A recent footage from remote-controlled submersibles reveals that rare deep-sea male squid of Pacific Ocean are bisexual and prefer to mate in the dark.

The deep-sea squid or Octopoteuthis deletron is a 5-inch long tentacled creature that lives in the depth of 400m to 800m. 

An 18-year study on this species reveals that males often fail to differentiate between sexes and end up mating fellow males. Extreme physiological similarities of both the sexes, rarity of encounters and absence of sufficient light can be blamed for their bisexual nature, U.S. researchers said.

Homosexuality among amorous males is so rare that the male squid do not pay attention to the gender of their sex object, added the scientists.

During mating, the male discharges sperm sacs that go into the female's tissues and leaves signs of recent mating. When studied in the Monterey submarine canyon off the coast of California, scientists found more males than females carrying the sperm sacs on the bodies which surprised them to discover the indiscriminate sexual behavior of the male squids.

For any other species, such a scattergun approach to mating is nothing but wasting valuable sperms. But the deep-sea squid prefers to waste sperm due to the rarity of encounters, says Henk-Jan Hoving, a marine biologist at the Monterey Bay Aquarium Research Institute in California.  .

For the deep-sea squid, sex is rapid and short as evolution favors them with the ability of multiple mating with any individual encountered.

Squid, including deep-sea species, only reproduces once and they have to find mates in time in an environment where encounters between individuals of the same species are few and far between, scientists said.

The strategy of live fast and die young is often found in many types of cephalopods including different squid and octopus, and homosexuality is common in more than 1,000 different animal species including penguins, dolphins and primates.

The report was published in the journal Biology Letters.