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Zones of elevated carbon dioxide (C[O.sub.2]) have the potential to deter the movement of fishes. Should C[O.sub.2] be used as a barrier, non-target organisms, such as freshwater mussels, have the potential to be impacted. In this study, the physiological responses of adult Fusconaia flava exposed to elevated partial pressures of C[O.sub.2] (pC[O.sub.2]) over both short-term (6 h exposure with 6 h recovery) and long-term (4-, 8-, and 32-day exposure) periods were measured. A 6 h exposure to either ~15 000 µatm (1 atm = 101.325 kPa) or ~200 000 µatm caused an elevation in hemolymph [Ca.sup.2+]. Exposure to ~200 000 µatm resulted in a decrease in hemolymph [Cl.sup.-], and exposure to ~15 000 µatm caused an increase in hemolymph [Na.sup.+], whereas ~200 000 µatm caused a decrease. Exposure to elevated pC[O.sub.2] for long-term periods caused a decrease in hemolymph [Mg.sup.2+] and an initial increase in hemolymph [Ca.sup.2+]. Body condition and hemolymph glucose were not significantly influenced by elevated pC[O.sub.2] for both experiments. This study shows that elevated pC[O.sub.2] had limited impacts on the physiological responses of adult freshwater mussels. Les zones de concentrations elevees de dioxyde de carbone (C[O.sub.2]) pourraient faire entrave aux deplacements de poissons. L'utilisation eventuelle du C[O.sub.2] comme barriere pourrait avoir un impact sur des organismes non cibles, comme les moules d'eau douce. Nous avons mesure les reactions physiologiques de fusconaias jaunes (Fusconaiaflava) adultes exposees a des pressions partielles de C[O.sub.2] (pC[O.sub.2]) elevees pendant de courtes (exposition de 6 heures avec recuperation de 6 heures) et longues durees (expositions de 4, 8 et 32 jours). Une exposition de 6 heures a des pC[O.sub.2] de ~15 000 µatm (1 atm = 101.325 kPa) ou ~200 000 µatm entrainait une hausse du [Ca.sup.2+] hemolymphatique. Une exposition a ~200 000 µatm se traduisait par une baisse du [Cl.sup.-] hemolymphatique et une exposition a ~15 000 µatm entrainait une hausse du [Na.sup.+] hemolymphatique, alors qu'une exposition a ~200 000 µatm entrainait sa baisse. L'exposition a de fortes pC[O.sub.2] pendant de longues periodes causait une baisse du [Mg.sup.2+] hemolymphatique et une baisse initiale du [Ca.sup.2+] hemolymphatique. Dans les deux experiences, des pC[O.sub.2] elevees n'ont pas eu d'influence significative sur l'embonpoint et le glucose hemolymphatique. L'etude demontre que de fortes pC[O.sub.2] ont des effets limites sur les reactions physiologiques des moules d'eau douce adultes. [Traduit par la Redaction], Introduction The introduction of non-native species can have long-lasting impacts on resident populations and 'invaded' environments (Pimentel et al. 2005; Ricciardi et al. 2013). Many invaders have been concentrated in [...]

The upper thermal tolerance of brook trout Salvelinus fontinalis was estimated using critical thermal maxima (CTmax) experiments on fish acclimated to temperatures that span the species' thermal range (5–25°C). The CTmax increased with acclimation temperature but plateaued in fish acclimated to 20, 23 and 25°C. Plasma lactate was highest, and the hepato‐somatic index (IH) was lowest at 23 and 25°C, which suggests additional metabolic costs at those acclimation temperatures. The results suggest that there is a sub‐lethal threshold between 20 and 23°C, beyond which the fish experience reduced physiological performance. [ABSTRACT FROM AUTHOR]

Multiple environmental stressors may interact in complex ways to exceed or diminish the impacts of individual stressors. In the present study, the interactive effects of two ecologically relevant stressors [increased temperature and partial pressure of carbon dioxide (Pco2)] were assessed for freshwater mussels, a group of organisms that are among the most sensitive and rapidly declining worldwide. The individual and combined effects of elevated temperature (22°C-34°C) and Pco2 (~230, 58,000 µatm) on juvenile Lampsilis siliquoidea were quantified over a 5- or 14-day period, during which physiological and whole animal responses were measured. Exposure to elevated temperature induced a series of physiological responses, including an increase in oxygen consumption rates following 5 days of exposure at 31°C and an increase in carbonic anhydrase ( ca) and heat shock protein 70 mRNA levels following 14 days of exposure at 28°C and 34°C, respectively. Treatment with elevated Pco2 activated acid-base regulatory responses including increases in CA and Na+-K+-ATPase activity and a novel mechanism for acid-base regulation during Pco2 exposure in freshwater mussels was proposed. Thermal and CO2 stressors also interacted such that responses to the thermal stressor were diminished in mussels exposed to elevated Pco2, resulting in the greatest level of mortality. Additionally, larger mussels were more likely to survive treatment with elevated Pco2 and/or temperature. Together, exposure to elevated Pco2 may compromise the ability of juvenile freshwater mussels to respond to additional stressors, such as increased temperatures, highlighting the importance of considering not only the individual but also the interactive effects of multiple environmental stressors. [ABSTRACT FROM AUTHOR]

Abstract: Freshwater mussels may be exposed to elevations in mean partial pressure of carbon dioxide (pCO2) caused by both natural and anthropogenic factors. The goal of the present study was to assess the effects of a 28‐d elevation in pCO2 at 15 000 and 50 000 μatm on processes associated with biomineralization, ion regulation, and cellular stress in adult Lampsilis siliquoidea (Barnes, 1823). In addition, the capacity for mussels to compensate for acid‐base disturbances experienced after exposure to elevated pCO2 was assessed over a 14‐d recovery period. Overall, exposure to 50 000 μatm pCO2 had more pronounced physiological consequences compared with 15 000 μatm pCO2. Over the first 7 d of exposure to 50 000 μatm pCO2, the mRNA abundance of chitin synthase (cs), calmodulin (cam), and calmodulin‐like protein (calp) were significantly affected, suggesting that shell formation and integrity may be altered during pCO2 exposure. After the removal of the pCO2 treatment, mussels may compensate for the acid‐base and ion disturbances experienced during pCO2 exposure, and transcript levels of some regulators of biomineralization (carbonic anhydrase [ca], cs, cam, calp) as well as ion regulation (na+‐k+‐ATPase [nka]) were modulated. Effects of elevated pCO2 on heat shock protein 70 (hsp70) were limited in the present study. Overall, adult L. siliquoidea appeared to regulate factors associated with the control of biomineralization and ion regulation during and/or after the removal of pCO2 exposure. Environ Toxicol Chem 2018;37:538–550. © 2017 SETAC [ABSTRACT FROM AUTHOR]

Weak acidification can occur in freshwater ecosystems when free carbon dioxide (CO) levels increase, which can happen for a variety of reasons. To define the state of knowledge for how weak acidification influences freshwater biota and ecosystems, a review of the primary literature was conducted. Despite few empirical studies focused on weak acidification in the primary literature (~100 studies), some themes have emerged from our literature review. Most studies focused on physiological responses at the organismal level, and fish were the most studied taxa. Animals exhibited reduced individual growth rates, and, in contrast, primary producers demonstrated increased individual and population growth rates. In animals, mortality, sub-lethal injuries, and changes to behaviours were also observed. Negative consequences to reproduction in macrophytes were found. Few studies have focused on population, community, or ecosystem levels, though broad scale studies suggest that weak acidification can limit species community diversity, specifically in invertebrates and fish. Moving forward, researchers need to continue to advance our understanding of the consequences of weak acidification for freshwater biota. Furthermore, priority should be placed on research that can evaluate the potential for weak acidification in freshwater to lead to changes in ecological regimes or economical outcomes, such as fisheries collapses. [ABSTRACT FROM AUTHOR]

Studies with marine fishes indicate that exposure to elevated partial pressures of CO2 ( pCO2) related to climate change have negative consequences for fish behaviour. Freshwater fishes may experience similar increases in pCO2 due to a number of different mechanisms, but there is a paucity of information on how freshwater fishes may respond to exposure to elevated pCO2., To define the effects of elevated pCO2 on a free-swimming freshwater fish, 19 adult largemouth bass ( Micropterus salmoides) were tagged with acoustic transmitters, held in water with pCO2 levels of either ˜10 000 μatm or ambient pCO2 (<100 μatm) for 5 days and released into a naturalised, earthen-bottom pond outfitted with an acoustic telemetry array., Findings indicate that largemouth bass not exposed to elevated levels of pCO2 decreased movement over 35% during the daylight periods; however, fish exposed to elevated levels of pCO2 did not exhibit this pattern. This difference in diel movement patterns between fish exposed to elevated pCO2 and fish not exposed was not detectable after 11 days., Changes in home range size and daily distance travelled were not observed. However, based on an assessment of position estimates after the completion of the telemetry monitoring portion of the study, space use differed for fish exposed to elevated pCO2., Exposure to elevated pCO2 therefore can have consequences for some movement behaviours of freshwater fish and this may influence a variety of ecological processes including energetics, foraging and predator-prey dynamics. CO2-induced alterations to behaviour should recover upon a return to ambient water. [ABSTRACT FROM AUTHOR]

The present study examined the effects of maternal social status, with subordinate status being a chronic stressor, on development and activity of the stress axis in zebrafish embryos and larvae. Female zebrafish were confined in pairs for 48 h to establish dominant/subordinate hierarchies; their offspring were reared to 144 h post-fertilization (hpf) and sampled at five time points over development. No differences were detected in maternal cortisol contribution, which is thought to be an important programmer of offspring phenotype. However, once zebrafish offspring began to synthesize cortisol de novo (48 hpf), larvae of dominant females exhibited significantly lower baseline cortisol levels than offspring of subordinate females. These lower cortisol levels may reflect reduced hypothalamic-pituitary-interrenal (HPI) axis activity, because corticotropin-releasing factor (crf) and cytochrome p450 side chain cleavage enzyme (p450scc) mRNA levels also were lower in larvae from dominant females. Moreover, baseline mRNA levels of HPI axis genes continued to be affected by maternal social status beyond 48 hpf. At 144 hpf, stress-induced cortisol levels were significantly lower in offspring of subordinate females. These results suggest programming of stress axis function in zebrafish offspring by maternal social status, emphasizing the importance of maternal environment and experience on offspring stress axis activity. [ABSTRACT FROM AUTHOR]

Rising atmospheric carbon dioxide (CO2) has caused a suite of environmental issues, however, little is known about how the partial pressure of CO2 (pCO2) in freshwater will be affected by climate change. Freshwater pCO2 varies across systems and is controlled by a diverse array of factors, making it difficult to make predictions about future levels of pCO2. Recent evidence suggests that increasing levels of atmospheric CO2 may directly increase freshwater pCO2 levels in lakes, but rising atmospheric CO2 may also indirectly impact freshwater pCO2 levels in a variety of systems by affecting other contributing factors such as soil respiration, terrestrial productivity and climate regimes. Although future freshwater pCO2 levels remain uncertain, studies have considered the potential impacts of changes to pCO2 levels on freshwater biota. Studies to date have focused on impacts of elevated pCO2 on plankton and macrophytes, and have shown that phytoplankton nutritional quality is reduced, plankton community structure is altered, photosynthesis rates increase and macrophyte distribution shifts with increasing pCO2. However, a number of key knowledge gaps remain and gaining a better understanding of how freshwater pCO2 levels are regulated and how these levels may impact biota, will be important for predicting future responses to climate change. [ABSTRACT FROM AUTHOR]

Rising atmospheric carbon dioxide (CO2) has caused a suite of environmental issues, however, little is known about how the partial pressure of CO2 (pCO2) in freshwater will be affected by climate change. Freshwater pCO2 varies across systems and is controlled by a diverse array of factors, making it difficult to make predictions about future levels of pCO2. Recent evidence suggests that increasing levels of atmospheric CO2 may directly increase freshwater pCO2 levels in lakes, but rising atmospheric CO2 may also indirectly impact freshwater pCO2 levels in a variety of systems by affecting other contributing factors such as soil respiration, terrestrial productivity and climate regimes. Although future freshwater pCO2 levels remain uncertain, studies have considered the potential impacts of changes to pCO2 levels on freshwater biota. Studies to date have focused on impacts of elevated pCO2 on plankton and macrophytes, and have shown that phytoplankton nutritional quality is reduced, plankton community structure is altered, photosynthesis rates increase and macrophyte distribution shifts with increasing pCO2. However, a number of key knowledge gaps remain and gaining a better understanding of how freshwater pCO2 levels are regulated and how these levels may impact biota, will be important for predicting future responses to climate change. [ABSTRACT FROM AUTHOR]

Individuals often show considerable variance in social behaviour and aggression, leading to defined social roles. Removal of individuals with particular roles from groups may have impacts on group function, leaving those groups less able to locate critical resources and avoid danger. In recreational fisheries, capture by humans constitutes a mortality risk, and therefore angling has the potential to fundamentally alter social structure in exploited populations if individuals with defined social roles are disproportionately captured. However, little work has examined the linkage between social behaviour and angling vulnerability. To address this gap, we conducted a study on bluegill, Lepomis macrochirus , a freshwater fish known to be socially gregarious, and a common target of recreational anglers in North America. Fish were angled in a naturalistic pond setting, and a subset of captured and uncaptured fish was then assessed for sociability in a shoaling assay and aggression/dominance in paired dyadic contests. Results showed a significant effect of time spent in the social zone on capture status, with captured individuals spending significantly more time near a transparent divider separating it from a shoal of conspecifics compared to uncaptured fish. Dominance was not associated with angling vulnerability, and sociability was not linked with dominance. Collectively, these results show that more social bluegill are more likely to be captured by anglers. This could in turn lead to decreased social functionality in exploited populations as a result of the removal of particularly social individuals, as well as possible evolution of social behaviour in exploited populations due to this selection. [ABSTRACT FROM AUTHOR]