Is Evolutionary Trend to Herbivory in Fish Frozen by Temperature?

Ivana Matějíčková (1,2), Lukáš Vejřík(1,2), Jari Syväranta (3), Mikko Kiljunen (4), Martin Čech (1),Mojmír Vašek (1), Marek Šmejkal (1,2), Jaroslava Frouzová (1), Jiří Peterka (1)

1 Biology Centre of the Czech Academy of Sciences, v.v.i., Institute of Hydrobiology, Na Sádkách 7, 37005 České Budějovice, Czech Republic. E-mail:

2 Faculty of Science, University of South Bohemia in České Budějovice, Branišovská 31,37005 České Budějovice, Czech Republic

3 Aarhus University, Department of Bioscience, Vejlsøvej 25, 8600 Silkeborg, Denmark

4 Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35, FI-40014 University of Jyväskylä, Finland

Rudd (Scardinius erythrophthalmus) and roach (Rutilus rutilus) are omnivorous cyprinid fish species widely spread in temperate zone with most distinct tendency to herbivory. Hypothetically, the herbivorous specialization of ectothermic animals is advantageous while water temperature increases above 20 °C. Our study focused on rudd and roach feeding preferences using stable isotope analysis (SIA) and digestive tract content analysis (DTCA) during summer season in two oligotrophic lakes. DTCA, conducted during summer season, revealed 88 % preference of rudd for macrophytes, whereas SIA using mixing models showed the preferences to be about 50 % reflecting long-term food utilization. Rudd prefered plant- like food source even if the animal prey was accessible, whereas roach do not switch to herbivory unless animal prey was absent. To test the hypothesis that herbivory in rudd is controlled by temperature, an experiment was conducted. Two temperature conditions combined with various macrophyte/animal prey ratio were tested; optimal high water temperature during late summer as well as suboptimal water temperature for ectothermic herbivores during late autumn.