Gill arches are usually less digested than the external parts of the fish. Therefore, for a partially digested fish, gill arches are in relatively better shape and suitable to be used as a characteristic for prey fish identifications.
The gill-raker count format is: U + L; where U is the raker count for the upper limb, and L is the raker count for the lower limb.
The general pattern of the gill-raker is expressed in the following format: A~B + C~D = E~F; where A~B is the range of the raker count on the upper limb, C~D is the range of the raker count on the lower limb, and E~F is the range of the total raker count. Most of the gill-raker counts shown represent the individual specimens.
Images are generally taken from the right side gill arch of the fish. And usually only the first gill arches were taken from the specimen fish. For each gill-arch, pictures of the outer view and inner view (when inner-rakers exist) were taken. Though outer views of gill arches and gill-raker counts were usually used, inner views of gill arches are sometimes useful for taxonomical identifications (e.g. in walleye pollock and capelin).