Capros aper commonly reach a length of about 13 cm in males, with a maximum length of about 30 cm. The weight reaches about 85 g. The female is larger than male. This fish shows large eyes, a quite long snout and a very protractile mouth, that forms a short tube when extended.
The general form of the body can be defined rhombic, quite deep and compressed. The dorsal fin is unique, the caudal fin rather large and spatulate with convex edge, the ventral fins are very large and have a thorny spine, while the pectoral fins are quite small.
The color of the body is reddish orange, sometimes with three wide darker bands, one behind the eye, one in the center of the body and one on the caudal peduncle. During the breeding season there is a striking sexual dimorphism, the male has a body covered with sinuous orange lines and the dorsal and ventral fins become red, while the female is orange with a faint dark band in the middle of the body and has belly and basal part of the ventral fins white silver, the final part of the ventral fins is rather dark orange. It feed on crustaceans, especially copepods and mysid shrimps, or on molluscs and worms.
Capros aper usually lives close to the floor of the sea (demersal), mainly on muddy bottoms or near rocky bottoms or coral. It forms numerous herds at a certain distance from the substrate, but occasionally it can reach a depth of about 700 m, especially at night.
- "WoRMS taxon details—Capros aper (Linnaeus, 1758)". World Register of Marine Species. http://www.marinespecies.org/aphia.php?p=taxdetails&id=127419. Retrieved 11 January 2013.
- "Capros aper (Linnaeus, 1758)". FishBase. http://www.fishbase.org/summary/Capros-aper.html. Retrieved 11 January 2013.