Introduction to PERCIS V, the 5th percid international symposium

From 18 to 23 September 2022, over 80 scientists met at the Faculty of Science of the University of South Bohemia, České Budĕjovice, Czech Republic. This was the fifth gathering of percid biologists since the first one in 1976. The symposium was organised by the Biology Centre of the Czech Academy of Sciences, Institute of Hydrobiology (DeBruyne et al., 2023). The participants represented more than 20 countries and four continents (Europe, Asia, North America and Africa). Presentations included five invited keynote speeches, 50 contributed talks and 21 posters. Topical sessions were wide-ranging, including the biology of European perch Perca fluviatilis L. 1758, yellow perch Perca flavescens (Mitchill 1814), pikeperch Sander lucioperca (L. 1758), walleye Sander vitreus (Mitchill 1818), sauger Sander canadensis (Griffith & Smith 1843) and ruffe Gymnocehalus cernua (L. 1758); early life history and ontogeny; population dynamics; behaviour; evolution; fish stock management; diet; recreational fishing; invasive species; aquaculture; hydroacoustical research; physiology; genetics; predators and parasites; interspecific interactions. Presentations at PERCIS V and published in this special issue highlighted important aspects of percid biology. These included the generation of three genome assemblies of P. fluviatilis which will lead to improved understanding of the interactions between ecological and evolutionary processes (Vasemägi et al., 2023). Also spotlighted were geographical and within-waterbody distribution (in particular those in reservoirs; Blabolil et al., 2023; Sajdlová et al., 2023). Changes in diet, including methods used (gut content and stable isotope analyses) to compare them (Vejříková et al., 2023), and responses to eutrophication or oligotrophication (Jůza et al., 2023), and to invasive species (Jordan et al., 2023; Yang et al., 2023), were outlined. Percid management and the determination of both commercial and recreational fisheries policy, adaptation to climate change and continued improvement in their culture including overcoming bottlenecks were covered in the symposium. The significance of long-term investigations such as those on pikeperch in Finnish coastal waters (Olin et al., 2023), Lake Erie walleye (Yang et al., 2023), European perch in Swedish lakes (Holmgren & Petersson, 2023) and the continued investigations of yellow perch in Oneida Lake (Jordan et al., 2023) was emphasised. Contributors were invited to submit papers for publication in special issues in either of two journals published by Wiley, Inc. These were Ecology of Freshwater Fish (EFF) or Aquaculture, Fish and Fisheries (AFF). Manuscripts consistent with the scope and editorial practices of EFF appear in this special issue. Over the years, percid species, like salmonids, have received considerable attention from research scientists, fishers (commercial and anglers), aquaculturists and conservationists. Why was so much attention paid to one family of fishes? North American percids, walleye, sauger and yellow perch and European perch and pikeperch are economically and ecologically important fishes in their native geographic range. Other members, such as the darters (Etheostomatinae) of North America exhibit extensive diversity. There are at least 215 recognised species of darters. Unfortunately, c. 33% are at risk of becoming extinct according to the IUCN Red List (IUCN, 2018). The volume of information amassed on percids has been extensive and indicates that these fishes make perfect models for studying teleost biology, the impacts of fishing and fish culture. The first Percid Fish International Symposium, PERCIS I, was held at the Quetico Centre, Ontario, Canada, in 1976, and the proceedings were published in 1977 (Stevenson, 1977), PERCIS II was held in Vaasa, Finland (1995), and the proceedings were published in 1996 (Ranta, 1996), PERCIS III, held in Madison, Wisconsin, U.S.A. (2003), and the proceedings published in 2004 (Barry & Malison, 2004), and PERCIS IV, held in Tartu, Estonia (2016). As well as numerous published papers on percids, two FAO synopses written by Thorpe (1977) (on P. fluviatilis and P. flavescens) and Colby et al. (1979) (on Stizostedion vitreum vitreum, now S. vitreus), and at least five books [The Biology of Perch and Related Fish (Craig, 1987), Percid Fishes Systematics, Ecology and Exploitation (Craig, 2000), Biology and Culture of Percid Fishes Principles and Practices (Kestemont et al., 2015), Biology of Perch (Couture & Pyle, 2016), and Yellow Perch, Walleye, and Sauger: Aspects of Ecology, Management, and Culture (Bruner & DeBruyne, 2021)] have been published. All of the above have tended to concentrate on the ‘economically important’ members of the family and hopefully synthesised the knowledge accumulated in the scientific literature at the time of publication. The content of PERCIS 1 set a solid base for the study of these fishes across North America and Europe: The proceedings of the Symposium are the most comprehensive collection of papers on the biology and ecology of the more economically important members of the family Percidae assembled to date. The proceedings present a balance of fact and theory for the benefit of researchers, resource managers, and informed laymen. The reader will find an exceptional compilation of long-term data series showing changes in various fish communities with time. Also presented are numerous innovative and conceptually stimulating hypotheses and models relevant to contemporary management needs. PERCIS has focused on improved descriptions of percid habitats and compilation of information which permits a prediction of community changes resulting from habitat modification, exploitation, and other cultural disturbances. The contributions from Europe introduce the reader to or further inform him of the implications of functional morphology, the value of the guild concept in predicting community changes and species succession when habitat is altered, new methodology for estimating age composition of fish populations, advantages of precise knowledge of fishing effort to making management decisions, and a description of percid habitats in eastern Europe (Colby, 1977). The foundations in all aspects of percid taxonomy, morphology, physiology, ecology and fisheries management were well established by the mid-1980s. In the interval of 13 years between my first (1987) and second (2000) book on percids, I noted the number of publications had been considerable, although it was interesting to establish that gains in knowledge had not been in proportion to the prolific output. The most important and novel research during this time-period included molecular genetics and the use of DNA in stock identification. The techniques were used to trace the ancestry and evolution of the family. There had also been rapid development in aquaculture and rearing of several members of the family with improved knowledge on reproductive physiology and constraints in aquaculture. The role of percids in freshwater communities was also better understood especially the effects of predation and both inter- and intra-competition, which enabled managers to make improved predictions about the state of their stocks. The application of bioenergetic and ecosystem models, which had become more sophisticated and realistic, aided fishery policy and conservation. A quantitative approach was necessary to predict and manage the effects of varying harvest rates, climate change, pollutants and stocking. Several stocks had been monitored over a long-time period providing invaluable information. However, direct causative factors controlling population dynamics, in particular recruitment, were still poorly understood, as was the role played by percids in the ecosystem and how they could be used in biomanipulation. Further, it was still difficult to predict how percids responded to natural and human-induced perturbations. Fifteen years later on, in the Biology and Culture of Percid Fishes Principles and Practices (Kestemont et al., 2015), 75 authors from 15 countries contributed 35 chapters. The book is a comprehensive account of the biology and culture of percids. Subjects covered included systematics, ecology, reproduction, early life stages, development, growth, metabolism, nutrition, behaviour, husbandry, genetic modification, domestication, stress, immunology, diseases, health, commercial production, marketing and economics. Highlights were new molecular tools which allowed the elucidation of evolutionary diversification, development of out-of-season spawning (controlled by the environmental cues of temperature and photoperiod), molecular analyses to determine the quality of ova, embryos and larvae, development of the sensory systems and the gut, nutritional requirements and the function of lipids and fatty acids, biophasic growth, hormonal sexual reversal, selective breeding programmes, domestication, the use of intensified recirculating aquaculture systems (RAS), intensive laviculture, bioenergetics modelling, and culture of percids for enhancement. There was still a lack of information on controlling reproduction by hormones and lack of knowledge on the immune system. The Biology of Perch (Couture & Pyle, 2016) confined itself to the three perch species, P. fluviatilis, P. flavescens and Balkhash perch Perca schrenkii Kessler 1874 in 10 chapters. Again molecular tools, which are used in systematics and determining the current distribution of the three species both on a broad- and a fine-scale (spawning groups within the same lake) are described. More information is provided on the poorly known P. schrenkii. The value of long-term studies is highlighted in the study of over 20 years of P. flavescens in the St Lawrence River and the over 70-year study of P. fluviatilis in Windermere (sadly ending in 2019). The latter has led to a much better understanding of population dynamics of the species. Also covered in the book are advances in our knowledge of reproduction, parasites, behaviour and the use of P. flavescens in ecotoxicology research. From 2015 to the present there has again been an abundant outpouring of publications on percids, including another book Yellow Perch, Walleye, and Sauger: Aspects of Ecology, Management, and Culture (Bruner & DeBruyne, 2021). Chapters in this book compile recent research, including management and aquaculture of walleye, sauger and yellow perch in North America. These include techniques to evaluate current habitat and predict future habitat conditions, provide managers with detailed baseline information and biophysical models useful for evaluating adaptive management practices. Determination of habitat use and movement assessments were shown to have improved substantially with technological advancements in acoustic tags and extensive receiver array networks, which, combined with genetic and genomic tools, refined percid stock assessments and management. Advances in percid aquaculture techniques have enhanced growth, survival and disease resistance, improving percid stocking efforts and the production of marketable fishes. Emphasis is placed on the exchange of information between researchers and managers which must continue so as to advance techniques of percid management for commercial and recreational exploitation and the improvement of aquaculture practices to provide a lucrative commercial aquaculture industry. Based on a search of ResearchGate and using the keyword Perca, a considerable number of papers in the last 2 years are available. These include topics which relate to climate change such as the combined effect of body size and temperature on oxygen consumption rates; how cardiorespiratory adjustments to chronic environmental warming improve hypoxia tolerance; population ecology, growth, and physico-chemical habitat of anadromous European perch. There are also many papers relating to aquaculture such as the identification of microsatellites useful in selective breeding and assessment of behavioural and physiological traits as indicators of suitability for European perch aquaculture. These are just the tip of the iceberg. What are the important aspects of percid biology now and in the future? What are the major perturbations impacting on the health of percid stocks and how flexible are they in responding to these? Do we have the tools to enhance and conserve these fishes? Will aquaculture provide sufficient fishes for both direct consumption and stocking of dwindling populations? Do we have sufficient knowledge on the impact of invasive percids introduced outside their native range? Climate change needs careful consideration. Warmer temperatures can induce earlier spawning and extend distribution to cooler waters especially among larger fishes, which may not be able to adapt metabolically to increased temperatures (Christensen et al., 2020). Four species of percids, yellow perch, European perch, pikeperch and ruffe, however, have been found to be evolutionarily and phenotypically adapted to warmer temperatures including through morphological changes and behaviour (Xie et al., 2019). Studies, especially long-term ones, need to continue not only in the laboratory but also in the field. Can these studies be synthesised for PERCIS VI? A final note on long-term studies such as P. fluviatilis in Windermere. Studies on their biology started in the late 1930s and consistent annual monitoring commenced in 1943. As mentioned above this monitoring ceased in 2019 (76 years of data collection). Large numbers of perch were trapped during the Second World War and canned as ‘Perchines’. Results of this study up to 2013 are recorded in a chapter in the Biology of Perch. I would like to reiterate here the concluding remarks made in that chapter: The long-term study of perch in Windermere is both remarkable and unique. It originated during the dark days of a world war, survived a period of uncertainty and organisational change towards the end of the twentieth century, and is now the focus of extended international and interdisciplinary collaborations. This review alone cites 47 publications arising directly out of the perch programme and it is by no means exhaustive (Craig et al., 2016). Of special note was the relationships between growth and mortality in perch, i.e. between fast and slow growers, between cohort strength and biomass, and between stock and recruitment and the influence of biotic and abiotic factors. Without doubt, research at Windermere has made major contributions to understanding perch biology and ecosystem-based studies and management of fresh waters. It is particularly pleasing that the research programme has certainly met, and in many ways surpassed, the original vision described by Worthington (1950) of increasing scientific understanding of the ‘overfishing problem’ then (and still now) challenging fisheries biologists around the world. In closing, it is fitting to follow Le Cren (2001) and quote a statement that he originally made in his earlier review of Le Cren (1987), i.e., “Each period in our studies of fish in Windermere has produced new events, interpretations, and ideas which have caused us to modify previous conclusions. Long-term studies have a special value in fishery research”. In our view, this conclusion still remains relevant and continuation of the Windermere study has much to offer to future generations. It has been a privilege for us to play a role in it. Recently (summer 2022) the problems of increased eutrophication and warm temperatures in Windermere have been highlighted in the media (https://www.bbc.co.uk/news/uk-england-cumbria-62560942). Such conditions have great potential to produce algal blooms, which could very probably cause massive fish kills in the lake. These perturbations could have opened a new chapter in the amazing long-term investigation but the programme has closed, a sad end-note. However, ending on the positive, it is notable to see so many current projects on this important family of fishes as illustrated by speakers at PERCIS V and this issue who presented their latest findings on subjects such as response of percids to the environment, behaviour, recreational fishing, diets, genetics, invasive species, aquaculture and stock monitoring.

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