Prey selection and growth in 0+ Eurasian perch Perca fluviatilis L. in littoral zones of seven temperate lakes

We studied the relationships between the planktonic food base and feeding patterns of juvenile mid-summer/ early autumn Eurasian perch Perca fluviatilis L., a common predatory freshwater fish in large parts of Europe and Asia. The feeding of 0+ perch was studied during summer and autumn in littoral habitats of seven lakes with different environmental conditions –four Latvian (Auciema, Riebinu, Vārzgūnes, Laukezers) and three Estonian (Kaiavere, Prossa and Akste) lakes. Simultaneously, the abundance, biomass and structure of zooplankton communities were examined. We focused on the littoral areas because many studies in lakes suggest that littoral habitats are particularly important for 0+ fish growth and survival. We were interested in the question: can the diet and growth of 0+ perch be explained by zooplankton community structure? We also presumed that if the amount of zooplankton is low, more benthic invertebrates will be consumed by 0+ perch. Opposite to expectations, we found that zooplankton always counted for over 90% of diet biomass in perch. There were also clear correlations between the zooplankton biomass in a given lake, the zooplankton biomass in 0+ perch stomachs, and the fish growth rate. The study also suggested that nutrient enrichment can positively impact the 0+ perch feeding conditions in lakes.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”. Funding for this project was also provided by the European Union‘s Horizon 2020 research and innovation programme under Grant Agreement No. 951963 (TREICLAKE “Towards Research Excellence and Innovation Capacity in Studying Lake Ecosystems Functional Structures and Climate Change Impact”).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”. Funding for this project was also provided by the European Union‘s Horizon 2020 research and innovation programme under Grant Agreement No. 951963 (TREICLAKE “Towards Research Excellence and Innovation Capacity in Studying Lake Ecosystems Functional Structures and Climate Change Impact”)

Larval and juvenile perch feeding in some Estonian and Latvian study lakes : [poster]

The presentation took place at the Lahti Lakes 2021 Symposium.The research is a part of the project „Fish feeding conditions in lakes with different planktonic food web structure and macrovegetation “(MICROFISH), No.1.1.1.2/VIAA/1/18/301. Agreement with State Education Development Agency of the Republic of Latvia No. Programme number 1.1.1.2/16/I/001. The project has received funding from the European Regional Development Fund, from the State budget of the Republic of Latvia, from the foundation „Institute for Environmental Solutions” and from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963. Greatest thanks to PhD Priit Zingel.The research is a part of the project „Fish feeding conditions in lakes with different planktonic food web structure and macrovegetation “(MICROFISH), No.1.1.1.2/VIAA/1/18/301. Agreement with State Education Development Agency of the Republic of Latvia No. Programme number 1.1.1.2/16/I/001. The project has received funding from the European Regional Development Fund, from the State budget of the Republic of Latvia, from the foundation „Institute for Environmental Solutions” and from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963. Greatest thanks to PhD Priit Zingel

The influence of macrophyte ecological groups on food web components of temperate freshwater lakes

Aquatic macrophyte taxonomic composition, species abundance and cover determine the physical structure, complexity and heterogeneity of aquatic habitats – the structuring role of macrophytes. These traits influence richness, distribution, feeding and strength of the relationships between food web communities in lakes. The aim of this study was to determine how lakes with different dominating macrophyte ecological groups affect planktonic food web components, emphasising the influence on young of year (YOY) fish and large (≥1 +) fish community. We hypothesised that different dominating macrophyte ecological groups have different structural effects on food web components and YOY fish growth, abundance and feeding. Studied lakes categorised into three different macrophyte ecological groups – lakes dominated by emergent, floating+floating-leaved or submerged vegetation. We found that all dominating ecological groups had a strong influence on plankton communities (except heterotrophic bacterioplankton and nanoflagellates), YOY fish and large fish. Floating-leaved plant dominance was positively related to planktonic food web structure and YOY fish weight, length, abundance and the consumption of zooplankton as a prey of all major species of YOY fishes. Larger fish tended to favour the presence of emergent vegetation. This conclusion has important implications for local managers and conservationists in respect to the maintenance and protection of littoral habitats and fish resources.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”. Also, this project has received funding from the European Union‘s Horizon 2020 research and innovation programme under Grant Agreement No. 951963.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”. Also, this project has received funding from the European Union‘s Horizon 2020 research and innovation programme under Grant Agreement No. 951963

The comparison of the feeding of European perch Perca fluviatilis L. larvae in littoral and pelagic habitats of northern temperate lakes

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. 1.1.1.2/VIAA/1/18/301, in agreement with State Education Development Agency of the Republic of Latvia Programme No. 1.1.1.2/16/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.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. 1.1.1.2/VIAA/1/18/301, in agreement with State Education Development Agency of the Republic of Latvia Programme No. 1.1.1.2/16/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

The diet of Eurasian perch larvae in lakes with different zooplankton assemblages

Eurasian perch has a great ecological importance in freshwaters as it is often a dominating predatory fish in ecosystems. The knowledge of perch feeding patterns, strategies, and adaptivity to food environment in their early life stages is essential to understand its population development and dynamics. It has been demonstrated that there exists a positive relationships between preferred prey availability and larval feeding success. We examined the diet of larval perch in their natural habitats of different zooplankton assemblages in three small lakes with varying ecological status. In each lake, both pelagial and littoral were studied. We found significant relation between zooplankton biomass in the lake and zooplankton biomass consumed by fish larvae. The most important food objects were crus- taceans (Bosmina longirostris, Chydorus sphaericus). Ciliates were consumed only in one lake. Our results show that perch larvae are flexible in their choice of food and can adapt to different food environments.The research is a part of the project "Fish feeding conditions in lakes with different planktonic food web structure and macrovegetation (MICROFISH)", No.1.1.1.2/VIAA/1/18/301. Agreement with State Educa- tion Development Agency of the Republic of Latvia No. Programme number 1.1.1.2/16/I/001. The project is financed by the European Regional Development Fund, the State budget of the Republic of Latvia and the foundation "Insti- tute for Environmental Solutions". Funding of this project was also provided by the European Union's Horizon 2020 research and innovation programme under grant agreement No 951963. Our great thanks to Nicholas Anthony Heredia from Latvian Institute of Aquatic Ecology who checked English.The research is a part of the project "Fish feeding conditions in lakes with different planktonic food web structure and macrovegetation (MICROFISH)", No.1.1.1.2/VIAA/1/18/301. Agreement with State Educa- tion Development Agency of the Republic of Latvia No. Programme number 1.1.1.2/16/I/001. The project is financed by the European Regional Development Fund, the State budget of the Republic of Latvia and the foundation "Insti- tute for Environmental Solutions". Funding of this project was also provided by the European Union's Horizon 2020 research and innovation programme under grant agreement No 951963. Our great thanks to Nicholas Anthony Heredia from Latvian Institute of Aquatic Ecology who checked English

Comparison of larval perch feeding between littoral and open-water sites of the lakes : [presentations]

The presentation took place at the 10th International Conference on Shallow Lakes in 2021.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963