Spotted ratfish, Hydrolagus colliei, are cartilaginous fishes (meaning their skeletons are composed of cartilage) related to sharks, rays, and skates. Males have a club-like structure on the snout called a tenaculum, which they use to hold the female’s pectoral fin during mating. Staying connected is important since mating may last anywhere from half an hour to two full hours.
Females produce 20 to 29 tough egg cases over the course of a year, each containing a single embryo. These long cylindrical egg cases may take several hours to emerge, and will then stay connected to the female’s body by long filaments for 3–6 days. Occasionally these cases can be seen attached to female ratfish in the Aquarium’s Underwater Dome exhibit. After being deposited on the substrate, the embryo in each egg case develops for the next 5–10 months or so.
Both sexes have a venomous spine at the front of their dorsal fin. Incautious handling can lead to a scratch from this spine, producing a dull ache on human skin that can last from 30 minutes to several days.
Estimates put the ratfish population in Puget Sound to about 200 million. Ready to learn more? Come see the ratfish at the Seattle Aquarium!