Orange roughy

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iOrange roughy

Not evaluated (NE)

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Beryciformes
Family:	Trachichthyidae
Genus:	Hoplostethus
Species:	H. atlanticus

Binomial name

Hoplostethus atlanticus
Collett, 1889

The orange roughy or red roughy, Hoplostethus atlanticus, is a relatively large deep-sea fish belonging to the slimehead family (Trachichthyidae). It is found in cold (3–9°C), deep (bathypelagic, ca. 180–1,809 m) waters of the Western Atlantic (off northern Nova Scotia), Eastern Atlantic (from Iceland to Morocco; and from Walvis Bay, Namibia to off Durban, South Africa), Indo-Pacific (off New Zealand and Australia), and in the Eastern Pacific off Chile. The orange roughy is notable for its great age—a recorded (but hotly disputed) maximum of 149 years—and great importance to commercial deep trawl fishery. Actually a bright brick red in life, the orange roughy fades to a yellowish orange after death.

Like other slimeheads, the orange roughy is slow-growing and late to mature, resulting in a very low resilience. They are extremely susceptible to overfishing because of this, and many stocks (especially those off New Zealand and Australia, which were first exploited in the late 1970s) have already crashed; recently discovered substitute stocks are rapidly dwindling. Even so, the United States continues to import up to 8,620 tonnes (19 million pounds) of orange roughy per year. The flesh is firm with a mild flavour; it is sold skinned and filleted, fresh or frozen.

1 Physical description
2 Life history
3 See also
4 References
5 Further Reading
6 External links

[edit] Physical description

Fishes in the Faroe Islands:
Orange roughy (Hoplostethus atlanticus)
Faroese stampi ssued: 7 Feb 1994
Artist: Astrid Andreasen

The body is very deep and the rounded head is riddled with muciferous canals (part of the lateral line system), as is typical of slimeheads. The single dorsal fin contains 4–6 spines and 15–19 soft rays; the anal fin contains 3 spines and 10–12 soft rays. The ventral scutes (modified scales forming a hard, bony median ridge between the pelvic fins and anus) number 19–25. The pectoral fins contain 17–20 soft rays each; the pelvic fins are thoracic and contain one spine and six soft rays; the caudal fin is forked. The interior of the mouth and gill cavity is a bluish black; the mouth itself is large and strongly oblique. The scales are ctenoid and adherent. The lateral line is uninterrupted with 28–32 scales whose spinules or ctenii largely obscure the lateral line's pores. The eyes are large.

The orange roughy is the largest known species of slimehead at a maximum standard length (a measurement excluding the tail fin) of 75 centimetres and a maximum weight of 7 kilograms. However, the average commercial catch size is ca. 30–40 centimetres SL.

[edit] Life history

Orange roughy are generally sluggish and demersal; they form aggregations with a population density of up to 2.5 per square metre. These 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 or feeding; it is thought that the fish cycle through metabolic phases (active or feeding and inactive or resting) and seek areas with ideal hydrologic conditions to congregate during their active and inactive phases. Observations made of orange roughy aggregations during submersible dives have also shown that the fish lose almost all pigmentation whilst inactive, during which time they are very approachable. Predators of orange roughies include large deep-roving sharks, cutthroat eels, merluccid hakes, and snake mackerels.

When active, they feed primarily on zooplankton such as mysid shrimp, euphausiids, amphipods and other crustaceans; adults also take smaller fish and squid. The orange roughy's metabolic phases are thought to be related to seasonal variations in the fishes' prey concentrations, with the inactive phase being a means to conserve energy during lean periods.

Orange roughy are oceanodromous, non-guarding pelagic spawners: that is, they migrate several hundred kilometres between localised spawning and feeding areas each year and form large spawning aggregations (possibly segregated according to gender) wherein the fish release large, spherical eggs (2.25 millimetres in diameter, made buoyant by an orange-red oil globule) and sperm en masse directly into the water. The fertilized eggs (and later larvae) are planktonic, rising to ca. 200 metres to develop, with the young fish eventually descending to deeper waters as they mature. The time between fertilization and hatching is thought to be ca. 10–20 days; fecundity is low, with each female producing only ca. 30–50,000 eggs. Orange roughy are very slow-growing, reaching maturity at ca. 20–30 years of age.

The maximum published age of 149 years was determined via radiometric dating of trace isotopes found in an orange roughy's otolith ("ear bone"). Similarly, counting the growth rings of orange roughy otoliths has given a maximum age of 125–156 years. The validity of these results are questioned by some researchers, as the former method is itself controversial and the latter method is known to be unreliable in older specimens. Analysis of otolith micro-increments (believed to be formed on a daily basis) has given a maximum age of 18–25 years, whereas analysis of otolith calcium and fluorine composition has given a maximum age of 7–8 years. The issue has yet to be resolved definitively, but carries important implications relating to the orange roughy's conservation status.