Bothragonus swanii

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Bothragonus swanii
Bothragonus swanii Oregon Coast Aquarium.jpg
A rockhead on top of a rock scallop at the Oregon Coast Aquarium.
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Perciformes
Suborder: Cottoidei
Family: Agonidae
Genus: Bothragonus
Species:
B. swanii
Binomial name
Bothragonus swanii
(Steindachner, 1876)
Synonyms [1]
  • Hypsagonus swaniiSteindachner, 1876
  • Bothragonus swani(Steindachner, 1876)

Bothragonus swanii, the rockhead, deep-pitted poacher or deep-pitted sea-poacher, [2] is a species of 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

  1. ↑ Synonyms of Bothragonus swanii at www.fishbase.org.
  2. ↑ Common names for Bothragonus swanii at www.fishbase.org.
  3. 1 2 3 Bothragonus swanii at www.fishbase.org.
  4. ↑ 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.
  5. 1 2 3 4 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.
  6. 1 2 3 Buehler, Jake (January 16, 2026). "This fish may play a hole in its head like a drum". Science News. Retrieved January 19, 2026.
  7. ↑ 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.
  8. ↑ Spawning for Bothyragonus swanii at www.fishbase.org.
  9. ↑ Food items reported for Bothragonus swanii at www.fishbase.org.


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