Sneaky silverside fish steal eggs of fake partners

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Male Sailfin silversides have found a novel of nutrition " the eggs of females of another species they trick into spawning " according to a study published in the most recent issue of the Journal of Fish Biology.

Suzanne Gray, Jeffrey McKinnon, Fadly Tantu and Lawrence Dill report this unusual mode of nutrition in males of Telmatherina sarasinorum, a Sailfin silverside endemic to Lake Matano in Sulawesi.

Although T. sarasinorum is documented to regularly feed on the freshly laid, unguarded eggs of both heterospecific and conspecific spawning pairs (that is, the eggs of its other species as well as its own), the authors have observed a previously unreported method of obtaining eggs " by tricking females of another species to spawn.

In what the authors term sneaky egg-eating, ...a focal male T. sarasinorum that was guarding a pair of mating T. antoniae chased off the paired T. antoniae male and began courting the T. antoniae female.

When the heterospecific pair went to the substratum to spawn, the female T. antoniae quivered but the T. sarasinorum male did not.

Instead, he remained still alongside the female until she finished quivering, then immediately turned around and attempted to eat the eggs that the heterospecific female had just laid.

The female left immediately after spawning, but the T. sarasinorum male did not follow as would generally happen when mating with females of his own species.

These observations were made in the field on four independent occasions, suggesting that sneaky egg-eating occurs at a low but appreciable frequency.

It is thought that egg eating has evolved in the Sailfin silversides as a result of the lack of alternative sources of nutrition within the lake.

The current theory of the evolution of filial cannibalism suggests that males eat eggs to recoup energy spent on courting when the reproductive value of the spawning event is low; sneaky egg-eating is thought to be an extension of this behaviour.

For more information, see the paper: Gray, SM, JS McKinnon, FY Tantu and LM Dill (2008) Sneaky egg-eating in Telmatherina sarasinorum, an endemic fish from Sulawesi. Journal of Fish Biology 73, pp. 728"731.