the fin on the median line behind the vent 
The fin behind the anus of a fish
Fin just behind anal opening.
The unpaired fin that lies along the midline of the body beneath the anus, usually on the back half of the fish.
The fin located on the ventral median line and behind the anus.
A single fin on the midline of the ventral surface, posterior to the anus. Varies greatly in size, shape, point of insertion, and composition (spines and/or rays) among species.
(anal relating to anus) single, unpaired fin positioned on the undersurface of a fish between the anus and the tail.
The fin located on the ventral median line and behind the anus.
the fin on the median line behind the vent
The fin on the underside of some sharks. Situated between the pelvic fins and the caudal fin.
a single fin located beneath the tail
a single fin located on the underside of of most sharks, behind the anus.
Single fin mounted vertically below the fish.
the median, unpaired fin on the ventral margin between the anus and the caudal fin in fishes. See diag. under