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Spotted ratfish
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Spotted ratfish
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Holocephali
Order: Chimaeriformes
Family: Chimaeridae
Genus: Hydrolagus
Species:
H. colliei
Binomial name
Hydrolagus colliei

The spotted ratfish (Hydrolagus colliei) is a chimaera found in the north-eastern Pacific Ocean. Often seen by divers at night in the Pacific Northwest, this cartilaginous fish gets its characteristic name from a pointed rat-like tail. The ratfish lays leathery egg cases on the bottom of muddy or sandy areas, which are often mistaken by divers as something inanimate. While mainly a deep-water species, it occurs at shallower depths in the northern part of its range. The generic name, Hydrolagus, comes from the Greek words ὕδωρ, meaning water,[2] and λαγώς/λαγῶς, meaning hare,[2] and the specific name honors Alexander Collie, who was a ship surgeon and early naturalist. The spotted ratfish is common in much of its range, not typically eaten by humans, and is not commercially caught.[1][3]

Description

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The spotted ratfish has a very distinct appearance compared to unrelated fish species. The female is up to 97 cm (38 in) long, much bigger than the male. These fish have a smooth and scaleless skin that is a silvery-bronze color, often with sparkling shades of gold, blue, and green. The speckled white spots along their backs contribute to their name. Dark edges outline both the caudal and dorsal fins, whereas the pectoral fins have a transparent outline. Their pectoral fins are large and triangular, and extend straight out from the sides of their bodies like airplane wings. They have a venomous spine located at the leading edge of their dorsal fin, which is used in defense. It does not present a serious danger to humans, but can cause painful wounds and has been known to kill harbor seals that ate spotted ratfish (caused by the spine penetrating vital tissue in the stomach or esophagus after the ratfish was swallowed).[4] The tail of the ratfish constitutes almost half of its overall length and closely resembles a pointed, rat-like tail. The body of this fish is supported by cartilage rather than bone. It has a duckbill-shaped snout and a rabbit-like face. The mouth is small and contains one pair of forward-directed, incisor-shaped teeth in the bottom jaw and two pairs in the top jaw. Unlike sharks, which have sharp teeth that are easily replaceable, spotted ratfish teeth are plate-shaped, mineralized, and permanent, which assist them in grinding their prey. Like many bony fishes, but unlike its sister group, the Elasmobranchii, the upper jaw of the chimaera is fused with the skull.[5][6] Although their jaws are soft and mouths are relatively small, they have the largest biting force and jaw leverage found within the Holocephali, which supports their ability to consume large prey. One of their most mesmerizing features is their large, emerald green eyes, which are able to reflect light, similar to the eyes of a cat.

Frontal view of the plate-shaped, mineralized, and permanent teeth of H. colliei
Lateral view of the generalized features of the skull: The upper jaw is fused to the cranium. Both the upper and lower teeth are plate-shaped (9). Of note, the spotted ratfish does not have a cartilaginous appendage to the frontonasal region (2), which is a common feature of the chimera.

Distribution and habitat

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The spotted ratfish can be found in the northeastern Pacific Ocean, ranging from Alaska to Baja California, with an isolated population in the Gulf of California.[1][3] They are abundant in much of their range.[1][3] They be found most commonly off the Pacific Northwest. The range of depths in which this fish is found extends from 0 to 913 m (0 to 2,995 ft) below sea level, but it is most common between 50 and 400 m (160 and 1,310 ft).[3] Spotted ratfish typically live closer to the shore in the northern part of their range than in the southern, but it is also found as shallow as 30 m (98 ft) off California.[1] Spotted ratfish tend to move closer to shallow water during the spring and autumn, then to deeper water in summer and winter. For most of the year, they prefer temperatures between 7.2 and 8.9 °C (45 and 48 °F), but seasonally they do move into slightly warmer water.[1][7] They can most commonly be found living near the sea floor in sandy, muddy, or rocky reef environments. Unlike most of its relatives, which are entirely restricted to deep waters, the spotted ratfish has been held in public aquaria.[7][8] It has also been bred in such aquaria, where two of the main issues are the requirements of low light and low temperature (generally kept at 8–12 °C or 46–54 °F).[7][8]

Diet

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The spotted ratfish swims slowly above the seafloor in search of food. Location of food is done by smell. Their usual hunting period is at night, when they move to shallow water to feed. They are particularly drawn to crunchy foods such as crabs and clams. Besides these, the spotted ratfish also feeds on shrimp, worms, small fish, small crustaceans, and sea stars. Species known to prey on the spotted ratfish include soupfin sharks, dogfish sharks, Pacific halibut, pinnipeds, and pigeon guillemots.

Reproduction

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Like some sharks, spotted ratfish are oviparous. Their spawning season peaks during the spring to autumn. During this time, the female releases up to two fertilized eggs into sand or mud areas of the seabed every 10–14 days. The extrusion process can last 18–30 hours and the actual laying can last another 4–6 days. The egg sack is leather-like, 12.7 cm (5.0 in) long, and has a filament connected to it which is used to attach it to the ocean floor when it is let go by the mother. A female may be seen swimming around her newly laid eggs, in hopes of preventing predators from finding them. Development of the egg can take up to a year, which can be dangerous because the eggs are sometimes mistaken for inanimate objects by divers. When the young finally hatch, they are about 14 cm (5.5 in) in length and grow, reaching 30 cm (12 in) in length their first year.

The cephalic clasper, or frontal tentaculum, of the spotted ratfish chimaera is shown in color.

Male spotted ratfish have multiple secondary sexual characteristics, which include paired pelvic claspers, a single frontal tentaculum, and paired pelvic tentacula.[9] The pelvic claspers are located on the ventral side of the fish. They protrude out from the pelvic fins and are responsible for the movement of sperm to the oviduct of the female.[9] The interior of the pelvic clasper is supported by cartilage and separates into two branches, ultimately ending in a fleshy lobe on the posterior end.

The cephalic clasper (tentaculum) is a unique, club-like organ not found in any other vertebrate.[10] The cephalic clasper is located on the head of the fish, just anterior to the eyes. The tip of the retractable organ is fleshy and lined with numerous small, sharp barbs. For the male to stay attached during courtship, the clasper has been observed to clamp down on the pectoral fin of the female.[11][9] Additional evidence for this use has been found in the form of scars and scratches on the dorsal sides of females. The significantly smaller body size of males, which is a sexually dimorphic characteristic, may be a contributing factor to this mating behavior.[11]

Behaviour

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The ratfish prefers to maintain a safe distance from divers, and are usually not aggressive. However, if they feel their territory has been invaded, they are able to inflict a mildly toxic wound with their dorsal fin spines. As they swim, they perform barrel rolls and corkscrew turns, as if they are flying. Ratfish swim using large pectoral fins, and this has often been termed aquatic flight given the resemblance to a bird.[12]

Albino Puget Sound ratfish

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A rare albino Puget Sound ratfish was discovered near Whidbey Island, Washington. It is the only pure albino among the 7.2 million specimens in the University of Washington's fish collection.[13]

References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Spotted ratfish

View on Grokipedia
from Grokipedia
The spotted ratfish (Hydrolagus colliei) is a deep-dwelling cartilaginous fish in the family , notable for its smooth, scale-less skin, iridescent brown-gray body adorned with white spots, large green eyes, rabbit-like snout, and elongated that can comprise nearly half its . Reaching a maximum of about 100 cm, it features triangular pectoral fins used for propulsion in a rowing motion, platelike grinding teeth adapted for crushing hard prey, and a prominent venomous spine in front of its first . Males possess a unique clublike appendage on the forehead called a , used during to grasp the female. Native to the northeastern Pacific Ocean, the spotted ratfish ranges from southeastern to and the northern , with highest abundances off to . It is a bathydemersal species, inhabiting soft , , or rocky bottoms in temperate waters at depths from the to 913 m, though it is most commonly encountered between 50 and 400 m in cooler temperatures of 7–9°C. A slow swimmer that relies on electroreception and olfaction to locate food, it preys on clams, , , worms, echinoderms, and small benthic fishes, occasionally exhibiting . Reproduction is oviparous, with females laying pairs of leathery egg cases year-round but peaking in spring and autumn; these capsules incubate for about 12 months before hatching into juveniles measuring around 14 cm. is reached at approximately 19 cm, and the species exhibits distinct during . Predators include sharks such as the sixgill and , as well as . Classified as Least Concern by the IUCN due to its wide distribution and low impact, the spotted ratfish is occasionally caught as in trawl and longline fisheries, with its venomous spine posing a risk to handlers. As a representative of the ancient holocephalan lineage, it serves as an important model for understanding the evolution of jawed fishes.

Taxonomy

Classification

The spotted ratfish, Hydrolagus colliei, belongs to the kingdom Animalia, phylum Chordata, class Chondrichthyes, subclass Holocephali, order Chimaeriformes, family Chimaeridae, genus Hydrolagus, and species H. colliei. This classification places it within the cartilaginous fishes (Chondrichthyes), a group characterized by skeletons composed of cartilage rather than bone. The binomial name Hydrolagus colliei was originally described as Chimaera colliei by Lay and Bennett in 1839, later reclassified into the genus Hydrolagus. As members of the subclass , spotted ratfish represent an ancient lineage of cartilaginous fishes often regarded as "living fossils" due to their morphology remaining largely unchanged since the era, over 300 million years ago. The diverged from the elasmobranchs (sharks, rays, and skates) approximately 400 million years ago during the period, marking one of the earliest splits within . This evolutionary divergence highlights their basal position among modern chondrichthyans, with holocephalans retaining primitive features such as a single and a diphycercal tail. Within the family Chimaeridae, the genus Hydrolagus is distinguished from the related genus primarily by the absence of a separate anal fin (confluent with the caudal fin in Hydrolagus), whereas Chimaera has a distinct anal fin. Hydrolagus comprises around 50 species, many in the including the northeastern Pacific endemic H. colliei, while has about 12 species distributed across the Atlantic, Indian, and Pacific oceans.

Etymology

The scientific name Hydrolagus colliei derives from Greek roots, with the genus Hydrolagus combining "hydro-" (ὕδωρ, meaning water) and "lagos" (λαγώς, meaning or ), alluding to the species' rabbit-like head shape or protruding tooth plates resembling rabbit incisors. The specific epithet colliei honors Alexander Collie (1793–1835), a Scottish and naturalist who served aboard HMS Blossom during its 1825–1828 expedition and collected the type specimen from the . Collie's field notes contributed to the formal description of the species. The common name "spotted ratfish" reflects the fish's distinctive white spots across its body and its elongated, tapering tail that resembles a rat's. An alternative vernacular name, "ghost shark," arises from the species' ethereal, otherworldly appearance, evoking a spectral quality in the deep-sea environment. The spotted ratfish was first scientifically described in 1839 by George Lay and Edward Turner Bennett as Chimaera colliei, based on specimens obtained during the HMS Blossom voyage to the northeastern Pacific Ocean, particularly the Pacific Northwest region. This description appeared in the Zoology of Capt. Beechey's Voyage, marking the initial taxonomic recognition of the species in scientific literature.

Description

Physical appearance

The spotted ratfish (Hydrolagus colliei) exhibits a distinctive external morphology typical of chimaeriform fishes, with females reaching a maximum total length of 97 cm, while males are notably smaller, typically attaining lengths of 40-60 cm. Individuals can weigh up to approximately 1.5 kg, though larger specimens have been recorded at around 2 kg. The body is elongated and tapers gradually toward the rear, comprising a smooth, scale-less skin that lacks denticles, providing a sleek, cartilaginous texture. Coloration varies slightly but generally features a silvery-bronze or brownish hue on the dorsal surface, accented by numerous small white spots scattered across the body and fins, which contribute to an iridescent sheen of gold, green, and blue tones when light reflects off the skin. The ventral surface is paler, often silvery-white, while the fins display translucent grayish-blue shades. The head is large and bulbous, featuring a broad, duckbill-like that is bluntly rounded and a pair of prominent, large green eyes adapted for vision in dim conditions. The pectoral fins are expansive and triangular, with fleshy bases that aid in and maneuverability, resembling wings in their broad span. A prominent first rises sharply from the back, preceded by a venomous spine capable of inflicting painful injuries, while the tail is long and slender, tapering to a thin, rat-like filament that constitutes nearly half the total body length. is evident not only in size differences but also in male-specific features, including a frontal tentaculum or on the head and paired claspers near the pelvic fins used in .

Unique adaptations

The spotted ratfish possesses an entirely cartilaginous , a primitive trait shared among chondrichthyans that provides flexibility but lacks the mineralization found in the bony skeletons of actinopterygian fishes. This skeleton includes a reduced, short lower with autostylic suspension, where the upper fuses directly to the cranium, and a vaulted ethmoidal region that enhances structural stability during feeding. Specialized for durophagy, the bear three pairs of plate-like dental plates—two maxillary and one mandibular—that continuously grow and feature hypermineralized anterior blades for nipping and broad posterior surfaces for grinding, enabling the processing of hard-shelled prey through high bite forces up to 191 N posteriorly. In terms of sensory adaptations, the spotted ratfish has large, iridescent green eyes that enhance light capture in low-illumination deep-sea environments, where it frequently occurs at depths exceeding 200 meters. Complementing this visual capability, clusters of electroreceptive are distributed across the head, connected to jelly-filled canals that detect bioelectric fields as weak as 1 µV/cm, allowing precise localization of hidden or buried prey in murky or dark conditions. Reproductive anatomy in the spotted ratfish is distinctive among chondrichthyans, with males developing paired pelvic s—elongated extensions of the pelvic s armed with denticles—to transfer sperm internally during copulation. Uniquely, males also possess a frontal , a single cephalic emerging from the as a toothed, club-shaped appendage derived from cranial , which grasps the female's pectoral to position her for fertilization, a specialization exclusive to holocephalans. For defense, the first is supported by a stout, serrated spine integrated with paired glands at its base, which can erect rapidly to puncture attackers and inject toxic proteins, causing intense and swelling. In cases of by predators like seals, the spine can cause lethal internal tissue damage through . This apparatus, housed in a groove along the back when the fin is depressed, underscores the ' reliance on chemical deterrence in vulnerable deep-water habitats.

Distribution and habitat

Geographic range

The spotted ratfish (Hydrolagus colliei) inhabits the northeastern along the western coast of , with its primary range extending from (Cape Spencer)—southward to central , , and the northern . This distribution spans a latitudinal extent of approximately 59°N to 9°N, with scattered records to . The species is most abundant off the coasts of , Washington, , and , where it occurs in temperate coastal waters. Recent studies suggest a northward shift in distribution due to warming waters (Tolimieri et al. 2020), with continued monitoring needed as of 2024. In terms of depth, the spotted ratfish occupies a broad profile from the —though sightings there are rare—to maximum depths of 913 m, with peak abundance typically recorded between 50 and 400 m. It undergoes seasonal vertical migrations, shifting to shallower waters during spring and autumn before retreating to deeper zones in summer and winter. Throughout its range, the spotted ratfish is considered common in areas surveyed by trawl and methods, reflecting its widespread presence with possible discrete subpopulations across its range.

Habitat preferences

The spotted ratfish (Hydrolagus colliei) primarily inhabits soft-bottom substrates such as , sand, and gravel on the continental shelf and upper slope, where it forages and deposits cases. Juveniles show a strong preference for soft sediments like , while adults utilize a mix of soft and hard substrates, including rocky reefs and boulder fields. In shallower coastal areas, individuals may also occupy eelgrass beds and structured habitats like ridges. These fish favor temperate coastal waters with cool temperatures ranging from 5.1°C to 9.7°C (mean 7.5°C), though they tolerate up to 12°C seasonally. They are commonly found in bays, , fjords, and along continental shelves at depths of 50–400 m, with occasional occurrences from the to 900 m or more. Such conditions support high densities of benthic , aligning with their prey availability, though spotted ratfish do not form dense schools and are typically observed in loose aggregates or solitarily. Seasonally, spotted ratfish exhibit vertical migrations to maintain preferred thermal regimes, moving to shallower depths under 200 m during spring and autumn for spawning, when water temperatures are slightly warmer. In contrast, they descend to deeper waters exceeding 400 m during summer and winter. This pattern is evident in regions like , where diel and seasonal shifts influence their distribution on the seafloor.

Ecology

Diet and feeding

The spotted ratfish (Hydrolagus colliei) is a carnivorous benthic forager that primarily targets slow-moving or stationary and small fishes on the seafloor. Its diet consists mainly of crustaceans such as (Pandalus and Crago spp.), mollusks including bivalves (Musculus spp.) and gastropods (Amphissa spp.), and echinoderms like heart urchins (Brisaster spp.), with shrimp and mollusks comprising the majority of occurrences in examined specimens (up to 33.4% for gastropods). Small flatfishes and polychaete worms are also consumed occasionally, along with rare instances of on conspecifics or egg cases. To process its hard-shelled prey, the spotted ratfish employs specialized molariform dental plates that generate high bite forces (up to 191 N posteriorly), enabling durophagous feeding despite relatively soft tissues compared to other chondrichthyans. These plates crush exoskeletons and shells, as evidenced by wear patterns on the teeth indicating shearing actions during prey handling. The species is classified as a benthivore, occupying a mid-trophic level in deep-sea food webs through opportunistic consumption of abundant seafloor organisms. Foraging occurs primarily at night, when the ratfish glides slowly above the substrate in shallow to moderate depths (50–400 m), using olfaction and electroreception via its to detect buried or hidden prey. This nocturnal pattern aligns with observed diel vertical movements and higher scavenging activity during nighttime hours, potentially reducing competition and predation risk. Small cephalopods are taken infrequently, supplementing the invertebrate-dominated diet.

Predators and prey interactions

The spotted ratfish (Hydrolagus colliei) occupies an intermediate position in northeastern Pacific marine food webs, serving as prey for a variety of larger predators. Key predators include elasmobranchs such as soupfin sharks (Galeorhinus galeus), spiny dogfish (Squalus acanthias), and bluntnose sixgill sharks (Hexanchus griseus), as well as teleosts like Pacific halibut (Hippoglossus stenolepis) and lingcod (Ophiodon elongatus). Marine mammals, particularly harbor seals (Phoca vitulina) and California sea lions (Zalophus californianus), also prey on spotted ratfish, with documented cases of spine-induced mortality in seals after consumption. Seabirds such as pigeon guillemots (Cepphus columba) target smaller individuals or juveniles in nearshore areas. Predation risks for spotted ratfish are heightened by their relatively small adult size (up to 100 cm total length) and relatively low for chondrichthyans, with annual estimates of 19.5-28.9 egg cases over a 6-8 month season, rendering populations potentially susceptible to by predators. Although equipped with a venomous dorsal spine capable of deterring smaller attackers or causing severe to larger ones like seals, this defense is less effective against fast-moving or heavily armored predators that can engulf the fish whole. Seasonal movements into shallower coastal waters (as low as 10-50 m) during winter and spring for expose them to increased encounters with nearshore hunters, amplifying vulnerability compared to their preferred habitats at depths of 50-400 m. Additionally, their post-mortem scavenging by opportunistic feeders like and crabs contributes to nutrient recycling but underscores their role as a readily available food source. Interspecific interactions further shape the spotted ratfish's ecological niche, including competition with co-occurring benthic species for limited seafloor resources. It competes directly with Pacific halibut and potentially skates (Raja spp.) in soft-sediment habitats, where overlapping foraging behaviors can limit access to shared prey like polychaetes and crustaceans. The species also serves as an intermediate or definitive host for metazoan parasites, such as the trematode Otodistomum hydrolagi (Azygiidae), which utilizes mollusks as first intermediate hosts before infecting ratfish via ingestion, and cestodes like Gyrocotyle spp. in the spiral intestine; these parasites facilitate trophic transmission within the community. Such interactions highlight the ratfish's connectivity in parasite-mediated food webs. Ecologically, the spotted ratfish contributes to benthic balance as an abundant deep-sea chondrichthyan, linking primary consumers to apex predators and stabilizing trophic dynamics. Its high in outer shelf and upper ecosystems supports predator while its helps regulate abundances, preventing in soft-bottom habitats. As both predator and prey, it plays a pivotal role in energy transfer and resilience of northeastern Pacific food webs, with stability buffering against perturbations in structure.

Reproduction

Mating and fertilization

The spotted ratfish (Hydrolagus colliei) reaches at a precaudal (PCL) of approximately cm for males and 38 cm for females in populations off , corresponding to total lengths of around 40–50 cm; 50% maturity occurs at about 12 years for males and 14 years for females. Maturity sizes and ages vary by region, with smaller thresholds in southern populations, such as median snout-vent lengths (SVL) of 15.7 cm for males and 20.3 cm for females off . Mating occurs primarily from spring to autumn, with peaks in summer corresponding to the main period of ovarian and egg production from May to . During , males employ their cephalic , or frontal , to grasp the female's pectoral , facilitating positioning for copulation; this process can last 37–120 minutes. involves distinct movements, including color changes in males and undulating swims that resemble barrel rolls and fin flares to attract and hold the female's attention, often in deeper waters during nocturnal aggregations. Fertilization is internal, achieved through the male's prepelvic claspers, which attach to the female's ventrum to transfer sperm directly into the oviduct. The species exhibits a promiscuous mating system, with females capable of storing sperm in the oviducal gland for extended periods, allowing fertilization by multiple partners over the several-month fertile window without synchronized mating events. This strategy supports the production of multiple egg cases throughout the season, enhancing reproductive success in their deep-sea habitat.

Egg laying and development

The spotted ratfish (Hydrolagus colliei) is oviparous, with females producing leathery, spoon-shaped egg cases that encapsulate a single embryo each. During the breeding season, which peaks from May to October, mature females (>54 cm total length) extrude one to two egg cases per laying event, with each event lasting 18–30 hours; cases remain attached to the female via tendrils for 3–6 days before being deposited on the seafloor substrate, such as sand or rocky areas. These egg cases measure approximately 12–15 cm in length and 4–5 cm in width, featuring anterior and posterior tendrils that anchor them to the bottom, preventing displacement by currents. Laying occurs at intervals of 10–14 days, allowing females to produce an estimated 19.5–28.9 egg cases annually during the 6–8-month season. Embryonic development within the egg case lasts 9–12 months in the wild, though durations of 12.2–14.5 months have been observed in controlled aquarium conditions at 7–11°C, indicating temperature as a key influencing factor; higher temperatures may accelerate development but increase mortality risk. Nourishment is provided solely by a large , which subdivides early in development (around 3 months), supporting the growth of fully formed embryos with visible eyes, fins, and external features by mid-incubation. No is provided post-deposition, and the egg case's tough, horny structure protects against predation and environmental stress during this prolonged period. Upon hatching, juveniles emerge fully independent at approximately 9–14 cm total length, immediately capable of and avoiding predators without further reliance on reserves. Initial growth is relatively rapid in the first year, reaching about 30 cm total length, but slows thereafter; is attained at approximately 12–14 years in northern populations. This extended developmental timeline contributes to low rates.

Behavior

Locomotion and movement

The spotted ratfish (Hydrolagus colliei) primarily utilizes labriform locomotion, relying on its large, flexible pectoral fins to generate thrust through undulatory waves that propagate posteriorly along the fin surface, enabling gliding and precise maneuvering in benthic environments. These fins flap in an oscillatory manner at low to moderate speeds, with the downstroke producing faster motion than the upstroke, while the tail fin contributes to during transitions to higher velocities via whole-body undulation. This style allows for efficient steady swimming without significant chordwise bending in the fins, supported by a higher proportion of distal muscle insertion compared to related species like the . Activity patterns in the spotted ratfish are predominantly nocturnal, with significantly higher abundance and activity levels observed at night across various demersal habitats such as rock ridges, boulders, and mud, where up to 92% of individuals are active. During the day, they rest by burying themselves partially in sediment, minimizing exposure and conserving energy. Diel vertical migrations occur, with individuals shifting depths in response to light cycles, often moving shallower at night. Swimming speeds are generally slow, with a maximum sustained rate of approximately 0.15 m/s (0.54 km/h), though short bursts can reach up to 0.8 body lengths per second (around 1.4 km/h for adults averaging 0.5 m in length). is limited, as their low-speed profile restricts prolonged activity in strong currents, but transitions—from pectoral undulation at 0.1–0.3 body lengths per second to oscillatory flapping at 0.3–0.6 body lengths per second, and finally whole-body undulation beyond 0.6 body lengths per second—facilitate adaptive responses to varying demands. Vertical migrations may align with tidal cycles to optimize foraging or access, though specific tidal synchronization remains tied to broader diel patterns. The spotted ratfish is typically solitary or found in small, loose aggregations rather than forming tight schools, with groups often segregated by sex and size to reduce competition or facilitate mating. This social structure supports low-energy cruising over the seafloor, where pectoral fin beats maintain stability during slow, meandering paths.

Defensive mechanisms

The spotted ratfish possesses a prominent venomous spine at the leading edge of its first dorsal fin, serving as its primary physical defense against predators. This spine is associated with a venom apparatus consisting of glandular tissue that produces and delivers toxins upon penetration, inflicting painful wounds and localized tissue damage to deter attackers. In humans, contact with the spine causes intense pain and swelling but is rarely life-threatening. Documented incidents demonstrate its lethality in harbor seals, where ingested spines perforate the esophagus or stomach, migrate to vital organs, and cause fatal conditions such as peritonitis, hemothorax, or pneumothorax; seven such cases were reported in Washington State between 2006 and 2011. To evade detection, the spotted ratfish relies on cryptic coloration, with its body exhibiting a mottled of , gray, or reddish hues accented by small spots that blend seamlessly with the seafloor's sandy, muddy, or substrates. When threatened, individuals often bury themselves partially in the , a behavior observed in the genus Hydrolagus, enhancing concealment from visual predators such as larger or marine mammals. Its docile disposition further reduces encounters, as it avoids territorial disputes and confrontation.

Conservation and human relations

Conservation status

The spotted ratfish (Hydrolagus colliei) is classified as Least Concern on the , with the most recent assessment confirming this status in 2024 due to its extensive distribution across the northeastern from to and its occurrence over a broad depth range (0–1,463 m), which buffers it against localized pressures. No evidence of global population decline has been observed, and the species is considered stable, though comprehensive quantitative data remain limited. Primary threats to the spotted ratfish stem from incidental capture as in commercial trawl fisheries targeting such as , groundfish, and , particularly in the coastal waters of the . Bottom trawling not only results in direct mortality but also disrupts benthic habitats frequented by the , including soft sediments and rocky areas on the continental shelf and slope. Potential climate change impacts, such as northward distribution shifts due to ocean warming, have also been identified as an emerging threat. While not commercially targeted, bycatch levels can be substantial; for instance, British Columbia groundfish fisheries reported approximately 650 metric tons of spotted ratfish caught incidentally in alone. Population estimates are challenging due to the species' deep-water habits and patchy survey coverage, but it is recognized as abundant in its core range off and the U.S. , where trawl surveys indicate it often comprises a significant portion of the biomass—up to 70% in some nearshore areas during certain seasons. Data gaps persist in southern populations near and the , where abundance appears lower and less documented. Management efforts focus on bycatch mitigation rather than direct regulation, as the spotted ratfish is not commercially harvested. In Canada, it falls under the Department of Fisheries and Oceans' Sustainable Fisheries Framework, with ongoing assessments to inform bycatch policies and monitoring in groundfish fisheries. In the United States, it is designated an ecosystem component species under the Pacific Fishery Management Council's Pacific Coast Groundfish Fishery Management Plan, which includes measures to minimize bycatch through gear restrictions, seasonal closures, and habitat protections in essential fish habitat areas. These frameworks ensure incidental catch is regulated without specific quotas for the species, promoting ecosystem-based management.

Interactions with humans

The spotted ratfish (Hydrolagus colliei) is not commercially targeted but is occasionally captured as in trawl fisheries and operations along the northeastern . Although its flesh is edible, it is often described as bland with an unpleasant aftertaste, and the species is typically discarded due to the hazardous venomous spine on the leading edge of the first , which can inflict painful wounds on handlers. In captivity, spotted ratfish have been successfully maintained in public aquariums, including the and , where they are displayed to showcase deep-sea environments. Optimal husbandry conditions include water temperatures of 7–9°C to mimic their natural cold-water , supporting embryonic development and long-term juvenile survival. These exhibits contribute to on chimaeroid , including reproductive and husbandry techniques for holocephalans. The species holds appeal in , particularly among scuba divers in the , where nocturnal dives often yield sightings of these elusive gliding over sandy or muddy bottoms. Their otherworldly appearance and rarity during daytime encounters enhance their allure for enthusiasts, though they lack value for sport fishing due to low market demand. Cultural interactions with the spotted ratfish are limited, with minimal documented indigenous uses beyond occasional inclusion in First Nations diets along the , evidenced by teeth found in archaeological heaps.

Notable variants

Albino specimens

in the spotted ratfish (Hydrolagus colliei) is a rare genetic characterized by the absence of pigmentation, resulting in a predominantly white or pinkish body coloration, translucent fins, and red eyes due to visible blood vessels. This condition contrasts sharply with the species' typical silvery-gray body adorned with white spots, which aids in on the ocean floor. The first and only documented albino specimen was captured on June 17, 2007, during a marine survey approximately 0.8 km east of in , Washington, at a depth of about 60 meters. This female individual measured 33 cm in total length and exhibited a pure white dorsal surface with a subtle silvery sheen from a crystalline layer, marking it as the inaugural record of albinism in any chimaeriform fish. The specimen, cataloged as UW 115754, is preserved in the University of Washington's fish collection, where it stands as the sole albino among over 7.2 million preserved fishes, underscoring its extreme rarity. Such albinos likely face heightened vulnerability to predation due to their conspicuous appearance against the muted seafloor environment, potentially reducing rates in the wild. No records of breeding or among albino spotted ratfish exist, as the documented case represents a singular occurrence without evidence of viable populations or offspring.

References

  1. https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/spotted-ratfish/
  2. https://www.fishbase.se/summary/Hydrolagus-colliei
  3. https://wdfw.wa.gov/species-habitats/species/hydrolagus-colliei
  4. https://www.montereybayaquarium.org/animals/animals-a-to-z/spotted-ratfish
  5. https://www.marinespecies.org/aphia.php?p=taxdetails&id=271417
  6. https://www.gbif.org/species/5215461
  7. https://www.fishbase.se/summary/Hydrolagus-colliei.html
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  13. https://etyfish.org/ETYFish_Chimaeridae.pdf
  14. https://www.aquariumofpacific.org/onlinelearningcenter/species/spotted_ratfish
  15. https://saveourseas.com/worldofsharks/podcast/ghost-sharks-chimaeras-the-sharks-forgotten-cousins
  16. https://www.sharksandrays.com/spotted-ratfish/
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  22. https://pubmed.ncbi.nlm.nih.gov/23060509/
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  24. https://www.iucnredlist.org/species/60191/124449845
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  26. https://escholarship.org/content/qt5t94c30s/qt5t94c30s_noSplash_5807c606a09c32d96cd8177dfe7a54ef.pdf
  27. https://www.plu.edu/biology/wp-content/uploads/sites/7/2017/09/final_hydrolagus-colliei_robinson_201700914.pdf
  28. https://spo.nmfs.noaa.gov/sites/default/files/pdf-content/1972/702/johnson1.pdf
  29. https://sites.bu.edu/davieslab/files/2017/12/davies_pigleg.pdf
  30. https://www.researchgate.net/publication/226576506_Maturity_fecundity_and_reproductive_cycle_of_the_spotted_ratfish_Hydrolagus_colliei
  31. https://www.researchgate.net/publication/224004045_Evidence_of_stability_in_a_chondrichthyan_population_Case_study_of_the_spotted_ratfish_Hydrolagus_colliei_Chondrichthyes_Chimaeridae
  32. https://www.sciencedirect.com/science/article/abs/pii/S0967064513004414
  33. https://www.yournec.org/creature-feature-the-spotted-ratfish/
  34. https://www.researchgate.net/publication/338776096_Prevalence_and_Intensity_of_Otodistomum_hydrolagi_Trematoda_Azygiidae_in_Spotted_Ratfish_Hydrolagus_colliei_Chondrichthyes_Chimaeridae_from_the_Coastal_Waters_of_British_Columbia_Canada
  35. https://www.sciencedirect.com/science/article/abs/pii/0020751972900355
  36. https://escholarship.org/uc/item/5t94c30s.pdf
  37. https://onlinelibrary.wiley.com/doi/full/10.1002/zoo.21813
  38. https://biomechanics.ucr.edu/Foster_Higham_2010.pdf
  39. https://sicb.org/abstracts/the-curious-case-of-chimaera-kinematics-gait-transitions-in-the-spotted-ratfish-hydrolagus-colliei/
  40. https://sites.harvard.edu/glauder/files/2022/03/Wilga_Lauder_BioSharks2012.pdf
  41. https://www.researchgate.net/publication/287557144_Day_and_night_abundance_distribution_and_activity_patterns_of_demersal_fishes_on_Heceta_Bank_Oregon
  42. https://spo.nmfs.noaa.gov/content/depth-distribution-and-seasonal-and-diel-movements-ratfish-hydrolagus-colliei-puget-sound
  43. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/hydrolagus
  44. https://wdfw.wa.gov/publications/01044
  45. https://old.psmfc.org/tsc-drafts/2024/DFO_2024_TSC_Report.pdf
  46. https://www.pcouncil.org/documents/2025/08/g-2-attachment-2-pacific-coast-groundfish-fishery-management-plan.pdf
  47. https://www.fishbase.org/summary/2589
  48. https://www.researchgate.net/publication/376937414_Husbandry_conditions_of_spotted_ratfish_Hydrolagus_colliei_Chimaeriformes_in_aquaria_for_successful_embryonic_development_and_long-term_survival_of_juveniles
  49. https://www.seattletimes.com/pacific-nw-magazine/rise-of-the-ratfish-in-puget-sound/
  50. https://www.scubabc.ca/footage/pacific-northwest/fish/spotted-ratfish-night-dive-footage/
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  52. https://www.researchgate.net/publication/232664300_First_Record_Of_An_Albino_Chimaeriform_Fish_Hydrolagus_colliei
  53. https://www.washington.edu/news/2007/09/24/rare-albino-ratfish-has-eerie-silvery-sheen/
  54. https://www.seattletimes.com/seattle-news/uws-albino-ratfish-is-1-in-7-million/
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