Fish of the Day
Happy Monday, everybody! Today's fish of the day is the colossal squid!
The colossal squid, also known by scientific name Mesonychoteuthis hamiltoni. This squid is known for being the largest invertebrate, and largest squid in the world! This squid is incredibly unique, being the only known animal in the genus Mesonychoteuthis, which is within the family of glass squids, Cranchiidae. Some of you may have seen in the recent news that humans have, for the first time since discovering the species, recorded a colossal squid in its natural habitat. This is a huge advancement, as previous to this all recorded film and video of these animals consisted of sick, injured, or otherwise dying adults! Previously, capturing this species in video and as a sample has only happened a handful of times throughout history, since our discovery of the colossal squid in 1925. This is believed to be due to the location of this squid. The colossal squid can be found in and around the Southern Ocean, ranging from the area around Antarctica to the southern tips of Africa, New Zealand, and South America. Most often found in the Weddell sea, close to the trenches surrounding the Antarctic west. Another reason for the rarity of this animal is due to their often exceptional depth. We know due to sperm whale predation activity that adult colossal squid can be found as high up as 2,200 meters below the surface. But, it is believed that their range may go well below that. Colossal squids hatch in shallow waters, with surviving individuals slowly migrating into deeper and deeper waters as their lives progress. Juveniles, the most often predated on, can be found within the top 1000 meters below sea level.
There is often a comparison made between the colossal squid and the giant squid Architeuthis dux, due to the large size of each cephalopod. Giant squid happen to be the longest cephalopod, coming in at just over 14 meters long in a recorded specimen, and with talk of specimens over 20m existing. This is compared to the colossal squid, which is considered the largest due to the far heavier weight than that of the giant squid. The colossal squid has a body that can weigh around 495kg (1,100lbs), with a body length from 10-14 meters. The mantle alone stretches from 2-4 meters, and below that are 8 arms and two feeding tentacles. These tentacles are known for a unique feature found only in the Cranchiidae family, a series of 25 rotatable hooks, which are used to catch and hold prey. These squids are also well known for having the largest eyes of any animal, 30-40cm in diameter or 12-16in. These eyes partially work in the depth due to a series of photophores, or light producing organs found around the arms of the squid, and in the eyes themselves.
This eye is used not only by the squid to catch prey, but also to hide from predators. As indicated by the hooks of the colossal squid, they expend no energy on chasing down prey. Instead these giants of the deep will progressively move downward as they grow and age, always moving to where they can no longer be seen by prey animals, lying still and in wait for prey to come close enough before they lunge. These eyes serve a purpose as having the ability to see where potential prey is above or in front of them, regardless of the oppressive darkness around them. These, of course, also double as a tool to avoid predation, as these eyes can see movement well beyond 120 meters, longer than the sonar range of a sperm whale. This of course is to make up for the fact that despite their ability to hear noises, they can only perceive noises below 500 hz. Well below the high pitched noises of sonar. Many large whales hunt for colossal squid, primarily the sperm whale, but others such as pilot whales, and cuvier's beaked whale are also known for sporting the scars of colossal squid battle. These colossal squid are mostly associated with the sperm whale as the sperm whale is the main predator, going so far as to make up 77% of the diet of Antarctic sperm whale pods.
Most of their prey is patagonian toothfish, lanternfish, deep-sea smelt, and other squid; which are torn apart by the large chitin beak. This rips prey into fine ribbons as the brain of the squid surrounds the esophagus in a donut shape, so all food must be tiny. Influenced by their hunting behavior, these squid do not actively chase after prey, despite their impressive ability to swim upwards of 20mph. Once again influenced by their hunting prowess, these squid expend no energy on hunting, and in almost all cases of found specimens have an entirely empty stomach, leading to the idea they may be able to survive long periods of time without food. Some estimates even state they can live off of 5kg of food supporting 500kg of squid for up to 200 days, although this may be influenced by all current caught specimens being near death, or already dead.
The swimming pattern of the colossal squid is a hotly debated topic, as the position of their front facing eyes would mean holding their arms out in front of them would block the view. This is why there is ongoing discussion as to if they likely swim in a "cockatoo" or "reverse cockatoo" position. The cockatoo position is one where the arms are held above the head, making the feeding tentecles on the bottom longer, and easier to catch prey, this can be supported by the position of the hooks. This would substantially cover the eyes however. The reverse cockatoo on the other hand positions the arms flat and below the mantle, which is supported only by the location of the eyes. However, we won’t know for sure until there is video of an adult squid.
Information on the lifecycle of colossal squid is minimal, but we do know some key details. Like all squids, the colossal produces a mass of eggs. After these eggs are laid in the uppermost waters of the Southern Ocean, they go through an unknown length juvenile stage, where they are primarily translucent. A long thought theory, proven true for the first time by the first ever wild specimen captured on video. As time goes on, these squid will progressively move into deeper and deeper waters, as they become a striking red color, their eyes grow larger, and bioluminescence develops. This depth serves several roles to the squid, as it allows them protection from predators, and an ability to hide in the shadows, waiting to lunge at prey. Young, most still entirely translucent, can be found at depths of 0-500 meters, adolescents ranging from 500-2000, and full grown adults stretching from anywhere below 2000 meters. There is no current known maximum depth the colossal squid ranges. The lifespan of the colossal squid is currently unknown, but sexual maturity is estimated to occur anywhere from 1-3 years of age. In warm summer months of the Antarctic when surface waters can get as high as a whooping 0 to 0.9 degrees Celsius the colossal squid of age will come together to breed. Nothing is known about how colossal squid find one another, or where they meet. However, we do know that unlike most other cephalopods the colossal squid males contain penises, which they use to implant sperm directly into female squids. As opposed to the regular squid method of broadcasting sperm into the water over or around eggs. The female squid will then make a last journey to the surface, and it's thought possibly to the same location she was born in. This is where she will lay her thousands of eggs, in these warm shallow waters, before passing away. Like all cephalopods, after breeding the colossal squid dies too. This is the time period all living colossal squid have been caught by humans.
The human history of cataloguing and seeing the colossal squid starts 100 years ago in 1925. Found partially digested in the belly of a sperm whale the tentacles were found with their distinctive hook structures, discovered by E. Hamilton. After this the next specimen was found in 1981 as a juvenile female only 4 meters long found along the surface of the Ross sea in the Antarctic. In 2003 a second specimen was collected, a subadult female found along the surface only 8meters long. The first recording of a colossal squid was taken in 2005, a rather unclear video of a squid taking a tooth fish off the line of a deep sea fisher at a depth of 1,625meters below surface. After that is perhaps the most notable capture of an adult female who had recently spawned, found weak and sickly beside a deep sea fishing boat in 2007. She was 10meters long and collected by the fishers and taken to the nearby New Zealand. This is where the preserved sample remains in their national museum. This preserved sample is how we know that larger colossal squids exist, as far larger beaks have been found in the stomach of sperm whales. After this is the most recent sighting of the colossal squid, recorded in late March of 2025 is the first ever recorded sighting of a colossal squid in its natural habitat. Recorded by the Schmidt’s Oceanographic institute near the South Sandwich Islands at a depth of 600 meters we recorded a juvenile colossal squid. Only 30cm or around 12 inches long, and still translucent in color primarily, with some coloration implying they may be able to turn translucent. This sighting is particularly exciting as the first wild sighting of a live and healthy squid, and we’ll be seeing more information about these animals over time!
That’s the colossal squid everybody! Hope everyone is having a wonderful day and had a good time learning about the squid!
