Craziest Ways Sea Creatures Give Birth

Let's explore the most incredible ways sea creatures give birth!

June 26, 2023・

19 min read

For humans, the miracle of birth is one of life’s most unforgettable experiences. But we’re not alone. Sea creatures also undergo some pretty miraculous births but for slightly more bizarre reasons. From crazy pregnant crabs dancing in the moonlight to marine moms who give birth to millions, here are some of the craziest ways that sea creatures give birth!

Stingray

Stingrays are best known for looking like the ravioli of the sea, growing up to 4 ½ foot wide, and having painful venomous stingers. But, if you thought those freaky features were otherworldly, wait until you learn about how these guys give birth.

Like most marine life, stingray mothers produce eggs inside their body. However, unlike typical sea critters, stingrays are ovoviviparous, meaning that the mothers keep the eggs inside their bodies, even after they hatch! Usually after a gestation period of three months, the embryos emerge from the eggs.

The developing stingray pups receive nutrition from a milky, rich substance developed in the mother’s uterus and attached to them via sacs, helping them grow big and strong! Eventually, when labor day comes, stingray moms pop out some haunting horrors.

Those embryos grow big and strong. And in fairness to the pups, they need it! Most juvenile stingrays start their lives away from their parents, so having the ability to swim and fend for themselves is crucial.

Elephant Seals

Seals are considered to be the doggo of the sea, and they can just melt our hearts. Although before you get too carried away, you need to see the metal birthing methods of the elephant seal, which are less heart-melting and more soul-destroying.

From September to November, the average 10 ft long, 1,300 lb females arrive onshore on islands off the coast of South America, South Africa, and Australasia. About a week after arriving, they’ll give birth to pups that they’ve been carrying for the last 7 months.

Judging by what an elephant seal giving birth looks like, it’s a day that those moms have been deeply fearing for those 7 months. The video clip below may look gruesome but it’s actually an elephant seal mother pushing one of these pups out headfirst. Considering that these pups weigh around 88 pounds and stretch over 4 feet long, it’s no easy task.

Tiger Sharks

Whether it’s their sharp serrated teeth, creepy eyes, or chunky 10-foot length, sand tiger sharks are one of the ocean’s most hardcore inhabitants. But, if you think their appearance is hardcore, you haven’t heard what happens during their pregnancy.

For humans, the womb is a peaceful, cozy home for fetuses to develop. Sadly, the same can’t be said for sand tiger sharks. Females have two uterine horns that, during pregnancy, house 6 to 9 embryos in each uterus. Yet, sand tiger sharks have one of the lowest reproductive rates out of all sharks.

So, where are all those babies going? Well, their siblings’ gut, that’s where! In what’s known as intrauterine cannibalism, the developing embryos are munched up by the largest sand tiger shark embryo until only one remains.

Some of the sand tiger shark’s close relatives, including great whites and mako sharks, produce embryos that consume unfertilized eggs in the uterus. But none boast the same grisliness as sand tiger shark embryos, who happily eat up their hatchling brothers and sisters. And you thought your siblings were bad!

When the two killer pups eventually emerge from each uterus, they’re already over 3 feet long, big enough to protect them from most predators and make themselves capable killers. Fortunately for them, that size comes in handy for putting off any would-be predators.

Splashing Tetras

Thankfully, splashing tetra babies don’t have such a gruesome welcome to the world, but that doesn’t make their birthing process any less bizarre. When these frisky fish, found in the rivers of South America, are ready to reproduce, the male looks for a suitable leaf.

It may sound odd that a fish is into plant life, but that greenery plays a vital role in the birth of splashing tetra young. The male goes in search of the perfect leaf on which to lay eggs. And, when he finds a mate, they perform a crazy jump!

But they’re not just hopping around for the fun of it. The pair leap out of the water in perfect unison, so much so that, to the human eye, they appear as one. After landing on the leaf, the female will deposit her eggs, and the male must fertilize them immediately.

After the strange ritual is complete, the male splashes water on the eggs with his tail to prevent his young from drying out. It may seem like a strange way to bring your kids into the world, but it’s with good reason.

By laying their eggs above the water, these parents save their young from any fish that would feast on their scrumptious spawn. After a couple of days of getting splashed by dad on their lofty leaf, the eggs hatch, and the fry plunge into the water. Now that’s a parkour pregnancy!

Banggai Cardinalfish

Residing in the waters off the coast of the Banggai Islands in Indonesia, male Banggai cardinalfish perform their parental duty admirably. Reproduction begins with the female courting a male with a dance that he joins in. It’s more of a ‘follow the leader’ kind of dance, a two-fish conga if you will!

If she’s impressed by his moves, she’ll release around 40 eggs, which are fertilized by the male. Although his job is far from over. After fertilizing the eggs, dad opens his mouth wide and sucks all of them in! Though he doesn’t eat them. Instead, he scoops the eggs up in his mouth to incubate them.

It may seem weird, but for fish like the yellow-headed jawfish and of course, Banggai cardinalfish, this ‘mouth brooding’ is the most reliable way to ensure their unhatched kids don’t get gobbled up by another fish.

But, with this great fishy power comes great fishy responsibility, because if dad drops dead for some reason, there’s not much chance of the fishy fry surviving either. If dad does make it through the brooding period, there’s one more teeny-tiny problem: the eggs are always in the male’s mouth, so he can’t eat at all for a whole month!

But before we all start applauding Banggai cardinalfish dads, things don’t always go smoothly. Males that haven’t built up sufficient energy reserves are known to snack on their own young! In fact, most of the time not all Banggai cardinalfish fry make it out of their father’s maw. On average, out of 40 eggs, only about 20 fries make it.

Seahorses

Banggai cardinalfish aren’t the only dads who do their bit when it comes to pregnancy. After an elaborate courtship dance, female seahorses deposit their eggs in a mate. But this time they don’t end up in dad’s mouth. Instead, the male seahorse has his own belly brood pouch where he fertilizes his mate’s eggs.

As the embryos grow, so does the seahorse’s abdomen, just like with human pregnancy, only it’s not the female whose belly gets a bump. It's not known for sure why sea horses have this gender reversal when it comes to pregnancy. One theory is that giving the male the job of bearing the young leaves the female free to start producing the next batch of eggs.

After about 30 days, labor day finally arrives for dad. Although it may look like he’s got a bout of the sneezes, male seahorses open their abdomen before having contractions that release their teeny-tiny babies, most of which are less than 12 millimeters in size. And then, they’re left to fend for themselves.

But seahorses aren’t the only determined dads who have a brood pouch to help raise their young. The closely related sea dragon has a spongy brood patch on the underside of its tail. During mating, the female will deposit around 250 bright pink eggs onto the male’s tail. The eggs then lock onto the brood patch.

After about 9 weeks of riding on dad’s tail, the spawn begins to hatch. And, with a little shake, the babies say goodbye to the tail, and hello to the open ocean! But, just like their horsey cousins, sea dragon young don’t get any help from mom or dad the moment they’re born.

Another close relative of the seahorse and sea dragon, known as the pipefish, completes the trio of fishy fathers. Female pipefish drop up to 40 eggs into the brood pouch of the male’s belly. Here, they fertilize the eggs and carry them until the offspring hatch a couple of weeks later. Sound like loving dads, right? Well, not entirely.

Male pipefish are pretty picky parents, to put it lightly. These guys are known to selectively remove youngsters from their pouch if they’ve mated with an unattractive female. Harsh as it is, males are likely to put more resources into broods from larger, more attractive females. Does personality count for nothing in the fish world?

If that wasn’t brutal enough, male pipefish can also turn to cannibalism if the pregnancy gets too tough. If they’re running low on food supplies, the dad-to-be will literally absorb some of his own brood for nutrition. Forget great whites, pipefish fathers may just be the most cut-throat creature of the sea.

Surprising as it sounds, there are some dads out there who actually are happy with their batch of young. When the birthing time comes, the young blast out of dad’s belly. Nice to know there are some good guys out there!

Lumpsuckers

Luckily not all fishy fathers resort to devouring their own young at the first opportunity. Lumpsuckers may not have the most glamorous name of all sea critters, but that doesn’t stop them from putting their bodies, which range from less than an inch long up to 2 ft depending on the species, on the line for their kids literally.

During mating season, males compete to create the best nest to lure a female’s attention. The lady lumpsucker will then pick her favorite and lay around a jaw-dropping 350,000 eggs, before swimming off and leaving the guys to take care of things.

Dad will remain with his eggs by attaching to nearby rocks with a sucker formed from modified pelvic fins that have evolved into suction discs. The male’s job is to protect the eggs from predators, and fan water over them to keep them oxygenated.

It would be easy enough if it wasn't for the waves constantly crashing into the shallow pools where they reside. Fortunately, that’s where their special suction-cup comes in handy! But walloping waves aren’t the father’s only problem.

This process can take an eye-watering 8 weeks! Imagine being stuck on a rock with nothing to do but fan eggs for over 1,300 hours! Though boredom isn’t the only problem. When the tide recedes, these daring dads still stay with their spawn, even in the face of any hungry gulls and crows.

Sounds like a fearless father but that’s only until his kids are born. When the little lumpsuckers eventually hatch from their eggs, dad returns back to deeper waters, leaving his kids to fend for themselves.

Blue Whales

Not all sea life lays eggs, however. Take the blue whale, aka the biggest animal on the entire planet, with the average length of a mature female measuring in at more than 72 ft and weighing in at close to 250,000 lbs! Because whales are marine mammals, the females carry the offspring in their wombs and have live births.

The fetus develops inside the mother’s uterus, growing at about 1 inch per day after 3 months of gestation. But, if you think that sounds big, baby blue whales stretch to a whopping 12 feet in length after 7 months in the womb! For some context, a human baby usually measures about 14 inches long after 7 months of pregnancy, less than one-tenth the size of blue whale babies.

After 12 long months, they emerge tail-first, stretching about 23 feet and weighing in at a staggering 3 tons, making them four times heavier than a cow. If pushing a truck-sized kid out wasn’t enough of a pain, these mothers actually have to go through the effort of caring for their kid as well!

Mama supplies the young calf with more than 40 gallons of milk, that’s about a bathtub’s worth of milk, every day for up to 7 months! That’s more than 8800 gallons.

Bullhead Shark

Unlike blue whales, bullhead shark mothers don’t have the tricky task of pushing out a 3-ton baby. But that doesn’t make the birth of their own babies any less bizarre. These sharks are oviparous, meaning that they birth their young by laying eggs.

Not much is known about how these guys spawn, but one thing we do know is that mother bullhead sharks lay some of nature’s gnarliest-looking eggs. You probably think of eggs in the classic oval-shaped, chicken-laid shape, or maybe even a small, spherical fish egg. But it seems Bullhead Sharks didn’t get the memo.

Female bullhead sharks lay up to 16 spiral-shaped, 4-inch-long eggs every year. They look more like a pinecone than something that’s come out of an animal!

What’s the reason for these eccentric egg cases? Unlike most fish, who carelessly spurt their eggs and sperm into the water, bullhead shark mothers carefully find a suitable home for their eggs.

The mama will carry the swirly egg in her mouth, before locking the specially adapted egg between rocks in hard-to-reach places. This prevents them from washing away and stops any predators from finding an easy snack of scrambled shark egg for breakfast.

You’d probably think that the mother would be waiting impatiently for her spiral eggs to eventually hatch, but no. As soon as she finds a suitable crevasse for her young, she leaves them to figure the rest out. So much for motherly love!

Sea Turtles

Of course, bullhead sharks aren’t the only ocean-dwelling critters to birth their young by laying eggs. All seven species of sea turtles also produce eggs. But, unlike bullhead sharks, sea turtle eggs look a tad more traditional. But what’s amazing about the birth of these cuties, is the unique process that their mothers go through to ensure their survival.

Adult sea turtles spend their life at sea, with females only ever leaving the water to lay their eggs. Pregnant females utilize the earth’s magnetic field like a GPS, using it to locate the beaches where they themselves hatched years before which they’ll head to en mass.

But, what’s the reason for this? Are sea turtles sentimental? Not exactly. Female sea turtles from different islands tend to have specific genes which vary in what they’re immune to. So, returning to the island where they were born aids their babies in fighting off local diseases.

But before their babies are actually born, these mamas have to lay their eggs. Using their back flippers, the females dig a nest in the sand, before popping out around 110 golf ball-like eggs. All of a sudden, sea turtles have got a whole lot less cute.

After mom has finished up, she returns to the sea, leaving the eggs to incubate in the warm sand for about 60 days. Eventually, the eggs hatch, usually at night, giving the hatchlings a better chance of avoiding predators on their journey to the water.

And it seems like they need all the help they can get, considering only about 1 in 1,000 turtles survive to adulthood, with many either suffering from dehydration or falling prey to predators. And that's why mama turtle popped out so many eggs.

Christmas Island Red Crabs

We couldn’t talk about beach babies without giving a mention to Christmas Island red crabs. These crimson crustaceans are found on Christmas Island off the northwest coast of Australia. Each year they make a mass migration from the island’s forests to its coast to breed.

Over 50 million of these critters migrate across the island each year. And, considering that Christmas Island is over 1,000 times smaller than Florida, you can imagine the constant red tailback. In fact, it’s so busy, that the red carpet of crabs even forces roads to close!

After migrating in their millions, the colorful crabs breed by the coast. At this point the male’s job is done, so he returns to the forest, how endearing. But, unlike her mate, the female’s work is far from finished. They lay about 100,000 eggs each, which they then incubate in their abdominal brood pouch.

Without fail, red crabs spawn their almost infinite supply of babies at high tide during the last quarter of the moon. This happens because, at this time, the female crabs have a shorter distance to reach the sea before releasing their eggs. With a manic shaking, they release hundreds of thousands of eggs.

Red crab eggs hatch as soon as they make contact with the water, and from that point, they’re on their own. If they make it, the baby crabs will remain at sea for the next 3 to 4 weeks as they develop before the survivors return to invade the beaches in their millions, sometimes billions!

But sadly, their chances of survival aren’t very high. The vast majority will never make it out of the water, swallowed up by fish, manta rays, or even enormous whale sharks. Talk about shellfish parents!

Squids

Back in the depths of the ocean, you’ll find a squid with a very peculiar style of protecting her eggs. Most species of squid reproduce by depositing their egg cases on the ocean floor, but some squids take a more tentacles-on approach.

Researchers have recently discovered two species of squid, the gonatus onyx and bathyteuthis berryi, that carry eggs in their arms. It may look like these mothers are sprinkling fairy dust in the deep sea, but those speckles are their eggs!

Currently, not much is known about the behavior of bathyteuthis berryi mothers. But the struggles of gonatus onyx moms is more well-understood. Carrying just one baby sounds like hard work, but these mamas have to hold some 3,000 of them, for a whole 9 months!

Sadly, for these squids, the struggle doesn’t end at tired arms. Some gonatus onyx have been observed with nubs, where two feeding tentacles should’ve been. It’s believed that mothers bite them off before spawning, to make up more space for their egg mass. But arms aren’t the only sacrifice that these mettlesome mothers make.

Carrying so many embryos means that the mothers aren’t able to swim quickly, putting them at risk of being caught by predators. Fortunately for gonatus onyx, floating around and depths between 5,000 and 7,000 feet means they avoid most predators.

However, some deep-diving animals, like elephant seals would no doubt make a quick snack if they crossed paths. But hungry hunters aren’t the only problem for mama squid. The gonatus onyx doesn’t feed while holding her batch of young at all. These mothers will go without food for up to 9 months, by which time they’re both starving and exhausted.

After a 9 month-long struggle, mom eventually gives birth to what looks like a cluster of mini stars! Sadly, not everything about this birth is so majestic. After the eggs hatch and float off, mommy dearest perishes from starvation and sinks to the seafloor, where she and her empty egg sack become food for scavengers.

Smalltooth Sawfish

The story behind how sawfish, which, despite the name, are actually part of the Ray family, can give birth is even weirder than their kooky appearance. Usually, there’s nothing unremarkable about the way the smalltooth sawfish gives birth. The male fertilizes an egg from a female, who after 12 months, can give birth to up to 20 pups, similar to the previously mentioned stingray.

Sadly, however, these creatures are critically endangered due to habitat loss. And fewer rays mean fewer chances of finding a mate. Luckily, female smalltooth sawfish have a trick up their fin. Scientists discovered that about 3% of sawfish living in a Florida estuary were born without ever having fathers. That takes being a single mother to a new level!

This form of asexual reproduction is called parthenogenesis. It occurs when there are no males present to fertilize the female’s eggs! Usually, reproduction involves an egg cell and a sperm cell, each providing 50% of the genetic information to create an organism.

But, with parthenogenesis, the egg cell combines with what’s called a polar body; a cell that’s a byproduct of egg production. When push comes to shove, these clever critters can use the polar body to fertilize the egg cell! In the short term, it’s a pretty ingenious solution to solving the sawfish population problem.

However, further down the line, these less genetically diverse offspring are more vulnerable to harmful mutations and environmental changes. Even so, if it wasn’t for these marvelous mommas and their virgin births, the whole species may already have been wiped off the face of the earth!

Sunfish

Sawfish aren’t the only creepy-looking sea critters to have crazy birthing stories though. Sunfish are huge ocean dwellers that can reach 10 ft fin-to-fin and weigh more than 2,200 lbs, and they look more like a massive pancake than something you’d expect to find in the ocean.

But like with the sawfish, the way these guys give birth is even more shocking than their shape. Sunfish reproduce through a method known as broadcast spawning, where the male and female release both eggs and sperm into the water, and they fertilize externally.

The female can produce a massive 300 million eggs, the most of any vertebrate on the planet. When the eggs hatch, sunfish larvae are only 3/32 of an inch long and weigh less than a paperclip!

Yet, despite their slight size at birth, they grow a colossal 60 million times their original weight when mature. If humans had that kind of growth, adults would weigh around 220,000 tons. For some context, that’s about the same weight as the 1,730-foot-high Willis Tower in Chicago!

You may be wondering where all these giants are lurking, considering that mama pops out 300 million eggs. However, the chances of a sunfish egg surviving are pretty slim, with just 0.0003% of sunfish larvae surviving to tell the tale of their birth and colossal growth. And you thought human kids went through crazy growth spurts.

If you were amazed at these crazy ways sea animals give birth, you might want to read our article about the best animal parents. Thanks for reading!