I've always used 4-bits (16 levels) of Alpha for the fish textures (DXT3).
The problem I'm describing has not been much of an issue before, because I've always used a heirarchy of objects within the fish (fins, eyes, etc.), and manually changed the order in which they are painted depending on viewing angle. But now that I'm trying to go to a single object, the drawing order is no longer reasonably within my control. I say "reasonably" because there is a way of doing it, but it would involve calculating the distance from the camera of every polygon, for every object, every frame. Even this would only give an approximation, as a polygon which runs deeply into the scene could easily have points which are both nearer AND farther than the next polygon.
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