A landmark study by the ICAR-Central Marine Fisheries Research Institute (CMFRI) in Kochi has documented both heterosexual and homosexual mating behaviour in the Indian squid (Uroteuthis duvaucelii) for the first time, offering a significant new window into the reproductive biology of one of India's commercially vital marine species. The findings, published in the Journal of Natural History, are based on squid samples collected from waters off Kochi in the Arabian Sea.

Key Findings of the CMFRI Study

The research was led by Dr Geetha Sasikumar and Dr K K Sajikumar from the institute's Shell Fish Fisheries Division. An analysis of 232 female squids revealed that nearly 40 per cent carried spermatangia — sperm-containing structures attached to their buccal membranes, the fleshy tissue surrounding the mouth. The data indicates that mating activity occurs throughout the year, with peak reproductive activity recorded in October.

In one particularly striking case, researchers counted as many as 385 spermatangia around a single female squid's mouth region, suggesting repeated mating with multiple males ahead of egg laying.

First Documented Evidence of Same-Sex Behaviour in a Coastal Squid

The study's most striking discovery was the identification of spermatangia implanted on the buccal membrane of a male squid — the first documented evidence of same-sex sexual behaviour in the Indian squid. While similar behaviour had previously been reported in certain deep-sea squid species outside Indian waters, scientists had largely attributed it to low-visibility conditions in the deep ocean. This finding is the first such documented instance in a coastal squid species, making it scientifically significant beyond Indian marine biology alone.

Scientists believe such highly opportunistic mating interactions may be linked to dense spawning aggregations, where competition is intense and encounters between individuals are frequent.

Early Mating and Statolith Analysis

Using statolith analysis — a technique comparable to reading growth rings in fish — researchers estimated that Indian squid may begin mating as early as 98 days after hatching, a notably early onset that underscores the species' rapid maturation cycle. This technique allowed the team to reconstruct individual growth histories and correlate them with reproductive milestones.

Implications for Fisheries Management

The researchers stressed that a thorough understanding of the squid's mating system is essential for refining stock assessments and designing sustainable fisheries management strategies. This comes at a time when squid resources are growing in importance to India's marine economy, with demand from both domestic markets and export channels rising steadily.

The team has called for further behavioural and physiological studies to deepen understanding of the species' reproductive dynamics and ecological adaptations. The study adds a new layer of complexity to how marine biologists and fisheries managers must approach the conservation and harvesting of Uroteuthis duvaucelii going forward.