The position and shape of swim bladder in the viscera of crucian carp are obvious. Observing the swim bladder tube, you can press other organs with your fingers, and you can see a slender swim bladder tube protruding forward from the front of the ventral side of the posterior chamber. If you want to confirm whether it is a swimming tube, you can gently pick it up with a scalpel. If the digestive tract can be affected, it means swimming tube.
According to the natural position, the reproductive system often covers the digestive system, so it is best to observe the reproductive system first. Let the students distinguish male and female fish from the structure of reproductive system, and the groups can exchange observations. Finally, the swim bladder and reproductive system are removed, and the esophagus and tortuous intestine of crucian carp can be seen. Be careful not to rush to straighten the intestine, so as not to damage the hepatopancreas.
When observing the respiratory system, let the students insert the dissection needle from the mouth of crucian carp and pass through the gill hole at the back edge of the gill cover. Then use anatomical needle to test whether the nostrils of crucian carp communicate with the oral cavity, so that students can understand the situation of water flowing through the gills, and then instruct students to open the gills with tweezers to observe the branchial fissure between the gills, and then cut off a gill and soak it in clear water to observe the bright red gills.