The Chimaera families

5/15/2016

In the Chimaeridae family, the spotted ratfish (Hydrolagus colliei). © Life of Sea

Before we delve into “ghost sharks” any further, we would like to make a distinction: chimaeras actually belong to three families (Callorhinchidae, Chimaeridae and Rhinochimaeridae), even though they are often lumped into one.

You have the Callorhinchidae family, made up of the ploughnose chimaeras, the Chimaeridae family, which consists of the shortnose chimaeras (featuring critters like the leopard chimaera, the purple chimaera, the brown chimaera, the mottled ghostshark, little black ghostshark, giant black ghostshark, brown ghostshark and the purple ghostshark) and the Rhinochimaeridae family, which consists of the longnose chimaeras (featuring critters like the longnose chimaera, smallfin spookshark and the longnose ghostshark).

In this brief blog post, we’ll discuss the differences and similarities between three families.

Rhinochimaeridae family. © www.fishesofaustralia.net.au

TFUI has discussed “ghost sharks” (also known as “rabbitfishes” and “ratfishes”) briefly before, not really focusing on a specific species but the chimaeras as a whole. This was before Melissa even knew there were three families of chimaeras (see, you can learn something new every day). The chimaeras (Chimaeridae family) are a cosmopolitan species, found in temperate and tropical seas around the world. They occur in every ocean basin, but are absent anywhere 60° N or S. They can be found in benthic to benthopelagic zones, continental and insular slopes, nearshore waters and the deep sea (they’ve been recorded over 1,000 meters deep!). Like elephantfish, they like muddy seabeds, but some observations have seen these animals over rocky bottoms. Worldwide, there are 36 species in the two generas. In New Zealand, we have both generas and eight species recorded (thus far… after all, we are always discovering the ocean’s secrets). They aren’t commercially sought out, and tend to be caught as bycatch instead (something that Melissa is studying in her MSc research).

Unlike other elasmobranchs (i.e. sharks, skates and rays) the chimaeras have a fleshy operculum that covers their single gill slit. Like elephantfish, they also have a spine in front of their first dorsal fin for protection. They have big eyes and a small mouth, with a fleshy, pointy snout to add to the strangeness. Did I mention this is all on a rather large head? It’s a comical animal to picture in your head. It is okay to laugh (trust me, we did).

The Callorhinchidae, or plough-nose chimaeras, are similar to both families above, except are identified by their fleshy club-shaped noses. Their color is usually black, brown or a mixture of the two, and they too have an operculum. They prefer muddy and sandy ocean bottoms, and here is where they feast upon small shellfish.

Longnose chimaeras (Rhinochimaeridae family) are also found globally in temperate and tropical waters. However, unlike the chimaeras that can be found in nearshore waters, these fellas tend to stick to deeper waters on the continental slopes and abyssal plains (anywhere from 1,000 m to over 2,000 m). Like the Chimaeridae family, they also prefer muddy seabeds. Worldwide there are eight species in three generas. In New Zealand, we have two of the three generas, with three species recorded thus far. Also known as “spookfishes,” their long, fleshy snouts definitely give this fish an odd look. The reason for these long snouts is still being debated (though we have some ideas…). They also have a fleshy operculum that covers their single gill slit. They vary in color from silver-gray to dark brown to black. Their dorsal fins are interesting in that the first one (also with a spine) looks like a regular dorsal fin (think shark-like) while the second one is long and low.

Since they are deep-water animals, they are all poorly studied and… well, this is all we’ve got for them. As more is learned about either family, we will update this space! All their IUCN assessment is currently Data Deficient (DD).

did you know the difference between these families?

glossary

Abyssal plains: The deep-sea floor.
Benthic zone: The bottom of an ocean or lake.
Benthopelagic zone: The region about 100 meters off the bottom.
Bycatch: The part of a fishery’s catch that is made up of non-target species.
Commercial fishery: The activity of catching fish and other seafood for profit.
Continental shelf: Extends from a continent underwater, resulting in a shallow-water area.
Continental slope: Steep slope descending from continental shelf to the continental rise; typically about 20 km (12.4 miles) wide, consisting of mud and silt.
Cosmopolitan: Worldwide distribution.
Dorsal fin: Fin located on the back.
Generas: Plural form of genus.
Genus: A group of organisms ranking above a species and below a family.
Insular slope: The shelf around an island.
IUCN: International Union for Conservation of Nature.
Ocean basin: Anywhere on Earth covered by seawater.
Operculum: Gill cover.
Temperate waters: The water between tropical seas and the Polar Regions (10-21° C, 50-69.8° F).
Trawl fisheries: Fisheries that pull a fishing net through the water behind one or more boats.
Tropical waters: Waters that are between the Tropic of Cancer (23.5° N) and the Tropic of Capricorn (23.5° S).