Setarches guentheri

Lore & Background

The channelled rockfish was first formally described in 1862 by English zoologist James Yate Johnson, with the type locality given as Madeira. Johnson placed the new species in the new monotypic genus Setarches. Subsequent workers added other species to this genus, but in 1966 William N. Eschmeyer and Bruce B. Collette synonymised most of these with S. guentheri, making Setarches consist only of this species and S. longimanus. This was later re-examined, and three species were accepted as belonging to the genus: S. armata, S. guentheri, and S. longimanus. A review in 2021 by Wada, Kai & Motomura resurrected the genus Lythrichthys, placing S. cypho, S. longimanus, and two newly described species in that resurrected genus, while S. armata is now considered a synonym of the flathead Thysanophrys armata. This left the channelled rockfish as the only species in the now monotypic Setarches. As of January 2022 this change has been accepted by Catalog of Fishes. The genus name Setarches was not explained by Johnson; it may be derived from saeta meaning 'bristle', while the specific name honours Johnson's friend, the German-born British ichthyologist and herpetologist Albert Günther.

The channelled rockfish has a body depth equivalent to 28-37% of its standard length, with larger fish having less deep bodies. It has 11-13 spines and 9-11 soft rays in the dorsal fin, and the anal fin has 3 spines and 4-6 soft rays. The lateral line is almost continuous and is a trough covered by thin membranous scales, which are deciduous. The second spine on the preoperculum is longer and better developed than the first and third spines. Living specimens are pinkish red to orange with reddish black spots on the head and body; smaller individuals are more reddish grey with black spots, and the smallest fishes (about 40 mm) have dark colouration concentrated in a patch above the pectoral fin and below the soft-rayed part of the dorsal fin, with a smaller amount of dark colour on the caudal peduncle. This species grows to a maximum total length of 31.4 cm.

The channelled rockfish has a circumglobal range on continental shelves in tropical and warm temperate oceans. In the eastern Atlantic it is found from Madeira south to South Africa; in the western Atlantic from off southern Rhode Island south to northern Brazil, including the Gulf of Mexico; along the Pacific coasts of the Americas from southern British Columbia to Chile; and across the Pacific and Indian Ocean to the east coast of Africa. Despite this wide range, there is very little genetic difference between widely separated populations. It is a benthopelagic species with a depth range of 150 to 780 m over soft bottoms and water temperatures between 5.5 to 12.5 °C.

Reader's Guide

The channelled rockfish is significant as the most widely distributed scorpaenid, with a circumglobal range spanning tropical and warm temperate oceans. Its taxonomy has been subject to considerable revision: originally described in 1862 by James Yate Johnson in the monotypic genus Setarches, subsequent workers added species, but a 1966 synonymization by Eschmeyer and Collette reduced the genus to two species. Later re-examination accepted three species, and a 2021 review by Wada, Kai & Motomura resurrected the genus Lythrichthys, moving several species out of Setarches and leaving S. guentheri as the sole species in the now monotypic Setarches. This taxonomic history highlights the ongoing refinement of scorpionfish classification. The species is benthopelagic, living close to the bottom but feeding in the water column predominantly on pelagic invertebrates; in the Gulf of Mexico its diet is dominated by benthic crustaceans such as shrimp and prawns in the genus Oplophorus and a variety of amphipods. The spines in its fins bear venom glands and can envenomate humans if handled. Although sometimes caught in fisheries in the Gulf of Mexico, it has only slight commercial value in Mexico. Its wide distribution with little genetic differentiation between populations suggests a remarkable capacity for dispersal across ocean basins.