Moving Underwater

Inspired by our time observing Betta, Kindergartners began to discuss how different marine animals move their bodies. We noticed that our warrior fish swims by moving his tail from side to side. The fins positioned on either side of his body seemed to help him balance and steer. For swimming quickly, we saw that these side fins were held flat against his body but when the fish wanted to stop quickly, it extended its side fins out at the same time, using them as a break. We mentioned that most fish have several fins and we talked about how the fins positioned on the top and bottom of its body might prevent the fish from rocking back and forth, side to side.

We learned that some fish have a swim bladder (an air-filled sac inside the fishes body) that enables the fish to rise in the water. As our Betta comes up to the surface, he allows air to enter through his mouth, or from the bloodstream, into his swim bladder. As the bladder fills with air, the fish rises in the water. The fish sinks when he lets the air leave the bladder.

To demonstrate how a swim bladder works to allow a fish to move up and down we used:

A wide-mouth jar
tap water
2 glass marbles
2 round balloons

Using marbles and balloons we made two different sized swim bladders. We filled the jar with tap water and placed 1 marble inside each balloon. In the first balloon we tied a knot as close to the marble as possible. We inflated the second balloon slightly with air and tied the knot as close to the mouth of the balloon as possible. Then I asked students to predict what would happen when we dropped each balloon in the jar of water. Just as some of them had predicted, the inflated balloon floated and the deflated balloon sank to the bottom of the jar. The smaller, or more deflated the swim bladder, the deeper the fish can swim.

Not all marine animals have swim bladders though and we started to think about how and why marine animals might need to move around so much. Students said that fish move "to find food" and "to get away." After watching a few minutes of Oceans, we talked about how different marine species might be uniquely shaped to help their bodies move in very different ways through the water. Students were especially excited to watch the marine iguana move; we enjoyed seeing it make very deep dives and lumber along the rocky beach in the video. We noticed that its long tail and spiky fins seemed to help it to move quickly through the ocean and that its long sharp claws helped it to climb along the rocky shoreline.

Other animals shown in the video, such as the sea urchin, seem to hardly move at all. But when we watched very carefully, we saw that the sea urchin was actually crawling along the ocean floor. Pumping water into and out of its tubed feet, the urchin slowly glides along the sand. With their long spines we all agreed that other animals would be smart to stay away from the sea urchin!

We are looking forward to future investigations and are excited to learn about how other marine creatures move their bodies through the ocean.