Clasping gouramis squeeze out semen

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Japanese ichthyologists have proposed that male gouramis bend their bodies around the females during breeding to squeeze semen out of their testes.

In a study on the Dwarf gourami Trichogaster lalius (formerly Colisa lalia) to be published in an upcoming issue of the journal Ichthyological Research, Youichi Hayakawa and Makito Kobayashi observed the mating behaviour of T. lalius in aquaria and examined the male reproductive system anatomically and histologically in order to investigate the role of clasping during mating.

The authors found that the testes of the male gourami were not longitudinally elongate (ie. parallel to the body axis) as in most fishes, but were latitudinally elongate (ie. vertical with respect to the body axis).

The authors hypothesise that when the male gourami bends his body, the testes are located in the vicinity of the bent fulcrum and pressure is exerted on the latitudinal testes, causing the semen to be squeezed out of the body (via a mechanism analogous to that of a nutcracker).

This is apparently verified by the fact that sperm emission does not take place in the absence of the clasping behaviour.

For more information, see the paper: Hayakawa, Y and M Kobayashi (2009) Clasping behavior and the asymmetrically latitudinal structure of the testes in the male dwarf gourami Colisa lalia. Ichthyological Research doi: 10.1007/s10228-009-0121-2