Smooth Toadfish

With a total adult length of anywhere from 3 to 16 cm (1+1⁄8–6+1⁄4 in), 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. The round eyes are adnate (unable to rotate), their upper border level with the profile of the back and their lower border well above the mouth. In a slightly depressed area just in front of the eyes are two small nipple-shaped structures (papillae) that are the nasal organs.

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. It is one of the most abundant fishes in the muddy areas of Port Philip Bay. It generally lives in shallow water less than 3 m (10 ft) deep, often over mudflats in estuaries. In areas of seagrass beds, smooth toadfish are more commonly found in sand areas bordering on the seagrass patches. They are more commonly found in seagrass patches in water less than 1.5 m (5 ft) deep rather than deeper water of 3.5–6 m (11–20 ft). A South Australian field study on wrack and associated fauna found that the smooth toadfish was associated with larger volumes and aggregations containing green algae.

The smooth toadfish has strong jaws that readily crush shellfish and crustaceans. It feeds predominantly on benthic (bottom-dwelling) organisms in the substrate of the bodies of water in which it forages. Its diet includes molluscs such as black mussels, pipis, white sunset shells (Soletellina alba) and oysters (Crassostrea), crustaceans such as semaphore crabs and shrimp, and brown algae. The proportions of crustaceans to molluscs can vary widely depending on the abundance of food items; hence in a 1999 field study, the soldier crab (Mictyris longicarpus) predominated in Cowan Creek while the black mussel did so in nearby Berowra Creek. Field experiments showed it was a consumer of oysters and the gastropod Bembicium auratum, and had a major impact on their numbers.

The breeding habits of estuary-dwelling pufferfish have been little researched in general. Fieldwork in the Hawkesbury River and tributaries north of Sydney found that the smooth toadfish breeds between April and July, building up fat stores in its liver from February to April beforehand.

Its large range, abundance and stable population mean the smooth toadfish is classified as least concern on the IUCN Red List. Although no decline in numbers has been recorded, the effects of disappearance of its habitat—mangroves and seagrass beds—is unknown.