Spatial variations in feeding habits and trophic levels of two small pelagic fish species in the central Mediterranean Sea.

Trophic ecology of adults of European sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) was examined and compared among various regions of central Mediterranean Sea. Carbon and nitrogen stable isotope analyses (δ(13)C and δ(15)N) were adopted as a tool to determine changes in feeding behaviour of adults of sardines and anchovies. In the study period (summer) a clear geographical pattern was recognized in the isotopic composition of both species, with an increasing trend northward. The highest variations in isotopic signal were linked to the geographical positions of the samples and, especially, between pairs of areas: South Sicily/South Campania and Gulf of Gaeta/South Elba. Higher isotope values were found in the anchovies and sardines caught in northern Tyrrhenian Sea, while lower values were mostly estimated in the southern region. Higher carbon and nitrogen isotopes may reflect a more coastal behaviour of both species, being (13)C-enriched source from benthic primary producers in addition to phytoplankton. Variations in the nitrogen isotope ratio may reflect not only differences in the trophic level of prey species, but also variations in the baseline level of food webs. Our results support the hypothesis that feeding behaviour of both species is directly or indirectly influenced by local factors, or by resource partitioning based on zooplankton size. Findings can supply knowledge needed for improving fish stock management and promoting plans able to take into account also local ecosystem analysis.

Mercury in fishes from Augusta Bay (southern Italy): risk assessment and health implication.

Our study reports on the total mercury (HgT) concentrations measured in the muscles and livers of several benthic, demersal and pelagic fish species caught inside and outside of Augusta Bay (southern Italy), a semi-enclosed marine area, highly contaminated by the uncontrolled (since the 1950s to 1978s) discharge of the largest European petrochemical plant. Mercury levels in fish tissues are discussed with regard to specific habitat, size and/or age of the specimens and HgT distribution in the bottom sediments. Results suggest a still active Hg release mechanism from the polluted sediments to the marine environment. Also, the high HgT concentrations measured in fishes caught in the external area of the bay imply a potential role of Augusta Bay as a pollutant source for the Mediterranean ecosystem. Finally, values of hazard target quotient (THQ) and estimated weekly intake (EWI) demonstrate that consumption of fishes caught inside the bay represents a serious risk for human health. Also, data indicate that intake of fishes caught from the external area of the bay, especially for that concern demersal and benthic species, could be represent a significant component of risk for the local population.

Evidence that severe acute stress and starvation induce rapid atresia of ovarian vitellogenic follicles in Atlantic bluefin tuna, Thunnus thynnus (L.) (Osteichthyes: Scombridae).

The effects of different stressors on the atretic degeneration of ovarian vitellogenic follicles, as well as on the ovarian mass, were examined in female Atlantic bluefin tuna, Thunnus thynnus (L.), from the Mediterranean Sea. The stressors taken into consideration were short-term starvation (up to 14 days), long-term cage rearing (1 year) and crowding-induced severe panic frenzy. Wild-caught individuals were used as a control group. Fish subjected to either severe panic frenzy or starvation exhibited a decrease in gonad mass and had significantly higher intensity of α atresia in the vitellogenic follicles (means: 78% and 58%, respectively; range: 36-100%) than either wild or long-term caged individuals (means: 32% and 30%, respectively; range: 19-44%). The extensive atresia in fish stressed by severe panic frenzy was observed as early as 24 h after the stressing event. The present study represents the first evidence of the extreme susceptibility of Atlantic bluefin tuna to severe acute stress during vitellogenesis; it also shows that starvation is associated with progressive reabsorption of vitellogenic oocytes.