Dead Horse itself is not typically great fishing. The creek coming up through Buck pasture is nice fly fishing for little guys. I hear Ejod may have some lunkers.
Amethyst Basin has good fishing. Ostler and Toomset probably have the larger fish but the others have good populations. And the meadow below BR-24 is a riot to dry fly fish.
Another nice option would be to head out from Hayden Pass and cross over Rocky Sea into Rock Creek. The lakes along the high west and north edges of that are said to hold nice fish and it's not as busy as a lot of other places.
Or if you don't want to go over a pass, just cut right and head into Four Lakes Basin. You can even head down to Allen and hook into some Arctic Grayling.
Lots of trip reports on all these places in the backpacking section.