#benthic fish

Hellbent on the Pacific Hagfish

Pacific hagfish, or California hagfish (Eptatretus stoutii) are one of the most well-known members of the hagfish family. They commonly seen on the ocean floor of the Pacific Ocean, at depths of anywhere between 16–966 metres (52–3,169 ft). They generally prefer muddy substrate, but may also be found on rocky outcroppings with plenty of crevices and caves. Because of their extremely low metabolism, they are also capable of surviving in zero-oxygen environments for several hours.

Like other hagfish, the Pacific hagfish has a long, eel-like body. In fact, hagfish are the only living animals that have a skull but no vertebrae. They also lack jaws, and the perpetually-open mouth is surrounded by a number of barbels. The skin is smooth, loose, and usually purple, pink, or grey. E. stoutii can reach up to 63 cm (25 in) in length; females are typically larger than males. They have very small, rudimentary eyes, and prominent nostrils.

Because they lack fully functioning eyes, California hagfish rely on a combination of smell and taste via a series of Schreiner organs along the sides of the body to detect their prey. They feed opportunistically on polychete worms, eggs, and carrion. Their primary predators are harbor seals, sablefish, and humans, which they avoid by producing large amounts of slime and tying themselves in knots.

There is little information on hagfish reproduction. Adults are thought to transition between sexes depending on the local ratio of males to females; adults with both sets of reproductive organs have also been recorded. They tend to reproduce every 2-3 years, when females lay 20-30 eggs. After hatching, the juveniles are fully independent, and become mature when they reach 42 cm (17 in) in length.

Conservation status: According to the IUCN, the Pacific hagfish is Data Deficient. Due to its habitat, there is not enough information on the species to determine population size or trends. However, they are increasingly harvested by fisheries for human consumption, which is a concern given the low reproductive rate

Photos

Masakazu Suzuki

NOAA

The Beloved Blackfin Icefish

The blackfin icefish (Chaenocephalus aceratus), also known as the Scotia Sea icefish, is a species of fish found in the Southern Ocean, around the Antarctic shelf. They typically reside along the bottom of the ocean closer to the sore, at depths no greater than 770 m (0.47 mi). These waters stay at around -2 °C (28 °F) all year.

Male blackfish are slightly smaller than female blackfish; the former reaches 34–40 cm (13-15 in) in length while the latter reaches 48–49 cm (18-19 in). The blackfin icefish is noted for its unique appearance. It is a scaleless fish, with a white or grey body sporting darker strikes all down its sides.

Part of this color comes from their blood, which lacks hemoglobin and is translucent in color. The icefish family are the only vertebrates in the world that lack hemoglobin. This lack severely reduces the oxygen carrying capacity of their blood; as a trade-off their blood is thinner to reduce viscosity and carries 'anti-freeze' proteins which allow the fish to survive below-freezing waters.

Spawning typically takes place in the autumn or winter. Females may only reproduce every other year due to the high energy costs of egg production. Male C. aceratus dig shallow depressions in the sand, and females lay clutches of up to 10,000 eggs. These eggs can take anywhere from 2-6 months to hatch, and during this time the males do most if not all of the guarding of the nest. After hatching, juveniles may take anywhere from 5-7 years to become fully mature.

The diet of Scotia Sea icefish consists primarily of krill, mackerel icefish, and crustaceans. Juveniles typically consume more krill than fish, and are more often found swimming in the water column, while adults stay along the ocean floor and ambush their prey. It is unknown whether they have any natural predators.

Conservation status: The IUCN considers the blackfin icefish as Vulnerable. Its primary threats are fatalities from fishing by-catch and climate change, which is increasing the temperature of its natural habitat.

Photos

Uwe Kils

Thomas Desvignes

Take Off with the Flying Gurnard

The flying gurnard, also known as the helmet gurnard or the Atlantic flying gurnard (Dactyloperus volitans) is a species of bottom-dwelling fish found along the tropical coasts of the Atlantic ocean, typically from Brazil to the northern United States on the western side, and from Angola to the English Channel on the eastern side. They are also commonly spotted throughout the Mediterranean Sea. Helmet gurnards prefer warm waters. They generally stay close to muddy or sandy ocean flats, although they may occasionally be seen among rocks or kelp forests.

Flying gurnards are named for their peculiar swimming motion; rather than propelling themselves with their tails, they have large wing-like pectoral fins to glide through the water when startled. When foraging, D. volitans also uses its folded up 'wings' to 'walk' along the ocean floor. They feed primarily on small fish, crustaceans and other small invertebrates found in the sand. Although they are covered in spines and thick, sheath-like scales, helmet gurnards are prey for a large variety of larger fish such as groupers, wrasse, and sharks, as well as sea birds; however, in addition to providing a quick getaway, their broad, colorful fins can make them appear bigger than they really are, startling potential predators.

On average, D. volitans reaches 50 cm (20 in) in length and 1.8 kg (4.0 lb). They are rather plain colored at first glance, usually brown or olive with light and dark spots that allow them to blend seamlessly into the ocean floor. Their most dazzling feature are their pectoral fins, which sport bright blue phosphorescent spots and a blue lining around the edge.

Flying gurnards have two spawning periods; one from May to August and another from November to February. During the spawning periods, both males and females release their respective reproductive materials (sperm and eggs) into the water, where they combine and fertilize. After hatching, the larvae will spend several months being carried by the currents before they settle down onto the ocean floor. Juveniles can reach maturity between 1-2 years old, and can live to be at least 4-5 years old in the wild, although their true lifespan has yet to be confirmed.

Conservation status: D. volitans is considered Least Concern by the IUCN. They are occasionally caught as by-catch in fishing nets.

Photos

Beck Mannjan

Thomas Menut

A Stingray Abroad: The Broad Stingray

Bathytoshia lata is a stingray known by many names: the broad stingray, the brown stingray, and thorn tail stingray; Dasyatis lata, Dasyatis thetidis, and Dasyatis ushii. The species has accumulated all these names-- and quite a few others-- thanks to its broad distribution. It can be found in the Atlantic, Pacific, and Indian Oceans, as well as the Mediterranean sea. Typically the species stays on reefs or in coastal bays with muddy bottoms. Prior to 2012, genetic testing of stingray species revealed them to be populations of B. lata, hence the multitude of latin names.

The broad stingray is one of the largest species of stingrays; the average individual is about 1.5 m (5 ft) across and 56 kg (123 lb), with some populations reaching an excess of 2.6 m (8.5 ft) across and 290 kg (639 lbs). Females also tend to be larger than males. The body is diamond shaped, and the tail is often more than twice its length. B. lata is dark in color, often tan or black, with a white underbelly. Perhaps its most distinctive feature are the 'spines'-- also known as dermal denticles-- that line the tail and rear portion of the body, giving it the name 'thorn tail'.

The brown stingray is fairly docile, and spends most of the day lying inactive on the sea bed. At night they forage for crustaceans, polychaete worms, and small fish. They can use their powerful pectoral fins to burrow through the sand and uncover prey, and like sharks they have special organs called ampullae of Lorenzini that allow them to detect electrical fields emitted by their prey. The primary predator of B. lata is the hammerhead shark, and when threatened individuals will raise the spines along their tail to deliver whip-like blows.

Females become ready to mate in the summer, typically from November to March. Males are attracted to pheromones released by the female, and initiate a dance-like courtship ritual. If the female is receptive, he will bite down on her pectoral fins while grasping her with special claspers located at the base of the tail. Following the mating ritual, the female gestates her young internally for 10-12 months. This species is ovoviviparous, and the pups recieve nutirents from both a yolk and internally secreted milk. Following her pregnancy, the mother gives birth to live young, typically 3-4 in a litter. The pups are completely independent, and receive no parental care after being born. It takes them about 14-16 years to become fully mature, and individuals can live up to 28 years in the wild.

Conservation status: The broad stingray is considered Vulnerable by the IUCN. Its most common threat comes from being caught as by-catch in fishing nets, and intentionally for their meat and skin.

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Photos

Andy Murch

Sarah Speight

Andrew Green

Stones can move quite quickly...when they’re fish. Stonefish are generally sedentary beings, spending their time camouflaged on the ocean floor waiting for prey-- usually small fish and crustaceans-- to swim past. When an opportunity presents itself, they strike with incredible speed! The fastest recorded attack was clocked at only 0.015 seconds.

(Image: A reef stonefish (Synanceia verrucosa) hiding among the coral by Erik Schlögl)

The Handsome Hagfish

Requested by @anxiouspuddle

Hagfish, of the family Myxini, are a group of 75 jawless fish species that reside in the Pacific, Atlantic, and Indian Oceans. Although they are vertebrates, they are the only known animals that have a vertebral column but no skull. Many scientists consider them to be an evolutionary descendant of the ‘stepping stone’ between fish with and without jaws. Their evolution and juvenile development has been the subject of much study, trying to determine the pathway of the evolution of jaws, skulls, and eyes in vertebrates.

Although they are sometimes mistaken for eels, hagfish have many easy-to-distinguish physical differences. For one, hagfish have a skeleton made of cartilage while eels have a harder bone skeleton. Secondly, Myxini species have open holes for gills rather than the slits more characteristic of eels and fish, and can also breathe through their skin if needed. Lastly, hagfish have no eyes or identifiable jaws; rather, their mouths are made of several protruding barbs and a set of horizontal cartilaginous structures that can expand outward. The main resemblance to eels is the body structure: hagfish have long flexible bodies and a paddle-like tail suited for smooth swimming. Hagfish species can be anywhere from 18 to 127 cm long, although the average length is around 50 cm, and their colors can range from pink to dark blue to brown.

Like eels, little is known about hagfish reproduction. The mating process in particular is a mystery, although females will lay eggs year round. Eggs are laid in batches of 30-40, and can take up to 11 months to hatch-- longer than many other jawless vertebrates. Freshly hatched hagfish are precocial, meaning they require no parental care or supervision. It is not known how long Myxini species age before they are sexually mature; however, it’s generally believed that they grow reproductive organs at around 35 cm. Evidence indicates that they are a hermaphroditic group. This means that at some point in their lives, hagfish change their sex from male to female or vice versa.

Outside of mating, hagfish are solitary. They are benthic animals, spending most of their time at the bottom of the ocean. They feed mainly on polychete marine worms, although carcasses like whales are famous for drawing massive aggregations of hagfish. When presented with large meals, hagfish will burrow inside the body and consume it from the inside out. However, they only exhibit this behavior on dead or dying animals, and generally only prey on living creatures smaller than themselves. Myxini species can survive for months between feedings, as do many benthic animals. Similarly, hagfish are nocturnal and hide in burrows of mud on the ocean floor.

Hagfish are preyed upon by many different animals, including sharks and harbor seals. To evade predation, they can twist themselves into complex knots or-- perhaps most famously-- produce large amounts of slime. This slime, or mucus, is produced from glands along the hagfish’s body. It’s protein-based and made of thick filaments that, when combined with salt water, expand into a thick membrane that doesn’t dissolve or dry out. The amount of slime produced seems only dependent on how much water is available and how long the hagfish perceives a threat. If ingested, the slime can choke a potential predator or clog its gills, giving the hagfish ample time to escape.

Conservation status: Hagfish are fairly common throughout the ocean, although some species are threatened. Although they are part of human diets in some countires, the main threat comes from the lack of food available; as larger marine fauna like whales and sharks disappear, the amount of carcasses for Hagfish to feed on also diminishes.

Photos

Andy Murch

A Nice Nurse Shark

Requested by @internetdog06

Yes, it’s true! Sharks can be smooth! The nurse shark (Ginglymostoma cirratum) defies many shark stereotypes, from their appearance to their demeanor and, yes, the texture of their skin. Although they have a bad reputation among divers for their bite, these sharks are more often slow, shy, and skittish. These traits, combined with its distinctive whiskers, give rise to its other common name: the cat shark.

G. cirratum resides in warm shallow waters, including coral reefs, mangroves, seagrass beds, and cliff edges. They can be found in both the Atlantic and Pacific Ocean along the coasts of North America, Central America, South America, and West Africa. Wherever they live they are bottom dwellers; they spend most of their days swimming slowly along the ocean floor or lounging near the reefs. Another stereotype broken: nurse sharks do not need to move continuously to breathe.

Despite their shy nature, the nurse shark’s size can make it an intimidating threat to any other fish-- or people-- that happen to spot it. G. cirratum can be between 3 and 4.5m long and can weigh up to 115 kg. And, yes, their skin is smooth, more like a dolphin’s than a shark’s. Their mouths don’t resemble that of other shark either, lacking the distinctive large, triangular teeth. Rather, they have several rows of smaller fan-shaped serrated teeth in a small, round mouth; best for crushing shellfish and coral. They also make for good defense, primarily against other sharks, curious humans, and occasionally American Alligators.

These sharks are suction feeders, and are able to draw invertebrates and small fish into their mouths from up to 3 cm away. They hunt mainly at night, swimmingly slowly along the ocean floor in search of food. During the day return to a home area to rest with other nurse sharks. Within these groups, also called shivers, they communicate mainly using sound, touch, and electroreception. Their distinctive ‘mustaches’ may be used for the latter two senses, forming a similar role to a cat’s whiskers.

Nurse sharks are territorial, both in their daily resting places and their mating sites. Individuals will return every summer to the same area to reproduce. Males and females with both mate with multiple partners, although males are known to ‘flush out’ competing sperm before copulation to ensure their genetics are the ones passed on, although litters with multiple paternities are common. Males also reinforce social hierarchies by biting both other males and females, which they reinforce within their day-to-day groups. G. cirratum is an ovoviviparous species which means the eggs hatch within the mother, and she give slive birth to about 20 pups after a 5 to 6 month pregnancy. Young cat sharks are spotted, and only grow into their brown coloring when they reach sexual maturity, at around 10 to 20 years old.

Conservation status: The IUCN lists the Nurse Shark as Vunerable. Historically they have been captured for their fins, skin and meat, as well as for the aquarium trade. They are also caught as by-catch in fishing nets. However, the species has several protected habitats along the North and Central American Atlantic coast and is currently being evaluated to better protect its migratory pathways.

Photos

Tchami

Gary Rinaldi

The Remarkable Spotted Ratfish

requested by @an-earwig

Spotted Ratfish

    The spotted ratfish (Hydrolagus colliei) is a small fish from the Pacific Ocean along the North American coast. These fish are a member of the Chimera group meaning that they have cartilage in the place of bones, and they are closely related to both rays and sharks. Because of its unique morphology, the spotted ratfish is fairly easy to identify. In an uncommon reversal of sexual dimorphism, females are larger than the males at 97 cm long; approximately a half of this length is composed of the fish’s long, pointed tail. In contrast, the head is flat, bulbous, and sports a duckbill-like snout. Like sharks and rays, these fish are smooth and scale-less, and usually iridescent silvery-bronze with speckled white dots.    

    Because of their thinner tail, spotted ratfish are relatively poor swimmers, so to defend themselves they use a poisonous spine on their dorsal fin. When they can, sharks, bass, rockfish, halibut, and marine mammals all readily consume spotted ratfish. In turn, H. colliei hunt slowly on the sandy ocean floor at night, using a combination of chemical and electrical receptors to find their prey; primarily crunchy animals like crustaceans, mollusks, and polychaete worms, as well as small fish. Interestingly, spotted ratfish share a trait with bony fish: the upper jaw is fused with the skull. This gives spotted ratfish a large biting force, which they use in combination with their upper two pairs of teeth to break the shells of of their prey. 

H. colliei, like their prey, are almost exclusively benthic fish, and prefer muddy or rocky habitats. They also tend to stay in cool, shallow waters around 7-9 °C and up to 1000m deep, moving steadily deeper as their range moves south. While populations are found as far as the southern United States, they are most commonly found in the Pacific Northwest, where they are occasionally attracted to shallower waters by dock or boat lights. They also move with the seasons; swimming in more shallow waters in the cooler spring and fall, and deeper again in the summer and winter.

Alongside some sharks, spotted ratfish reproduce by laying eggs in the spring or fall. These fish have a unique copulation process that lasts up to 30 hours, in which the male uses a club-like appendage on the head called a cephalic clasper to grip the female’s pectoral fin. After mating, the female releases one or two eggs over a period of several days. The eggs are attached to the ocean floor by thin tendrils, and the female will guard them for a few weeks to ensure they are not eaten by predators or mistaken by inanimate objects by unsuspecting divers. The eggs themselves take over a year to hatch, and young emerge already 14 cm long and fully independent.