Let me try answering your question briefly. When we're talking about fish it seems important to me to make a distinction between 2 groups of fish there are - fresh water and marine fish. I will talk about species present in Karnataka in general, even though you asked for coastal region only. In case of the coast, please do refer to the second part of the answer - Marine water species.
Species of fish living in fresh waters
As a state, Karnakata is very abundant in water resources of both types - fresh and marine. It is of no surprise then, that there are many types of fish present there. The general count says that in fresh waters of Karnakata, there are 201 species of fish (from 84 genera, 27 families and 9 orders). 40 of those species are endangered.
The state produces around 1.2 lakh metric tonn of fish yearly which represents less than 50% of the state's production potential.
The most popular types are:
Species of fish living in marine waters
Coastal line of Karnakata is 300 km long with 27 000 sq. km of continental shelf. It's a very good habitat for many species of fish from which mackerals, sardines, anchovics and other elupeids are the most abundant. In case of deep sea fishing, threre are also many atfishes, Sciaenids, Perches, sharks and rays.
There are 276 species of fish living at the coast for Karnata with the following types being the most popular ones:
I hope that was helpful to you.