Sepioteuthis lessoniana

Geographic Range

This species, known as either the bigfin reef or oval squid, is generally found in Indo-West Pacific waters, including the tropical waters of the Indian Ocean around the Red Sea and the seas between northern Australia, New Zealand and Asia, which connect the Indian and Pacific Oceans. Oval squid also occur as far north as the Mediterranean Sea and in eastern portions of the Pacific Ocean near the Hawaiian Islands.

• Biogeographic Regions
• australian australian
  • native native
• indian ocean
• pacific ocean pacific ocean
  • native native
• mediterranean sea
  • native native

Habitat

Bigfin reef squid live in warm (typically 16°C to 34°C) coastal waters. At night, when they are most active, they are commonly found in shallow areas (0 to 100 m) around reefs, sea grass beds, sandy bottoms, or rocky shorelines. At the shore, where there are greater fluctuations in salinity, bigfin reef squid are found in waters varying from 28 ppt to 36 ppt. They surface at night, when they are less likely to be detected by predators. During the day, they generally move to deeper waters or near any form of cover, such as floating driftwood, reefs, rocks, or grasses.

• Habitat Regions
• tropical tropical
• saltwater or marine saltwater or marine

• Aquatic Biomes
• reef reef
• coastal coastal

Physical Description

Bigfin reef squid possess a characteristic cephalopod body plan that is fusiform in shape, with a large mantle, attached head, and multiple arms. The genus name Sepioteuthis describes its cuttlefish ( Sepia officinalis )-like appearance. Its main body mass is contained in the mantle (sometimes referred to as the "hood"), where the organs for reproduction, respiration, digestion, circulation, excretion, and propulsion are found. The mantle is a highly muscular organ which surrounds the entire body of the squid. The muscles of the mantle are made of two different types (circular and radial) of fibers that have different orientations. The majority of the mantle is made up of the circular muscle fibers. The remnant of an ancestral shell is also found within the mantle, and is known as the internal gladis (commonly called the "pen"). The distinguishing "big fins" referred to in the common name are located on the superior portion of the mantle. The fins extend along over 90% of the length of the mantle and give the squid a characteristic oval appearance. The maximum reported mantle length in males is 422 mm and 382 mm in females. The mantle length is regularly 200-300 mm. When fully grown, this small squid can weigh anywhere from 1 pound to 5 pounds.

The head contains the brain, eyes, and buccal mass (the beak/mouth and salivary glands) and is located below the mantle. Squid species have complex eyes that are capable of focusing and forming clear images. The pupils are adjustable, based on the amount of light entering the eye. Eight arms (not generally of identical length) and two tentacles are attached to the bottom portion of the head. The tentacles are primarily used for the capture of prey. Each of the arms is lined with toothed suction cups for manipulating prey, and the two tentacles possess toothed suction cups at their distal end.

Between the head and the mantle is the hyponome, which is a funnel that water is forced through as a means of propulsion. The giant axon controls part of the water jet propulsion system in squid. Action potentials in the giant axon cause contraction of mantle muscle fibers, forcing water though the hyponome. The squid can adjust the position of the hyponome to change the direction of propulsion.

Oxygen and carbon dioxide are exchanged at the gills, which are located within the mantle. Bigfin reef squid (and other squid species) have a closed circulatory system with three hearts, two of which are brachial hearts found at the base of their gills. These are used to pump oxygen deficient blood through the gills, where carbon dioxide in the blood is exchanged for oxygen and pumped out of the body through the siphon. The third heart pumps oxygenated blood throughout the rest of the body. Hemocyanin, rather than hemoglobin, is the oxygen carrying protein in this species' blood. Hemocyanin is copper based, making the blood appear blue.

Like all cephalopods, bigfin reef squid have a complex digestive system, consisting of a stomach, a caecum, and a liver. Following digestion and absorption of nutrients by these structures, solid waste is passed out of the rectum. Both the mantle and the digestive gland tissues are used in energy storage.

Energy expenditure shifts towards the reproductive system gains priority as squid mature. Female bigfin reef squid have a large ovary (which can be seen through the transparent mantle tissue) and a nidamental gland for the production of egg cases and nutrients. Males have a large testis and a spermatophore gland and sac. Males also have modified arms, with the presence of hectocotyli to store spermatophores. This is one of the key characteristics used in determining the sex of individuals.

Bigfin reef squid can control their pigmented skin cells, called chromatophores, to rapidly change their body color and pattern. This species also has an ink sac, which can release a dark cloud of ink to disorient predators.

• Other Physical Features
• endothermic endothermic
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger
• sexes colored or patterned differently
• ornamentation ornamentation

Development

Egg capsules incubate for about 3 weeks, depending on temperature. The incubation period can last anywhere between 15 to 22 days. Upon hatching, the paralarvae are planktonic and are about 4.5 to 6.5 mm in mantle length (excluding tentacles), with fully functioning fins and ink sacs. They resemble miniature adults and are already strong swimmers.

• Development - Life Cycle
• indeterminate growth indeterminate growth

Reproduction

When bigfin reef squid enter their reproductive stage, they tend to exhibit the same shoaling behavior exhibited when they first hatched. The group breeds in shoals during the day and separates at night to feed. During mating, male and female bigfin reef squid form close pairs that can last up to several days. Mating can occur in two different ways: "head-to-head” or “male-parallel” mating. In “head-to-head” mating, the male swims upside down and lunges forward towards the female, having already ejected several spermatophores from his funnel onto his hectocotyli, which he attempts to deposit into the female’s mouth funnel. The female will then transfer the spermatophores to her oviduct for fertilization. “Male-parallel” mating involves the male and female swimming side by side. The male then moves below the female, clasps her neck with his arms, and inserts his hectocotylus into the mantle cavity of the female, attaching the spermatophores at the opening of the oviduct.

Elaborate breeding behaviors are known in this species, which largely involve the display of complex body patterns during courtship. One of the body patterns displayed is referred to as the “accentuated gonads” pattern, which occurs when squid reduce their body coloration and enhance the colors of their reproductive organs. This is likely an initial sign of reproductive maturity and receptiveness to other individuals. There are also sex-specific chromatophore displays used by males and females for breeding. Male oval squid use a “Stripe” pattern and a “Flicker” display, while females show a display known as the sexual “Saddle”. The “Stripe” display, similar to the “Zebra” display discussed below, indicates a willingness to mate to females. The male swims parallel to the female displaying this pattern to get her attention. Females respond to the “Stripe” pattern with the sexual “Saddle” pattern, which indicates that the female is mature and ready to breed. It is known as the “Saddle” because the female lightens her entire body except for a central band where the male grasps the female for mating. The male then indicates his intent to pass spermatophores to the female with a “Flicker” chromatophore display.

Prior to mating, male bigfin reef squid can become aggressive and they will battle other males using certain body patterns and postures to determine who will breed with the mature females. Males display color pattern variations to deter or compete against other intruding males. The “Zebra” display is characterized by the presence of irregular dark stripes on the squid’s skin and is agnostic towards other male, warding them off from breeding with paired females. Unpaired males will also sometimes mimic color displays of paired females, to get a paired male to waste spermatophores, leaving the unpaired male open to mate with the paired female. Males guard their mate while she lays her eggs, exhibiting additional agonistic display behaviors to ward off other males. These displays involve both body positioning, such as spreading their arms to look larger, and chromatophore displays. The male usually leaves once the female has spawned.

• Mating System
• polygynous polygynous

Bigfin reef squid can lay eggs year round and the onset of the major spawning season can vary by location. In warmer waters, such as around India, spawning can occur as early as January while in cooler waters near Japan, spawning can begin as late as September. Females can release 20 to 1180 eggs per individual, in egg capsules that contain up to 13 eggs each. These capsules are laid in single straight strands on rocks, corals, plants, submerged branches, and other surfaces along shore lines. Once the female lays her eggs, her body usually deteriorates and she usually dies before she can mate again, but a male can usually mate with several more females before he dies. Sexual maturity in the wild is reached, on average, 171 days after hatching, but this can vary from 161 to 315 days. In captive populations, males reached sexual maturity at approximately 140 days after hatching, while females began spawning when they were 156 to 196 days old. Both males and females mature earlier in captivity than in the wild. Growth to sexual maturity is distinguishable by size and close examination only, as juveniles closely resemble adults.

• Key Reproductive Features
• semelparous semelparous
• seasonal breeding seasonal breeding
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• oviparous oviparous
• sperm-storing sperm-storing

Paired males generally remain with the females for protection while the eggs are being laid, but mating partnerships are only temporary. Females coat the eggs in a gelatinous substance, forming an egg capsule that offers protection and nourishment while the egg develops. The eggs are layed in areas where the hatchlings will have cover to hide, in to attempt to avoid predation, but there is still a high risk of mortality. There is no parental care, imprinting, or protection from predators or the environment post-hatching.

• Parental Investment
• no parental involvement
• precocial precocial
• pre-fertilization
  • protecting
    • male
• pre-hatching/birth
  • provisioning
    • female

Lifespan/Longevity

Bigfin reef squid generally complete their entire life cycle within 4 to 6 months of birth. Water temperature may affect rates of growth and sexual maturation in squid. In hot, equatorial waters, they have a shorter lifespan and reach smaller body sizes than individuals that live in “cooler” subtropical waters.

Behavior

Bigfin reef squid move from deep water during the day to shallow water at night, which correlates with the movement of their food supply of plankton and fish. This species engages in both solitary and shoaling behaviors at various times during its development and life cycle. From hatching, vulnerable young squid tend to aggregate towards the sea floor in shoals, engaging other individuals primarily through visual communication. Once mature, bigfin reef squid tend to be solitary. However, during the reproductive season, mature squid once again form shoals and participate in a number of social interactions, including displays of dominance, courting, territorial behavior, and signaling the presence of predators. They sometimes engage in cannibalism (more commonly in the early stages of life), potentially serving as a means of signifying an informal hierarchy when simple size advantages and aggressive displays are insufficient, or when there is inadequate prey and/or the squid being cannibalized is already weak or dying. They have identifiable hunting behaviors when actively seeking prey (suck as stalking, luring, etc.) and elusive behaviors for escaping predation.

• Key Behaviors
• natatorial natatorial
• nocturnal nocturnal
• motile motile
• sedentary sedentary
• solitary solitary
• social social

Home Range

Bigfin reef squid are not known to occupy a specific home range or defend territories, beyond males defending the space occupied by their mate.

Communication and Perception

Bigfin reef squid are typically solitary, limiting the amount of communication that occurs between individuals. However, when in close proximity to others, as in feeding groups or breeding shoals, this species does display distinct communication behaviors. It uses rapid, vivid changes in its body color pattern (via chromatophores) to convey information about potential threats, food sources, or dominance. Physical intimidation, such as chasing or biting of other individuals, as well as additional visual displays of dominance, such as genital presentation and limb-spreading, have also been observed in shoals and in mating groups. They do not possess any specialized organs for sound detection or production (although vibrations are perceived), instead relying upon their highly developed sense of sight for communication and perception of their environment. In addition, bigfin reef squid possess sensitive chemoreceptors near their mouth and on the suckers (more developed in octopi and cuttlefish), which helps to distinguish between prey and non-prey items.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Other Communication Modes
• photic/bioluminescent photic/bioluminescent
• vibrations vibrations

• Perception Channels
• visual visual
• polarized light polarized light
• tactile tactile
• vibrations vibrations
• chemical chemical

Food Habits

Bigfin reef squid are strictly carnivorous. They primarily feed on other mollusks and fish, but also consume non-insect arthropods, zooplankton, and other marine invertebrates, depending upon life cycle stage and prey availability. This species has also been known to cannibalize smaller conspecifics. Squid use their specialized tentacles to capture live prey. The tentacles are then used to guide the prey to the specialized buccal region and the sharp, muscular beak, which is specialized for the tearing and crushing of prey.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • molluscivore molluscivore

• Animal Foods
• fish
• mollusks
• aquatic crustaceans
• other marine invertebrates
• zooplankton zooplankton

Predation

Some common predators of bigfin reef squid are large fish, such as blue-fin ( Thunnus thynnus ) and skipjack ( Katsuwonus pelamis ) tuna, Atlantic blue marlin ( Makaira nigricans ), and sharks, as well as birds, whales, and humans. They are most vulnerable to predation during larval stages. Squid hatchlings are often cannibalistic, which is one of the main sources of predation on young squid. However, the rate of cannibalism is lower in this species than in other squid species.

Newly hatched young will swim in shoals and can interact with one another to increase chances of survival, by warning each other of predators and helping one another find food sources. During all life stages, bigfin reef squid rely on camouflage, changing their coloration based on their surroundings using their chromatophores. They may also use differently polarized skin patterns as a means of communication between individuals, which would allow them to communicate with each other while remaining camouflaged from predators that are unable to perceive polarized light. The ink produced by threatened squid can cause predators to lose their sight and sense of smell, due to the color and alkalinity of the ink.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Bigfin reef squid are predators of a number of species, primarily pisfishes and mollusks, but also eat zooplankton and other marine invertebrates. This species also serves as prey to a number of common predatory species. They can consume up to 50% of their body mass during their growth period and they have fast metabolic and growth rates, so they assist in the transfer of energy through trophic levels of the food web in marine ecosystems.

Economic Importance for Humans: Positive

This species is among the most commercially important squid species. Since it is not a seasonal species, it can be fished throughout the year. It is used not only for food, but also as bait for many other species. Since bigfin reef squid have a rapid growth rate, short life span, low rates of disease, low rates of cannibalism, and tolerance to handling and captivity, they are commonly observed and raised in labs. This not only assists in learning about the lifecycle and reproduction of the squid, but also aids in determining the effects of temperature, salinity, and different food sources on the squid. Another positive aspect of raising bigfin reef squid in labs is that they offer a constant supply of giant squid axons, which are used in neuroscience and physiology research.

• Positive Impacts
• food food
• research and education

Economic Importance for Humans: Negative

Squid species in general do not threaten humans in any measurable way. They do not actively prey upon humans and are rarely provoked to attack. There are no known adverse economic effects of bigfin reef squid.

• Negative Impacts
• injures humans
  • bites or stings

Conservation Status

Bigfin reef squid are not found on any threatened or endangered species list. Their robust population and wide distribution makes it unlikely that it will become a threatened species in the near future.

Additional Links

Encyclopedia of Life

Contributors

Kimberly Filcek (author), Radford University, Stacey Kennedy (author), Radford University, Christine Small (editor), Radford University, Jeremy Wright (editor), University of Michigan-Ann Arbor.

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