Auspicious meaning. In China culture, eating fish has auspicious meaning, because "fish" and "surplus" are homophonic, so eating fish means "surplus every year", which means a good omen for next year's harvest. In addition, fish scales also mean "year after year", because fish scales have a continuous meaning. Fish is the oldest vertebrate. It is easy to accumulate heavy metals. Some hybrid offspring with different chromosome numbers still have fertility. They inhabit almost all aquatic environments on earth, from freshwater lakes and rivers to saltwater oceans. Fish are divided into two categories: scaleless order and scaleless order. Naked branchial subclass includes circadian rhythm fish and armored fish, and hard branchial subclass includes shield fish, cartilaginous fish and kiwifruit. Most fish are temperature-changing vertebrates, living in water all the year round, breathing through gills and using fins to help balance and move. Some African lungfish, mudskippers and perches can live on land for a long time. There are more than 22,000 kinds of fish in the world? , accounting for more than half of the named vertebrates, and new fish species are constantly being discovered, with an average of about 150 species per year, and more than 1500 species should be increased in more than ten years.