Fish first appeared: a) after the "age of the dinosaurs" during the mesozoic era. b) during the ordovician period of the paleozoic era. c) in the cretaceous period of the mesozoic era. d) when land plants evolved during the carboniferous period. e) when amphibians dominated the oceans.

during the Cambrian Period of the Paleozoic Era.

Explanation:

The Paleozoic is the earliest era (of three) of the Phanerozoic Eon and is composed of six geologic periods: the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian (in that order from earliest to the latest). Fish first appeared about 530 million years ago during the Cambrian explosion.

C. Fish first appeared when land plants evolved during the Carboniferous period

Explanation:

The age of fish was 410-360 million years ago which was called the Devonian period of the Paleozoic Era. This period immediately followed the Carboniferous Era which is 360-286 million years ago when amphibians dominate the land animals on the planet. Agnathans or jawless fishes are the first backboned fish. These fishes survived by sucking food in through the holes in their head.