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Animalia >Chordata >Osteichthyes >Gasterosteiformes >Gasterosteidae >Gasterosteus >

Female three-spined sticklebacks and groups of floating individuals of Moroco steindachneri (a fish species living sympatrically with the three-spined stickleback) sometimes eat stickleback eggs guarded by male parents. The rate of egg predation is said to be relatively high at Hongan-shimizu because of the high stickleback density. It is thus necessary for male three-spined sticklebacks to use various strategies to avoid egg predation.

At the front of the screen, a male stickleback is guarding and fanning eggs in a nest. As female three-spined sticklebacks and groups of floating individuals of Moroco steindachneri approach the nest, the male stops funning. After a while, a female three-spined stickleback at the back of the screen eats something (eggs?), and other female sticklebacks and M. steindachneri aggregate around the female to grab the food (31-38 sec.).
The nest guarding male joins the aggregation, leads the aggregation to another spot on the bottom, and then assumes a spawning-inducing posture by tilting the body (twice, at 45 sec. and 54 sec.; the second one can be played in a slow speed). Lured by this male posture, other fish aggregate around a spot that the male pointed with the mouth; meanwhile, the male leaves the aggregation. Later the male went back to the nest, but it did not resume fanning. Rather, it carried sand into the nest with the mouth. The male kept carrying the sand for about three minutes until finally it resumed fanning.

It is not clear whether the observed male behavior is effective against egg predation. Assuming a spawning-inducing posture may delay the arrival of other fish to the nest, or it may deflect the attention of other fish from the nest. One interesting finding is that heterospecific Moroco steindachneri were also lured by this spawning-inducing posture. The sand carried to the nest may hide the eggs inside. Alternatively, sand carrying makes other fish ¡Æthink¡Ç that the male is still in the middle of nest building and that there are no eggs in the nest.
(By Osamu Ishida, Fukui City Museum of Natural History)

(This video picture was prepared by ¡ÆFriends of Fukui City Museum of Natural History during a project ¡ÆEducational Videos on the Three-spined Stickleback.¡Ç http://www.nature.museum.city.fukui.fukui.jp/friends/itoyo/)
(translated by Asoh)

(Data No.momo051103ga07b)

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