Fish are vertebrates and therefore have backbones. Fish are sometimes observed with curved backbones. This is attributed to a variety of factors, including lack of vitamin C, injury, birth defect, temperature change while in egg and parasites.
Fish with curved backbones are still safe to consume. The lack of vitamin C as the culprit is usually found in hatchery fish.
Most fish are cold-blooded animals, with the exception of the Pacific salmon shark and the tuna. Fish breathe oxygen through their gills, and some fish have scales. There are approximately 30,000 identified fish species worldwide, according to the International Union for Conservation of Nature, and the United States is home to approximately 800 fish species.