What is one similarity that birds share with the most fish such as goldfish and angelfish?

One similarity that birds share with most fish, such as goldfish and angelfish, is that both groups are ectothermic at certain life stages. While fish are primarily ectothermic, meaning their body temperature is regulated by the environment, some bird species can exhibit similar behaviors, such as basking in the sun to warm up. Additionally, both birds and fish have evolved specialized respiratory systems—birds have lungs and air sacs for efficient oxygen exchange, while fish use gills to extract oxygen from water.