Are most fish dioecious?

The answer is yes.
A feature of dioecious animals is the presence of testes in males and ovaries in females, as well as the production of reproductive gametes. Fish, both cartilaginous and bony, belong to such. Most of the process of their reproduction is called spawning, while individuals overcome long distances. For those representatives who are not worried about the safety of their generation, the production of fry is one million, and those who care – produce fewer individuals.