The prowfish is a solitary ocean dweller that hides inside the bells of jellyfish

Nature · Published 3 October 2026 Swipe more like this →

In short: In the cold depths of the northern Pacific, the prowfish leads a life defined by its unique anatomy and strange habits. Lacking a swim bladder, this benthic predator spends its days near rocky bottoms, yet its young seek protection by living inside the pulsating bells of drifting jellyfish.

The prowfish (Zaprora silenus) is the sole living member of the family Zaproridae. Its name derives from the Greek word for prow, a nod to its distinctive, convex head and projecting snout. Growing up to 88 cm in length, these fish possess elongated, laterally compressed bodies with enlarged pectoral fins but notably lack pelvic fins. Their appearance is further marked by sensory pores highlighted by blue or white fringes and a coloration that shifts from bluish-grey to olive brown.

While adults are benthic, preferring rocky substrates at depths reaching 675 meters, the life cycle of the prowfish is marked by a dramatic shift in habitat. Juveniles are pelagic, residing in the middle water column where they remain closely associated with their primary food source: jellyfish. They are so dependent on these gelatinous hosts that they often seek shelter within them, a behavior that has historically caused them to be confused with the medusafish. This reliance on jellyfish continues into adulthood, as the fish use their sharp, closely set teeth to tear chunks from the bells of scyphozoans and salps.

Despite their presence in the northern Pacific—ranging from the Aleutian Islands to Japan and California—much about the prowfish remains a mystery. Scientists believe females reach maturity around age five, but reproduction remains poorly understood. While they are a staple for subsistence fisheries in remote regions, they also face pressure from larger predators like Pacific halibut and skates. The family history is equally sparse; beyond the extant Zaprora silenus, the fossil record reveals only two extinct species, including the Middle Miocene Zaprora koreana and the Southern California-based Araeosteus rothi.

It is important to distinguish the northern Pacific prowfish from the warty prowfish (Aetapcus maculatus), an unrelated species endemic to the coastal waters of southern Australia. While both share a name, the warty prowfish is significantly smaller, reaching only 21 cm in length, and belongs to a different genus entirely. Understanding these distinctions highlights the diversity of marine life that often goes unnoticed beneath the surface of the world's oceans.

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