This paper reports the first record of the Atlantic soft pout Melanostigma atlanticum Koefoed, 1952, from the eastern Mediterranean Sea. The specimen was caught in a pelagic trawl during a research trip carried out north of the island of Crete (Greece) in December 2019. The fish measured 66.1 mm in total length and weighed 0.810 g. The presence of M. atlanticum in the eastern Mediterranean Sea indicates that the geographical distribution of the species is not restricted only to the western part of it but spreads throughout the basin. Melanostigma atlanticum is typically found in the deep sea, where limited surveys and research have resulted in major data gaps. The lack of recording of the species until recently in the eastern Mediterranean Sea is attributed to the species' small size and slender body shape that allow it to escape traditional fishing gears, as well as the low trawling activity in depths greater than 400 m and the lack of surveys targeting the mesopelagic fish communities.

Understanding the role played by sunken vessels in Mediterranean marine ecosystems is acquiring increasing importance. The aim of this research was to study the fish communities associated with four shipwrecks, by means of underwater visual censuses performed by a remotely operated vehicle, and to test the differences in composition of fish assemblages between these shipwrecks and the adjacent soft bottoms, considered as control sites. Multivariate analysis on the total fish assemblage showed significant differences between wrecks and controls. Results also showed higher levels of species richness and abundance near all wrecks than at a short distance from them on soft bottoms, thus indicating that these sunken vessels, thanks to their higher habitat complexity, act as artificial reefs, attracting aggregations of fish species and leading to a greater diversification of the local fish assemblage. Nevertheless, shipwrecks, which are an ideal target for recreational fishermen, could contribute to the over-exploitation of some high-value fish species, such as Mycteroperca rubra, Dentex dentex and Diplodus spp., attracted by the artificial hard substrate of the vessel-reefs. The recent European directives suggest an urgent need for a better understanding of the crucial role played by these potential sources of pollutants on marine environments and ecosystems. An ecosystem approach to study and monitor these pollutant sources is, therefore, mandatory for appropriate remediation and/or mitigation of the potential negative effects on a productive and healthy ocean.

Variations in fish communities of shallow lakes in the Yangtze basins were investigated from September 2007 to September 2009. Six lakes were chosen for comparative study of species composition and diversity in relation to environmental variations. Lake heterogeneity was described with environmental physico-chemical variables, using principal component analysis. Sixteen families, composed of 75 species of fish were found in the studied lakes, Cyprinidae being the dominant group. Fish species were divided by habitat preference and trophic guild: benthopelagic and herbivorous fish were the most common guilds in all lakes. Species diversity and richness were significantly higher in spring, while the evenness, expressed by equitability of Simpson’s index, was not significantly different among seasons. Species richness and diversity were significantly higher in vegetated lakes (e.g. Liangzihu Lake) than in non-vegetated lakes (e.g. Biandantang Lake), with the largest area (Liangzihu Lake) harbouring the largest species richness and the greatest diversity. The relationship between environmental variables and fish assemblage were analysed using canonical correspondence analysis (CCA). The dominant gradients describing species composition and abundance among the sampling sites were: total phosphorus, total nitrogen, chlorophyll a, transparency and water depth. Our study led to the following conclusions: 1) the water quality was better - i.e. high transparency, low total phosphorus (TP) and total nitrogen (TN) and chlorophyll a- in vegetated lakes than in unvegetated lakes; 2) vegetated lakes had higher fish diversity than unvegetated lakes; 3) fish relative abundance (CPUE: number of fish per fishing pass) was significantly related to water chemical parameters. Consequently, the details of the findings are useful and relevant for developing suitable conservation strategies to sustain the integrity of fish communities in these lakes.

In recent decades, marine reserves have been established either to protect ecosystem structure and biological diversity or to serve as management tools to counter the overexploitation of fish stocks. The Cape Roux marine protected area (MPA), in the Mediterranean Sea, was established in December 2003 for the management of artisanal fisheries and enhancement target fish stocks.

Monitoring of littoral fish assemblages (0–30 m depth) in this zone began one year after the MPA was set up. The survey was conducted at 6 stations, located inside and outside the MPA, using three methods: underwater visual census (UVC) on transects, UVC using a new fish assemblage survey technique (FAST), and experimental net fishing performed by a fisherman. The FAST indices were derived from visual censuses, performed along a random pathway, scoring species on a presence/absence basis and size on a 2-class basis. Indices were calculated seasonally, by applying “weights” according to species and size. This study presents results obtained between October 2005 and June 2007. In the protected area, the experimental fishing yielded significantly higher abundance and species richness, and the FAST method highlighted a decrease in seasonal fluctuations. These two complementary methods (UVC and experimental fishing) revealed the early changes in fish assemblages in response to protection. The FAST method employed here seems to be relevant for the study of artisanal fishery target fishes, as a low-cost and sensitive UVC method.

The fish diversity of the Slovak segment of the Danube (representing the transitional zone from the rhithron to the potamon) was under the control of the inland delta which existed in this region until 1992. Seventy-six species were recorded in the studied river section: 61 species were native, 11 were exotic, 5 or 7 were invaders from the lower sections of the Danube, 3 species (and one form) became extinct, and 7 species were not detected during the past 20 years. The increasing pollution until 1985 decreased the fish species richness, but the improvement of water quality thereafter rose their number. However, the construction of the Gabcíkovo River Barrage System put in operation in October 1992 started to change substantially fish species richness and quantity, and fish catch. The formerly functional inland delta controlled by the pulsating discharge disappeared, and was changed to an artificial system of isolated or only marginally connected habitats. The upstream fish migration was stopped by the Gabcíkovo dam and weirs in Cunovo. Therefore, the fish fauna of the side arms lost contact with fish of the main channel and of the bypass canal downstream. The loss of spawning habitats had fatal effects, especially for the wild carp and the pike, which number rapidly decreased. In general, the number of fish species, their density, and fish catch decreased significantly. To improve the situation, it is proposed: 1) to restore the bilateral connection between the main channel and the side arms, 2) to ensure fish migration between the main channel and the side arms, and 3) to simulate the original flooding of the floodplain.

The sudden, large-scale cessation of industrial and agricultural practices following the collapse of the communist regimes in the former Czechoslovakia and East Germany, coupled with a set of programmes aimed at reducing industrial and municipal pollutant loads, provided an unique opportunity to observe changes in a severely polluted river, the Elbe. Several sets of data for the post-communist Elbe reflect water quality and ecological health, including surface water pollutants, accumulation in mussels and several species of fish, and diversity of fish species. The ecological health of the Elbe has indeed benefited, and greatly, from post-communist change. The loads of most pollutants in the Elbe surface water have declined significantly over the last decade. Contaminant loading in fish tissue is also declining. Finally, the diversity of fish species in the Elbe is increasing, with a majority of the returning species being native fishes, characteristic of the pre-World War Two Elbe. Nonetheless, several pollutants remain a concern, including nitrate, suspended sediments, mercury, cadmium, hexachlorobenzene, two DDT metabolites, and three HCH isomers. The reasons for these problems include relicts from the communist era and current activities in the Elbe watershed. Further, the invasion of the river by exotic species, while not yet a concern, does remain a threat.