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  • In the foreground of this image are several clutches of eggs, being watched over by the fat greenling (Hexagrammos otakii) male in the background. The purple eggs in the middle, however, belong to an all-female hybrid species (Hexagrammos octogrammus and H. otakii) that produces all-female clones, using males of H. otakii to protect its eggs. There is no genetic benefit to the male. This is an example of hemiclonal reproduction.
    hexagrammos-otakii-protecting-hybrid...tif
  • This is a pair of Pagurus brachiomastus hermit crabs. The male on the right is holding on to the female on the left. During the reproductive season, males grasp females in this manner. Other males approach to challenge, often resulting in a protracted tussle, with the victorious male claiming the female.
    pagurus-brachiomastus-hermit-crab-re...tif
  • This is a male Pagurus constans hermit crab grasping a smaller female, behavior that is typical of hermit crabs during reproductive season. This species of hermit crab is associated with Hydrissa sodalis hydroids, which cover the shells inhabited by the crustaceans and give the crustaceans their characteristic spiky appearance. Photographed in Miyagi Prefecture, Japan.
    pagurus-constans-hermit-crab-reprodu...tif
  • Pictured here is a male Pteromys volans orii flying squirrel (left) checking the reproductive status of a female (right). The female was approaching estrus. This male was doing his best to keep other males away, having to engage in combat several times a day in order to do so.
    pteromys-volans-orii-flying-squirrel...tif
  • Close-up view of 3mm eggs of a hemiclonal hybrid sub-species. The female that spawned the eggs passed on her Hexagrammos octogrammus DNA while making use of a Hexagrammos otakii male to produce viable young. All the fish hatched from these eggs will be females that continue this process, in effect perpetuating a line of all-female fish that carry the same maternal DNA through each generation.
    hexagrammos-octogrammus-otakii-hemic...tif
  • This is a pair of pharoah cuttlefish (Sepia pharaonis), female in the foreground. Having copulated with the male, the female is preparing an egg via internal fertilization, which she will then deposit under a nearby rock. The male in the background stands guard to ward off other males that might approach.
    sepia-pharaonis-cuttlefish-reproduct...tif
  • These are Zoarchias major eelpouts. The orange individual is female; the one in the hole is male. The female has approached the male, curled around him and rubbed him in a manner that divers in the area interpreted as affection or interest in the courtship context. In actuality, the female is trying to dislodge the male from the hole in order to occupy it herself. It is an antagonstic encounter, not one characterized by amorous interest. Given that these fish come up from deeper waters to congregate and socialize in this specific place at a specific time of year, the possibility that this activity is related to reproduction in the greater context is high, though how and when reproduction takes place remains unknown. Image 1 in a sequence of 3.
    zoarchias-major-female-getting-ready...tif
  • These are Zoarchias major eelpouts. The orange individual is female; the one in the hole is male. The female has approached the male, curled around him and rubbed him in a manner that divers in the area interpreted as affection or interest in the courtship context. In actuality, the female was attempting to dislodge the male from the hole in order to occupy it herself. It is an antagonstic encounter, not one characterized by amorous interest. The male retaliated by biting the female, which caused her to leap and twist in order to escape, as pictured here. Given that these fish come up from deeper waters to congregate and socialize in this specific place at a specific time of year, the possibility that this activity is related to reproduction in the greater context is high, though how and when reproduction takes place remains unknown. Image 3 in a sequence of 3.
    zoarchias-major-female-fighting-with...tif
  • These are Zoarchias major eelpouts. The orange individual is female; the one in the hole is male. The female has approached the male, curled around him and rubbed him in a manner that divers in the area interpreted as affection or interest in the courtship context. In actuality, the female is trying to dislodge the male from the hole in order to occupy it herself. It is an antagonstic encounter, not one characterized by amorous interest. Given that these fish come up from deeper waters to congregate and socialize in this specific place at a specific time of year, the possibility that this activity is related to reproduction in the greater context is high, though how and when reproduction takes place remains unknown. Image 2 in a sequence of 3.
    zoarchias-major-female-getting-ready...tif
  • Pictured here are two male Zoarchias major eelpouts engaged in a mouth-to-mouth confrontation. This behavior is perhaps linked to establishing dominance, as a precursor to reproduction. There is not much known about these fish. Reproduction has not been witnessed or documented.
    zoarchias-major-males-fighting-japan...tif
  • Pictured here are two male Zoarchias major eelpouts engaged in a mouth-to-mouth confrontation. This behavior is perhaps linked to establishing dominance, as a precursor to reproduction. There is not much known about these fish. Reproduction has not been witnessed or documented.
    zoarchias-major-males-fighting-japan...tif
  • This is a female Japanese pygmy squid (Idiosepius paradoxus) taking a break after depositing an egg on a blade of eelgrass (Zostera marina). Reproductive season takes place twice a year..Adults of this species die after reproduction, which means that there are two generations each year. Size descriptions generate indicate maximum size of up to 18mm. The females in this area were considerably larger, in the range of 30mm. Photographed at two times life-size magnification.
    idiosepius-paradoxus-female-depositi...tif
  • This is a female Japanese pygmy squid (Idiosepius paradoxus) depositing eggs on a blade of eelgrass (Zostera marina). Reproductive season takes place twice a year.. Adults of this species die after reproduction, which means that there are two generations each year. Size descriptions generally suggest maximum size of up to 18mm. The females in this area were considerably larger, in the range of 30mm. Photographed at magnification of two times life-size.
    idiosepius-paradoxus-female-depositi...tif
  • This is a pair of Pteromys volans orii flying squirrels that have emerged from the nest at dusk. The female seated above is entering estrus. The male is checking her readiness for mating.
    pteromys-volans-orii-flying-squirrel...tif
  • This is a polychaete worm in the Syllidae family, perhaps a Epigamia magna. Normally benthic residents, these segmented worms transition to sexually mature pelagic epitokes for the purpose of reproduction (as pictured here, carrying thousands of eggs). This individual was part of a swarm comprising many thousands of worms split up across multiple groups swimming in shallow water (surface to around 7m depth). I came across this aggregation in the 10 days leading up to full moon. Though I was unable to witness spawning, it seems that spawning took place after dark. Spawning did not appear to be synchronized. The swarm began to decrease in numbers after the full moon, suggesting the possibility of sequential spawning over a period of days.
    syllidae-polychaete-worm-with-eggs-j...tif
  • This is a head-on view of a polychaete worm in the Syllidae family, perhaps a Epigamia magna. Normally benthic residents, these segmented worms transition to sexually mature pelagic epitokes for the purpose of reproduction (as pictured here, carrying thousands of eggs). This individual was part of a swarm comprising many thousands of worms split up across multiple groups swimming in shallow water (surface to around 7m depth). I came across this aggregation in the 10 days leading up to full moon. Though I was unable to witness spawning, it seems that spawning took place after dark. Spawning did not appear to be synchronized. The swarm began to decrease in numbers after the full moon, suggesting the possibility of sequential spawning over a period of days.
    syllidae-polychaete-worm-with-eggs-j...tif
  • Two mature male Zoarchias major eelpouts opening their mouths as wide as possible during a protracted confrontation. From personal observation, it seems likely that the size of the mouth when wide open serves as a means of relative strength comparison. This type of behavior is exhibited during the spring and summer months, presumably associated with reproduction.
    zoarchias-major-male-eelpouts-compet...tif
  • This is a long shanny (Stichaeus grigorjewi) male guarding two clutches of eggs. This species lives in deep water, down to 300m, in the Northwest Pacific. They come up to shallow water for reproduction. Photographed in Miyagi Prefecture, Japan.
    stichaeus-grigorjewi-protecting-eggs...tif
  • Two male Zoarchias major eelpouts engaged in competitive fighting, with a female eelpout visible in the background, peeking out from a hole in the hard coral. This competitive fighting behavior is likely related to reproduction, though there does not seem to be a one for one correlation with female acceptance of winning individuals.
    zoarchias-major-male-eelpouts-compet...tif
  • This is a side view of a polychaete worm in the Syllidae family, perhaps a Epigamia magna. Normally benthic residents, these segmented worms transition to sexually mature pelagic epitokes for the purpose of reproduction (as pictured here, carrying thousands of eggs). This individual was part of a swarm comprising many thousands of worms split up across multiple groups swimming in shallow water (surface to around 7m depth). I came across this aggregation in the 10 days leading up to full moon. Though I was unable to witness spawning, it seems that spawning took place after dark. Spawning did not appear to be synchronized. The swarm began to decrease in numbers after the full moon, suggesting the possibility of sequential spawning over a period of days.
    syllidae-polychaete-worm-with-eggs-j...tif
  • A group of bigeye trevally (Caranx sexfasciatus) swimming around a grey reef shark (Carcharhinus amblyrynchos), with one of the fish rubbing its body against the shark's skin. Bigeye trevallies and other species of fish engage in this activity from time to time, perhaps to remove parasites or other irritations from their skin. For the most part, the sharks do not seem to mind, though they sometimes take off at high speed. Note also that one of the bigeye trevallies is dark. The change in coloration is associated with reproduction. Photographed at Blue Corner in Palau.
    bigeye-trevally-rubbing-against-grey...tif
  • Pictured here is a female Japanese pygmy squid (Idiosepius paradoxus) depositing eggs on a blade of eelgrass (Zostera marina). During reproductive season, females receive spermatophores from multiple males (white strands visible) and deposit eggs multiple times. Adults die at the end of the reproductive period. Eggs hatch and mature within a few months, reproducing again to repeat the cycle. Two reproductive cycles take place each year.
    idiosepius-paradoxus-female-depositi...tif
  • Known as koke-ginpo in Japanese, this chaenopsid blenny is a male Neoclinus bryope. This dark coloration with the bright blue dorsal fin spot is indicative of the winter breeding season in this area, where he and other males shake, shimmy and perform to attract the attention of females. Photographed at a magnification of two times life-size.
    neoclinus-bryope-blenny-male-reprodu...tif
  • This is a male elkhorn sculpin (Alcichthys elongatus) watching over a carpet of bright yellow eggs. This is a difficult scene to document, as males of this species select tight crevices for their reproductive dens, sites characterized by cramped, restricted access. This species reproduces via internal gametic association, meaning copulation takes place, but fertilization only occurs when females spawn the eggs and contact with seawater happens. The Japanese name is Niji-kajika. Photographed in Hokkaido, Japan.
    alcichthys-elongatus-elkhorn-sculpin...tif
  • This is a Japanese red squirrel (Sciurus vulgaris orientis) holding a branch in its mouth. In the final days of winter, this squirrel was building a nest to prepare for the reproductive season.
    sciurus-vulgaris-orientis-ezo-red-sq...tif
  • This is a male Neoclinus bryope chaenopsid blenny, active during the winter reproductive season. This species is known as koke-ginpo in Japanese.
    neoclinus-bryope-blenny-male-reprodu...tif
  • This is a Japanese red squirrel (Sciurus vulgaris orientis) dealing with a long branch it has collected. The branch was too big to carry, so the squirrel had to break it into two pieces. The squirrel was building a nest in preparation for reproductive season.
    sciurus-vulgaris-orientis-ezo-red-sq...tif
  • This is a Japanese red squirrel (Sciurus vulgaris orientis) breaking off a branch for the purpose of constructing a nest to prepare for the upcoming reproductive season.
    sciurus-vulgaris-orientis-ezo-red-sq...tif
  • This is a male Korean seashorse (Hippocampus haema) giving birth. This birth took place at the very end of the reproductive season. As such, this male carried only about 25 young. The number of juveniles that pregnant males carry declines through the season, because the number of eggs produced and passed to males by females drops over time.
    hippocampus-haema-korean-seahorse-ma...tif
  • This is a male Opistognathus iyonis jawfish hatching a mouthful of eggs. A few of the juveniles can be seen swimming away. There are also two unfertilized eggs visible. Like other jawfish, the males of this species care for and protect developing juveniles, keeping the eggs in their mouths through the gestation period. The reproductive season is during the summer months. This shy small fish is known from the waters of the northwest Pacific, including South Korea and southern Japan. It reaches a length of about six centimeters.
    opistognathus-iyonis-jawfish-hatchin...tif
  • This is a pair of tri-spine horseshoe crabs (Tachypleus tridentatus) walking across the ocean bottom in shallow water just prior to spawning. The smaller male uses modified legs (pedipalps) to grasp onto the female in front. The male stays attached in this manner throughout the reproductive season, going wherever the female goes.<br />
<br />
Although these animals are called crabs, they are not members of the Subphylum Crustacea. They belong to a separate Subphylum—Chelicerata—which also comprises sea spiders, arachnids, and several extinct lineages such as sea scorpions. The earliest known fossils of horseshoe crabs date back 450 million years ago, qualifying these animals as living fossils, as they have remained largely unchanged.<br />
<br />
Tachypleus tridentatus is the largest of the four living species of these marine arthropods, all of which are endangered.<br />
<br />
Though habitat loss and overharvesting of these animals for food are primary contributors to the population decline of horseshoe crabs, the biomedical industry is also a major factor. Horseshoe crabs are bled for their amoebocytes (akin to white blood cells), which are used to derive an extract that reacts in the presence endotoxin lipopolysaccharide, which is found in the membranes of gram-negative bacteria. Estimates suggest that between three and 30% of the animals die as a result. There have also been suggestions that taking up to a third of each animal's blood adversely affects their ability to undertake vital functions, such as procreation, even if the animals survive.<br />
<br />
Synthetic substitute tests have been available since 2003. The biomedical industry has however been reluctant to discontinue the practice of bleeding live animals.
    tachypleus-tridentatus-horseshoe-cra...tif
  • Two male Zoarchias major eelpouts intertwined in competitive battle, mouths wide open, pectoral fins flared. These fish, called ookazunagi in Japanese, engage in this behavior during the spring and summer, presumably as part of their reproductive process.
    zoarchias-major-males-competitive-fi...tif
  • This is a Japanese red squirrel (Sciurus vulgaris orientis) leaping among the branches of a fir tree while collecting material for the construction of a nest in the final days of winter. The squirrel was preparing for the upcoming reproductive season.
    sciurus-vulgaris-orientis-ezo-red-sq...tif
  • This is a Japanese red squirrel (Sciurus vulgaris orientis) constructing a nest to prepare for the upcoming reproductive season.
    sciurus-vulgaris-orientis-ezo-red-sq...tif
  • This is a large male broadclub cuttlefish hovering above a coral reef during the reproductive season. Multiple males like this were engaged in competition for females that were ready to mate and deposit eggs.
    sepia-latimanus-broadclub-cuttlefish...tif
  • This is a female Japanese pygmy squid (Idiosepius paradoxus) during the reproductive season. The white strands are spermatophores that have been passed to her by males. Here she is extending her two tentacles while searching for prey.
    idiosepius-paradoxus-female-with-spe...tif
  • This is a female East Asian common octopus (Octopus sinensis) protecting a clutch of eggs during the winter, which is not the usual time of year for this species to brood eggs. Reproductive activity is most common during the summer months. This female was eventually successful. Some eggs started to hatch after 62 days, running until 76 days. Hatching during the normal season requires only a few days.
    octopus-sinensis-east-asian-common-o...tif
  • Pictured here are three male Neoclinus bryope blennies. They are engaged in a stand-off during the reproductive season. As is apparent in this photo, the blennies are able to adjust their coloration to fit the situation and their surroundings. When these blennies emerge fully from the protection of their holes in the reef, they often become drab and bland in color as seen here, perhaps to blend-in with the background. The color of their distinctive dorsal fin spots also seems capable of shifting in hue.
    neoclinus-bryope-blennies-engaged-in...tif
  • This is a well-camouflaged male Neoclinus bryope chaenopsid blenny peeking out from the safety of his hole in the reef, on the lookout for eligible females during the winter reproductive season. This species is known as koke-ginpo in Japanese.
    neoclinus-bryope-blenny-male-reprodu...tif
  • This is a male Neoclinus bryope chaenopsid blenny active during the winter reproductive season. This species is known as koke-ginpo in Japanese.
    neoclinus-bryope-blenny-male-reprodu...tif
  • This fat greenling (Hexagrammos otakii) male is tending to several clutches of eggs, which are the result of spawning with multiple females. The bright yellow-orange coloration of the male is indicative of reproductive season. The multiple clutches and large number of healthy eggs show that this is a successful male, meaning that he has attracted many females and has done well protecting the eggs from predators.
    hexagrammos-otakii-fat-greenling-pro...tif
  • Two male Zoarchias major eelpouts engaged in competitive battle, mouths wide open. The fish on the left is ensconced in a hole in the coral, while the challenging fish on the right is fully exposed in the water column. These fish, called ookazunagi in Japanese, engage in this behavior during the spring and summer, presumably as part of their reproductive process. Despite these confrontations, it does not appear that the fish inflict harm on one another.
    zoarchias-major-males-competitive-fi...tif
  • Two female Zoarchias major eelpouts engaged in a mouth-to-mouth fight. Males of many animals engage in competitive battles as part of the reproductive process. Both males and females of this species fight, usually with the same sex, though there seem to be occasional open-mouth conflicts between males and females as well.
    zoarchias-major-females-fighting-ope...tif
  • Two female Zoarchias major eelpouts engaged in a fight. Males of many animals engage in competitive battles as part of the reproductive process. Both males and females of this species fight, usually with the same sex, though there seem to be occasional open-mouth conflicts between males and females as well.
    zoarchias-major-female-eelpouts-figh...tif
  • This is a Japanese red squirrel (Sciurus vulgaris orientis) wrangling small branches it has gathered for the purpose of constructing a nest in preparation for reproductive season.
    sciurus-vulgaris-orientis-ezo-red-sq...tif
  • This is a male fat greenling (Hexagrammos otakii) watching over several clutches of developing eggs. Normally drab and mottled, males of this species become a bright yellow-orange for the reproductive season.
    hexagrammos-otakii-fat-greenling-pro...tif
  • Two male Zoarchias major eelpouts intertwined in competitive battle, mouths wide open. These fish, called ookazunagi in Japanese, engage in this behavior during the spring and summer, presumably as part of their reproductive process. Despite these confrontations, it does not appear that the fish inflict harm on one another.
    zoarchias-major-males-competitive-fi...tif
  • Three porcupine pufferfish (Diodon holocanthus) pursuing a female. There were originally five males in pursuit when I first came across this group. The courtship process lasts for several hours, culminating when only one or two males remain. This happened in the evening, around 20:00 hours. The female swam to deep water, around 23m, then rushed for the surface at high speed with the males in pursuit. She released a cloud of eggs at 12m, and the males followed with release of sperm. The courtship process is energetic, with the males chasing and biting the female. The female hid from the males on several occasions, forcing them to find her.
    Diodon-holocanthus-porcupinefish-cou...tif
  • These variegated lizardfish (Synodus variegatus) have come together in preparation for spawning. There were dozens in the area. Spawning takes place in the evening, with a female rushing towarding the surface, males following.
    synodus-variegatus-lizardfish-japan-...tif
  • This is a female broadclub cuttlefish (Sepia latimanus) depositing eggs among branches of table coral (Acropora sp.) shortly after mating.
    sepia-latimanus-cuttlefish-depositin...tif
  • These are developing embryos of endangered Japanese horseshoe crabs (Tachypleus tridentatus), 3mm to 4mm in size. Eggs molt during the development, as can be seen here. The stage of development is perhaps four to six weeks after spawning took place.
    tachypleus-tridentatus-horseshoe-cra...tif
  • This is a juvenile endangered Japanese horseshoe crab (Tachypleus tridentatus) swimming into the water column after birth. Measuring about 7mm, this little crustacean and siblings burst forth from their nest in a frenzy of activity approximately two months after spawning by the adults.
    tachypleus-tridentatus-horseshoe-cra...tif
  • This male Laiphognathus multimaculatus Spotty Blenny is looking out from his home in the coral reef during breeding season. He is searching for females that are ready to spawn. Normally dull and drab in color, this male had donned a bright yellow, blue and orange pattern for this purpose. When a female approaches, he performs an elaborate, somewhat comical dance to entice her.
    laiphognathus-multimaculatus-spotty-...tif
  • This is a female whitespotted pygmy filefish (Rudarius ercodes) tending to a clutch of eggs that she has deposited on a rope. Development of this species is rapid, with the juveniles hatching in approximately three days.
    rudarius-ercodes-tending-eggs-whites...tif
  • This is a yellow-green wrasse (Thalassoma lutescens) male engaging in courtship display. He spawned several times while I observed, each time with a different female. He also chased away a number of other males.
    thalassoma-lutescens-banana-wrasse-m...tif
  • Close-up profile of a male Neoclinus bryope chaenopsid blenny during the winter breeding season. This species is known as koke-ginpo in Japanese. Photographed at a magnification of two times life-size.
    neoclinus-bryope-blenny-japan-202101...tif
  • Horseshoe crabs (Tachypleus tridentatus) generally move in a measured, relatively slow manner, when they move at all. When females emerge after spawning however, they occasionally do so with surprising speed and force, as seen here. The female in the foreground has lifted herself out of the gravel and mud in one rapid motion, creating this momentary effervescence from the release of small pockets of air that had been trapped in the substrate.
    tachypleus-tridentatus-horseshoe-cra...tif
  • This is a male fat greenling (Hexagrammos otakii) protecting eggs. The eggs comprise several clutches from a number of females. During the autumn to winter breeding season, mature males like this one establish territories and adopt a brilliant yellow-orange coloration. The males court passing females, which can choose to spawn with or to ignore a given male.
    hexagrammos-otakii-fat-greenling-mal...tif
  • This is a female Zoarchias major eelpout attempting to dislodge a male from a hole in the reef. Females sometimes approach males and curl up next to them, rub against their bodies. This has been misinterpreted as behavior suggesting affection, in the courtship context. Males do the same to females as well. In reality, one fish is attempting to dislodge the other from a prime piece of real estate. Sometimes the intruder succeeds, sometimes not. Image 3 of 6 in a sequence illustrating this behavior.
    zoarchias-major-female-pulling-male-...tif
  • Two male Zoarchias major eelpouts with mouths wide open facing off in the middle of Sargassum hemiphyllum algae. The fishes blend-in well with both the coloration and texture of these brown algae and other surrounding vegetation and substrate, providing some measure of protection in the form of camouflage from larger fish patrolling the reef.
    zoarchias-major-eelpouts-fighting-sa...tif
  • These are two mature male Asian sheepshead wrasses (Semicossyphus reticulatus) fighting over territory during the breeding season. During this season, the mature males take on a whitish coloration, particularly when they are approaching female wrasses and when they engage in territorial disputes with other males. The male on the left in this image is Yamato, the dominant male in this area. He is the successor to Benkei. Wrasses are protogynous hermaphrodites, meaning that all individuals start life as females, then eventually turn into males. This image is licensed on an exclusive basis to BBC through 29 October 2021.
    asian-sheepshead-wrasse-males-fighti...tif
  • Red Light District: A pair of mandarinfish (Synchiropus splendidus) mating at late dusk, photographed to appear as if illuminated against a red lantern suggestive of red light districts. Photographed in the Lembeh Strait, North Sulawesi, Indonesia.
    mating-mandarinfish-at-night-synchir...tif
  • Pictured here are freshly deposited eggs of a seven-lined prickleback (Ernogrammus zhirmunskii). This species is found in the Northwest Pacific. The eggs are around 3mm in size, excluding the signature spikes.
    ernogrammus-zhirmunskii-prickleback-...tif
  • This is a Japanese red squirrel (Sciurus vulgaris orientis) carrying a branch it has collected for the purpose of constructing a nest.
    sciurus-vulgaris-orientis-ezo-red-sq...tif
  • This is a pair of mud crabs (Scylla sp.) preparing to mate in the late summer. The male is on top, with the female upside-down beneath.
    scylla-mud-crabs-mating-japan-202208...tif
  • Pictured here are eggs of sergeant major damselfish (Abudefduf sexfasciatus). The juveniles are well-developed, with eyes clearly visible. Photographed at 4x life-size magnification.
    abudefduf-sexfasciatus-sergeant-majo...tif
  • The pair of Pteromys volans orii flying squirrels in the center of the photo comprise a male (left, facing camera) and female (right). The female is in estrus. At this point, the pair had copulated several times, but also attracted the attention of rival males, like the one above, which was poised to pounce in an attempt to dislodge the primary male.
    pteromys-volans-orii-flying-squirrel...tif
  • When female Pteromys volans orii squirrels go into estrus, there is usually a primary male with her. He fends off challengers and does his best to monopolize copulation opportunities. Females will mate with other males when the opportunity arises however. Here, the female has snuck out to copulate with another male. The primary male has just realized what is happening and has rushed out of the den to confront the interloper.
    pteromys-volans-orii-flying-squirrel...tif
  • This is a juvenile Japanese horseshoe crab (Tachypleus tridentatus) climbing up and out of the substrate where it had just hatched with dozens of siblings. When spawning takes place, eggs are deposited, fertilized and buried. Upon hatching, the young horseshoe crabs need to burrow up through 10-20cm of sand, mud and muck.
    tachypleus-tridentatus-horseshoe-cra...tif
  • Pictured here are developing embryos of endangered Japanese horseshoe crabs (Tachypleus tridentatus). These eggs are on the cusp of hatching, approximately two months after they were deposited. The embryos are mobile inside the eggs, moving their legs and turning in circles. By this stage, the eggs are about 5mm in diameter.
    tachypleus-tridentatus-horseshoe-cra...tif
  • This is a male spotty goby (Laiphognathus multimaculatus) sending babies into the world. Females of this species deposit eggs into the burrows of males, which fertilize and care for the developing young. When juveniles are mature, the males take the young fish into their mouths, dart out of their burrows and spit the babies into the water, sometimes one at a time, sometimes several at once. The action is rapid, the direction and timing of launching babies unpredictable. When the males send the babies out like this, their bodies usually lose the bright coloration of breeding season, becoming relatively drab, though not quite as dull as normal.
    laiphognathus-multimaculatus-spotty-...tif
  • These spotty blennies (Laiphognathus multimaculatus) have just finished spawning. The female has emerged from the male's burrow after depositing all of her eggs. At this juncture, the male was attempting to kick the female out by hovering, prodding and even hitting her. The sooner he could force her to depart, the sooner the male could court other females and spawn again.
    laiphognathus-multimaculatus-spotty-...tif
  • This is a male spotty goby (Laiphognathus multimaculatus) sending one of his babies into the world. Females of this species deposit eggs into the burrows of males, which fertilize and care for the developing young. When juveniles are mature, the males take the young fish into their mouths, dart out of their burrows and spit the babies into the water, sometimes one at a time, sometimes several at once. The action is rapid, the direction and timing of launching babies unpredictable. When the males send the babies out like this, their bodies usually lose the bright coloration of breeding season, becoming relatively drab, though not quite as dull as normal.
    laiphognathus-multimaculatus-spotty-...tif
  • Close-up view of a male Leiaster leachi starfish extruding sperm from one of its arms whille engaged in spawning.
    leiaster-leachi-sea-star-spawning-ja...tif
  • This is a large male Leiaster leachi starfish engaged in spawning, releasing streams of sperm into the water. Spawning is tandem with other nearby individuals, synchronized by tide time and flow. This starfish was between 40cm and 45cm in size.
    leiaster-leachi-sea-star-spawning-ja...tif
  • This is a female whitespotted pygmy filefish (Rudarius ercodes) tending to a clutch of eggs that she has deposited on a cluster of bryozoans that have grown on the branches of a dead tree lodged in the substrate. Development of this species is rapid, with the juveniles hatching in approximately three days.
    rudarius-ercodes-tending-eggs-whites...tif
  • This is a Korean sandlace (Hypoptychus dybowskii) male tending to fresh eggs which multiple females have deposited on sargassum (Sargassum horneri (Turner) C.Agardh). Each egg is a few millimeters in size. Korean sandlances grow up to 10cm in length. They produce a sticky secretion in their kidneys that they use to adhere eggs to sargassum.
    hypoptychus-dybowskii-eggs-korean-sa...tif
  • Pictured here are intermediate sea urchins (Strongylocentrotus intermedius) spawning in the evening. Found in the northwest Pacific, this species is one of several that are regularly consumed by people. The orange urchin is a female releasing eggs after detecting sperm that has been released by males.
    strongylocentrotus-intermedius-inter...tif
  • These two hairy frogfish (Antennarius striatus) are seconds away from spawning. The smaller male has positioned himself beneath the female to push her up into the water column. Her belly is swollen with eggs, and she has inflated herself to around twice her normal size in preparation for release of eggs. This may make it difficult for her to swim effectively without help. The male is positioned near where the eggs will be released. Being in this position may be critical for him to judge the precise moment when he should break away from the female and release sperm to fertilize the eggs.
    antennarius-striatus-striated-frogfi...tif
  • This is a juvenile of an endangered tri-spine horseshoe crab (Tachypleus tridentatus). It measured about 37mm, which suggests that this juvenile was at the fifth instar of development, about a year since hatching. This species takes 15 years to mature, molting 18 times during that period. The estimated lifespan for this species is 25 years.<br />
<br />
These horseshoe crabs are generally only active when the water temperature exceeds 18 degrees Celsius. As such, they are dormant for much of the year, resting in deeper water until the ocean warms again.<br />
<br />
Though habitat loss and overharvesting of these animals for food are primary contributors to the population decline of horseshoe crabs, the biomedical industry is also a major factor. Horseshoe crabs are bled for their amoebocytes (akin to white blood cells), which are used to derive an extract that reacts in the presence endotoxin lipopolysaccharide, which is found in the membranes of gram-negative bacteria. Estimates suggest that between three and 30% of the animals die as a result. There have also been suggestions that taking up to a third of each animal's blood adversely affects their ability to undertake vital functions, such as procreation, even if the animals survive.<br />
<br />
Synthetic substitute tests have been available since 2003. The biomedical industry has however been reluctant to discontinue the practice of bleeding live animals.
    tachypleus-tridentatus-juvenile-tri-...tif
  • This is a juvenile of an endangered tri-spine horseshoe crab (Tachypleus tridentatus), juxtaposed with a five Yen coin for scale. The animal’s carapace measured about 37mm, which suggests that this juvenile was at the fifth instar of development, about a year since hatching. This species takes 15 years to mature, molting 18 times during that period. The estimated lifespan for this species is 25 years.<br />
<br />
These horseshoe crabs are generally only active when the water temperature exceeds 18 degrees Celsius. As such, they are dormant for much of the year, resting in deeper water until the ocean warms again.<br />
<br />
Though habitat loss and overharvesting of these animals for food are primary contributors to the population decline of horseshoe crabs, the biomedical industry is also a major factor. Horseshoe crabs are bled for their amoebocytes (akin to white blood cells), which are used to derive an extract that reacts in the presence endotoxin lipopolysaccharide, which is found in the membranes of gram-negative bacteria. Estimates suggest that between three and 30% of the animals die as a result. There have also been suggestions that taking up to a third of each animal's blood adversely affects their ability to undertake vital functions, such as procreation, even if the animals survive.<br />
<br />
Synthetic substitute tests have been available since 2003. The biomedical industry has however been reluctant to discontinue the practice of bleeding live animals.
    tachypleus-tridentatus-juvenile-tri-...tif
  • This is a pair of Korean seahorses (Hippocampus haema) engaged in spawning. The lighter-colored female on the left is depositing eggs into the brooding pouch of the male (right, looking toward the camera). The male’s pouch is swollen and distended to make room for the eggs, which he fertilizes once they are deposited. The male broods the eggs for three to ten weeks. After hatching the juveniles, the male engages in courtship with the female and mates again throughout the spring and summer breeding season. Pair bonds are reasonably consistent, though there seems to be some mixing that takes place. Described in 2017, this species is found in the waters of Korea, as well as along the southern and western coasts of Japan.
    hippocampus-haema-korean-seahorse-sp...tif
  • This is a pair of Korean seahorses (Hippocampus haema) engaged in unusual post-mating courtship activity. Earlier in the morning, the pair had completed hours of courtship, culminating with the female (background) depositing eggs into the brooding pouch of the male (foreground). Once this takes place, the pair usually return to independent activity, most often foraging for food. In this instance, the pair stayed together. They maintained body contact, often with their prehensile tails intertwined. The male broods the eggs for three to ten weeks. After hatching the juveniles, the male engages in courtship with the female and mates again throughout the spring and summer breeding season. Pair bonds are reasonably consistent, though there seems to be some mixing that takes place. Described in 2017, this species is found in the waters of Korea, as well as along the southern and western coasts of Japan.
    hippocampus-haema-korean-seahorse-co...tif
  • A female Japanese dwarf flying squirrel (Pteromys volans orii) in oestrus often attracts the attention of more than one male. When that happens, males chase one another, leap from and glide among trees, and sometimes engage in physical skirmishes. The male in the background of this image is stalking the male in the foreground in an attempted sneak-attack during one such contest for an eligible female.
    japanese-dwarf-flying-squirrel-males...tif
  • This is a pair of spotnape cardinalfishes (Ostorhinchus notatus) engaged in spawning. The female on the right has just released a clutch of eggs, and the male is fertilizing them. Wisps of the male’s sperm are visible. both coming out of the male and around the eggs. After fertilization, the male moves behind the female to take the eggs into his mouth for brooding. He will care for the eggs until maturity. The gestation period varies with water temperature, but hatchout takes place after approximately two weeks. Females in this situation eventually leave the male, but they first exhibit an odd behavior after laying eggs. They appear to harass the male, chasing him and targeting the eggs in his mouth. While avoiding these charges by the female, the male spits out and takes the eggs back into his mouth multiple times. This occurs at blinding speed. The purpose of this post-coital behavior is not clear. It appears almost as if the female is attempting to steal the eggs from the male.
    ostorhinchus-notatus-spawning-spotna...tif
  • These are eggs of a sculpin named <br />
Bero elegans, found in the northwest Pacific. The eggs of this species have a blue tint and measure about 2mm to 3mm in size. Photographed at a magnification of two times life-size.
    bero-elegans-sculpin-eggs-japan-2019...tif
  • This is a 40cm mature male smooth lumpsucker (Aptocyclus ventricosus) watching over a brood of eggs. This species resides in deep water, down to about 1700m. During the winter to spring breeding season, mature fish come up to shallow water. After fertilizing a brood of eggs laid by a female fish, the male watches over and protects the developing young. Adult fish die during the breeding season, the female after laying eggs, the male once the juveniles have hatched. Following extended observation, I realized that the eggs in this photo were not viable. They had not been fertilized and were therefore never going to produce juveniles. The male, unaware of this fact, was destined continue to protect the infertile eggs, weakening day by day, eventually succumbing to death.
    aptocyclus-ventricosus-smooth-lumpsu...tif
  • This is a female Zoarchias major eelpout (the orange fish) wrapping her caudal fin around the head of a male eelpout occupying a hole in the reef. The female is preparing to try to displace the male from the hole. Image 1 in a sequence of 4 photographs.
    zoarchias-major-eelpout-female-displ...tif
  • This is a female Zoarchias major eelpout attempting to dislodge a male from a hole in the reef. Females sometimes approach males and curl up next to them, rub against their bodies. This has been misinterpreted as behavior suggesting affection, in the courtship context. Males do the same to females as well. In reality, one fish is attempting to dislodge the other from a prime piece of real estate. Sometimes the intruder succeeds, sometimes not. Image 5 of 6 in a sequence illustrating this behavior.
    zoarchias-major-female-pulling-male-...tif
  • This is a female Zoarchias major eelpout attempting to dislodge a male from a hole in the reef. Females sometimes approach males and curl up next to them, rub against their bodies. This has been misinterpreted as behavior suggesting affection, in the courtship context. Males do the same to females as well. In reality, one fish is attempting to dislodge the other from a prime piece of real estate. Sometimes the intruder succeeds, sometimes not. Image 4 of 6 in a sequence illustrating this behavior.
    zoarchias-major-female-pulling-male-...tif
  • Slender Sandgoby (Fusigobius gracilis) watching over a clutch of eggs hanging from the ceiling of an extremely narrow burrow. The silver reflection from the eggs are the eyes of the embryonic fish. The goby was about 4cm in length, the burrow at 15m depth.
    slender-sandgoby-fusigobius-gracilis...tif
  • This is a male hairchin goby (Sagamia geneionema) protecting a brood of eggs. Males of this species mate several times with females, which lay their eggs on the upper surfaces of confined spaces and then leave the area to the care of the male. In this case, this burrow was at 20m depth, with water ranging between 14 and 16 degrees Celsius. The males protect the eggs until they hatch, somewhere between one and two weeks depending on water temperature, and then mate again. Throughout this process, the male does not eat much. As a result, after several matings, the males become too weak to carry on, and they die. The name for this species in Japanese is sabihaze (サビハゼ).
    hairchin-goby-sagamia-guarding-eggs-...tif
  • Twinspot snapper (Lutjanus bohar) engaged in a mass spawning aggregation early in the morning. This photograph was the winner of the Under Water category of the 52nd Wildlife Photographer of the Year competition in 2016 (#WPY52) organized by the Natural History Museum in London.
    twinspot-snapper-spawning-aggregatio...tif
  • Massive aggregation comprising tens of thousands of sailfin snapper (Symphorichthys spilurus) in preparation for group spawning. These fish normally live in deep water. They gather several times a year for this spawning phenomenon. Photographed in Palau.
    sailfin-snapper-aggregation-for-grou...tif
  • This is a close-up view of the egg mass of a giant cuskeel (Spectrunculus grandis). Each egg is less than 2mm in size. Pigmentation is black. This is a bathydemersal species, living on the ocean floor at depths of 1000m to 6000m. These eggs were found floating at the ocean surface. See also photograph of entire egg mass. Photographed in Shizuoka Prefecture, Japan.
    spectrunculus-grandis-giant-cuskeel-...tif
  • This is a female Radulinopsis derjavini sculpin hatching her clutch of eggs by agitating them with her mouth. Females of this genus tend to their eggs, using their specialized mouths to suck or vacuum water across the developing juveniles to aerate them. In other sculpin genuses, males take responsibility for nurturing eggs.
    radulinopsis-derjavini-sculpin-eggs-...tif
  • This is a female Radulinopsis derjavini sculpin hatching her clutch of eggs by agitating them with her mouth. Females of this genus tend to their eggs, using their specialized mouths to suck or vacuum water across the developing juveniles to aerate them. In other sculpin genuses, males take responsibility for nurturing eggs.
    radulinopsis-derjavini-sculpin-eggs-...tif
  • This is a female Radulinopsis taranetzi sculpin carrying a bellyful of fertilized eggs. She is in the process of choosing a place to deposit the eggs, which she will then cover with sand and rubble. Females of this species use their wide mouths to suck water over the eggs in order to aerate them and care for the eggs until they mature and hatch.
    radulinopsis-taranetzi-sculpin-pregn...tif
  • This is a pair of Radulinopsis taranetzi sculpins copulating, with the male on top. Internal fertilization takes place in this species, with the female depositing her clutch of eggs after choosing a suitable location, then covering them with sand and rubble. Females of this species use their wide mouths to suck water over the eggs in order to aerate them.
    radulinopsis-taranetzi-sculpins-copu...tif
  • This is a pair of mud crabs (Scylla sp.) preparing to mate in the late summer. The male is on top, with the female upside-down beneath.
    scylla-mud-crabs-mating-japan-202208...tif
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Tony Wu Underwater Photography

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