian carp is more tolerant to anoxia compared to the others,

because it can maintain physical activity while affected with anoxia; unlike those of the Trachemys

and the Chrysemys.

Although they face anoxic conditions differently, they still are able to withstand its effects. This

makes them very perfect samples for studies, especially for medical causes. Indeed, special animals

that are evolved by nature never cease to amaze us.

Figure 7. The graph shows the relationship of anoxia-tolerance to an animal’s body temperature.

We can see that the crucian carp, with body temperature almost 0°C, survive anoxia longer

compared to the other vertebrates. It is followed by the Midland Painted turtle, then by the Red-

eared slider. (Nilsson & Lutz, 2004)

Figure 8. The graphs above shows the changes of ATP and neurotransmitter levels in the crucian

carp, the turtles and a typical mammal.

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