The comparison of the feeding of European perch Perca fluviatilis L. larvae in littoral and pelagic habitats of northern temperate lakes
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We studied the feeding of European perch Perca fluviatilis L. larvae in littoral and pelagic habitats of four different lakes – one Latvian (Auciema) and three Estonian (Akste, Kaiavere, and Prossa). Altogether, 162 perch larvae (81 from both habitats) were collected to estimate the diet composition of gathered larval specimens in spring (2019) using gut content analysis via epifluorescence microscopy. Attention was paid particularly to the question how does the larval perch food composition differ in pelagic and littoral habitats. We hypothesized that the consumption of zooplankton is higher and the larval condition is better in littoral habitats. We assessed the feeding on both protozoo- (ciliates) and metazooplankton and applied multiple indices (Hurlbert’s standardized niche breadth, Ivlev’s selectivity and relative importance index) to evaluate, respectively, the larval fish prey importance, feeding homogeneity and strategies. The results showed that larval length and weight were slightly higher and body condition was slightly better in the lakes’ littoral habitats. The feeding niche of perch larvae was narrower in the littoral, which can indicate more favourable feeding conditions in littoral than lake pelagic habitats. While the small cladocerans (Bosmina longirostris Müller) were generally the preferred and important food objects, ciliates were avoided and consumed only when their share in the total zooplankton biomass was >40%. However, in shortage of cladocerans, ciliates could be vitally important food objects for perch larvae.This project has received funding from the European Union’s Horizon 2020 research and innovation pro- gramme under grant agreement No. 951963. The research is part of the project “Fish feeding conditions in lakes with different planktonic food web structure and mac- rovegetation” (MICROFISH), No. 18.104.22.168/VIAA/1/18/301, in agreement with State Education Development Agency of the Republic of Latvia Programme No. 22.214.171.124/16/I/001. The project is financed by the European Regional Development Fund, the State budget of the Republic of Latvia and the foundation Institute for Environmental Solutions. We would like to thank Jukka Ruuhijärvi and an anonymous reviewer for their helpful comments on the earlier version of the manuscript. The publication costs of this article were covered by the Estonian Academy of Sciences.