Bothragonus swanii
| Bothragonus swanii | |
|---|---|
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| A rockhead on top of a rock scallop at the Oregon Coast Aquarium. | |
Scientific classification 
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Perciformes |
| Suborder: | Cottoidei |
| Family: | Agonidae |
| Genus: | Bothragonus |
| Species: | B. swanii
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| Binomial name | |
| Bothragonus swanii (Steindachner, 1876)
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| Synonyms[1] | |
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Bothragonus swanii, the rockhead, deep-pitted poacher or deep-pitted sea-poacher,[2] is a fish in the family Agonidae.[3] It was described by Franz Steindachner in 1876, originally in the genus Hypsagonus.[4] It is found in the eastern Pacific Ocean from Alaska to Carmel Bay, California down to depths of 18 metres. It can also inhabit the intertidal zone. Males can reach a maximum total length of 8.9 centimetres.[3]
Cranial pit and hypothesized sound production
Bothragonus swanii has a prominent bowl-shaped cranial pit on the top of its skull, roughly the size of its brain.[5][6]
Using high-resolution micro-CT scanning, LSU researcher Daniel Geldof created 3D models of preserved specimens, revealing dense, flattened, mobile anterior ribs connected to powerful muscles beneath the pit.[7][5]
Geldof hypothesizes that these ribs strike the pit's underside to produce low-frequency vibrations (~20 Hz) via stridulation, potentially for communication in the species' noisy intertidal habitat (e.g., courtship or territorial signals), similar to substrate-transmitted sounds in some sculpins.[6][5] Biomechanist Adam Summers called the findings "stunning."[5]
The hypothesis is unconfirmed, with no direct observations or sound recordings from live fish. Functional morphologist Eric Parmentier has questioned whether bone-on-bone contact could produce the proposed low frequencies.[6]
The species epithet "swanii" refers to James G. Swan of Port Townsend, Washington.[3] The rockhead spawns nearshore, during the months of January–May in the California Current region.[8] Its diet consists of benthic shrimp and crabs.[9]
References
- ^ Synonyms of Bothragonus swanii at www.fishbase.org.
- ^ Common names for Bothragonus swanii at www.fishbase.org.
- ^ a b c Bothragonus swanii at www.fishbase.org.
- ^ Steindachner, F. 1876 [ref. 4225] Ichthyologische Beiträge (V). [Subtitles i-v.]. Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften. Mathematisch-Naturwissenschaftliche Classe v. 74 (1. Abth.): 49-240, Pls. 1-15.
- ^ a b c d Jacobs, Phie (December 22, 2025). "This fish seems to use its bizarre skull like a drum". Science. doi:10.1126/science.zulg7a0. Retrieved January 19, 2026.
- ^ a b c Buehler, Jake (January 16, 2026). "This fish may play a hole in its head like a drum". Science News. Retrieved January 19, 2026.
- ^ Geldof, Daniel L. (2025). The hole truth: Morphology of the cranial pit in the rockhead poacher, Bothragonus swanii (Agonidae) (Master's thesis). Louisiana State University. Retrieved January 19, 2026.
- ^ Spawning for Bothyragonus swanii at www.fishbase.org.
- ^ Food items reported for Bothragonus swanii at www.fishbase.org.