brick red with identically shaded fins, to dusky grey or silver, to black with dusky grey to transparent fins. The reds quickly fade to orange following death. Some species (e.g., Aulotrachichthys latus) are reported to be bioluminescent, probably by symbiotic bacteria as is found in other beryciform fish. The largest species is the orange roughy at a maximum standard length (SL; a measurement excluding the caudal fin) of 75 cm and a weight of 7 kg; however, most slimeheads are well under 30 cm SL. Life history Most slimeheads are sluggish and demersal, spending most of their time near the bottom of continental slopes. Cold, moderate benthopelagic depths (about 100 – 1,500 m) with usually hard, rocky substrates are frequented. The most elongate species are typically the most active and frequent the shallowest depths; for example, the slender roughy (Optivus elongatus) is found in photic coastal waters and is associated with rocky reefs. This species is nocturnal and hides in crevices during the day. Trachichthys australis is of the same habitus, but is rather deep-bodied and resembles a soldierfish. Both young and adult slimeheads feed primarily upon zooplankton such as mysid shrimp, amphipods, euphausiids, prawns, and other crustaceans, as well as larval fish. Slimeheads store energy as extracellular wax esters, which aid the fish in maintaining neutral buoyancy. Slimehead behaviour is not well studied, but some species sporadically form dense aggregations. In the case of the orange roughy, these aggregations (possibly segregated according to sex) may reach a population density of 2.5/m2;. The aggregations form in and around geologic structures, such as undersea canyons and seamounts, likely where water movement and mixing is high, ensuring dense concentrations of prey items. The aggregations do not necessarily form for the purpose of spawning; it is thought that the fish cycle through metabolic phases (feeding and resting) and seek areas with ideal hydrologic conditions to congregate during their inactive and active phases. Observations of orange roughy aggregations during submersible dives have also shown the fish lose almost all pigmentation while inactive, during which time they are very approachable. The orange roughy's metabolic phases are thought to be related to seasonal variations in the fish's prey concentrations, with the inactive phase being a means to conserve energy during lean periods. Slimeheads are pelagic spawners; that is, spawning aggregations are formed and the fish release eggs and sperm en masse directly into the water. Evidence