Bigfin Reef Squid

Also known as the glitter squid or oval squid, the bigfin reef squid belongs to the loliginid squid family Loliginidae. They get their name from the large oval fin connected to the mantle. Although they rank as a medium-sized species and only measure around 1.5 to 13 inches long, they grow faster than almost any other large marine invertebrate. They engage in elaborate mating displays and live relatively short lives, with a maximum age of just 315 days. 

5 Bigfin Reef Squid Facts

• You can often find bigfin reef squids near shorelines, coral reefs, and rocky outcrops. 
• Due to their fast growth rate, bigfin squids are fished in vast quantities as food in Asia. 
• Like other cephalopods, bigfin reef squids can rapidly change color by controlling their chromatophores.
• Bigfin squids exhibit shoaling behavior, often swimming close together and rarely cannibalizing each other. 
• Bigfin squids react strongly to the presence of light and often involuntarily stop all movement in the presence of strong light sources. 

Bigfin Reef Squid Scientific name

The bigfin reef squid goes by many other names, including the oval squid, glitter squid, and green-eyed squid. In Australia, people sometimes refer to it as the northern calamari. Its genus name, Sepioteuthis, derives from the Greek words sepia, meaning “cuttlefish,” and teuthis, or “squid.” This name references the similarities in appearance between the bigfin reef squid and another cephalopod, the cuttlefish. 

Bigfin Reef Squid Appearance 

Like other members of their genus, bigfin reef squid feature characteristic oval fins through the mantle that distinguish them from other squids. These fins extend anywhere from 83% to 97% of the mantle length and up to 70% of the mantle width. Due to these fins, people often mistake them for cuttlefish. The mantle appears cylindrical and tapers to a cone at the end. At its longest, the mantle can measure up to 15 centimeters, with males typically measuring larger than females. Males typically weigh between 0.9 and 3.1 pounds, while females weigh from 0.3 to 2.3 pounds. 

Bigfin reef squid possess large eyes and strong, curved beaks. They have 2 tentacles as well as 8 arms of varying lengths. The arms measure thickest near the body and taper to a narrow point. Each arm possesses two rows of suckers, with each sucker measuring less than 2 millimeters wide and sporting a ring of sharp teeth. 

Living bigfin reef squid range in color, including translucent white, pale yellow, and brownish pink. Chromatophores cover the top of the head, mantle, and arms, but not the underside of the fins. These chromatophores allow bigfin reef squid to rapidly change body color and patterns in a process called metachrosis. Additionally, they possess iridophores in the head, which produce iridescent red and green lights when exposed to light. 

Bigfin Reef Squid Behavior

Depending on their age, bigfin reef squid exhibit both shoaling and schooling behavior. Juvenile squid often swim together in groups, although not parallel to each other like some schooling fish. Also, unlike some other squid, adult bigfin reef squid rarely cannibalize one another. This allows squid of different sizes to swim together without the threat of larger members attacking and eating the smaller ones. 

In the presence of light, bigfin squid display intense phototactic responses. They will move close to the light and then stop all other movement. This behavior does not vary based on the color of the light, but stronger lights appear to generate a more powerful response. 

Bigfin Reef Squid Habitat

You will most likely encounter bigfin reef squid in warm, shallow water. They commonly inhabit depths up to 328 feet below sea level. Their preferred habitats include regions near shorelines, rocky outcroppings, and coral reefs, hence their name. The juveniles often congregate under driftwood or other obstructions to avoid predators, particularly during the daytime. 

Bigfin Reef Squid Diet

Bigfin reef squid are carnivorous predators that eat various marine life. They often hunt at night and retreat to deeper waters to hide during the day. Their diet consists primarily of prawns, crustaceans, and fish. They use their tentacles to grab and their 8 arms to hold onto their prey while they eat. Their strong, curved beaks are immensely powerful and perfectly suited for tearing flesh or breaking shells. While they can eat once every few hours, they can also go up to 24 hours between meals. 

Bigfin Reef Squid Predators and threats

Several species prey on bigfin squid, including marlin, tuna, swordfish, sharks, whales, and groundfish. They are most vulnerable during their larval stage when their small size makes them especially susceptible to predators. Bigfin reef squid rely on their camouflage skills and ink sacs to avoid and escape from predators, respectively. They also have rather acute hearing compared to most cephalopods, which allows them to detect nearby predators. Although adult bigfin reef squid rarely cannibalize one another, cannibalism frequently occurs among juveniles. In addition to predators, bigfin reef squid also serve as hosts for several marine parasites such as Doricicola similis, Dicyema koshidae, and Dicyema orientale. 

Bigfin Reef Squid Reproduction and Life Cycle

Although bigfin reef squid often spawn in May, they can mate and lay eggs year-round. They typically engage in two different posturing behaviors. The first is called “accentuated gonads,” in which the squid draws attention to its sexual organs by making its mantle translucent while the gonads appear bright white. The second method is often used by males and is called spread arms. This tactic involves the squid tilting its body forward and spreading its arms widely, and most often occurs when a male pursues a prospective female mate. 

When mating, bigfin reef squid employ several approaches, most of which last for only a few seconds. Sometimes, a male may swim rapidly back and forth beside a female before quickly depositing his spermatophores inside the female’s mouth funnel. Smaller males may also sneak up on females while they court a larger male in the hopes of successfully mating while the females are distracted. Other times, males and females may swim together side by side until the male directly deposits his spermatophore into the female’s mantle cavity at the opening of the oviduct. 

Female bigfin reef squid can lay anywhere from 20 to 1,180 eggs throughout their lives. They can lay eggs year-round and die shortly after spawning. The eggs are often attached to rocks, corals, plants, or other underwater surfaces. After incubating for around 3 weeks, the larval squid emerge. They develop rapidly and can exhibit complex color-shifting behavior shortly after birth that doesn’t develop until much later in most other squid species. Males reach sexual maturity at around 140 days, while females sexually mature between 156 and 196 days old. The oldest bigfin reef squid ever recorded lived a total of 315 days, which represents a relatively short lifespan compared to other squid. 

Bigfin Reef Squid Population

Due to their rapid growth rate and abundance, bigfin reef squid are among the most commercially popular squid species. Every year, fishers harvest millions of bigfin squid from the ocean through trawling, seine fishing, and net traps. While most abundant during full moons and in foggy weather, their populations remain stable year-round. This likely has to do with the fact that they do not breed seasonally, so populations are constantly replaced. Despite their increasing importance as a food source, their worldwide population remains stable. As a result, bigfin reef squid have become the subject of much debate concerning their viability for mariculture. 

Bigfin Reef Squid Locations

The bigfin reef squid is the most populous species in the genus Sepioteuthis. You can find them throughout the temperate and tropical waters of the Indian Ocean and the western Pacific Ocean. Their native range extends from the Hawaiian Islands to the Red Sea and from Japan to Australia and New Zealand. In recent years, their range has expanded to include parts of the Mediterranean Sea and the Aegean Sea. 

Bigfin Reef Squid Conservation Status

Given their fast growth rate, fecundity, and widespread distribution, bigfin reef squid are extremely prolific. Their abundance makes them extremely important to commercial fishing operations, and they are a popular food source for many cultures worldwide. Even though fishers collect millions of bigfin reef squid each year, their population shows no signs of decline. Still, the IUCN lists the bigfin reef squid as a Data Deficient species, as not enough information exists at this time to determine its conservation status.