Are some Indian White Squids gay? Kochi scientists discover mysterious sexual behaviour in India’s favourite seafood export

Kochi: In the animal kingdom, mating is usually seen as nature’s straightforward route to reproduction. But beneath the waters off Kochi’s coast, scientists have discovered something that doesn’t fit neatly into that rule. A new study on the Indian White Squid, the country’s most commercially valuable squid species and one of the crown jewels of India’s seafood export industry, has now discovered something startling about the secret lives of these fast-moving marine creatures: some male squids appear to be mating with other males, opening a fascinating new mystery about sexuality, instinct, and survival in the marine world.

The finding, published by researchers at the Shellfish Fisheries Division of ICAR-Central Marine Fisheries Research Institute (CMFRI) in Kochi, marks the first documented evidence of same-sex sexual behaviour (SSB) in a nearshore squid species.

The species in question – Uroteuthis duvaucelii, commonly known as the Indian White Squid – is found abundantly off India’s southwest coast and forms a major part of the country’s marine exports. But beneath the surface of Kerala’s coastal waters lies what scientists now describe as one of the most chaotic and poorly understood mating systems in the marine world.

The discovery began not with a search for homosexuality, but with a completely different scientific objective. Researchers were trying to determine the exact age at which Indian White Squids begin mating. During the process, they stumbled upon something unexpected: a young male squid whose buccal membrane – the soft, wet mucous membrane inside the mouth – was packed with 270 sperm packets, known scientifically as spermatangia. Because the squid itself was an immature male with incompletely developed reproductive organs, the sperm could only have been deposited there by another male squid. That observation changed the course of the study.

“We observed male-to-male mating behaviour in Indian white squid during our study. Similar homosexual behaviour has previously been reported in some deep-sea squid species. Like homosexuality seen in humans, this behaviour in squid is also not connected to reproduction. The behavioural or biological reasons behind it require further study,” said KK Sajikumar, Technical Officer at CMFRI and lead investigator of the study.

Scientists are careful not to casually label at least some of these marine animals as “gay” in the human identity sense. Human sexuality involves long-term emotional identity, social bonding, and psychological dimensions that cannot simply be projected onto marine animals.

Still, the finding raises fascinating questions about animal behaviour and whether same-sex sexual interactions may be far more widespread in nature than previously believed.

“We cannot directly attribute a complex human-like emotional structure or a psychological need to it based on this single observation,” explained Geetha Sasikumar, Principal Scientist at CMFRI and leader of the research team.

“But even if it is a rare occurrence, it opens up a completely new dimension in our understanding of the mating systems in Indian White Squids, which were previously assumed to be strictly heterosexual. It indicates that their mating interactions are much more complex and flexible than we originally thought,” she added.

Not the first in the ocean but the first near the shore
Same-sex sexual behaviour has already been documented in hundreds of species worldwide, including dolphins, penguins, insects, monkeys, and several marine organisms. But among squids, such behaviour had previously been reported only in deep-sea species living thousands of metres below the Atlantic and Pacific Oceans.

In those extreme environments, researchers believed males sometimes transferred sperm to any squid they encountered simply because locating females in the pitch-black deep sea was incredibly difficult.

But the Indian White Squid does not live in the darkness of the deep ocean. It thrives in relatively shallow coastal waters, often within 10 to 20 kilometres off the Kochi coast, at depths of around 100 metres. That means scientists cannot easily explain the behaviour as a result of darkness or the inability to identify females. Instead, researchers believe the answer may lie in the squid’s incredibly intense breeding environment.

“In our coastal species, they form massive spawning aggregations. When thousands of individuals gather in a very confined area for breeding, the intense competition and high density can lead to high hormonal levels and chaotic, aggressive mating interactions. In such crowded environments, accidental or mistaken-identity mating can happen. A male might mistakenly implant spermatangia on another male due to the sheer frenzy of the aggregation, or it could be a display of dominance,” Geetha said.

Underwater, mating among squids happens rapidly and violently. Male squids use a specially modified arm called a hectocotylised arm to transfer sperm packets onto a region near the female’s mouth. In dense swarms where animals move at high speed and compete aggressively, identifying another squid’s sex may not always be easy.

Scientists say some of these interactions could involve confusion, hormonal frenzy, dominance behaviour, or instinctive mating responses rather than long-term pair bonding. Still, the exact reason remains a mystery.

Reading a squid’s life through its 'ear stones'
To understand how mating fits into the squid’s short and dramatic life cycle, researchers turned to tiny balancing organs inside the squid’s head called statoliths, structures similar to ear stones in fish.

Like tree rings, statoliths record microscopic growth layers every single day of a squid’s life. By counting these daily rings, the CMFRI team reconstructed the life history of the species with remarkable precision. What they found was astonishingly brief.

Indian White Squids mature and begin mating between 98 and 162 days of age, effectively while still biological “teenagers.” Their total lifespan is less than six months.

The species follows a reproductive strategy called semelparity: they grow rapidly, mate intensely during a single breeding phase, lay eggs, and die shortly afterwards.

Researchers also found distinct structural “stress marks” in the statoliths of 36% of the mated females examined. “These marks essentially timestamp major biological events. The marks showed evidence of mating-related physical stress occurring approximately seven to 21 days before the squids were captured,” Geetha explained.

A reproductive dead end
Unlike females, male squids cannot store sperm in a way that leads to reproduction. That means the 270 sperm packets attached to the young male squid represented a total biological loss.

“Functionally, yes, it is a reproductive dead end. The sperm will eventually degenerate. It represents a significant loss of energy and gametes for the male that deposited it, and an unnecessary physical burden or tissue intrusion for the male that received it,” Sajikumar said.

Sajikumar clarified that although sperm packets can remain attached to another male, they cannot later be used for breeding because only female squids can store sperm in a reproductively functional way.

That leaves scientists with an intriguing unresolved question: why would evolution permit such apparently wasteful behaviour?

Researchers say the answer could reshape what scientists know about squid biology, animal sexuality, and marine behavioural systems.

Whether these male squids are engaging in mistaken-identity mating, hormonal overflow, dominance contests, or more complex social interactions, one thing is clear – the mating world of Indian White Squids is far stranger than anyone imagined.

Besides Sajikumar and Geetha, the research team included Principal Scientist V Venkatesan, Senior Scientist R Vidya, retired Principal Scientists Kolliyil S Mohammed, P Laxmilatha and Technical Assistant Jestin Joy.