A watercolor painting of a spotted ratfish. The ratfish's body is a brownish color, with white spots covering the body. It has a gold-brown line (lateral line) running down the side of its body, and several lines crisscrossing the face. The nose is sloped, almost like a ski jump shape. Its fins are a blueish grey in color, the pectoral (where an arm would be) fin noticeably large, with little gold reflective lines running down the fin. The fish's eye is brown, with orange and blue.

Species Spotlight: Spotted Ratfish

ByLivInSeas

The spotted ratfish (Hydrolagus colliei) is an adorable chimaera. It features charismatic white spots and a cute, almost cartoon-like rostrum. Chimaeras (Order: Chimaeriformes) are cartilaginous fish related to sharks, skates, and rays. Similar to these groups, their phylogeny is ancient, dating back hundreds of millions of years.

The species has been rated by the IUCN as Least Concern. They are abundant throughout their range, which stretches from the central Gulf of Alaska to Costa Rica. They are most commonly found living near the seafloor in both shallow and deep waters (maximum depth: 1463 meters/4800 feet).

A watercolor painting of a spotted ratfish. The ratfish's body is a brownish color, with white spots covering the body. It has a gold-brown line (lateral line) running down the side of its body, and several lines crisscrossing the face. The nose is sloped, almost like a ski jump shape. Its fins are a blueish grey in color, the pectoral (where an arm would be) fin noticeably large, with little gold reflective lines running down the fin. The fish's eye is brown, with orange and blue. Pin It

Water color painting of a Spotted Ratfish (H. colliei) by me. ©LivInSeas, 2025

Morphology – Size:

Males are smaller than females, maturing between 30 and 35 centimeters (11.8 – 13.8 inches). Females mature between 40 and 45 centimeters (15.8 – 17.7 inches).

Individuals in northern regions of the range are larger than those in the south. Differences in size distributions are likely due to lower temperatures and higher food availability in the north. However, several other factors could contribute to a latitudinal size gradient. These include discrete, regional breeding populations and differences in fishing intensity across the range, although the latter is an untested hypothesis.

Reproduction:

Spotted ratfish are oviparous. Oviparity refers to the laying of undeveloped eggs instead of live young.

Chimaeras lay one or two eggs at a time, and gestation is estimated to last nine to twelve months. Egg deposition occurs year-round, but it reaches a peak in late summer/early fall in California and summer in Washington state.

Venom:

Spotted ratfish have a mildly venomous dorsal spine, located ahead of their dorsal fin. In fish, venom apparatuses are generally comprised of venom glands on either side of a sharp spine covered with a layer of skin.

While they are mildly venomous, the sharp spine itself may pose a greater danger to potential predators than the venom itself. The spine could puncture the esophagus or digestive tract of a predator. However, early twentieth-century fishermen reported being more concerned about the ratfish’s jaws than their spines and venom, fearing the chimaera’s strong bite.

An infographic describing chimaera anatomy. The chimaera points to the right on the screen, its tail drooping slightly. It has brown skin, with white spots across the body. Its pectoral fin is large compared to its other fins. It has large, glossy black eyes, and a ski-jump snout. Its face is slightly more silver in color. Arrows point to the different morphological features, like the first dorsal fin, the fin spine (located ahead of the first dorsal fin), lateral line organ (a textured line running down the side of the chimaera), snout, mouth, operculum (the cheek), gill opening, pectoral fin, pelvic fin (on the bottom of the fish, towards the rear of the body), second dorsal fin, and the caudal fin (tail fin--very tiny on the chimaera) Pin It

The anatomy of a chimaera. Image sourced from Save Our Seas Foundation (Saldaña-Ruiz, 2019).

Electroreception:

Chimaeras, like sharks, skates, and rays, possess specialized pores on their rostrum, or their snout. These pores are used to detect electricity released by potential prey.

Electric charges are generated by muscular movement in living organisms. These charges interact with seawater and create a weak voltage. The chimaeras then use their specialized pores to detect this emitted voltage.

Aquatic Flight Movement Pattern:

Aquatic flight is the primary locomotive mode for spotted ratfish, as well as several other groups like penguins and turtles. While their shark relatives generate thrust with their caudal fin, spotted ratfish flap their pectoral fins to generate thrust. These chimaeras have well-developed pectoral muscles, indicating that they use their pectoral fins to “fly” through the water.

Certain morphological and kinematic characteristics show that spotted ratfish prioritize high maneuverability and the generation of lift. Interestingly, spotted ratfish move their pectoral fins in an ovular shape, rather than the figure-8 shape common to other organisms who move via aquatic flight. The downstroke of their movements is faster than the upstroke, which generates additional lift.

The distal, or far end, of the pectoral muscle is also well-developed. This indicates that spotted ratfish have fine control over the movement of the fin. As such, spotted ratfish are able to navigate a complex, seafloor environment.

Population Dynamics:

Spotted ratfish are ecologically important due to their high abundance and role in the ecosystem as both predator and prey. They are not fished for directly. However, they are caught as bycatch, and survival rates of discarded individuals are low.

Currently, their vulnerability to fishing activity is not fully understood. Methods for determining age in chimaeroids are limited and unreliable. An understanding of fish age and growth patterns is necessary for the development of informed conservation and management strategies. As a result, the effectiveness of certain age-based methods of population analysis is limited. 

In addition, fisheries-dependent data on spotted ratfish is lacking. Fisheries-dependent data refers to data collected from commercial fishing efforts. Non-target species caught as bycatch, like the spotted ratfish, are generally not recorded within commercial fisheries landing data.

Fisheries-independent data refers to data collected from scientific research surveys. These surveys are not associated with commercial fishing efforts, even if they use similar methods to commercial fishing. Following a review of fishery-independent surveys, researchers determined that spotted ratfish populations have significantly increased over time (data published in 2012). While oceanographic factors may play a role, the observed population growth may also be a result of successful fisheries management policies.

The trend could be attributed to reductions in groundfish quotas in commercial fisheries beginning in the 1990’s. These closures were intended to protect vulnerable rockfish populations, but many rockfish species have not yet recovered to the same extent as spotted ratfish.

Regardless of the exact cause, the observed population growth shows that marine populations are able to recover even after periods of increased mortality. This effect is especially impressive when observed within species with low fecundity/reproductive rates, like spotted ratfish.

Scientists have also observed aggregations of juveniles and egg cases at shelf breaks, before steeper slopes into deep waters. The tendency to aggregate by age class may also leave the species vulnerable to fishing activity, in addition to their low fecundity rates.

Pin this post to read later!

An infographic featuring a watercolor painting of a spotted ratfish. The spotted ratfish is a little, brown chimaera. It has greyish fins, and its tan body is covered in white spots. It has a brown-orange eye, and a cute, cartoon-like ski jump nose. The text on the bottom of the graphic says "Spotted Ratfish (Hydrolagus colliei)". Surrounding the watercolor are the following questions: "How am I venomous?" "What is fisheries management?" "What is aquatic flight?" and "What is electroreception?". The background of the images features purple lines and a purple, abstract blob. Pin It

References:

Similar Posts

Leave a Reply

Your email address will not be published. Required fields are marked *