Marco Bertoli

Energy Densities of Brown Trout (Salmo trutta) and Its Main Prey Items in an Alpine Stream of the Slizza Basin (Northwest Italy)

ABSTRACT In the present study, energy densities of 80 adult brown trout (Salmo trutta), seasonally sampled in an alpine stream in the eastern Alps and energy densities of their main prey items, were determined. The energy density (J/g wet mass) and dry weight content (%) of fish were highly correlated (p<0.00 1) and averaged 5, 611.6 ± 857.9 J/g wet mass and 25.3 ± 2.1% dry weight, respectively. Energy density values were significantly higher in fish sampled in spring than in other seasons. No major changes in the energy content were observed due to age or sex. Macroinvertebrates. particularly Ephemeroptera and Diptera, were the major food source of brown trout in the sampled area. Their gross energy content varied within a wide range of values (1, 654–5, 110 J/g wet weight), depending on the taxa and family or genus within a given taxon.

Seasonal multi-annual trends in energy densities of the midges (genus Chironomus) in a Mediterranean temporary wetland (Natural Regional Reserve of the Isonzo River Mouth, Northeast Italy)

The present study is an attempt to deepen the knowledge about energy patterns in a detritus-based ecosystem located within a temporary wetland, where changes of water level can affect productivity, turnover of organic matter and the flow-through energy. Energy density was directly measured using an adiabatic bomb calorimeter in samples collected in autumn, spring and summer. Dipterans belonging to the genus Chironomus were the most common and representative invertebrates within the study area. Starting from these measures, a predictive model based on the relationship between energy density and percentage of dry weight was developed, validated and applied to build a multi-annual dataset. This model was used to investigate seasonal energy density trends on longer time-scale, in relation to physical and chemical features, weather conditions and decomposition dynamics. The used approach allowed to build a 3-year dataset and to identify clear seasonal trends; moreover, the application of the model highlighted patterns in relation to precipitation regime, decomposition dynamics and the effects due to variations of these features in the investigated temporary detritus-based system over a multi-annual scale.