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L'Honore, T., Farcy, E., Chatain, B., Gros, R., Ruelle, F., Hermet, S., et al. (2019). Are European sea bass as euryhaline as expected? Intraspecific variation in freshwater tolerance. Mar. Biol., 166(8), 102.
Résumé: In teleosts, the regulation of hydromineral balance has a direct impact on several physiological functions, biochemical processes, and can influence behaviour, distribution and survival. As European sea bass Dicentrarchus labrax undertake seasonal migrations from seawater (SW) to brackish, estuarine and fresh water (FW) in their habitat, this study investigates their capacity to tolerate fresh water and explores intraspecific variations in physiological responses. Juvenile D. labrax were transferred from SW to FW at various ages. Freshwater-tolerant and non-tolerant phenotypes were discriminated according to behavioural and morphological characteristics. About 30% of the fish exposed to FW were identified as freshwater intolerant following FW challenges performed at different ages. Interestingly, intolerant fish exhibited the same phenotypic traits: erratic swimming, lower speed, isolation from the shoal and darker colour. Freshwater-intolerant fish were also characterised by a significant lower blood osmolality compared to tolerant fish, and significantly lower Na+/K+-ATPase alpha 1a expression in the posterior kidney. An imbalance in ion regulatory mechanisms was further confirmed by a blood Na+/Cl- ratio imbalance observed in some freshwater-intolerant fish. The analysis of glucocorticoid and mineralocorticoid receptor expression levels in gills and kidney revealed significant differences between freshwater-intolerant and -tolerant fish in both organs, suggesting differential stress-related responses. This study clearly shows an intraspecific difference in the responses following FW transfer with a decreased renal ion uptake capacity as a major cause for freshwater intolerance.
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Mostajir, B., Le Floc'h, E., Mas, S., Pete, R., Parin, D., Nouguier, J., et al. (2013). A new transportable floating mesocosm platform with autonomous sensors for real time data acquisition and transmission for studying the pelagic food web functioning. Limnol Oceanogr-Meth, 11, 394–409.
Résumé: We describe a new transportable floating mesocosm platform with autonomous sensors. The platform has 9 separate units that can be transported by medium-sized research vessels and positioned in coastal waters. The in situ mesocosms are equipped with a set of sensors for measuring water temperature, conductivity, chlorophyll a fluorescence (Chl a), and dissolved oxygen concentration. It can take measurements every 2 min, store these measurements, and transmit them in real time. Each mesocosm has a pump with regulated flow to mix the water column. One of the floating units is used as an in situ observatory to monitor the water temperature and Chl a in the water around the mesocosms as well as weather data and the incident light. The main data logger on the platform sends all the data collected to a remote PC computer. This floating mesocosm platform was successfully deployed in 2010 and 2011 in Mediterranean coastal waters (Thau lagoon and Cretan Sea, respectively). Simultaneous, automatic, high temporal resolution monitoring of physical, chemical, and biological parameters in the mesocosms proved to be a powerful, noninvasive, and effective approach for i) monitoring the variations in physical and chemical parameters in real time and ii) assessing the short-term variations in Chl a and the pelagic food web metabolism (e.g., the community respiration, gross primary production, and net community production) in the mesocosms without any manipulation of water samples.
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Panfili, J., Darnaude, A. M., Vigliola, L., Jacquart, A., Labonne, M., & Gilles, S. (2015). Experimental evidence of complex relationships between the ambient salinity and the strontium signature of fish otoliths. Journal of Experimental Marine Biology and Ecology, 467, 65–70.
Résumé: The otolith strontium:calcium ratio (Sr:Ca) has been widely used to assess the connectivity between fish populations in ocean, estuarine and freshwater environments as the concentration of Sr in the otoliths is strongly correlated with water salinity. This correlation was tested experimentally in hypersaline conditions by submitting the extremely euryhaline tilapia species Sarotherodon melanotheron heudelotii (Cichlidae), found throughout West African continental waters and commonly used as an aquaculture species, to a strong salinity gradient (15–106). Experimental and control individuals were reared from birth in a closed system at a constant salinity of 10 and injected with oxytetracycline (OTC) to mark the otoliths at the beginning of the experiment. Randomly selected control fish were maintained for 75 days at salinities of 10–20. The remaining experimental fish were acclimated to a salinity above 100 which was reduced by 10 each week to a salinity of 20. The salinity and temperature of the water were recorded every day and the Sr concentrations in the water were measured weekly by solution-based ICP-MS. The fish from the control and experimental groups were sampled weekly and otolith transverse sections were prepared for Sr:Ca measurements by laser ablation ICP-MS. No significant difference in the otolith growth rates after OTC marking was found between the control and experimental groups (ANCOVA, p = 0.63), showing that the experimental design did not affect fish growth. The Sr concentration in the water was closely related to ambient salinity (positive linear regression, R2 = 0.96). For most of the fish tested (~ 80%), the relationship between otolith Sr:Ca and salinity was positive but nonlinear (power law, R2 = 0.77 on log–log plot). However, about 20% of individuals from both the control and the experimental groups showed consistently low Sr:Ca ratios irrespective of the salinity, suggesting that the Sr incorporation into the otoliths in these fish was strongly regulated. This shows that there is high variability between individuals in the regulation of Sr incorporation by a euryhaline species and indicates that otolith datasets for ecological applications should be interpreted with caution.
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Poisson, F., Séret, B., Vernet, A. - L., Goujon, M., & Dagorn, L. (2014). Collaborative research: Development of a manual on elasmobranch handling and release best practices in tropical tuna purse-seine fisheries. Marine Policy, 44, 312–320.
Résumé: Abstract The reduction of by-catch mortality is an objective of the ecosystem approach to fisheries and a request made by consumers. Elasmobranchs, an important component of the French tropical tuna purse seine fishery by-catch, are currently thrown back into the sea. Fishers interact with various types of elasmobranchs that range widely in size, weight and shape, and could pose various degrees of danger to the crew. A diversity of discarding practices within the fleet were reported, some practices were considered suitable, others needed to be adapted and improved and others simply had to be banned. The majority of the crews were likely to improve their handling practices if they were presented with practical suggestions that were quick and easy. Combining scientific observations and empirical knowledge from skippers and crew, a manual, providing appropriate handling practices to ensure crew safety and increase the odds of survival for released animals has been developed and disseminated. Bringing these good practices onto the decks of fishing vessels should contribute to the reduction of the fishing mortality of some vulnerable species. It would be positively viewed by consumers as an act that reduces fishing's footprint on the environment and promoting animal welfare which would improve the image of fishing industry. Mitigation research is by definition an iterative process and different complementary methods must be carried out at different levels of the fishing process to significantly reduce the mortality of the by-catch.
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Russell, B. C., Hasan, M. E., & Durand, J. - D. (2019). Scolopsis igcarensis Mishra, Biswas, Russell, Satpathy & Selvanayagam, 2013, a junior synonym of S. vosmeri (Bloch, 1792) (Perciformes: Nemipteridae). Zootaxa, 4629(4), 589–599.
Résumé: Scolopsis igcarensis Mishra, Biswas, Russell, Satpathy & Selvanayagam, 2013 was described from specimens collected from coastal waters of southern India and Sri Lanka. A comparison of recently collected specimens from Bangladesh, initially identified as S. igcarensis, with Scolopsis vosmeri (Bloch, 1792) showed morphological differences between the two species are minor, and that specimens of S. igcarensis in fact represent juvenile and subadult colour forms of S. vosmeri. Underwater and aquarium observations, as well as molecular data based on the COI barcode region, support this conclusion. Accordingly, S. igcarensis is regarded as a junior synonym of S. vosmeri, which is redescribed herein. Phylogenetic analysis of COI barcodes of Scolopsis specimens produced in this study, together with those available from GenBank, indicate S. vosmeri is part of a species complex which includes two additional cryptic sister species that require further taxonomic investigation.
Mots-Clés: coi; molecular phylogeny; morphology; phenotypes; Synonymy; taxonomy
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