Unit

Animal Science

Problem Area

Aquaculture

Lesson

Effect of Temperature on Cold-Blooded Animals

Student Learning Objectives

1. Define the term poikilotherm. 2. Explain how the circulatory system of

poikilotherms is affected by changes in temperature.

3. Describe how temperature affects the metabolic rate of poikilotherms.

4. Describe the effect other factors, beside temperature, have on the activity of poikilotherms.

Terms

Circulatory system Dissolved oxygen Homeotherm Metabolism Poikilotherm

What is a poikilotherm?

A poikilotherm is an organism whose body temperature adjusts to its environment.

A. Poikilotherms are often referred to as cold-blooded or ectotherms. This includes most fish and reptiles. For this reason large fluctuation in water temperature in an aquatic environment can cause the aquacrop to be stressed or can effectively kill them.

B. Homeotherms are organisms whose body temperature is relatively constant. They are commonly called warm-blooded or endotherms.

How is the circulatory system of poikilotherms affected by changes in temperature?

The general rule is that as temperature increase so does bloodflow.

A. The circulatory system of the fish includes the heart, gill blood vessels, cranial veins, cardinal veins, aorta, portal vein, hepatic veins as well as capillaries. Blood cells move through the capillaries one blood cell at a time. Capillaries join together to form veins in the tail which do not pulsate.

B. When the water temperature decreases the blood flow decreases. The diameter of the arteries gets smaller and less blood gets circulated.

C. When the water temperature increases the blood flow also increases. The increased temperature causes the blood vessels to expand and allow more blood to flow.

What effect does temperature have on the metabolic rate of poikilotherms?

Metabolism is the process of converting food to energy.

A. Metabolism requires that oxygen and food be transported through the fish. When blood flow is reduced due to temperature, less oxygen is available to cells for respiration so the process is slowed. As a result, in fish that are in temperatures lower than their desired range, activity is reduced.

What factors, beside temperature, affect the activity of poikilotherms?

A. Water quality is of major importance in the general health of aquatic organisms. This includes nitrogen compounds and dissolved oxygen, among others. Nitrogen levels need to be carefully monitored to reduce the harmful effects of ammonia and nitrite. Generally dissolved oxygen, elemental oxygen that remains in solution under existing conditions, levels needed to be 4–5 ppm at a minimum. Dissolved oxygen depletion can result in large fish dying off in a matter of a few hours.

B. Stress levels associated with handling, injuries, crowding also reduce the activity of fish.

C. Poor nutrition will also reduce fish activity.

Review/Summary

What is a poikilotherm? How is the circulatory system of poikilotherms

affected by changes in temperature? What effect does temperature have on the

metabolic rate of poikilotherms? What factors, beside temperature, affect the

activity of poikilotherms?