An 18-year study of a deep-sea squid or Octopoteuthis deletron, a 5-inch long tentacled creature that dwells a depth of 400 to 800m, found that males attempt to mate with any deep sea squid it comes across, whether its a male or female.

With deep sea conditions favouring darkness, little difference between the sexes and rare encounters with fellow squids, a study led by U.S.-based researchers found that males are either unaware or unconcerned whether the object of their attention is female or male.

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.

Deep-sea squid are extremely important in the oceanic food webs as tuna and many other fish feed primarily on them. However, our knowledge of these animals is very limited, Henk-Jan Hoving, a marine biologist at the Monterey Bay Aquarium Research Institute in California, told the Guardian.

The sexual strategy used is typical of the live fast and die young life strategy adopted by many types of squid, octopus and similar species the scientists added.

Squid, including deep-sea species, only reproduce 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.

The Octopoteuthis deletron, which lives in the eastern Pacific, measures up to 15 cm in height and has eight long, hooked arms.

For the study, scientists based at the Monterey Bay Aquarium Research Institute in California, studied 39 male and female individuals between 1992 and 2010 to try and learn more about their behavior.

They found that while ten out of 19 females had recently been mated with, so had nine out of 20 males.

Apparently, the costs involved in losing sperm to another male are smaller than the costs of developing sex discrimination and courtship, or of not mating at all, the researchers said.

Same sex coupling has already been observed in more than 1,000 different animal species including penguins, dolphins and primates.