Tetra a tall dorsal fin characterized by a short connection to the fish’s body. Additionally, tetras possess a long anal fin stretching from a position just posterior of the dorsal fin and ending on the ventral caudal peduncle, and a small, fleshy adipose fin located dorsally between the dorsal and caudal fins. This adipose fin represents the fourth unpaired fin on the fish (the four unpaired fins are the caudal fin, dorsal fin, anal fin, and adipose fin), lending to the name tetra, which is Greek for four. While this adipose fin is generally considered the distinguishing feature, some tetras (such
Blob sculpin flap that covers the gills), the branchiostegal membranes are fused to the isthmus (the fleshy projection separating the gill openings), and there are many small cirri (fleshy threads) scattered over the head and body. The operculum is poorly ossified and is covered by a gelatinous layer. Behind the head, the body tapers rapidly to the caudal peduncle and there is a gelatinous layer between the skin and the muscle. The dorsal fin has eight spines and nineteen to twenty soft rays, and the anal fin has no spines and twelve to fourteen soft rays. The pectoral fins are broad and