The reason why the stickleback fish caught in the river has no spots is because the river water is polluted.

The stickleback is a common native fish in China, and because it looks like a goby, some people will mistake it for a goby. In fact, there's a clear difference between the two, and even newcomers can easily recognize it: the dorsal fin of the barramundi is wide and large, spreading out like a sail, but the dorsal fin of the goby is not as exaggerated.