Creatures of land and air often grace our pages, but not so many of an aqueous environment. Probably because photographing them in their own medium requires special equipment and approaches. In the interest of diversity, I'll add a couple. These fish were subsequently tagged and released as part of biological studies.
Rainbow trout (Oncorhynchus mykiss) in spawning colors
Brook trout (Salvelinus fontinalis), which is actually a char