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Guide Index

Polar Bear Picnic

The Wilder, the Better

Doctor Fish

Tuna in the Tank

Zoos as Arks

Return to the Wild

Viewer Challenge
in the classroom

The New Zoos: Doctor Fish

Alan Alda joins veterinarian Howard Krum on morning rounds at the New England Aquarium's Medical Center. On this visit, a bridled burrfish is scheduled for surgery. After the operation, a first for Dr. Krum, we meet Guthrie the sea lion, who has an appointment with the vet. After Guthrie passes his exams, Alan helps vets care for two other patients, abandoned harbor seals, who will be restored to health and later released into the ocean.

Curriculum Links
Related Frontiers Show and Activity
Activity: Fish Tales



fish, marine mammals


circulatory system




Biologists trace the evolution of the heart and circulatory system in mammals by studying the anatomy of hearts in other animals. In fish, the heart is a simple tube with two chambers, the atrium and ventricle, that pushes blood to the gills for oxygen, then through the body.

Amphibians have a three-chambered heart with partial separation of oxygenated and deoxygenated blood. In mammals, the heart is four-chambered with a complete separation of oxygenated and deoxygenated blood.

Operating on different animals requires a knowledge of circulatory and other systems in various species.


Model hearts of fish, amphibians and mammals.

  • clay of different colors
  • anatomical heart models (optional)

Use clay to build simple models of the hearts illustrated here and compare. Consult biology texts and the Web to research how the blood flows to and from the heart in each class of animal. Source: A Web-based tutorial on the circulatory system by Dr. Kenneth Chan, Department of Anatomical Sciences, University of Queensland.

  1. How does the arrangement of chambers in a fish heart compare to chambers in a mammal heart? In amphibians?

  2. How does a fish obtain oxygen and circulate it through its body? How does this differ from mammals and amphibians?

  3. In the story you watch on Frontiers, how do the surgeons keep oxygen circulating in the fish while it's out of water?

  4. Compare other systems and the anatomy features in fish, mammals and amphibians.
  1. How do the daily habits of the animal influence its circulatory needs? Why are most fish cold-blooded?

  2. The bluefin tuna is warm-blooded, though not an endotherm like mammals. Some scientists believe the tuna has an adaptation in one of its eye muscles that allows it to shunt warm blood to the brain. Why do you think the tuna evolved this adaptation, but other fish didn't? Do any other marine mammals have special adaptations?

  3. Write a script and/or draw story boards for a brief episode of an "Animal ER" drama.

  4. If you found an abandoned harbor seal pup on the beach, would you know what to do? Find out at the New England Aquarium website.

  5. People often confuse sea lions and harbor seals. Despite their similar appearance, they are not closely related. Each evolved from different ancestors, but both are pinnipeds, a suborder of marine animals. Sea lions have external ears and more developed limbs. Harbor seals are true seals. Next time you visit a zoo, see if you can tell them apart.

  6. You can explore the human heart online at the Franklin Institute.


Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.