ADIPOSE FIN
adipose fin: translation
a small fleshy fin lacking rays or spines but reinforced by actinotrichs posterior to the soft dorsal fins (rarely a hard ray or a few soft rays may be developed in the adipose fin of certain catfishes), e.g. in Salmonidae, Osmeridae, Argentinidae, Myctophidae, Ictaluridae, Percopsidae