As I said earlier, the fish needs to be filleted to determine if there is any deformity in the bone structure, or if the dorsal bones have been chewed off. The best way to tell.
I caught a few tailor many years ago with what appeared to be a deformity of the backbone, and when filleted, the backbone was actually deformed and curved a bit.
Bream with those bits missing along the dorsal fins, when filleted actually had the dorsal fins chewed off (obviously from a bite from a larger fish) and the backbone appeared perfect. Have only caught a few bream with a missing section of dorsal fin, and do not remember ever finding the backbone to be deformed.
No doubt some fish have imperfections in the bone structure, like humans, caused by other factors apart from mechanical injury (eg. collision with a boat), or bites from bigger fish. Fish swim in polluted waters at times, and there is no escaping toxic water when it spills into the ocean and rivers.
I can speak with some experience, as I have caught and filleted fish for something approaching 60 years.