Three new endemic species of Weedfish from Temperate Australia

Living among the seaweed of our temperate rocky reefs are fishes of the family Clinidae, aptly called Weedfish. These perfectly camouflaged and rarely seen fishes have kept taxonomists guessing, and after decades of building up our knowledge, we now have the information needed to describe three species as new to science, and unique to temperate Australian waters.

If you’ve ever been swimming, snorkeling or diving in the beautiful temperate rocky reefs around Sydney or the sheltered shorelines of southern Australia, watching the seaweed ebb and flow with the waves, then you would have unknowingly encountered Weedfish. Weedfish represent one of the most speciose groups of fishes distributed across southern Australia. They are cryptobenthic fishes, meaning they are generally small, hidden and camouflaged. So cryptic are two of our new species that they have never been photographed alive underwater. Being cryptic means that it has taken us a long time to gather enough data, morphological and genetic, to describe these three species as new to science in our paper published in Zootaxa.

These three new species, Coleman's Weedfish, Heteroclinus colemani, Longtail Weedfish Heteroclinus longicauda, and Whitley’s Weedfish, Heteroclinus whitleyi, are part of the Heteroclinus heptaeolus complex of species, which are distinct in having three segmented dorsal rays with the last two closely spaced and widely separate from the first ray. The species are primarily separated on the basis of live colouration and pectoral ray, dorsal spine, anal ray and gill raker counts; typical morphological characters used in ichthyology.

Coleman's Weedfish, Heteroclinus colemani, is distinctive from other species in usually having a reddish body coloration; 3 bars radiating from the eye, pectoral rays 13; second dorsal fin with 24–25 spines and anal fin II,18-19. Another distinguishing feature is the 6–8 clear windows between the spines. Reaching a maximum standard length of 83 mm, it is a deep bodied species often associated with red algae around rocky reefs from depths of 5–15 m. Known from Sydney, New South Wales to Kangaroo Island, South Australia, including Victoria and scattered localities in Tasmania. This fish is named for Neville Coleman, an Australian naturalist, underwater nature photographer, writer, and educator who sadly passed in 2012.

Longtail Weedfish, Heteroclinus longicauda, is readily distinguished from all other Australian Heteroclinus Weedfish by the absence of an orbital tentacle, and the elongate caudal peduncle. Overall head and body colour is greenish to light brown, with variable dark brown markings on the body, often faint ventrally. Another feature that distinguishes this species from other Weedfish is the dorsal fin origin further back on the head and body with stripes or horizontally elongate oval spots in life. Reaching a standard length of 141 mm and associated with sand, rock and algae to a depth of 8 m; often reported from tall kelp forests and dense Zostera beds. Known from Sydney, New South Wales to Queenscliff, Victoria and from northern Tasmania.

Whitley’s Weedfish, Heteroclinus whitleyi, looks very similar to the more common H. heptaeolus, but differs in having fewer spines in the second dorsal fin III, XXIII–XXV (rarely XXV), 2–3 (usually 3); and fewer anal rays II, 15–18 (usually 17). Overall colouration of the head and body is green, purple, or reddish brown. This species is known from Minnie Water, New South Wales to Wilsons Promontory, Victoria and Gulf of St. Vincent to Spencer Gulf, South Australia, and Fisherman Island to Recherche Archipelago, Western Australia, but apparently absent from western Victoria. Reaching a standard length of 80mm it is associated with small brown algae to depths up to 10 m. Additional features that separate H. whitleyi from H. heptaeolus include a body with stripes or horizontally elongated spots; round dark spots on the back that are broader than the interspaces between spots; and second dorsal and anal fins with distinct clear windows between spines, sometimes with the window containing one spine. This fish is named for Gilbert P. Whitley, formerly Curator of Fishes at the Australian Museum.

A challenge for the underwater photographers and citizen scientists out there: we would love to see images of Coleman’s and Longtail Weedfish in their underwater habitats. Please upload any Weedfish images to our Australasian Fishes project https://www.inaturalist.org/projects/australasian-fishes.

Environmental DNA tools have proven useful as well, with a monthly seawater sampling campaign at Camp Cove and Parsley Bay in southern Sydney Harbour detecting the presence of six species of Weedfish, including four species of Heteroclinus, though none of these were the new species described here.

These new species highlight that there is still considerable undescribed fish biodiversity in Australian waters. With one fish species described as new to Australian waters every week, this means that there are new fish species waiting to be discovered on the doorsteps of our major cities, beautiful temperate rocky reefs, tropical seas, deep oceans and museum collections.

• Hoese D.F., Hay, A.C. and DiBattista, J.D., 2024. A review of the Heteroclinus heptaeolus complex (Pisces: Blennioidei: Clinidae), with three new species and discussion of misuse of proportions in taxonomic studies. Zootaxa. TBC

• https://australian.museum/learn/collections/natural-science/ichthyology/
• https://australian.museum/blog/amri-news/bridging-the-dna-barcode-gap/