Opisthonema

Opisthonema
Opisthonema oglinum (Atlantic thread herring)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Clupeiformes
Family:	Clupeidae
Genus:	Opisthonema T. N. Gill, 1861

Opisthonema, the thread herrings, is a genus of herring found in tropical waters of the Western Hemisphere. They get their name from a filamentous nature of the last ray of the dorsal fin. There are currently five members of this genus.

...
Wikipedia