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Osmoregulation is by no means an energetically cheap process, and its costs have been extensively quantified in terms of respiration and aerobic metabolism. Common products of mitochondrial activity are reactive oxygen and nitrogen species, which may cause oxidative stress by degrading key cell components, while playing essential roles in cell homeostasis. Given the delicate equilibrium between pro- and antioxidants in fueling acclimation responses, the need for a thorough understanding of the relationship between salinity-induced oxidative stress and osmoregulation arises as an important issue, especially in the context of global changes and anthropogenic impacts on coastal habitats. This is especially urgent for intertidal/estuarine organisms, which may be subject to drastic salinity and habitat changes, leading to redox imbalance. How do osmoregulation strategies determine energy expenditure, and how do these processes affect organisms in terms of oxidative stress? What mechanisms are used to cope with salinity-induced oxidative stress? This Commentary aims to highlight the main gaps in our knowledge, covering all levels of organization. From an energy-redox perspective, we discuss the link between environmental salinity changes and physiological responses at different levels of biological organization. Future studies should seek to provide a detailed understanding of the relationship between osmoregulatory strategies and redox metabolism, thereby informing conservation physiologists and allowing them to tackle the new challenges imposed by global climate change.

International audience; To sustain eel aquaculture, development of reproduction in captivity is vital. The aim of this review is to assess our current knowledge on the nutrition of broodstock eels in order to improve the quality of broodstock under farming conditions, drawing information from wild adult eels and other marine pelagic spawners. Freshwater eels spawn marine pelagic eggs with an oil droplet (type II), and with a large perivitelline space. Compared with other marine fish eggs, eel eggs are at the extreme end of the spectrum in terms of egg composition, even within this type II group. Eel eggs contain a large amount of total lipids, and a shortage of neutral lipids has been implied a cause for reduced survival of larvae. Eel eggs have higher ARA but lower EPA and DHA levels than in other fish. Too high levels of ARA negatively affected reproduction in the Japanese eel, although high levels of 18:2n-6 in the eggs of farmed eels were not detrimental. The total free amino acid amount and profile of eel eggs appears much different from other marine pelagic spawners. Nutritional intervention to influence egg composition seems feasible, but responsiveness of farmed eels to induced maturation might also require environmental manipulation. The challenge remains to succeed in raising European eel broodstock with formulated feeds and to enable the procurement of viable eggs and larvae, once adequate protocols for induced maturation have been developed

We tested the hypothesis that in the euphotic zone of oligotrophic oceanic waters, the growth-limiting nutrients for bacterioplankton vary over a diel cycle due to competition with phyto- plankton, leading to distinct diel patterns in bacterioplankton. During a cruise across the subtropical Atlantic Ocean, a distinct diel periodicity in bacterioplankton was detectable, with highest bacterial abundance in the early morning and declining over the day. A peak in the frequency of dividing cells (FDC, 20 to 25% of the total bacterial community) was recorded at midnight; FDC rates were consis- tently low during the day and cell volume increased over the day until the early night period. No diel variations in these parameters were detectable in the layers below the deep chlorophyll maximum (DCM). Bio-assay experiments with freshly collected, N+P amended water were started in the early morning. No significant bacterial growth was detectable in the early morning while, in the bio-assays that started at noon, significant bacterial growth was detectable in the N+P treatments. P amendment alone also caused an increase in bacterial abundance although to a lesser extent. Thus, we have evi- dence that the bacterioplankton in the euphotic layer of the subtropical Atlantic are not limited by the availability of N+P in the morning (most likely limited in C) but at noon when they are competing with phytoplankton for the inorganic N+P sources. Based on the concomitantly measured decline in inorganic N+P in the bio-assays, we estimated the C:N:P ratio of newly produced bacteria. The mean atomic C:N:P ratio for the bacteria in the N+P amended bio-assay experiments started in the early morning was C:N:P = 15:13:1 while the corresponding ratio for bacteria in the bio-assays started at noon was C:N:P = 118:11:1. This diel variation in the C:N:P ratio was caused by the 1 order of mag- nitude higher bacterial C production at noon as compared to the early morning. Thus, excess uptake of N+P occurs during the morning and luxury C uptake during noon. This plasticity in the C:N:P ratio of bacterioplankton might be a strategy to overcome, at least partly, periods of shortage in a specific nutrient species in the oligotrophic subtropical Atlantic.

Oligotrophy, or the inability of bacterial cells to propagate at elevated nutrient concentrations, is a controversial phenomenon in microbiology. The exact cause of the unculturability of many indigenous marine bacteria on standard laboratory media has still not been resolved. Unfortunately the physiology of such cells is difficult to investigate as long as high cell density cultures cannot be obtained. An extensive evaluation of experiments relating to oligotrophy and the cultivation of marine bacteria is presented in this review. When incorporating the findings of studies performed with molecular biological methods, the picture emerges that indigenous marine bacteria can be cultivated under certain conditions and that the 'oligotrophic way of life' is a transient characteristic. Although strong generalisations should not be made with respect to a biological system as diverse as the world's oceans, it should be anticipated that cells with unique physiological characteristics appear to exist in the oceanic system. When combining conventional physiological approaches with molecular biological techniques it is feasible to unveil the phenotypes that go with the encountered genotypes. In view of the enormous complexity of the oceanic system this will prove an ambitious, yet resourceful undertaking.

A number of scientific studies have investigated aspects of soles ( Solea solea and S. senegalensis) ecology, population genetics and biology in their natural environment, and the species have been extensively studied in captivity during the last decade. Studies on the genetic population structure of sole indicate that several distinct breeding populations exist within its distributional range in European waters. Recent studies suggest a phylogenetic relatedness of S. solea and S. senegalensis, being found as closest sister lineages in most reconstructions. However, studies on molecular genetics and morphological traits give diagnostic differences that consistently lead to their taxonomic separation at the specific rank. Studies show that sole spawn readily in captivity, and the buoyant, fertilized eggs are easily collected. Stocking density during maturation should be 1-1.5 kg/m(2), and temperature should be kept above 16degreesC ( S. senegalensis) or between 8 and 12degreesC ( S. solea). In nature, the onset of spawning is related to a rise in temperature occurring during spring ( March-June). Salinity should be kept constant around 33-35& and the fish reared under simulated natural photoperiod ( LDN). In other cultured flatfish species, a change in the photoperiod is the key environmental signal used to manipulate and control maturation, but at present time there are no published work that verifies or contradicts this for either S. senegalensis or S. solea. Studies indicate that a mixture of inert and live food may increase the weaning success of sole fry, and this can be further enhanced by using attractants in the dry feed. Future experiments are needed to determine the ideal time to commence weaning and determine the minimum duration of this period. Studies on alternative feeding strategies are also required. The effect of temperature and photoperiod on juvenile growth has not been studied systematically in neither of the two species and the relative importance of a direct photoperiod effect on growth in sole therefore remains to be defined.