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This study examined the diet and assimilation of basal resources by the redeye piranha, Serrasalmus rhombeus, in a low-flow section of the Xingu River, Brazil. Samples of both individuals and basal resources were collected monthly from December 2020 to November 2021, encompassing a complete hydrological cycle. The stomach contents of the individuals and tissue samples of the species were submitted to stable isotope analysis for δ13C and δ15N. The species exhibited a predominantly piscivorous diet, with no observed variation in diet composition or feeding intensity across different hydrological periods. However, δ15N levels in the species varied between periods, indicating potential shifts in the availability and assimilation of basal resources during controlled flood pulses. The trophic position of the species was higher during flood periods and lower during low-water periods. Mixing models revealed the assimilation of different basal sources in each period, with the significance of terrestrial producers evident in almost all periods except during ascending. These findings are crucial for understanding the trophic dynamics of predators in flooded forests with reduced flow, highlighting the reliance of S. rhombeus on piscivory while being supported by terrestrial basal sources in its trophic chain. [ABSTRACT FROM AUTHOR]

The pumpkinseed Lepomis gibbosus (Linnaeus, 1758) is a small centrarchid fish species from North America that has invaded most European basins, with pronounced expected impacts. Analyses of pumpkinseed diet in its invasive range using gut content analysis (GCA) show macrozoobenthos as the most common dietary item, suggesting a competitive effect on native fish communities. Our study uses a combination of GCA and stable isotope analysis (SIA) to document pumpkinseed diet at two sites in its invaded range and relates pumpkinseed diet preferences with parasitic load. SIA revealed juvenile fish as a major prey item at one of the sites (63 and 50% of the diet of small and the large fish), while GCA showed pumpkinseed preying mostly on macroinvertebrates (chironomids, gastropods, Ephemeroptera, and Zygoptera larvae) at both sites. While infrequent infection by trophically transmitted parasitic nematodes could be related to low consumption of zooplankton, substantial infection by metacercariae of Posthodiplostomum centrarchi Hoffman1958 appears to reflect relatively high consumption rates of its intermediate host, physid snails. Using SIA allowed to demonstrate that pumpkinseed feeding in its non-native range can be based on piscivory, emphasising the need for combining multiple methods when studying the impact of non-native species on food webs. [ABSTRACT FROM AUTHOR]

Life-history tradeoffs between energy investments in reproduction versus somatic growth may be highly important for fish populations suffering from food limitations. This study addresses life-history tradeoffs in a stunted Arctic charr population from a subarctic lake sampled annually over a 12-year period. The vast majority of charr matured early, grew slowly toward average adult sizes of 13-14 cm, and had a short longevity with few fish reaching ages older than 6 years. Some gender differences in life-history strategies related to sexual maturation were revealed, likely due to energetic constraints from high cost of egg production. Some charr followed a highly different growth trajectory, growing rapidly and attaining lengths >40 cm. These fast-growing individuals matured later and reached higher ages than the stunted fish. Hence, there was a distinct tradeoff between early versus late sexual maturation, the former strategy resulting in short generation time enhancing the survival up to first spawning and the latter being related to a dietary shift to cannibalism resulting in increased growth and body size, and reproduction at a postponed maturation age. This dual pattern was sustained over the 12-year study period, apparently reflecting two contrasting stable strategies. [ABSTRACT FROM AUTHOR]

The success of predators in species invasion will depend on their interactions with their own predators and competitors. The present study examined whether the predation of piscivorous fish among other piscivorous fish could be an active mechanism in species invasion. The diet of eleven piscivorous fish found in the upper Paraná River basin was analyzed during eight years. Seven of the fish species were native to the river basin, and four were invasive species. The diet composition of the studied species did not differ from each other, and a high value of niche overlap was found among invasive species with native species. Invasive species consumed higher amounts of piscivorous species, mainly Hoplias sp. 1 and C. kelberi. Salminus brasiliensis was the only native species with high values of predation over piscivorous fish. There were no significant differences between the consumption of piscivorous fish and their abundance. Overall, the consumption of piscivorous fish by invasive species can act as a mechanism for their success and maintenance in a new environment. Piscivorous invaders radically change the composition of their new environment more than other trophic levels; therefore, we recommend special care with the introduction of piscivores. [ABSTRACT FROM AUTHOR]

Fish play a key role in the trophic dynamics of lakes, not least in shallow systems. With climate warming, complex changes in fish community structure may be expected owing to the direct and indirect effects of temperature, and indirect effects of eutrophication, water-level changes and salinisation on fish metabolism, biotic interactions and geographical distribution. We review published and new data supporting the hypotheses that, with a warming climate, there will be changes in: fish community structure (e.g. higher or lower richness depending on local conditions); life history traits (e.g. smaller body size, shorter life span, earlier and less synchronised reproduction); feeding mode (i.e. increased omnivory and herbivory); behaviour (i.e. stronger association with littoral areas and a greater proportion of benthivores); and winter survival. All these changes imply higher predation on zooplankton and macroinvertebrates with increasing temperatures, suggesting that the changes in the fish communities partly resemble, and may intensify, the effects triggered by eutrophication. Modulating factors identified in cold and temperate systems, such as the presence of submerged plants and winter ice cover, seem to be weaker or non-existent in warm(ing) lakes. Consequently, in the future lower nutrient thresholds may be needed to obtain clear-water conditions and good ecological status in the future in currently cold or temperate lakes. Although examples are still scarce and more research is needed, we foresee biomanipulation to be a less successful restoration tool in warm(ing) lakes without a strong reduction of the nutrient load. [ABSTRACT FROM AUTHOR]

Flexibility in the feeding habits of juvenile Nile perch (1–30 cm total length) was studied from September 1988 to September 1989 at four sites (depth range: 1–25 m) in the Mwanza Gulf of Lake Victoria. During this period haplochromine cichlids were virtually absent in the area. We looked at the combined effects of predator size, season and habitat. Stomach content analysis showed that with increase in size, the diet of Nile perch shifted from zooplankton and midge larvae, to macro-invertebrates (shrimps and dragonfly nymphs) and fish. At a size of 3–4 cm Nile perch shifted from size-selective predation on the largest cyclopoids to predation on the largest, less abundant, calanoids. Zooplanktivory ended at a size of ca. 5 cm. Although an ontogenetic shift in the diet of juvenile Nile perch was obvious at all sampling stations, the contribution of prey types appeared to be habitat related. With increasing water depth the frequency of occurrence in the diet of most prey types decreased, but that of shrimps increased. At the entrance of the gulf (20–25 m deep) shrimps were the main food source throughout the year. Halfway the gulf (12–16 m), Nile perch showed seasonality in their feeding behaviour. Shrimps were taken there especially during the rainy season (January to May) when their densities at this station were high, whereas cannibalism prevailed during the rest of the year. In an environment with Nile perch and dagaa as alternative prey, shrimps were taken almost exclusively. They could be regarded as a key prey for Nile perch between 5 and 30 cm. [ABSTRACT FROM AUTHOR]

The aim of the present study was to analyse and compare the feeding behaviour of large perch (>25 cm total length) in two lakes of different state and corresponding differences in food availability. Investigations were conducted in the Bautzen Reservoir, Germany, (biomanipulated, macrophyte cover <1%) and in Lake Ring, Denmark (non-biomanipulated, macrophyte cover ca. 20%). Fish were sampled regularly using trawl nets and gill nets. We focused our study on seasonal diet patterns. Further, we investigated size-related feeding and predation on both the juvenile fish and invertebrate communities. The availability of Chironominae was high in both lakes (e.g. ca. 1500 ind. m-2 in Lake Ring), but age-0 fish abundance was most probably higher in Bautzen Reservoir (6.4 individuals m-3 in the beginning of June 1998). Invertebrates and age-0 fish were the main food components of large perch of both populations. Mean lengths of prey fish were consistently smaller than those in situ. Large perch in Bautzen Reservoir started earlier to feed on age-0 fish, which was not related to prey fish sizes. Predation on the age-0 fish community was distinctly higher in Bautzen Reservoir than in Lake Ring. Generally, invertebrates represented the most important food of large perch in Lake Ring, whereas the by far dominant food resource of large perch in Bautzen Reservoir was the age-0 fish stock. In conclusion, it can be stated that the prey fish availability was an important factor in determining the feeding behaviour of large perch. [ABSTRACT FROM AUTHOR]