Few studies have examined multiple life‐history traits across a latitudinal gradient to test whether variation in growth rate and mortality schedules induces trends predicted by life‐history theory. We collected data for the following life‐history traits for 75 Eurasian perch (Perca fluviatilis) populations: growth coefficient (K) and asymptotic body length (L∞) from the von Bertalanffy growth model, size at ages one and two years, specific juvenile growth rate, instantaneous adult and juvenile mortality rates, life span, age and length at maturity, and reproductive life span and investment. All life‐history traits except L∞ were significantly correlated with latitude. In general, growth rates, mortality rates, and reproductive investment decreased with latitude, whereas age at maturity, size at maturity, and life span increased with latitude. Populations could be grouped into two categories based on variation in L∞: stunted (small sized) vs. piscivorous (large sized). Four trait–latitude relationships differed between these two types: the growth coefficient (K) and the juvenile growth rate were larger, and age and length at maturity were lower in the stunted populations compared with piscivorous populations. Perch from southern populations tend to grow fast and experience high juvenile and adult mortality rates. As predicted from life‐history theory, this selects for an early age and small size at maturity and relatively large investment in reproduction. The opposite pattern was found for northern populations.

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Summary 1.The gape size of the predator and the body depth of its prey are the main factors deciding whether a gape-limited piscivore can ingest a potential prey fish. The connection between morphological variation in pike and its prey was studied in five lakes with different proportions of pike, perch and roach. 2. At low prey abundance the prey fish are larger than in lakes with a higher prey density. In contrast, the pike are smaller but have relatively high gapes in the lake with the lowest prey availability, and larger but with smaller gapes at the highest prey density. There is a positive correlation with relative gape size of pike and relative body depth of prey among the five lakes. 3. Using the body depth in perch and roach and the gape size in pike, the proportion of the prey populations that could be eaten by the pike was calculated. In the low prey density lakes the pike could ingest a smaller proportion of the prey than in the high prey density lakes where most pike can eat all available prey sizes. 4. Competition for food in a situation where prey are big may cause a selection for a higher gape size. Our results indicate that this mechanism could be the reason that pike from different lakes vary in relative gape size.

Recent phylogenetic studies on Nematinae based on DNA sequences have shown extensive incongruencies with current nomenclature of genus-group taxa. Here, we expand previous DNA sequence datasets based on three genes (CoI, Cytb, and EF-1α), to include a fourth (NaK) and more genera. The analyses largely confirm the previous findings, particularly the existence of two well-supported large clades, Euura and Pristiphora, together comprising more than 75% of the species of Nematinae. Basal relationships within these two clades remain poorly resolved, mirroring the difficulties in delimiting genera based on morphology. In addition, a moderately supported small clade, Nematus, is found. The relationships between the Euura, Pristiphora, and Nematus clades are uncertain. Therefore, to stabilize the nomenclature we treat these clades as genera. This taxonomic treatment results in numerous new combinations of species names. The following synonymies are

Body shape of young-of-the-year (YOY) perch Perca fluviatilis, and number and size of potential predators (perch and pike Esox lucius) were compared across five lakes in northern Sweden. Body depth and dorsal fin ray length of YOY perch differed between lakes, with high relative body depth and long dorsal fin rays found in the lakes where the number of large piscivores was the highest. The most slender fish were found in the lake where the perch population had the smallest individuals and pike occurred in very low numbers. The average body mass in YOY perch from the two lakes with highest and lowest body depth, respectively, were the same, which indicates a difference between lakes in the relation between growth in length and in depth. Both body depth and fin ray length were correlated with predation risk by pike. Fin ray length was also correlated with number of piscivorous perch. Selection for different body shapes can be caused by different biotic and abiotic factors, singly or in combination, and the results from this study indicates that predation risk is one of these factors affecting body depth and fin ray length in perch.