Bigfin reef squid

Sepioteuthis lessoniana

''Sepioteuthis lessoniana'', commonly known as the bigfin reef squids or oval squids, is a commercially important species of loliginid squid. They are one of the three currently recognized species belonging to the genus ''Sepioteuthis''. Studies in 1993, however, have indicated that bigfin reef squids may comprise a cryptic species complex. The species is likely to include several very similar and closely related species.

Bigfin reef squids are characterised by a large oval fin that extends throughout the margins of its mantle, giving them a superficial similarity to cuttlefish. They are small to medium-sized squids, averaging 3.8 to 33 centimetres in length. They exhibit elaborate mating displays and usually spawn in May, but it can vary by location. The paralarvae resemble miniature adults and are remarkable for already having the capability to change body colouration upon hatching. Bigfin reef squids have the fastest recorded growth rates of any large marine invertebrate, reaching 600 g in only four months. They are a short-lived species, with a maximum recorded lifespan of 315 days.

The diet of bigfin reef squids comprises mainly crustaceans and small fish. They are found in the temperate and tropical waters of the Pacific and Indian Oceans, and have recently been introduced into the Mediterranean as a Lessepsian migrant. They are commonly found near the shoreline, near rocks, and coral reefs. They are fished in vast quantities for human food in Asia. Because of their rapid growth rate, short life span, and tolerance to handling and captivity, bigfin reef squids are regarded as one of the most promising species for mariculture. They are also a valuable source of giant axons for medical research.
Alien portrait Squid near the water surface Bigfin reef squidSepioteuthis lessoniana,Red Sea,Sepioteuthis lessoniana,Underwater,portrait

Appearance

Like other members of the genus ''Sepioteuthis'', bigfin reef squids are easy to distinguish from other squids in that they possess thick and muscular oval fins that extend around almost the entire mantle. The fins extend about 83 to 97% of the mantle length and are 67 to 70% of the mantle length in width. Because of these fins, bigfin reef squids are sometimes mistaken for cuttlefish, a fact reflected by their scientific names. A narrow blue or white line is visible at the point of attachment of the fins to the mantle. A fleshy ridge is also present where the fins meet at the back of the squid.

The mantles of bigfin reef squids are cylindrical, tapering to a blunt cone at the posterior. The mantle is usually 4 to 33 cm long in males and 3.8 to 25.6 cm long in females. Both sexes can reach a maximum mantle length of 38 cm . Adult males weigh 403.5 to 1,415 g , while adult females are 165 to 1,046 g . Both sexes can attain a maximum documented weight of 1.8 kg . The forward margin of the mantle on the ventral side is concave.

Their eyes are large and covered entirely by a transparent secondary cornea. They are greenish at the base. A pair of prominent ridges are present on the ventral surface of the head at the rear edge of the eyes. The mouth area is supported by seven triangular flaps , each with 0 to 7 suckers of less than 0.2 mm in diameter and 18 to 25 teeth. The strong, curved, and short beaks are mostly black to dark brown. The radula has seven rows of teeth.



The spermatophores of males are about 4.5 mm long and 0.15 mm wide. The ink sac is pear-shaped, with a silvery blue-green outer layer. The vane of the gladius is oval-shaped and pointed at both ends . It has a broad midrib .

The eight arms are thick, tapering to a narrow point. They are unequal in length, with arm pair I the shortest, followed by arm pair II and arm pair IV, and arm pair III the longest. All of them possess two rows of suckers. Each sucker has a diameter less than 2 mm , decreasing distally, and a ring of 17 to 28 sharp acute teeth. The left arm of pair IV in males is modified into a sexual organ known as the hectocotylus. They bear long fleshy protrusions with toothless suckers at the distal portion. The tentacles are thick and long, extending the length of the mantle when retracted. They are slightly compressed laterally. A prominent ridge is present on the outer surface of each of the tentacle clubs . There are four rows of suckers on the manus and the dactylus . The larger suckers in the centre of the manus have 17 to 18 widely spaced teeth.
Squadron This juvenile Bigfin Reef Squids - Sepioteuthis lessoniana showed up behind our Boat, attracted by the light at night.  They were feasting among the millions of planktons that showed up too. Bigfin reef squid,Geotagged,Maldives,Sepioteuthis lessoniana,Squid,Winter

Distribution

The bigfin reef squid is a neritic warm water-dwelling squid. They are usually found 0 to 100 m below the water's surface. They tend to remain close to the shoreline, near rocks and reefs. They are slightly more active during the night and will move to deeper waters or find cover in daytime. Large numbers of juveniles can often be found hiding beneath floating driftwood.

The bigfin reef squid is the most widespread species in the genus ''Sepioteuthis''. It is found in temperate and tropical regions of the Indian Ocean and the western Pacific Ocean. Their original range extends east to the Hawaiian Islands, west to the Red Sea, north to Japan, and south to Australia and New Zealand . The range has also expanded to include parts of the Mediterranean Sea. In 2002, bigfin reef squids were first documented in the Gulf of İskenderun of the southeastern Mediterranean Sea. They may have already existed in significant populations in the area as they have acquired a common name among the fishermen of the Aegean Sea – . It is a Lessepsian migrant, reaching the Mediterranean Sea through the Suez Canal.
Invaders Red sea. Night dive.
Two squid in dark water. Bigfin reef squid,Egypt,Red Sea,Sepioteuthis lessoniana,pair,portrait

Behavior

Bigfin reef squids are closely related to the Caribbean reef squid , a species noted for its complex social interactions. Like Caribbean reef squids, bigfin reef squids also exhibit elaborate mating displays.

Bigfin reef squids also exhibit both schooling and shoaling behaviours. Very young bigfin reef squids will also stay close together , but do not swim together parallel to each other . Unlike most other squid species, bigfin reef squids are rarely cannibalistic. Shoals can include animals of different sizes without the threat of larger members attacking and consuming the smaller members. Whether bigfin reef squids recognise each other individually still remains unknown.Bigfin reef squids exhibit two most common social body patterning and posturing behaviours related to mating.

The first is dubbed "accentuated gonads", in which they will sometimes increase the visibility of their gonads while reducing the rest of their body colouration. This makes their reproductive organs appear bright white through the transparent mantle. It may indicate the reproductive condition of the signalling squid.

Another common behaviour, primarily seen in males, is dubbed "spread arms", in which the squid will slightly tilt its body forward, head down and arms spread widely and raised above. The mantle is darkened. This behaviour is exhibited mostly when the squids are chasing or following another individual. It is thought to be a signal of reproductive arousal or aggression, similar to the "zebra display" behaviour of ''Sepioteuthis sepioidea'', the "intense zebra display" behaviour of ''Sepia officinalis'', and the "lateral display" of ''Loligo plei''. Females will also sometimes use this display to rebuff courting males.

There are three known courtship behaviours in bigfin reef squids, dubbed "male-upturned" mating, "male-parallel" mating, and "head-to-head" mating. Actual insertion in each position lasts for only a few seconds.

"Male-upturned" mating involves rapid back and forth swimming by the courting male beside a slower-swimming female. The male will then flip over so that he is swimming upside down and quickly lunge forward towards the female. He will quickly eject several spermatophores from his funnel into his hectocotylus and attempt to deposit them on the female's mouth funnel, then jet away from the female. "Head-to-head" mating is regarded as a variation of this tactic.

"Male-parallel" mating involves the male and female swimming side by side. The male will then raise one or two of his arm pair I upwards and swing them back and forth. He moves below the female and clasps the female's neck with his arms. In contrast to the previous behaviours, in this position the male actually inserts his hectoctylus into the mantle cavity of the female, attaching the spermatophores right at the opening of the oviduct rather than at the mouth. Possibly for this reason, it is usually more successful in fertilizing the female than other mating behaviours.

In addition to the above, males will often engage in "sneaking" behaviour. In this scenario, a smaller male will attach spermatophores to the female's mouth area while she is being courted by a larger male using the "male-upturned" behaviour. Even when successful, the male using this strategy is usually chased away by the larger male afterwards.

The spermatophores usually remain embedded near the mouth of the female. Mating usually occurs well before spawning, but may also happen on the spawning grounds themselves. In those cases, the male will stay near the female's side as she lays eggs.

Males have been observed to exhibit mating behaviours with other males. Some males have been found with numerous spermatophores embedded in their mouth funnels. Since bigfin reef squids distinguish sex by visual cues, this may be a form of deception. The smaller males might have assumed body patterning typical of females in order to trick larger males. Believing they are females, they will then waste their spermatophores on them. This behaviour has also been observed in other cephalopods.The main spawning season for bigfin reef squids usually begins in May, but they lay eggs all year round and spawning seasons can vary by location. A single female can spawn more than once in her lifetime. Females can release 20 to 1180 eggs per individual and will die soon afterwards.

The females spawn by passing eggs from their oviducts. These eggs are then coated in gelatinous substances from the nidamental glands and oviducal glands, forming an egg 'capsule'. The egg capsules of the bigfin reef squids contain two to nine eggs each. These are laid in single straight strands on rocks, corals, aquatic plants, submerged branches and other surfaces. At this point, the eggs are 3 mm in diameter and the egg capsules about 58.2 mm in length and 12.6 mm in width, on average.


The capsules incubate for about 3 weeks, depending on temperature. In warmer Indonesia, the incubation period was recorded to be only 15 to 16 days, while in Thailand it takes around 20 to 22 days. They gradually enlarge by absorbing water, reaching around 82.4 mm in length and 14.6 mm in width. Unfertilised eggs remain milky white and do not develop further. Fertilised eggs undergo cell division reaching a diameter of 16 mm with the developing embryo at 11 mm on the day before hatching. Upon hatching, the paralarvae are 6 mm in mantle length , with fully functioning fins and ink sacs. They resemble miniature adults and are already strong swimmers. They exhibit schooling behaviour two weeks after hatching.

Hatchlings are often cannibalistic. This is regarded as the main cause of death in young squids, particularly in dense populations. However, cannibalism usually happens only when eaten individuals were already weakened significantly or dead, so the actual cause of death may have been something else. Subadults are usually recognisable by their size, ranging from 20 to 60 mm in length. They reach sexual maturity at less than 210 days in the wild. Males reach sexual maturity earlier than females. In captive populations, males mature 140 days after hatching at most. Females will begin spawning at around 156 to 196 days after hatching. Both males and females mature earlier in captivity than in the wild. Water temperature may play an important role in the earlier sexual maturation of captive specimens. High temperatures may induce shorter lifespans and smaller body sizes, while cooler temperatures favour longer lifespans and larger individuals.

Bigfin reef squids have one of the fastest recorded growth rates for any large marine invertebrate. They can reach 600 g in only four months. Nonetheless, size can not often be reliably correlated with age, as variations of body size within a generation is fairly common. In captivity, bigfin reef squids have a lifespan of 161 to 315 days for both sexes.
Reef Fin Squid - Sepioteuthis lessoniana  Bali,Bigfin reef squid,Geotagged,Indonesia,Reef Fin Squid,Sepioteuthis lessoniana,Squid

Habitat

The bigfin reef squid is a neritic warm water-dwelling squid. They are usually found 0 to 100 m below the water's surface. They tend to remain close to the shoreline, near rocks and reefs. They are slightly more active during the night and will move to deeper waters or find cover in daytime. Large numbers of juveniles can often be found hiding beneath floating driftwood.

The bigfin reef squid is the most widespread species in the genus ''Sepioteuthis''. It is found in temperate and tropical regions of the Indian Ocean and the western Pacific Ocean. Their original range extends east to the Hawaiian Islands, west to the Red Sea, north to Japan, and south to Australia and New Zealand . The range has also expanded to include parts of the Mediterranean Sea. In 2002, bigfin reef squids were first documented in the Gulf of İskenderun of the southeastern Mediterranean Sea. They may have already existed in significant populations in the area as they have acquired a common name among the fishermen of the Aegean Sea – . It is a Lessepsian migrant, reaching the Mediterranean Sea through the Suez Canal.
Sea jewels Red sea. Night dive.
Reef squid. Bigfin reef squid,Night,Red Sea,Sepioteuthis lessoniana,squid

Reproduction

The main spawning season for bigfin reef squids usually begins in May, but they lay eggs all year round and spawning seasons can vary by location. A single female can spawn more than once in her lifetime. Females can release 20 to 1180 eggs per individual and will die soon afterwards.

The females spawn by passing eggs from their oviducts. These eggs are then coated in gelatinous substances from the nidamental glands and oviducal glands, forming an egg 'capsule'. The egg capsules of the bigfin reef squids contain two to nine eggs each. These are laid in single straight strands on rocks, corals, aquatic plants, submerged branches and other surfaces. At this point, the eggs are 3 mm in diameter and the egg capsules about 58.2 mm in length and 12.6 mm in width, on average.


The capsules incubate for about 3 weeks, depending on temperature. In warmer Indonesia, the incubation period was recorded to be only 15 to 16 days, while in Thailand it takes around 20 to 22 days. They gradually enlarge by absorbing water, reaching around 82.4 mm in length and 14.6 mm in width. Unfertilised eggs remain milky white and do not develop further. Fertilised eggs undergo cell division reaching a diameter of 16 mm with the developing embryo at 11 mm on the day before hatching. Upon hatching, the paralarvae are 6 mm in mantle length , with fully functioning fins and ink sacs. They resemble miniature adults and are already strong swimmers. They exhibit schooling behaviour two weeks after hatching.

Hatchlings are often cannibalistic. This is regarded as the main cause of death in young squids, particularly in dense populations. However, cannibalism usually happens only when eaten individuals were already weakened significantly or dead, so the actual cause of death may have been something else. Subadults are usually recognisable by their size, ranging from 20 to 60 mm in length. They reach sexual maturity at less than 210 days in the wild. Males reach sexual maturity earlier than females. In captive populations, males mature 140 days after hatching at most. Females will begin spawning at around 156 to 196 days after hatching. Both males and females mature earlier in captivity than in the wild. Water temperature may play an important role in the earlier sexual maturation of captive specimens. High temperatures may induce shorter lifespans and smaller body sizes, while cooler temperatures favour longer lifespans and larger individuals.

Bigfin reef squids have one of the fastest recorded growth rates for any large marine invertebrate. They can reach 600 g in only four months. Nonetheless, size can not often be reliably correlated with age, as variations of body size within a generation is fairly common. In captivity, bigfin reef squids have a lifespan of 161 to 315 days for both sexes.
Shared swimming reef squid Bigfin reef squid,Sepioteuthis lessoniana,back,night,reef,squid

Food

The bigfin reef squid eats a variety of different marine organisms. Its main prey are usually prawns and other crustaceans, and fish. Captive specimens were observed to consume one fish every 2 to 25 hours.

Bigfin reef squids are, in turn, preyed upon by tuna, marlin, swordfish, and other predator fish and groundfish.
Reef squid Night dive at Dahab. Egypt. Bigfin reef squid,Sepioteuthis lessoniana,macro,portrait,red sea,squid

Predators

The bigfin reef squid eats a variety of different marine organisms. Its main prey are usually prawns and other crustaceans, and fish. Captive specimens were observed to consume one fish every 2 to 25 hours.

Bigfin reef squids are, in turn, preyed upon by tuna, marlin, swordfish, and other predator fish and groundfish.
Bigfin Reef Squid Eggs - Sepioteuthis lessoniana Kareko Batu, Lembeh.
Nice info on the species in this link:
https://seaunseen.com/bigfin-reef-squid/ Bigfin reef squid,Geotagged,Indonesia,Sepioteuthis lessoniana,Spring

Uses

The bigfin reef squid is the first squid species to have been cultured for more than one generation. It is remarkable for its ability to readily adapt to being confined in tanks, and is one of the few squid species of which the entire life span has been observed under laboratory conditions.

Bigfin reef squids are also valuable sources for squid giant axons used in research in neuroscience and physiology. Unlike axons of other animals, squid axons are very large. Those of bigfin reef squids can range in diameter from 350 to 560 μm . In life, these giant axons are used by the squids to coordinate escape jetting behaviour, enabling the squid to contract its muscles in a split second directly from the brain.

References:

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Status: Unknown
EX EW CR EN VU NT LC
Taxonomy
KingdomAnimalia
DivisionMollusca
ClassCephalopoda
OrderTeuthida
FamilyLoliginidae
GenusSepioteuthis
Species