Bowmouth Guitarfish
Rhina ancylostoma
These unique fish get the guitar part of their common name from their body shape. The bowmouth part of the name is derived from their mouth shape that has wavy edges giving the appearance of a longbow, a large, powerful, wooden hand-drawn bow. The distinctive appearance of these rays, that of a shark-ray mix, is the reason for some of their other common names, shark ray and sharkfin guitarfish.
Credit: Aquarium of the Pacific
Credit: © Shin-Enoshima Aquarium. Creative Commons Attribution ShareAlike License v2.5
SPECIES IN DETAIL
Bowmouth Guitarfish
Rhina ancylostoma
CONSERVATION STATUS: Vulnerable
CLIMATE CHANGE: Not Applicable
At the Aquarium
The bowmouth guitarfish is not exhibited at the Aquarium. This information is presented for reference information about this guitarfish species.
Geographic Distribution
Indo-West Pacific: Red Sea and East Africa to Papua New Guinea, north to Japan, south to New South Wales, Australia
Habitat
Although they have been recorded as deep as 90 m (295 ft), bowmouth guitarfish generally prefer shallow water fairly close to shore in or near coral reefs or mangroves at depths of 1-20 m (3.3-85 ft). They are primarily bottom dwelling animals preferring sandy or muddy substrates but may swim above the bottom.
Physical Characteristics
The bowmouth guitarfish’s flat, broad, blunt, arc-shaped head spreads into two flat, distinct triangular-shaped pectoral fins. The nostrils, mouth, and gill slits are located on the ventral surface of the head, and the eyes and large spiracles are on the dorsal side. The jaws are heavily ridged with crushing teeth arranged in wave-like rows. Behind the head the body tapers into a more streamlined shape, much like that of sharks. There are sturdy ridges of heavy, sharp thorns next to the eyes, in the middle of the back, and above the pectoral fins. This guitarfish has two large, triangular dorsal fins, the second smaller than the first. The body terminates in a small but powerful caudal fin with an upper lobe that is larger than the lower. The tail of this species is much longer than the disc. Dermal denticles cover the body giving the rough skin a velvety appearance.
The color of bowmouth guitarfish changes with age. Young fish have brown bodies, pale ring-shaped spots covering their pectoral fins, and black bars between the eyes. Adults have charcoal or pale gray bodies with small white spots. The face bars fade to dark gray as they age, becoming faint and indistinct. Some adults have a bluish coloration. The creamy white underbodies in both adult and juvenile phases provides these rays with protective countershading.
Size
The largest bowmouth guitarfish on record was 2.9 m (9.5 ft) long. However, animals above 2.44 m (8 ft) in length are rare. One captured male weighed 135 kg (297 lbs), but most of these fish weigh much less.
Diet
These guitarfish primarily feed on crustaceans and mollusks they find on the ocean floor and in the sediment. Since their eyes are located on the top of the head, bowmouth guitarfish locate their prey primarily through smell. Once an animal finds a potential meal, it restrains it with its broad, blunt head, easing the prey into its mouth with a series of short sharp thrusts. The flat, heavily ridged teeth are used to crush the shells of their prey.
Reproduction
Fertilization in bowmouth guitarfish is internal. Reproduction among this species is called ovovivparity, or aplacental viviparity with histotrophy. Fertilized eggs are retained in the female’s body, where they are nourished by both the egg yolk and by uterine milk. In its early developmental stage, the embryo receives its nutrition from the egg yolk. Then it breaks and sheds the thin membrane of the egg capsule and receives its nourishment from a fluid called histotroph or ‘uterine milk’ which is secreted from villi, appendages in the wall of the female’s uterus. These uterine extensions also provide the embryo with oxygen and remove its waste.
Usually four to five pups are born live. The newborn pups are about 45 cm (18 in) in length. They disperse immediately after birth to live independent lives without parental care.
Behavior
Some scientists believe bowmouth guitarfish use the unusual spiked ridges over their eyes, nape, and pectoral fins to “head-butt” potential attackers, however, this theory has not been proven.
Adaptation
These fish have unusual spiked ridges over their eyes, nape, and pectoral fins. The ridges prevent larger would-be predators from biting vital parts of the head and body.
Longevity
In protected environments, bowmouth guitarfish live for about seven years. Lifespan in the wild is unknown.
Conservation
The IUCN Red List labels these animals as vulnerable. Since they reproduce slowly, they cannot recover quickly from the multiple threats facing them.
They are a targeted species in some areas and are also caught as bycatch in commercial fisheries utilizing trawl nets, gill nets, and hook and line techniques. Some turtle exclusion devices have minimally reduced their capture. Although not generally considered a good food fish, they are popular in some areas and are found in fish markets.
They are specifically hunted for their pectoral fins. In a process called finning, fishermen cut off the fins, usually while the animal is still alive. The rest of the animal is thrown back into the water, where it starves or bleeds to death. Once dried or salted, the fins reach the market, where they bring very high prices as the primary ingredient in sharkfin soups. Finning is illegal in United States waters and in many of the areas where this fish is caught, but enforcement is difficult and there is a lively black market in this lucrative practice .In small inshore fisheries in tropical countries, sun-drying of fins requires minimal technology and artisanal fishermen are encouraged by shark/ray fin-traders to target local populations. As a result, even coastal ray and shark populations in the remotest parts of the world are now vulnerable to over-exploitation, and rapid depletion of local populations often results from such trading activity.
Pollution, near shore development, silting, and global climate change are destroying the coral reefs these fish use for habitat. This species is also a victim of dynamite fishing for other species.
Special Notes
The bowhead guitarfish, often described as prehistoric in appearance, is considered by some scientists to be the ‘missing link’ between sharks and rays based on the ray-like placement of the mouth and gill openings, and disc shape of the front part of the body and the shark-like streamlined appearance of the rest of the body and the powerful tail.
SPECIES IN DETAIL | Print full entry
Bowmouth Guitarfish
Rhina ancylostoma
CONSERVATION STATUS: Vulnerable
CLIMATE CHANGE: Not Applicable
The bowmouth guitarfish is not exhibited at the Aquarium. This information is presented for reference information about this guitarfish species.
Indo-West Pacific: Red Sea and East Africa to Papua New Guinea, north to Japan, south to New South Wales, Australia
Although they have been recorded as deep as 90 m (295 ft), bowmouth guitarfish generally prefer shallow water fairly close to shore in or near coral reefs or mangroves at depths of 1-20 m (3.3-85 ft). They are primarily bottom dwelling animals preferring sandy or muddy substrates but may swim above the bottom.
The bowmouth guitarfish’s flat, broad, blunt, arc-shaped head spreads into two flat, distinct triangular-shaped pectoral fins. The nostrils, mouth, and gill slits are located on the ventral surface of the head, and the eyes and large spiracles are on the dorsal side. The jaws are heavily ridged with crushing teeth arranged in wave-like rows. Behind the head the body tapers into a more streamlined shape, much like that of sharks. There are sturdy ridges of heavy, sharp thorns next to the eyes, in the middle of the back, and above the pectoral fins. This guitarfish has two large, triangular dorsal fins, the second smaller than the first. The body terminates in a small but powerful caudal fin with an upper lobe that is larger than the lower. The tail of this species is much longer than the disc. Dermal denticles cover the body giving the rough skin a velvety appearance.
The color of bowmouth guitarfish changes with age. Young fish have brown bodies, pale ring-shaped spots covering their pectoral fins, and black bars between the eyes. Adults have charcoal or pale gray bodies with small white spots. The face bars fade to dark gray as they age, becoming faint and indistinct. Some adults have a bluish coloration. The creamy white underbodies in both adult and juvenile phases provides these rays with protective countershading.
The largest bowmouth guitarfish on record was 2.9 m (9.5 ft) long. However, animals above 2.44 m (8 ft) in length are rare. One captured male weighed 135 kg (297 lbs), but most of these fish weigh much less.
These guitarfish primarily feed on crustaceans and mollusks they find on the ocean floor and in the sediment. Since their eyes are located on the top of the head, bowmouth guitarfish locate their prey primarily through smell. Once an animal finds a potential meal, it restrains it with its broad, blunt head, easing the prey into its mouth with a series of short sharp thrusts. The flat, heavily ridged teeth are used to crush the shells of their prey.
Fertilization in bowmouth guitarfish is internal. Reproduction among this species is called ovovivparity, or aplacental viviparity with histotrophy. Fertilized eggs are retained in the female’s body, where they are nourished by both the egg yolk and by uterine milk. In its early developmental stage, the embryo receives its nutrition from the egg yolk. Then it breaks and sheds the thin membrane of the egg capsule and receives its nourishment from a fluid called histotroph or ‘uterine milk’ which is secreted from villi, appendages in the wall of the female’s uterus. These uterine extensions also provide the embryo with oxygen and remove its waste.
Usually four to five pups are born live. The newborn pups are about 45 cm (18 in) in length. They disperse immediately after birth to live independent lives without parental care.
Some scientists believe bowmouth guitarfish use the unusual spiked ridges over their eyes, nape, and pectoral fins to “head-butt” potential attackers, however, this theory has not been proven.
These fish have unusual spiked ridges over their eyes, nape, and pectoral fins. The ridges prevent larger would-be predators from biting vital parts of the head and body.
In protected environments, bowmouth guitarfish live for about seven years. Lifespan in the wild is unknown.
The IUCN Red List labels these animals as vulnerable. Since they reproduce slowly, they cannot recover quickly from the multiple threats facing them.
They are a targeted species in some areas and are also caught as bycatch in commercial fisheries utilizing trawl nets, gill nets, and hook and line techniques. Some turtle exclusion devices have minimally reduced their capture. Although not generally considered a good food fish, they are popular in some areas and are found in fish markets.
They are specifically hunted for their pectoral fins. In a process called finning, fishermen cut off the fins, usually while the animal is still alive. The rest of the animal is thrown back into the water, where it starves or bleeds to death. Once dried or salted, the fins reach the market, where they bring very high prices as the primary ingredient in sharkfin soups. Finning is illegal in United States waters and in many of the areas where this fish is caught, but enforcement is difficult and there is a lively black market in this lucrative practice .In small inshore fisheries in tropical countries, sun-drying of fins requires minimal technology and artisanal fishermen are encouraged by shark/ray fin-traders to target local populations. As a result, even coastal ray and shark populations in the remotest parts of the world are now vulnerable to over-exploitation, and rapid depletion of local populations often results from such trading activity.
Pollution, near shore development, silting, and global climate change are destroying the coral reefs these fish use for habitat. This species is also a victim of dynamite fishing for other species.
The bowhead guitarfish, often described as prehistoric in appearance, is considered by some scientists to be the ‘missing link’ between sharks and rays based on the ray-like placement of the mouth and gill openings, and disc shape of the front part of the body and the shark-like streamlined appearance of the rest of the body and the powerful tail.