International audience | Overall recruitment of European glass eels (Anguilla anguilla) has decreased significantly since the early 1980s. Due to their long life cycle, benthic/demersal habits and high lipid content, eels might accumulate high concentrations of contaminants, but data concerning glass eels are still scarce. This study provides original data on methylmercury (MeHg) concentrations in glass eels at spatial (marine and estuarine), annual and seasonal scales. The relationship between MeHg concentrations in glass eels and their propensity to migrate up estuaries was also investigated. MeHg data were individually related to the eels’ energetic condition which was estimated by dry weight. Glass eel migratory behaviour was investigated in an experimental flume and related to the MeHg concentration and dry weight at the individual scale. Marine and estuarine glass eels were caught from 2004 to 2011. There was a strong inverse correlation between MeHg concentrations and dry weight. MeHg concentrations increased in marine and estuarine glass eels from 2004 to 2009 and from 2004 to 2010, respectively, and then, both groups decreased in 2011. On a seasonal time scale, MeHg concentrations were higher at the end of the fishing season (April). MeHg bioaccumulation is likely to result from different sources, but the lack of significant differences between marine and estuarine glass eels suggests that direct contamination during estuarine migration is low. Other sources such as maternal transfer or oceanic contamination are discussed

In scope of complex physical-chemical and biological examination of water quality of the Bocac lake, the river Vrbas and tributaries Ugar and Crna Rijeka, examinations of phytoplankton and zooplankton were performed during 2002 (March-November). In qualitative structure of phytoplankton 7 division were registered, with 93 taxa from 49 genera in total. In warmer period extreme domination have fire algae (Pyrrophyta). In zooplankton structure (Rotatoria, Cladocera, Copepoda) 78 taxa were registered from 36 genera, with distinct domination of Rotatoria group. According to saprobiological analysis species of olligo- and beta-mesosaprobic character are prevailing.

This work show and compare results of chlorophyll 'a' and phaeophytin 'a' concentrations during three years systematic examination. The samples were collected from the fourth sector of Palic lake, ones a month, during 2000, 2001, and 2002 using method by Szilagyi. Comparing values, a great seasonic changes of chlorophyll 'a' and phaeophytin 'a' concentrations is noticed.

The paper presents the seasonal overview of horizontal distribution and abundance for the species of genus Oithona in Bokokotorski Bay. Three species have been recorded. Oithona helgolandica and Oithona plumifera have a wide horizontal distribution within the Adriatic Sea, while Oithona nana is a typical euritherm and eurihaline form that occupies shallow and closed coastal areas along the eastern coast of Adriatic. Also presented are seasonal oscillations and quantitative presence of these species in the Copepoda population during 2002.

In this paper we have presented the results of the investigation of phytoplankton carried out in the Hydrosystem DTD (Danube - Tisza - Danube) in Banat region from April 2003 till November 2004. Accordingly, halophilic algae community of eutrophic type has been described. Seasonal distribution and presence of algae taxa in the investigated water varied significantly. The diatoms were mostly represented by periphytic forms in the huge quantities, which was particularly the case with an avalanche of the eutrophic species such as: Bacillaria paradoxa, Anomoeoneis sphaerophora, Nitzschia acicularis, N. palea, Navicula cryptocephala, Fragilaria ulna, Melosira varians, Surirella ovalis, etc. The significant number of Cyclotella meneghiniana during summer and Euglenophyta in autumn revealed high trophic status in some sections of HS DTD.