Physiological Responses to Acute Silver Exposure in the Freshwater Crayfish (\u3cem\u3eCambarus diogenes diogenes\u3c/em\u3e)—A Model Invertebrate?

Adult crayfish (Cambarus diogenes diogenes) exposed to 8.41 ± 0.17 μg silver/L (19.4% as Ag+) in moderately hard freshwater under flow-through conditions for 96 h exhibited ionoregulatory disturbance, elevated metabolic ammonia (Tamm) production and substantial silver accumulation in the gills, hemolymph, and hepatopancreas. The ionoregulatory disturbance included both a generally reduced unidirectional Na1 influx and an increased unidirectional Na+ efflux, leading to a substantial net loss of Na+ from the silver-exposed crayfish. The Na+ uptake in silver-exposed crayfish differed overall from controls, while the increased Na+ efflux recovered to control values 48 h into the 96 h of exposure. The general inhibition of Na+ uptake could be explained by a reduced sodium/potassium-adenosine triphosphatase (Na/K-ATPase) activity in terminally obtained gill samples from the silver exposed crayfish. The silver-induced effect on Na+ uptake and loss translated to reduced hemolymph Na+ concentrations but not significantly reduced hemolymph Cl- concentrations. Hemolymph Tamm and Tamm efflux both increased in silver-exposed crayfish, indicating an increased metabolic Tamm production. The present study demonstrates that the toxic mechanism of waterborne silver exposure in freshwater crayfish resembles that of freshwater teleost fish. The crayfish might therefore be a useful model system for extending current environmental regulatory strategies, currently based on teleost fish, to invertebrates

Maximum salinity tolerance and osmoregulatory capabilities of European perch <i>Perca fluviatilis</i> populations originating from different salinity habitats

Brackish water European perch tolerates significantly higher salinities than freshwater conspecifics due to a physiological specialization. Therefore, brackish water European perch populations may not receive recruitment from freshwater, which raises conservation issues regarding brackish water perch populations due to climate change and fisheries. Although considered a stenohaline freshwater species, European perch ( Perca fluviatilis ) inhabit brackish waters. The present study determined the maximum salinity tolerance and osmoregulatory capability on individuals originating from brackish water and from freshwater populations. The fish were acclimated for 3 weeks to salinities of 0, 10, 12.5, 15, 17.5 and 20 after an initial stepwise increase to the target salinity. The maximum salinity tolerance was determined as the test salinity below which the fish could not acclimate and lost equilibrium. Blood plasma osmolality was measured if the fish had not lost equilibrium after the acclimation period. The maximum salinity tolerance was 17.5 for brackish water European perch and 10 for fresh water European perch. The high salinity tolerance of the brackish water European perch was caused by their ability to both hyper- and hypo-osmoregulate, whereas the freshwater originating fish could only hyper-osmoregulate. The results showed that maximum salinity tolerances and osmoregulatory capabilities depends on the origin habitat salinity. Due to genetic differentiation between European perch populations in brackish and fresh water, the possibility of brackish water European perch being a subspecies of European perch is discussed, yet vital knowledge concerning heritability of salinity tolerance traits is still missing. Regardless of species status, within-species plasticity in the ability to cope with varying salinities have substantial ecological and conservation implications and underlines the need for managing brackish water and freshwater European perch stocks separately

Intra-Specific Difference in the Effect of Salinity on Physiological Performance in European Perch (<i>Perca fluviatilis</i>) and Its Ecological Importance for Fish in Estuaries

Changes in environmental salinity challenge fish homeostasis and may affect physiological performance, such as swimming capacity and metabolism, which are important for foraging, migration, and escaping predators in the wild. The effects of salinity stress on physiological performance are largely species specific, but may also depend on intra-specific differences in physiological capabilities of sub-populations. We measured critical swimming speed (U crit ) and metabolic rates during swimming and at rest at salinities of 0 and 10 in European perch ( Perca fluviatilis ) from a low salinity tolerance population (LSTP) and a high salinity tolerance population (HSTP). U crit of LSTP was significantly reduced at a salinity of 10 yet was unaffected by salinity change in HSTP. We did not detect a significant cost of osmoregulation, which should theoretically be apparent from the metabolic rates during swimming and at rest at a salinity of 0 compared to at a salinity of 10 (iso-osmotic). Maximum metabolic rates were also not affected by salinity, indicating a modest tradeoff between respiration and osmoregulation (osmo-respiratory compromise). Intra-specific differences in effects of salinity on physiological performance are important for fish species to maintain ecological compatibility in estuarine environments, yet render these sub-populations vulnerable to fisheries. The findings of the present study are therefore valuable knowledge in conservation and management of estuarine fish populations

Comparative investigation of copper tolerance and identification of putative tolerance related genes in tardigrades

Tardigrades are microscopic aquatic animals renowned for their tolerance toward extreme environmental conditions. The current study is the first to investigate their tolerance toward heavy metals and we present a novel tardigrade toxicant tolerance assay based on activity assessments as a measure of survival. Specifically, we compare tolerance toward copper in four species representing different evolutionary lineages, habitats and adaptation strategies, i.e., a marine heterotardigrade, Echiniscoides sigismundi, a limno-terrestrial heterotardigrade, Echiniscus testudo, a limno-terrestrial eutardigrade, Ramazzottius oberhaeuseri, and a marine eutardigrade, Halobiotus crispae. The latter was sampled at a time of year, when the population is predominantly represented by aberrant P1 cysts, while the other species were in normal active states prior to exposure. Based on volume measurements and a general relation between body mass and copper tolerance, expected tardigrade EC50 values were estimated at 0.5–2 μg l(−1). Following 24 h of exposure, tolerance was high with no apparent link to lineage or habitat. EC50s (95% CI), 24 h after exposure, were estimated at 178 (168–186) and 310 (295–328) μg l(−1), respectively, for E. sigismundi and R. oberhaeuseri, whereas E. testudo and H. crispae were less affected. Highest tolerance was observed in H. crispae with a mean ± s.e.m. activity of 77 ± 2% (n = 3) 24 h after removal from ~3 mg l(−1) copper, suggesting that tardigrade cysts have increased tolerance toward toxicants. In order to identify putative tolerance related genes, an E. sigismundi transcriptome was searched for key enzymes involved in osmoregulation, antioxidant defense and copper metabolism. We found high expression of Na/K ATPase and carbonic anhydrase, known targets for copper. Our transcriptome, furthermore, revealed high expression of antioxidant enzymes, copper transporters, ATOX1, and a Cu-ATPase. In summary, our results indicate that tardigrades express well-known key osmoregulatory enzymes, supporting the hypothesis that copper inhibits sodium turnover as demonstrated for other aquatic organisms. Tardigrades, nevertheless, have high tolerance toward the toxicant, which is likely linked to high expression of antioxidant enzymes and an ability to enter dormant states. Tardigrades, furthermore, seem to have a well-developed battery of cuproproteins involved in copper homeostasis, providing basis for active copper sequestering and excretion

Acquisition of Ca2+ and HCO3−/CO32− for shell formation in embryos of the common pond snail Lymnaea stagnalis

Embryos of the freshwater common pond snail Lymnaea stagnalis develop to hatch within 10 days under control conditions (22°C, Miami-Dade tap water) and this development is impaired by removal of ambient calcium. In contrast, embryos did not exhibit dependence upon an ambient HCO3−/CO32− source, developing and hatching in HCO3−/CO32−-free water at rates comparable to controls. Post-metamorphic, shell-laying embryos exhibited a significant saturation-type calcium uptake as a function of increasing ambient calcium concentration. However, changes in ambient bicarbonate concentration did not influence calcium or apparent titratable alkalinity uptake. There was a distinct shift from no significant flux in pre-metamorphic embryos to net uptake of calcium in post-metamorphic stages as indicated by an increased uptake from the micro-environment surrounding the egg mass and increased net uptake in 24-h, whole egg mass flux measurements. Furthermore, HCO3−/CO32− acquisition as measured by titratable alkalinity flux is at least partially attributable to an endogenous carbonate source that is associated with acid extrusion. Thus, calcium requirements for embryonic shell formation are met via uptake but HCO3−/CO32−, which is also necessary for shell formation is acquired in part from endogenous sources with no detectable correlation to ambient HCO3−/CO32− availability

The effects of temperature acclimation on swimming performance in the pelagic Mahi-mahi (Coryphaena hippurus)

Mahi-mahi (Coryphaena hippurus) are a highly migratory pelagic fish, but little is known about what environmental factors drive their broad distribution. This study examined how temperature influences aerobic scope and swimming performance in mahi. Mahi were acclimated to four temperatures spanning their natural range (20, 24, 28, and 32{\deg}C; 5-27 days) and critical swimming speed (Ucrit), metabolic rates, aerobic scope, and optimal swim speed were measured. Aerobic scope and Ucrit were highest in 28{\deg}C-acclimated fish. 20{\deg}C-acclimated mahi experienced significantly decreased aerobic scope and Ucrit relative to 28{\deg}C-acclimated fish (57 and 28% declines, respectively). 32{\deg}C-acclimated mahi experienced increased mortality and a significant 23% decline in Ucrit, and a trend for a 26% decline in factorial aerobic scope relative to 28{\deg}C-acclimated fish. Absolute aerobic scope showed a similar pattern to factorial aerobic scope. Our results are generally in agreement with previously observed distribution patterns for wild fish. Although thermal performance can vary across life stages, the highest tested swim performance and aerobic scope found in the present study (28{\deg}C), aligns with recently observed habitat utilization patterns for wild mahi and could be relevant for climate change predictions.Comment: 24 pages, 3 figures main text, 6 figures supplemental text, published in Frontiers in Marine Science https://www.frontiersin.org/articles/10.3389/fmars.2021.654276/ful

Mahi-mahi (Coryphaena hippurus) life development: morphological, physiological, behavioral and molecular phenotypes.

BackgroundMahi-mahi (Coryphaena hippurus) is a commercially and ecologically important fish species that is widely distributed in tropical and subtropical waters. Biological attributes and reproductive capacities of mahi-mahi make it a tractable model for experimental studies. In this study, life development of cultured mahi-mahi from the zygote stage to adult has been described.ResultsA comprehensive developmental table has been created reporting development as primarily detailed observations of morphology. Additionally, physiological, behavioral, and molecular landmarks have been described to significantly contribute in the understanding of mahi life development.ConclusionRemarkably, despite the vast difference in adult size, many developmental landmarks of mahi map quite closely onto the development and growth of Zebrafish and other warm-water, active Teleost fishes

A proteinaceous organic matrix regulates carbonate mineral production in the marine teleost intestine

Marine teleost fish produce CaCO(3) in their intestine as part of their osmoregulatory strategy. This precipitation is critical for rehydration and survival of the largest vertebrate group on earth, yet the molecular mechanisms that regulate this reaction are unknown. Here, we isolate and characterize an organic matrix associated with the intestinal precipitates produced by Gulf toadfish (Opsanus beta). Toadfish precipitates were purified using two different methods, and the associated organic matrix was extracted. Greater than 150 proteins were identified in the isolated matrix by mass spectrometry and subsequent database searching using an O. beta transcriptomic sequence library produced here. Many of the identified proteins were enriched in the matrix compared to the intestinal fluid, and three showed no substantial homology to any previously characterized protein in the NCBI database. To test the functionality of the isolated matrix, a micro-modified in vitro calcification assay was designed, which revealed that low concentrations of isolated matrix substantially promoted CaCO(3) production, where high concentrations showed an inhibitory effect. High concentrations of matrix also decreased the incorporation of magnesium into the forming mineral, potentially providing an explanation for the variability in magnesium content observed in precipitates produced by different fish species