| dc.description.abstract | In eutrophic lakes, the omnivorous roach (Rutilus rutilus) is known to dominate over other species, due to competitive advantages. This study aims to explore the dietary behaviour of roach, rudd (Scardinius erythrophthalmus) and perch (Perca fluviatilis) in the eutrophic lake Årungen, with a particular focus on the predation and cannibalism exhibited by roach and perch. Field data were collected through gillnet fishing from May 26th to June 27th, followed by examination of gut contents enhanced with Alizarin red S to detect fish larvae remnants in roach and rudd. Additionally, the growth rates of free-swimming fish larvae were assessed to determine the predation window for roach and perch, and to investigate the effect of environmental factors on growth.
Findings from this study indicate no differences in the diets of the three species, suggesting they overlap and compete for resources. Roach engaged increasingly in facultative piscivory as temperatures rose, suggesting temperature as an important factor. Perch also engaged
increasingly in piscivory, to a larger degree than roach, but water temperature had no effect on its behaviour. The influence of maximum prey size was not different for roach and perch on the probability of piscivory, but roach had the highest optimum prey size of the two. Further, when analysing the age calculation data there was a significant interaction effect between species, temperature, and delta length (the difference between the empirical length of the predator at capture and its predicted length). Perch demonstrated increased piscivory at lower temperatures for individuals with poor growth, whereas roach piscivory increased at higher temperatures under similar conditions of poor growth. The fish larvae were identified as roach, suggesting roach may have engaged in cannibalism. The study also observed a negative growth rate for larval roach as the temperatures rose, with the empirical weight consequently below the predictions. This trend may align with density-dependent factors, including increased predation and potential competition for, and limitations in, available resources.
Overall, the results from this study highlight the complex interactions among fish species in eutrophic lakes, and the adaptive behaviours of the species in response to environmental shifts. It has revealed that facultative piscivory and cannibalism among cyprinids may be more prevalent than previously anticipated. | |
