The so called egg dummies, resembling fish eggs and formed on the various parts of the fish body, can be found in the different lineages of mouthbreeding cichlids and egg clustering darters. In cichlids, for example, patterns of yellowish, orangish and redish egg-spots, developed on the anal fin of males, are most abundant (e.g., Henning & Meyer, 2012; Theis et al., 2012). Tobler (2006) has considered the role of sexual selection in the evolution of egg-spots and hypotheses explained this evolution, including the hypothesis of sensory exploitation (see Ryan, 1990). The hypothesis of sensory exploitation can explain, in particular, the shortcomings of previously suggested hypotheses on the evolutionary origin of egg dummies and their further development.

An unexpected hypothesis that any predory fish can respond to the egg dummies was tested in the experiments described below.

Predatory Northern pike, Esox lucius, were selected as usable model fish. In the European ichthyofauna, there not egg-mimicking fish.

We examined the effectiveness of original Rattlin’ Rapala wobblers (6 cm length, Baby Bass color), marked ORR, in comparison with the experimental wobblers, marked ERR. ERR wobblers were equipped with the bilateral black and yellow eye-spots (5 flat spots, 4,8 mm diameter each) (see Fig.1) located along the flanks of the lures.

Figure 1. Rattlin’ Rapala wobbler equipped bilaterally with the 5 eye-spots

Using pike as usable predators, lures of both types were presented alternately at the estimated localities of these solitary fish. At each locality, 20 presentations (cast and retrieving) of lures were made: 5 with ORR, 5 with ERR, 5 with ORR and 5 with ERR. Then an experimentator moved to the other locality, where 20 presentations of the compared lures were made in the reverse order. Within one 3-day session, 27 relatively small pike (30-40 cm standard length) were landed (and released) in total. The numder of caught fish were distributed per earch ten lure presentations for lures of both types, correspondingly.

Student t-test was used to estimate the difference between the mean values of fish number for lures of both types, ORR and ERR. Pike preferred egg-marked lures (p < 0,05). Only one 3-day testing session was made, thereafter ERR like lures were used in fishing with the steady success.

Because the foregoing lures are relatively large, only 11 large perch, Perca fluviatilis, (12-14 cm standard length) were caught in parallel without their including into the calculations.

In the Europen region, predaty fish never meet with the egg-mimicking fish. They respond to the foregoing artificial lures beeing attracted by the bright egg-like or eye-like spots.

Generally, eye-spots and their combinations belong to the so called amimetic stimuli. Their effectiveness is determined by the common mechanisms of visual perception, common for animals and human. There are receptive units matched with the roundish and sequent stimuli.

For more information, please read Visual amimetic stimuli. An introduction

Basic References

Henning F., Meyer A. 2012. Eggspot number and sexual selection in the cichlid fish Astatotilapia burtoni. PLoS ONE 7(8): e43695

Ryan, M.J. 1990. Sexual selection, sensory systems and sensory exploitation. Oxford Surveys in Evolutionary Biology 7, 157-195

Theis A., Salzburger W., Egger B. 2012. The function of anal fin egg-spots in the cichlid fish Astatotilapia burtoni. PLoS ONE 7(1): e29878

Tobler M. 2006. The eggspots of cichlids: Evolution through sensory exploitation? Zeitschrift für Fischkunde 8, 39-46