© Baker, J.L. (2009) Marine Species of Conservation Concern in South Australia Full citation Baker, J.L. (2009) Marine Species of Conservation Concern in South Australia: Volume 1 - Bony and Cartilaginous Fishes. Report for the South Australian Working Group for Marine Species of Conservation Concern. J. Baker (consultant); Science and Conservation Division, and Coast and Marine Conservation branches of S.A. Department for Environment and Heritage (DEH); Marine and Coastal Community Network of S.A. (MCCN), and Threatened Species Network (TSN). Web version published by Reef Watch, South Australia.

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TRIPTERYGIIDAE: TRIPLEFINS

© D. Muirhead, MLSSA

Globally, the Tripterygiidae family is currently considered to contain around 30 genera, and at least 156 species (Fricke, 1997; Cavalluzzi and Olney, undated; Froese and Pauly, 2008).
Members of the family are variously distributed in the Indian, Pacific and Atlantic oceans. Around 13 genera and occur in Australian waters, including 9 from the southern coast (CSIRO, 2007). The most speciose genus in Australian waters is the tropical Enneapterygius (Fricke, 1997; CSIRO, 2007). One species in the family (Forsterygion lapillum Hardy, 1989) is presumed to have been introduced to Australian waters via ships’ ballast water (CSIRO, 2007).
Tripterygiids (triple-fins or threefins) are small, reef-dwelling fishes. They are characterised by a dorsal fin that is separated into 3 parts (the first 2 of which are spinous), and ventral fins that are reduced to a single spine and two or three segmented rays (Nelson, 1994, cited in Froese and Pauly, 2008; Kuiter, in Gomon et al., 1994). Members of the Tripterygiidae family are strongly site-associated, and guard benthic eggs, characteristics that may make populations vulnerable to habitat impacts. Male threefins attract females to the nesting site (Nelson, 1994, cited in Froese and Pauly, 2008). Tripterygiids lay eggs in clumps on the sea bottom, usually on a sloping rock surface, and each nest, which is guarded by the male against predators, may contain eggs laid by several females. The male fans the eggs with his fins to aerate them and prevent silt accumulating (Francis, 1996, cited by Pogonoski et al., 2002). When the eggs hatch the larvae become planktonic before settling on the bottom again during spring or summer. Most triplefins are short-lived, reaching a maximum age of about three years (Francis, 1996, cited by Pogonoski et al., 2002).
A number of triplefin species are commonly known within S.A., but are not included in synopses below due to their apparent abundance and/or wide distribution; however the potentially vulnerable population characteristics of the whole group should be noted, such as the guarding of benthic eggs, and use of shallow coastal habitats that may be subjected to localised impacts. Examples of the more widely distributed and/or more commonly recorded species of triplefins in southern Australia include the following (from Hutchins and Swainston, 1986; Kuiter, in Gomon et al., 1994; Fricke, 1994; Kuiter, 1996a and 1996b; Edmunds and Hart, 2003; J. Baker, pers. obs. 1996-2008):
Southern Barred Triplefin / Threefin (or Weedy Threefin) Brachynectes fasciatus: Found in southern Australian states, including Tasmania. The species occurs in shallow rock pools, and beds of macroalgae and seagrass in shallow coastal bays.
Yellowback (or Black-throated) Triplefin / Threefin Helcogramma decurrens: Found in W.A. and S.A. (including Spencer Gulf, Gulf St Vincent and Kangaroo Island), in shallow coastal reef areas, where it lives on rock surfaces and under ledges. The Yellowback Threefin is considered to be a common species, but is not often seen due to its small size. Females can be cryptically coloured, closely matching surface cover on reefs, such as crustose coralline algae. The species is used in the aquarium fish trade.
Western Jumping Blenny Lepidoblennius marmoratus: A larger triplefin species, found in W.A through to central South Australia. The Jumping Blenny occurs in rock pools and other parts of the intertidal zone, and feeds partly on algae;
Clarke’s (or Common) Triplefin / Threefin Trinorfolkia clarkei: A common species in south-eastern and southern Australia; T. clarkei is found in shallow inshore waters (e.g. in rock pools; on rocky reefs; in estuaries; and on jetty pilings or under jetties);
Notched Triplefin / Threefin Trinorfolkia incisa: A small species, to 3 - 4cm, found in Victoria, South Australia and W.A.. The species occurs on rocky reefs, at depths of around 3m – 30m, and appears more frequently in offshore habitats, compared with other southern Australian triplefins.
Bighead (or Bullhead) Triplefin / Threefin Trianectes bucephalus: Found in Victoria, Tasmania and South Australia (e.g. Spencer Gulf, Gulf St Vincent, Kangaroo Island). The species is nocturnally-active, and is found in shallow coastal waters (to around 5m), usually under rocks.
Only one species, the Crested Triplefin, is discussed in a synopsis below, due to its apparent endemic status within South Australia.

Associated taxa

Crested Threefin / Crested Triplefin

Trinorfolkia cristata (Kuiter, 1986) = Norfolkia cristata