Accessory structures to the male reproductive system are known in several families of teleost, but their role in sperm production patterns and fertilization dynamics is still unclear. The intraspecific variability in seminal vesicles, shown by the grass goby Zosterisessor ophiocephalus, presents an opportunity to examine both its possible correlation to alternative male mating tactics and the function of these accessory structures. In this species, males are known to release sperm in the form of sperm trails, bands of mucosubstances in which sperm are embedded.Surgical removal of seminal vesicles and histochemistry demonstrate that mucins, involved in the production of sperm trails, are secreted by the seminal vesicles. Gametes show a high longevity; sperm motility lasts on average 80 minutes. Eggs can be fertilized for several hours and do not need to be laid over trails because sperm are able to reach them via the surrounding water.Gonosomatic and seminal vesicle somatic indices, histology and histochemistry of gonads and seminal vesicles, sperm counts, and sperm trail longevity, suggest the presence of alternative male mating tactics in this species. Larger males have smaller testes and larger seminal vesicles compared to those of smaller males. The major role of seminal vesicles is mucin secretion in larger males, sperm storage in smaller ones. Trails of larger males last longer and release sperm more constantly over time than those of smaller males. Overall differences between males support the presence of differences in the intensity of sperm competition, with larger males performing nesting behaviour while smaller ones sneak spawnings.

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Elasmobranch populations are declining worldwide, calling for urgent assessment of fishery exploitation and application of effective conservation strategies. Here, we applied a novel approach, integrating long-term time-series of landings (1945–2012) and extensive surveys at the fish market of Chioggia, Italy, home of the major fishing fleet of the northern Adriatic Sea, to evaluate the status of elasmobranch populations and fisheries in the one of the most fished Mediterranean basins. The time-series highlight a dramatic decline in elasmobranch landings, particularly for skates and catsharks (Scyliorhinus spp.), whose current catch rates are 2.4 and 10.6% of the average 1940s levels, respectively. These data likely reflect similar large reductions in abundance, as indicated by the analysis of catch-per unit-effort time-series. The biomass of landed skates and catsharks showed regular fluctuations that disappeared after the collapse of the landings. Elasmobranch market composition, assessed through the sampling of 11 900 specimens from 2006 to 2013, included 14 species, but was dominated by just two: Mustelus mustelus and M. punctulatus, which represented more than 60% of the catch. The proportion of sexually immature individuals was generally very high, up to 83% of landed females and 71% of landed males, depending on the species. Although some correlations were detected between landings and local hydrography or climatic indices, the analyses of landings and surveys at the fish market identified fishery exploitation as the main driver of the striking, long-term elasmobranch decline in the northern Adriatic Sea, calling for urgent management actions to improve the conservation status of these fish.

The changes in a marine community in the northern Adriatic Sea were explored over a period of 65 years using landings data from a commercial fishing fleet, and the role of fishing pressure and environmental variations in driving these changes was investigated. A total of 40 taxonomic categories, including one or several species, were analysed, representing 93·7% of the total landings. From 1945 to 2010 a significant decrease in the evenness index was observed, indicating a trend towards landings dominated by fewer taxa. The composition of the landings showed a temporal shift during the 1980s; from 1945 to the 1980s a continuous, clear change in composition took place, probably driven by an increase in fishing pressure as well as riverine nutrient inputs. Since the 1980s, a different trend of changing composition emerged. Among the analysed predictors, fishing capacity, summer seawater temperature, inflow from the Po River (the major river of the northern Adriatic Sea) and nutrients were related to the changes in landings. In relation to life-history traits of the landed species, the community shifted from large, late-maturing species to more fecund, smaller and earlier-maturing species. A high fishing pressure is probably the major cause of these changes, possibly acting synergistically with environmental variations.