Slimeheads, also known as roughies and redfish, are mostly small, exceptionally long-lived, deep-sea beryciform fish constituting the family Trachichthyidae (derived from the Greek trachys – "rough" and ichthys – "fish"). Found in temperate to tropical waters of the Atlantic, Indian, and Pacific Oceans, the family comprises about 50 species in eight genera. Slimeheads are named for the network of muciferous canals riddling their heads. The larger species – namely the orange roughy (Hoplostethus atlanticus) and Darwin's slimehead (Gephyroberyx darwinii) – are the target of extensive commercial fisheries off Australia and New Zealand. Many populations have already crashed, while others are showing signs of severe overfishing; due to slimeheads' slow rate of reproduction, the future viability of these fisheries has been put into question. Orange roughies are food fish and are marketed fresh and frozen, whereas Darwin's slimeheads are used for their oil and made into fishmeal. Description With a typically deep-bodied, laterally compressed form, slimeheads are conspicuous for their large, titular heads, large eyes, and (in some species) bright colours. The head is especially notable for its network of mucus-filled canals, which constitute the cranial portion of the lateral line system. Similar cranial networks are found in the beryciform fangtooths (Anoplogastridae) and the stephanoberyciform ridgeheads (Melamphaidae). The trachichthyid head is typically blunt with a large and oblique mouth; the snout may project slightly in front of the upper jaw. A short, sharp spine is present on the preoperculum and/or operculum and post-temporal bone, the latter spine directed posteriorly. Species of the genera Optivus, Paratrachichthys, and Sorosichthys differ in form from other members of the family; their bodies are more elongated. All fins are spinous (excluding the low-slung pectoral fins) and rounded: the single dorsal fin has three to eight spines and 10–19 soft rays; the pelvic fins are thoracic with one spine and six or seven soft rays; the anal fin has two or three spines and eight to 12 soft rays; and even the forked caudal fin possesses four to seven procurrent spines on each lobe. The scales of slimeheads are ctenoid, but vary interspecifically; they range from deciduous to adherent. In most species, the ventral scales between the pelvic fin and anus have been modified into a median ridge of large, bony scutes. The lateral line is uninterrupted and fairly obvious; its pores are largely obscured by the scales' well-developed spinules or ctenii. Slimeheads range from a bright