Roundbelly cowfish (Lactoria diaphana)

Classification (WoRMS)

Full classification as recorded by WoRMS: Kingdom: Animalia · Phylum: Chordata · Class: Teleostei · Order: Tetraodontiformes · Family: Ostraciidae · Genus: Lactoria.

Accepted name: Lactoria diaphana · Authority: (Bloch & Schneider, 1801) · Taxonomic status: accepted · AphiaID: 219903.

Synonyms and superseded combinations recorded for this taxon: Lactoria diaphanus (Bloch & Schneider, 1801); Lactoria diaphinus (Bloch & Schneider, 1801); Lactoria schlemmeri Jordan & Snyder, 1904; Ostracion brevicornis Temminck & Schlegel, 1850; Ostracion diaphanum Bloch & Schneider, 1801; Ostracion diaphanus Bloch & Schneider, 1801.

Source: World Register of Marine Species (WoRMS) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=219903 (CC BY 4.0). Accessed 2026-09-23.

Biology and life history (FishBase)

Measured values published by FishBase for Lactoria diaphana. Only fields the database actually holds for this species are shown; these are database values, not aquarium guidance.

Maximum length: 34 cm · Depth range: 8–50 m · Habitat zone: reef-associated · Body shape: short and / or deep · Vulnerability index: 24 of 100 · Fishery importance: of no interest · Aquarium trade: commercial.

FishBase notes: Inhabit coral and rocky reefs of coastal areas (Ref. 9806, 48637). Also common on offshore sand and mudflats (Ref. 48637). Young fish occur in oceanic waters, at or near the surface (Ref. 2850); semi-transparent young may enter estuaries (Ref. 3141). Benthopelagic (Ref. 58302). Feed on benthic invertebrates (Ref. 9806). A large number of juveniles were found in the stomachs of flatheads (Ref. 48637).

Source: FishBase species summary (SpecCode 6554) — https://www.fishbase.se/summary/Lactoria-diaphana.html (CC BY-NC 3.0 — non-commercial use only). Accessed 2026-09-23.

Distribution and occurrence records (GBIF)

1,363 georeferenced occurrence records for Lactoria diaphana are published through GBIF from 27 countries or marine areas. The map above plots 234 distinct locations from a sample of 1,363 records, omitting 56 inland records that carry an institution's coordinates rather than a collection site; it shows where the species has been observed and reported, not a modelled range.

Most records by country or area: Australia (904); United States of America (125); Japan (81); South Africa (63); Mexico (43).

The full country table, WoRMS marine regions and the sampling notes are on this species' Distribution page.

Source: GBIF Occurrence Search (taxonKey 2408118) — https://www.gbif.org/occurrence/search?taxon_key=2408118&has_coordinate=true (records CC0 / CC BY); WoRMS distribution records (MarineRegions) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=219903 (CC BY 4.0); Natural Earth 110m basemap — https://www.naturalearthdata.com/ (public domain). Accessed 2026-09-23.

Conservation status (IUCN Red List)

The IUCN Red List assesses Lactoria diaphana (Bloch & Schneider, 1801) as Least Concern (code LC). No trend, population estimate or threat analysis is given here, because none is available from this source without the Red List API; follow the source link for the full assessment, including its date.

Source: IUCN Red List of Threatened Species (taxon 193692) — https://www.iucnredlist.org/species/193692/0; GBIF IUCN Red List category endpoint (taxonKey 2408118) — https://api.gbif.org/v1/species/2408118/iucnRedListCategory. Accessed 2026-09-23.

Description and natural history (Wikipedia)

Lactoria diaphana was first formally described as Ostracion diaphanum in 1801 by Marcus Elieser Bloch and Johann Gottlob Theaenus Schneider with no type locality given, although it is likely to be the East Indies. The 5th edition of Fishes of the World classifies the genus Lactoria within the family Ostraciidae in the suborder Ostracioidea within the order Tetraodontiformes.

Lactoria diaphana is classified within the genus Lactoria, an name that means a "milkcow", a reference to the large spines above the eyes resembling the horns of a cow. The fishes in this genus are known as cowfishes, as are some related species. The specific name diaphana, means "transparent", as it appears that the holotype was a transparent juvenile.

Lactoria diaphana has a thick, rectangular body that is largely enclosed in a carapace which is made up of thickened, hexagonal plate -like scales which are jointed to each other. There are five horizontal ridges on the carapace, a poorly developed one along the back and a pair, upper and lower, on each flank. There is a large spine above each eye and a spine at the rear end of each of the lower flank ridges and there is a spine halfway along the ridge along the back. They have small mouths located at the front of the snout, with fleshy lips and a row of no more than 15 moderately sized conical teeth in each jaw. The gill slits are short and oblique and are to the front of the bases of the pectoral fins. The dorsa and anal fins are at the back of the carapace and the caudal peduncle is thin and flexible. The caudal fin is fan shaped. The dorsal fin has 9 soft rays, as does the anal fin. The dorsal profile of the snout is steep and concave while the vetral profile of the body is rounded. The overall colour i and concave while the ventrals pale greensih-grey patterned with a honeycomb reticulation and brown blotches. The roundbelly cowfish has a maximum total length of 34 cm.

Lactoria diaphana has a wide distribution in the Indo-Pacific where it extends from the eastern coast of Africa in the western Indian Ocean where it's found off Mozambique and South Africa through the Indian and Pacific Oceans as far as the eastern Pacific between Santa Barbara, California and Chile. It extends as far north as Japan and south to Tasmania. This species is the only member of the genus Lactoria with a range that extends into the southeastern Atlantic as it is found around the Cape of Good Hope and along the southwestern coast of Africa as far north as Swakopmund, Namibia. The roundbelly cowfish is found on coastal and outer reefs, at depths down to 50 m.

The thornback cowfish, like other boxfishes, has the ability to release a soap-like toxin called pahutoxin through their skin when stressed. This poison can incapacitate, or even kill, potential predators. There has also been a case in Japan of the death of someone ingesting the flesh of this species through palytoxin poisoning.

Source: Wikipedia: Lactoria diaphana — https://en.wikipedia.org/wiki/Lactoria_diaphana (CC BY-SA 4.0). Accessed 2026-09-23.