• European Marine Science
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• Comparative Biochemistry and Physio... close

High CO2 (hypercapnia) can impose significant physiological challenges associated with acid-base regulation in fishes, impairing whole animal performance and survival. Unlike other environmental conditions such as temperature and O2, the acute CO2 tolerance thresholds of fishes are not understood. While some fish species are highly tolerant, the extent of acute CO2 tolerance and the associated physiological and ecological traits remain largely unknown. To investigate this, we used a recently developed ramping assay, termed the Carbon Dioxide maximum (CDmax), that increases CO2 exposure until loss of equilibrium (LOE) is observed. We investigated if there was a relationship between CO2 tolerance and the Root effect, β-adrenergic sodium proton exchanger (βNHE), air-breathing, and fish habitat in 17 species. We hypothesized that CO2 tolerance would be higher in fishes that lack both a Root effect and βNHE, breathe air, and reside in tropical habitats. Our results showed that CDmax ranged from 2.7 to 26.7 kPa, while LOE was never reached in four species at the maximum PCO2 we could measure (26.7 kPa); CO2 tolerance was only associated with air-breathing, but not the presence of a Root effect or a red blood cell (RBC) βNHE, or fish habitat. This study demonstrates that the diverse group of fishes investigated here are incredibly tolerant of CO2 and that although this tolerance is associated with air-breathing, further investigations are required to understand the basis for CO2 tolerance.

A shared characteristic among animals is their propensity to form stable, beneficial relationships with prokaryotes. Usually these associations occur in the form of consortia, i.e. a diverse assemblage of bacteria interacting with a single animal host. These complex communities, while common, have been difficult to characterize. The two-partner symbiosis between the squid Euprymna scolopes and the marine luminous bacterium Vibrio fischeri offers the opportunity to study the interaction between animal and bacterial cells, because both partners can be cultured in the laboratory and the symbiosis can be manipulated experimentally. This system is being used to characterize the mechanisms by which animals establish, develop and maintain stable alliances with bacteria. This review summarizes the progress to date on the development of this model.

Reproduction in vertebrates is controlled by the Hypothalamus-Pituitary-Gonad axis and the main hormone actions have been extensively described. Still, despite the scattered information in fish, accumulating evidence strongly indicates that corticosteroids play essential roles in reproductive mechanisms. An integrative approach is important for understanding these implications. Animal husbandry and physiological studies at molecular to organismal levels have revealed that these corticosteroids are regulators of fish reproductive processes. But their involvements appear strongly contrasted. Indeed, for both sexes, corticosteroids present either deleterious or positive effects on fish reproduction. In this review, the authors will attempt to gather and clarify the available information about these physiological involvements. The authors will also suggest future ways to prospect corticosteroid roles in fish reproduction.

Highlights: • Larvae upregulate genes associated with fatty acid and glycogen synthesis under moderate ocean acidification (OA) • Larvae under high levels of OA fail to regulate • Dysfunctional metabolism and stress associated with pathologies in internal organs • Lack of differential gene regulation and stress response in juveniles correspond to a higher resilience to OA stress Elevated environmental carbon dioxide (pCO2) levels have been found to cause organ damage in the early life stages of different commercial fish species, including Atlantic cod (Gadus morhua). To illuminate the underlying mechanisms causing pathologies in the intestines, the kidney, the pancreas and the liver in response to elevated pCO2, we examined related gene expression patterns in Atlantic cod reared for two months under three different pCO2 regimes: 380 μatm (control), 1800 μatm (medium) and 4200 μatm (high). We extracted RNA from whole fish sampled during the larval (32 dph) and early juvenile stage (46 dph) for relative expression analysis of 18 different genes related to essential metabolic pathways. At 32 dph, larvae subjected to the medium treatment displayed an up-regulation of genes mainly associated with fatty acid and glycogen synthesis (GYS2, 6PGL, ACoA, CPTA1, FAS and PPAR1b). Larvae exposed to the high pCO2 treatment upregulated fewer but similar genes (6PGL, ACoA and PPAR1b,). These data suggest stress-induced alterations in the lipid and fatty acid metabolism and a disrupted lipid homeostasis in larvae, providing a mechanistic link to the findings of lipid droplet overload in the liver and organ pathologies. At 46 dph, no significant differences in gene expression were detected, confirming a higher resilience of juveniles in comparison to larvae when exposed to elevated pCO2 up to 4200 μatm.

Fil: Joyner Matos, Joanna. Eastern Washington University; Estados Unidos Fil: Puntarulo, Susana Angela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Bioquímica y Medicina Molecular; Argentina Fil: Vásquez Medina, José Pablo. University of California Merced; Estados Unidos Fil: Zenteno Zabin, Tania. Instituto Politécnico Nacional; México

Mysid crustaceans have been put forward by several regulatory bodies as suitable test organisms to screen and test the potential effects of environmental endocrine disruptors. Despite the well-established use of mysid reproductive endpoints such as fecundity, egg development time, and time to first brood release in standard toxicity testing, little information exists on the hormonal regulation of these processes. Control of vitellogenesis is being studied intensively because yolk is an excellent model for studying mechanisms of hormonal control, and vitellogenesis can be chemically disrupted. Yolk protein or vitellin is a major source of nourishment during embryonic development of ovigorous egg-laying invertebrates. The accumulation of vitellin during oocyte development is vital for the production of viable offspring. In this context, we developed a competitive enzyme-linked immunosorbent assay (ELISA) for vitellin of the estuarine mysid Neomysis integer. Mysid vitellin was isolated using gel filtration, and the purified vitellin was used to raise polyclonal antibodies. The ELISA was sensitive within a working range of 4 to 500 ng vitellin/mL. Serial dilutions of whole body homogenates from female N. integer and the vitellin standard showed parallel binding curves, validating the specificity of the ELISA. The intra- and interassay coefficients of variation were 8.2% and 13.8%, respectively. Mysid vitellin concentrations were determined from ovigorous females and eggs at different developmental stages. The availability of a quantitative mysid vitellin ELISA should stimulate further studies on the basic biology of this process in mysids. Furthermore, it could provide a means to better understand and predict chemically induced reproductive effects in mysids.

Acidic freshwater habitats disrupt ion-homeostasis in fishes, yet the often acidic waters of the Mekong host the second highest diversity of freshwater fish in the world. To investigate how five Mekong fish species tolerate water acidity, we measured: time to loss of equilibrium (LOE) at sustained (4 days) low pH (3.5) and net ion flux in acute low pH (3.5 and 3) in Chitala ornata, Pangasianodon hypophthalmus, Osphronemus goramy, Trichogaster pectoralis, and Monopterus albus. Our sustained low pH exposures revealed that C. ornata was least tolerant, P. hypophthalmus and M. albus were moderately tolerant, and O. goramy and T. pectoralis were highly tolerant to low pH. In general, net ion loss in acute low pH exposures was greatest in species with the shortest time to LOE in the sustained low pH exposure. We also explored how low water [Ca 2+ ] (relative to current Mekong levels) affected ion flux at low water pH in the least tolerant C. ornata and highly tolerant T. pectoralis. In C. ornata, low water Ca 2+ (56 ± 1 μmol L −1 ) increased net ion loss relative to high Ca 2+ (342 ± 3 μmol L −1 ) water while no effect was observed in T. pectoralis. Finally, we find that T. pectoralis is among the most acid-tolerant fish species examined to date.