Explore the swim bladder

I remember once grandpa killed crucian carp, and I stood by and watched. Grandpa peeled the belly of crucian carp and took out a white peanut-like thing for me to play with. I asked my grandfather, "What is this?" Grandpa said, "It's a swim bladder." I took it in my hand curiously and found it was empty. I asked curiously, "What's the use of this thing?" Grandpa said, "Ask your teacher when you go to school. Grandpa doesn't know what's the use. "

One day at noon, I ate in the school cafeteria, and there was braised crucian carp in the dish box. Suddenly my brain recalled the swim bladder that my grandfather gave me, and my curiosity about the swim bladder came up again. So, I happily ran to ask the teacher: "Teacher Yu, what is the swim bladder for?" The teacher looked at me in surprise and then smiled: "The swim bladder is a structure in the fish, which is full of air. When it is filled with a lot of air, it can make fish float in the water; When the air inside is squeezed out, the swim bladder will shrink and the fish will sink. " I seem to understand, "well, do all fish have swim bladders?" I don't know where the idea came from, so I asked. The teacher frowned and thought for a moment. Some fish have no swim bladder, such as sharks and some deep-sea fish. "So, how do fish swim up and down without swim bladder?" The teacher frowned and didn't speak for a long time, then looked at me with a smile and stroked my head and said, "Kid, you are so smart! Your question stumped the teacher! If you are interested, how about we do experiments together and check the information together to solve this problem? " I nodded vigorously with pleasure.

One day later, in the afternoon, Teacher Yu gathered me and several classmates in a classroom. Start our experiment to explore the function of swim bladder.

Experiment 1

To explore whether the fluctuation of fish in water is related to the size of swim bladder.

Question: Is the fluctuation of fish in water related to the size of swim bladder?

Hypothesis: the fluctuation of fish in water is related to the size of swim bladder.

Experimental design: Four live crucian carp were selected, and two of them were carefully cut into the abdomen, and the swim bladder was taken out with tweezers, cut with a knife, stitched with a needle and thread, and marked. The remaining two fish served as the control group without any operation. Put four fish into the water and observe their ups and downs and suspensions carefully.

Experimental phenomenon: 1. The results showed that the two marked fish (crucian carp with its swim bladder cut) were not flexible, but they could rise and fall in the water. 2. When all four fish are ups and downs, their fins are constantly moving.

Experimental conclusion: the ups and downs of fish have little to do with the swim bladder, but with the fins.

So, we did the second experiment.

Experiment 2

Explore the relationship between fish's ups and downs in water and fins.

Experimental steps: 1. Select some live crucian carp and divide them into four groups, 3 in each group. The first group, carefully cut off the pectoral fin and ventral fin of the fish; The second group, carefully cut off the tail fin; In the third group, all fins were carefully cut off; The fourth group did not cut any fins, and only served as the control group. Put four groups of fish into the fish tank and carefully observe their ups and downs and suspensions in the water.

Observation record: in the first group, the fish can float freely, but they can't suspend or stop to rest. The second group of fish can float and sink, but the balance is not good and the speed is slow. The third group of fish is very slow, unstable and poorly balanced.

Experimental conclusion: The fish's ups and downs in water are really related to fins, and the fish's ups and downs in water are mainly realized by the movement of fins, especially the movement of tail fins.

After the experiment, we consulted a lot of facts and related materials with the teacher, and then came to the conclusion that the relationship between the fish's ups and downs and the size of the swim bladder is not very big, which is mainly realized by the movement of the fins. The volume change of the swim bladder is passive during the ups and downs, and the swim bladder can be used as an auxiliary respiratory organ to provide oxygen for the fish.