White-tailed eagle more vulnerable than many. Besides vulnerability, habitat and prey behaviour, fish body size may be a driver in the piscivorian dietary preferences. Studies have indicated that fish less than are taken infrequently, since they have a lower yield, fish of up to are taken secondarily and fish between are preferred since they have the highest nutritional benefit. Fish taken can exceed but since they can start to considerably exceed the weight of the eagle itself, they may be prove too difficult to overpower. One large Atlantic halibut ("Hippoglossus hippoglossus") was found with the disembodied feet of a white-tailed eagle still
Fish anatomy Their retinas generally have both rod cells and cone cells (for scotopic and photopic vision), and most species have colour vision. Some fish can see ultraviolet and some can see polarized light. Amongst jawless fish, the lamprey has well-developed eyes, while the hagfish has only primitive eyespots. The ancestors of modern hagfish, thought to be the protovertebrate were evidently pushed to very deep, dark waters, where they were less vulnerable to sighted predators, and where it is advantageous to have a convex eye-spot, which gathers more light than a flat or concave one. Unlike humans, fish normally adjust focus by