Elisabetta Pizzul

Mineralogy and geochemistry of otoliths in freshwater fish from Northern Italy

Asteriscus, sagitta and lapillus otoliths of freshwater fishes (Cyprinids) from the Friuli Plain were mineralogically and chemically analyzed. All the analyzed fish showed that sagitta and lapillus consist of aragonite whereas asteriscus is made of vaterite. Chemical analysis showed that different Na, K, Mg and Sr concentrations are highly correlated with the mineralogy of the otoliths. Moreover there was a different trend of accumulation between vateritic and aragonitic otoliths. In particular it has been found that Mg is mainly present in vaterite otolith (asteriscus), while Sr is mainly present in aragonite otolith (lapillus). This fact was confirmed by statistical analyses. Our hypothesis is that this unusual high content of Mg could be related to the organic matrix present in asteriscus otolith, and, consequently, that the different organic matrix responsible for the different calcium carbonate polymorph is strictly correlated with the concentrations of at least some microelements.

Proposed standard mass equations for European chub Leuciscus cephalus in Italy.

Total length (L(T)) and mass measurements of 28,596 specimens of European chub Leuciscus cephalus, collected from a variety of waterways across Italy, were used to compute standard mass (W(s)) equations by both empirical percentile (EmP) and regression line percentile (RLP) methods. The use of the EmP W(s) equation [log(10) W(s) = -4·79 + 2·68log(10) L(T) + 0·10(log(10) L(T))(2)] to compute relative mass (W(r)) of L. cephalus in Italy is suggested, as it was not influenced by length-related bias (L(T) range of application = 70-470 mm).

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.

Biology of pike, Esox lucius (Esocidae), in the lower plain of Friuli‐Venezia Giulia (north‐eastern Italy)

Abstract This study investigates the biology of Esox lucius in an irrigation ditch, Storta Roggia (Torviscosa, Udine), in the lower plain of Friuli‐Venezia Giulia (north‐eastern Italy). About twenty fish were captured monthly from May 1996 to May 1997. Variables such as age (as determined from reading scales) and stomach contents were recorded from these fishes. Additionally, the gonads were excised and fixed to assess the reproductive stage. These fishes were from eight age‐classes (0–7 years). Age classes 6 and 7 were chiefly females. Their diet was chiefly fish and benthic macroin‐vertebrates. Their reproductive period was from the second half of March to May. Several female specimens collected within the second half of April and May were in a spent‐spawning condition or with degenerative oocytes. Some male pike from age‐class 1 attained maturity, while females did not attain sexual maturity until age‐class 2 or later.

Histomorphological and Biochemical (Serum 17β-estradiol) Characterization of the Reproductive Cycle of Female Common Carp (Cyprinus carpio) in Northeast ltaly

ABSTRACT To clarify the spawning seasonal dynamics of common carp (Cyprinus carpio) in northeast Italy, female fish were collected monthly from July 2002 to June 2003. The gonadosomatic index (GSI), histomorphology, 17β-estradiol serum concentration, and relative fecundity were compared. Between March-April and May-June, statistically significant differences were found in GSI, 17β-estradiol, and relative fecundity. Intermediate multispawner stages were found by histological analysis of specimens caught in July-August 2002 and May-June 2003. Final maturation stage was found mostly in March-April. Development trends were well correlated with water temperature. Histomorphological analysis revealed that oocytes at the exogenous vitellogenesis stage were retained throughout the winter and final maturation was reached during a short period (March-April). The beginning of the spawning season was fixed between April and May, and the end of spawning occurred during July and August.

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.