Smooth toadfish

Smooth toadfish
Conservation status
Least Concern  (IUCN 3.1)[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Tetraodontiformes
Family:	Tetraodontidae
Genus:	Tetractenos
Species:	T. glaber
Binomial name
Tetractenos glaber (Fréminville, 1813)
Synonyms
Tetrodon glaber Fréminville, 1813 Gastrophysus glaber Bleeker, 1855 Tetrodon hamiltonii Günther, 1870 Sphaeroides hamiltoni Waite, 1906 Sphaeroides liosomus Waite, 1928 Sphaeroides glaber Whitley, 1953 Aphanacanthus hamiltoni Le Danois, 1959 Amblyrhynchotes glaber Halstead, 1867 Torquigener glaber Robertson, 1980

The smooth toadfish or smooth toado (Tetractenos glaber, formerly classified as Tetrodon glaber or Torquigener glaber^[2]) is a species of fish in the family Tetraodontidae native to coastal and estuarine waters of southern Australia. Up to 16 cm long, it feeds on crustaceans and molluscs in bottom sediment. It is highly poisonous, and eating it results in neurological symptoms that can be fatal. The active agent is tetrodotoxin.

Taxonomy

French naturalist Christophe-Paulin de La Poix de Fréminville described the smooth toadfish in 1813 as Tetrodon glaber, from a specimen collected in Adventure Bay in southeastern Tasmania by Claude Riche. This holotype was then catalogued in the collection of Alexandre Brongniart but was subsequently lost; upon his death, Brongniart's collection was bequeathed to the Paris Museum and the specimen did not appear there nor at any other institution.^[3] The species name glaber is the Latin adjective glăber "bald".^[4]

The genus Tetrodon became a wastebasket taxon.^[3] The smooth toadfish was assigned to several other genera after it became clear that it fell outside a more restricted definition of Tetrodon.^[3]

British icthyologist Charles Tate Regan described Spheroides liosomus in 1909 as distinct from Tetrodon hamiltonii, noting that it had previously been part of the latter species. He noted its lack of spines compared with T. hamiltonii.^[5]

Recognising that the smooth and common toadfish were distinct enough from other species to warrant their own genus and that no valid genus name existed, Australian biologist Graham Hardy reassigned the two species to the new genus Tetractenos in 1983.^[3]

Common names include smooth toadfish, smooth toado,^[6] slimey toadfish or smooth blowie.^[7] Along with related toadfish species, the smooth toadfish is known in Australia as a "toadie."

The smooth toadfish was confused with the closely related common toadfish (Tetractenos hamiltoni) before 1983.^[6]

Description

Anywhere from 3 to 16 cm (1.2–6.2 in) long,^[7][3] the smooth toadfish has an elongate body with a rounded back and flattened belly. The body narrows posteriorly to the slender tail, and its fins are all elongate and rounded. The dorsal fin has 9 to 11 rays. The pectoral fin has 15 to 18 rays, the first of which is very short. It arises well below the level of the eye. The anal fin has 7-9 rays and caudal fin has 11. The smooth toadfish has a small mouth with thin lips at its apex and a tiny chin. It has tiny spines that are entirely within the skin layer, and the skin is smooth even when the fish is inflated. The smooth toadfish has a base colour of pale tan to yellow-green, marked with irregular brown spots and several broad dark brown bands. The round eyes are adnate, their upper border is level with the profile of the back and the lower border is well above the mouth.^[3] Fieldwork in Sydney waters found females to be larger and heavier than males.^[8]

The smooth toadfish can be distinguished from the common toadfish by its lack of spines and its bolder-patterned markings on its upperparts.^[3]

Distribution and habitat

The smooth toadfish is found along Australia's eastern and southeast coast, from Moreton Bay in southeastern Queensland to Port Lincoln in South Australia as well as Kangaroo Island and Tasmania.^[6] It is one of the most abundant fishes in the muddy areas of Port Philip Bay.^[9] It generally lives in shallow water less than 3 m (10 ft) deep,^[3] often over mudflats in estuaries.^[10]

The smooth toadfish can venture well into freshwater past brackish areas. In 1964 a school of toadfish were found in the Lang Lang River at the South Gippsland Highway—34 km (21 mi) from Western Port Bay and well beyond tidal areas.^[11]

Conservation

Its large range and abundance means the smooth toadfish is classified as Least Concern on the IUCN Red List. No decline in population has been recorded, though the effects of disappearance of its habitat—mangroves and seagrass beds—is unknown.^[1]

Breeding

Fieldwork in the Hawkesbury River and tributaries north of Sydney showed that it breeds between April and July, building up fat stores in its liver from February to April beforehand.^[10]

Feeding

view from above, showing pattern on back (dorsum)

The smooth toadfish has strong jaws that readily crush shellfish and crustaceans, feeding predominantly on benthic (bottom-dwelling) organisms in the substrate of the body of water they forage in.^[10] Its diet includes molluscs such as black mussels, pipis,^[8] and oysters (Crassostrea),^[10] crustaceans such as semaphore crabs and prawns, and brown algae.^[8] Occasional items recorded from stomach contents include green algae and jellyfish. It often follows the tide into estuaries in search of food.

Because it is a common estuarine fish, it has been used in studies of heavy metal contamination in coastal waters. Fish tested around Sydney showed uptake was highest in the gonads, then muscle, gills and liver. It is unclear why metal concentrations were lower in toadfish livers (compared with studies of contamination in other fish) but their liver cells may be more effective at removing these elements. Lead, cadmium and nickel levels corresponded with those in the sediment the fish were taken in, suggesting dietary intake. The gonads of male fish had twenty times as much arsenic than those of females, while the gills of female fish contained thirty times as much lead as those of males. Raised levels of arsenic, cobalt, cadmium and lead in gills suggested the fish were absorbed these from the surrounding water.^[12] Fieldwork in Sydney waterways showed raised arsenic, lead, cadmium and cobalt corresponded with decreased lipid levels in liver and gonadal tissue, and raised cobalt and nickel correspond to increased protein levels in muscle, liver and gonadal tissue. Raised lead levels corresponded with smaller egg size.^[8]

Toxicity

As with other fish of this family, the flesh of the smooth toadfish is poisonous. This is due to tetrodotoxin, which is concentrated particularly in the liver, ovaries, intestines and skin. The symptoms are predominantly neurological, and include numbness and/or paraesthesia (tingling) around the mouth and lips, and limb extremities and ataxia. Eating the fish can have fatal consequences.^[13] Even leaving the fish where pets can eat it can be hazardous.^[7]

Uses

Notorious for stealing bait, the smooth toadfish is an unwanted catch for fishermen as its toxicity renders it unfit for consumption.^[7]

References

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