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Background Considering wild inter-populational phenotypic differentiation can facilitate domestication and subsequent production of new species. However, comparing all populations across a species range to identify those exhibiting suitable key traits for aquaculture (KTA; i.e. important for domestication and subsequent production) expressions is not feasible. Therefore, proxies highlighting inter-populational divergences in KTA are needed. The use of such proxies would allow to identify, prior to bioassays, the wild population pairs which are likely to present differentiations in KTA expressions in aquaculture conditions. Here, we assessed the relevance of three alternative proxies: (i) genetic distance, (ii) habitat divergence, and (iii) geographic/hydrologic distances. We performed this evaluation on seven allopatric populations of Perca fluviatilis for which divergences in KTA had already been shown. Results We showed differences in the correlation degree between the alternative proxy-based and KTA-based distance matrices, with the genetic proxy being correlated to the highest number of KTA. However, no proxy was correlated to all inter-populational divergences in KTA. Conclusion For future domestication trials, we suggest using a multi-proxy assessment along with a prioritisation strategy to identify population pairs which are of interest for further evaluation in bioassays. Supplementary Information The online version contains supplementary material available at 10.1186/s12862-021-01937-z.

The density and mean size of 0 + pikeperch (Sander lucioperca) were studied in late summer in 2004-2017 in clay-turbid and eutrophic Lake Tuusulanjarvi in southern Finland. Hydroacoustics and simultaneous experimental trawling were used to estimate the density of 0 + pikeperch. In some autumns, 0 + pikeperch was the most abundant species in the pelagic fish assemblage. However, the annual amplitude of pikeperch density was extremely high (1,300 -19,900 individuals ha(-1)). The density and size variations of 0 + pikeperch were analysed in relation to air temperature sums and degree days. Unexpectedly, the density of 0 + pikeperch showed no correlation with the air temperature sums or degree days, but both the mean length and weight of 0 + pikeperch correlated positively with these temperature variables. The highest correlation coefficients between mean size and temperature were found with temperature sums over 10 degrees C and degree days over 5 degrees C. The correlation between density and condition of 0 + pikeperch was negative but non-significant. The high density of 0 + pikeperch in some autumns suggests that pikeperch may play a central role in the pelagic food web in eutrophic lakes - not only as a predator of planktivores but also by its own planktivory.

Generalist fish species can feed on a wide resource spectrum and across trophic levels depending on resource availability and trophic interactions. Crucian carp (Carassius carassius) represents a good candidate species to investigate variation in the trophic ecology of generalist fish as it can be found in highly variable fish communities and its resource use is well documented. In this study, we explored the trophic ecology of crucian carp at the individual and population levels using stable isotope and gut content analysis. We tested if trophic resource use varied according to lake productivity, predation risk, intra- and interspecific competition, or individual fish size. We found that crucian carp resource preference was highly variable among and within lakes. In predator-free lakes, small crucian carp occurred in high densities, showed increased interindividual specialisation, and relied mainly on pelagic zooplankton. In presence of predators, large crucian carp occurred in low densities and included greater proportions of benthic macroinvertebrates in their diet. This shift in resource use was further favoured in productive, shallow lakes where littoral prey were probably abundant. Resource partitioning was an important factor determining crucian carp niche use, as fish had higher trophic position in absence of other cyprinids. Crucian carp showed highly dynamic resource use and food preferences in response to variable environmental conditions. Overlooking complex diet preferences of generalist fish may lead to an oversimplification of freshwater community dynamics.

We dedicate this paper to the late Maria Rosa Miracle, who was a key researcher in the shallow lakes community, always enthusiastically dedicated to science, and always ready to discuss and guide younger scientists and fellow colleagues on the dynamics of zooplankton as well as on shallow lakes functioning at large. She will be sadly missed.Plant habitat complexity can buffer against predator-prey interactions by offering physical refuges, and also novel microhabitats for alternative prey. In shallow lakes, submerged and free-floating plants affect predator-prey interactions with expected differences related to climate-driven differences in fish community structure. We tested the overall hypothesis that fish predation shapes the structure of plant-associated macroinvertebrate communities. By introducing artificial free-floating and submerged plants in a total of 14 shallow lakes under contrasting climate regimes (temperate and subtropical), we predicted that higher densities of macroinvertebrates would occur in the temperate zone where littoral fish predation is comparatively weaker than in the subtropics. We also tested the hypothesis that different structural complexities and % PVI would lead to different association patterns. Taxonomic richness, diversity, and densities of plant-attached macroinvertebrates were several fold higher in the temperate lakes. Macroinvertebrate densities per unit of plant weight were generally higher on the more complex free-floating than on the more abundant (as % PVI) submerged plants. The structure of littoral macroinvertebrates showed no clear relationship with the trophic state gradient. Fish communities, whose structure (biomass, density and habitat use) differed consistently between the temperate and subtropical locations, seemingly shaped the macroinvertebrate communities, most likely via predation and in the subtropics potentially also by competition. Free-floating plants appeared as a better anti-predation refuge or a preferred habitat for macroinvertebrates, particularly in the subtropics, but with increasing water turbidity this pattern became less distinct. In contrast, in the temperate lakes, the use of artificial plants by macroinvertebrates was rather related to the biomass of periphyton than to their refuge capacity, thus suggesting stronger bottom-up effects. A stronger fish predation pressure, which is to be expected with climate warming and eutrophication, may reduce the richness and abundance of plant-associated macroinvertebrates, with potentially strong impacts on shallow lake functioning. A warming-driven expansion of free-floating plants could, if moderate, weaken such effects, but a more diverse macrophyte community would facilitate co-existence of macroinvertebrate and fish.

Most studies of animal personality attribute personality to genetic traits. But a recent study by Magnhagen and Staffan (Behav Ecol Sociobiol 57:295-303, 2005) on young perch in small groups showed that boldness, a central personality trait, is also shaped by social interactions and by previous experience. The authors measured boldness by recording the duration that an individual spent near a predator and the speed with which it fed there. They found that duration near the predator increased over time and was higher the higher the average boldness of other group members. In addition, the feeding rate of shy individuals was reduced if other members of the same group were bold. The authors supposed that these behavioral dynamics were caused by genetic differences, social interactions, and habituation to the predator. However, they did not quantify exactly how this could happen. In the present study, we therefore use an agent-based model to investigate whether these three factors may explain the empirical findings. We choose an agent-based model because this type of model is especially suited to study the relation between behavior at an individual level and behavioral dynamics at a group level. In our model, individuals were either hiding in vegetation or feeding near a predator, whereby their behavior was affected by habituation and by two social mechanisms: social facilitation to approach the predator and competition over food. We show that even if we start the model with identical individuals, these three mechanisms were sufficient to reproduce the behavioral dynamics of the empirical study, including the consistent differences among individuals. Moreover, if we start the model with individuals that already differ in boldness, the behavioral dynamics produced remained the same. Our results indicate the importance of previous experience and social interactions when studying animal personality empirically.

Estimates of gut evacuation rates of Nephrops norvegicus (Linnaeus, 1758) (Crustacea, Decapoda) were obtained during laboratory and field experiments. Individuals were collected off the south coast of Portugal in December 1997 and July 1998. Gut evacuation rates (R.h-1) were calculated from the slope of the regression of the natural logarithm of dry stomach content weight versus time, using data obtained by the serial slaughter method. The values obtained during laboratory (R=0.172 h-1) and field experiments (R=0.177 h-1) are compared with gut evacuation rates reported for other marine organisms. The results obtained for both experiments are within the range of the values in the literature, even in the case in which different methodologies were used., No disponible

International audience; 1. Sampling of lake fish assemblages is a challenging task in fish science, and the information obtained strongly depends on the choice of sampling gear. The use of more than one sampling technique is generally preferred in order to achieve a comprehensive view on fish assemblage structure. Therefore, the knowledge of whether catches between fishing gears are comparable is crucial. 2. We compared catches in benthic multi-mesh gillnets with fish biomass estimates obtained by vertical hydroacoustics in 18 European lakes strongly varying in morphometry and trophic status. Separate analyses were conducted for different depth strata and for several fish length thresholds to account for depth- and size-selective gillnet catches. 3. Gillnet catches and hydroacoustically obtained fish biomass estimates were significantly correlated. The strength of correlations was independent of the fish length thresholds applied, but varied across different depth strata of the lakes, with the strongest correlations occurring in the shallow strata. 4. The results support the applicability of vertical hydroacoustics for the quantification of fish biomass in stratified lakes. Survey designs combining hydroacoustics with limited gillnetting at sampling dates shortly one after the other, the latter for the purpose of inventory sampling only, are a cost-effective strategy for sampling fish assemblages in lakes. However, gillnet sampling does not provide reliable fish density estimates in very deep lakes with separate, pelagic-dwelling fish assemblages.