Respiration Rate Allows Survival in Low Oxygen

two small white sharks with a prominent black spot rest in an aquarium in arizona

Biological Strategy

Epaulette shark

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Maintain Homeostasis

When a living system is in homeostasis, it means that internal conditions are stable and relatively constant. For example, a human’s internal temperature is approximately 37 degrees Celsius (98.6 degrees Fahrenheit) unless there’s an illness. The human body maintains this temperature despite external ambient temperature. However, as with all physiological processes, maintaining homeostasis requires communication and coordination. So living systems have ways to detect changes from the norm, mechanisms to cause an adjustment, and negative feedback connections between the two. A desert lizard called the Gila monster offers a good example of maintaining homeostasis. The lizard goes from eating large meals to fasting for extended time periods. To maintain its blood sugar levels at a steady level, when food is scarce, its endocrine system releases a hormone that raises its blood sugar levels.

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Protect From Loss of Gases

Gases are part of most living systems’ environment, especially those exposed to the earth’s atmosphere. Many gases are crucial to survival, with the two most important being oxygen and carbon dioxide. In some environments, oxygen or other essential gases may be in low supply, such as underwater where there’s been a decrease in the amount of dissolved gases. Living systems must have strategies to survive in that depleted environment. An example is a shark that reduces its respiration rate to survive when oxygen levels are low.

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Fish

Class Agnatha (“without jaws”), Class Chondrichthyes (“cartilage fish”), Superclass Osteichthyes (“bone fish”): Sharks, eels, snapper, hagfish

The fish are a diverse group, comprising multiple classes within Phylum Animalia. The most well-known classes are Chondrichthyes, which has sharks and rays, and superclass Osteichthyes, which has all bony fish like cod and tuna. Unlike other vertebrates, fish only live in water. They use special adaptations like fins, gills, and swim bladders to survive. Most are ectothermic, meaning their body temperature depends on the water temperature around them. Over half of all vertebrates are fish. They’re found from the bottom of the sea to high mountain lakes.

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Heart, arteries, lungs, and cells of epaulette shark allow survival in low oxygen by reducing respiration rate.

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Epaulette shark (Hemiscyllium ocellatum) at the Adventure Aquarium, Camden

Image: mrpbps / Wikimedia commons /

Epaulette shark (Hemiscyllium ocellatum) on a beach in Port Tribulation, Queensland.

“The epaulette shark (Hemiscyllium ocellatum) is a tropical marine vertebrate. It lives on shallow reef platforms that repeatedly become cut off from the ocean during periods of low tides. During nocturnal low tides, the water [O2] can fall by 80% due to respiration of the coral and associated organisms. Since the tides become lower and lower over a period of a few days, the hypoxic exposure during subsequent low tides will become progressively longer and more severe. Thus, this shark is under a natural hypoxic preconditioning regimen. Interestingly, hypoxic preconditioning lowers its metabolic rate and its critical PO·. Moreover, repeated anoxia appears to stimulate metabolic depression in an adenosine-dependent way.” (Nilsson and Renshaw 2003:3131)

Last Updated August 18, 2016

References

Journal article

Hypoxic survival strategies in two fishes: extreme anoxia tolerance in the North European crucian carp and natural hypoxic preconditioning in a coral-reef shark

Journal of Experimental Biology | 06/08/2004 | G. E. Nilsson

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