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The recruitment of scyphomedusae planulae to the benthic polyp stage is important for population size and may be affected under projected climate change scenarios. In a laboratory study, we determined the combined effects of elevated temperature and reduced salinity on the behaviour, survival and settlement of Aurelia coerulea planulae. Three temperature levels (21, 24 and 27°C) and two salinity levels (31 and 22) were used. Reduced salinity had a significant negative effect on the swimming behaviour and settlement of A. coerulea planulae. The planulae moved quickly and preferred to settle under ambient salinity conditions. The settlement rate of A. coerulea planulae was high during the current ambient summer temperature (24°C), and elevated temperature increased the mortality rate and reduced their settlement rate. A. coerulea planulae were significantly smaller under the combined conditions of elevated temperature and reduced salinity. Our study provides information on the response of A. coerulea planulae to temperature and salinity, which is helpful for understanding how environmental factors will influence the recruitment dynamics of A. coerulea. [ABSTRACT FROM AUTHOR]

Aquatic hypercarbia (elevated environmental CO2) results in a blood acidosis in fish, which is compensated by the exchange of Na+ and/or Cl− for its acid/base counterpart (H+, HCO3−) across the gill epithelium. To date, no studies exist on how a single species, capable of inhabiting both fresh and saltwater, responds to hypercarbia, at rest or during sustained exercise. Rainbow trout was acclimated to soft water (in mmol l− 1: Na+, 0.08; Cl−, 0.05; pH 6.7-6.8), hard water (in mmol l− 1: Na+, 2.4; Cl−, 0.2; pH 7.9-8.0), or 85% saltwater (28 ppt) (in mmol l− 1: Na+, 410; Cl−, 476; pH 7.8-8.0). Acid-base relevant blood parameters were measured during a 1 kPa CO2 hypercarbia exposure, both at rest and during sustained exercise (~ 60% Ucrit). After 48 h of hypercarbia, resting hard-, and saltwater trout fully restored blood pH, whereas soft-water-acclimated trout was only 60.6 ± 10.5% recovered. In all fish, recovery was associated with an increase in plasma [HCO3−] and an equimolar reduction in plasma [Cl−]. Following 8 h of hypercarbia during sustained exercise, saltwater fish fully restored blood pH, while soft- and hard water fish were 42 ± 18.1 and 64 ± 6.8% recovered, respectively. Results provide intra-specific support demonstrating that saltwater acclimated fish acid-base compensate faster than freshwater fish during hypercarbia. Furthermore, data indicate that recovery during hypercarbia in trout is more rapid during exercise than rest. This not only demonstrates an important link between ambient water ion levels and ability to recover from acid-base disturbances, but also it presents novel data, suggesting that exercise may enhance acid-base regulation. [ABSTRACT FROM AUTHOR]

Otolith chemistry is used widely to reconstruct the environmental histories of fish. Examining the relationships between environmental conditions and otolith chemistry is an essential first step towards accurately reconstructing environmental histories, with lack of information potentially resulting in the erroneous interpretation of fish movement and the environments they have inhabited. We evaluated the influence of seawater temperature and salinity on the otolith chemistry of juvenile King George whiting ( Sillaginodes punctatus ) (Cuvier 1829), a commercially and recreationally important fish species in southern Australia. Juveniles were reared under controlled laboratory conditions at four temperatures (16, 19, 22 and 25 °C) and two levels of salinity (30 and 40) for 90 days. Otoliths were analysed for barium ( 138 Ba), strontium ( 88 Sr), magnesium ( 24 Mg) and manganese ( 55 Mn) using laser ablation inductively coupled plasma-mass spectrometry (LA ICP-MS), and ratioed to calcium ( 43 Ca). Otolith chemistry data were analysed using generalized linear mixed models (GLMM). Analyses showed that Mg:Ca and Mn:Ca in the otolith of the fish increased with increasing salinity, whereas Sr:Ca and Ba:Ca decreased with increasing salinity. Temperature only had a minor influence on elemental concentration. The influence of salinity on otolith chemistry suggests that otolith chemistry could be used as a potential tool for reconstructing the salinity and movement history of King George whiting from estuaries to open coast regions. [ABSTRACT FROM AUTHOR]

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This study was conducted to investigate the effect of salinity on growth, survival, osmoregulation, metabolism, hematological and biochemical parameters and T-complex protein (TCP-1) mRNA expression levels in Malaysian red tilapia at declining tank water temperatures. Five salinity concentrations (0, 5, 10, 15, 20 ‰) were evaluated during the study period. Samples were collected on a range of biochemical parameters at 16.5 (week 2), 12 (week 4) and 9.5 °C (week 6). No significant growth (body weight) was showed in the study ( P > 0.05). Survival was monitored in the groups of fish until the holding tank temperature reached 5.6 °C. The lowest temperature in the study population of Malaysian red tilapia tolerated was 9 °C, although the fish were able to survive in temperature of 5.6 °C if they had been reared at 10 ‰ water salinity. The salinity and change in water temperature had significant effects on hematological and biochemical parameters and the TCP-1 gene expressions in Malaysian red tilapia ( P < 0.05). The effect of temperature and salinity on superoxide dismutase (SOD), malondialdehyde (MDA) and hemoglobin (HGB) levels was significant ( P < 0.05 or P < 0.01); with decreasing temperature, SOD and MDA activities increased, whereas HGB concentrations decreased. With increasing level of salinity, the SOD, MDA and blood glucose levels significantly increased ( P < 0.05). The highest cholesterol (TC), triglycerides (TG), red blood cells (RBC) and HGB values were apparent in the moderate salinity groups, whereas the highest high-density lipoprotein cholesterol (HDL-C) was in the moderately high-salinity group. Rearing at low temperature, Na-K-ATPase (NKA) increased with increasing level of salinity at 16.5 °C, although it initially declined before rising again at water temperatures 12 and 9.5 °C. Rearing at low temperature, fish in the low-salinity groups significantly up-regulated the expression of the TCP-1 genes ( P < 0.05), whereas fish in mild to moderate salinity groups significantly down-regulated the expression ( P < 0.05). Taken together, these results suggest that exposure to environmental conditions of low temperature, low salinity and high salinity influence osmoregulation, metabolic parameters and the fish physiology. However, a change in the isotonic point at cold temperatures was observed by rearing in a salinity of under 10 ‰. This could potentially provide a means to increase cold tolerance of overwintering Malaysian red tilapia. [ABSTRACT FROM AUTHOR]

Pike in the western Baltic Sea live on the edge of their salinity tolerance. Under physiologically challenging conditions, organism may respond by moving to environmentally more benign areas during critical periods, such as during spawning. We hypothesised that pike in a brackish lagoon (8-10 ppt salinity) would perform spawning- and feeding-related movements between areas with different salinity regimes. Twenty-two pike were caught prior to spawning, tagged with acoustic transmitters, and their movements were tracked for 18 months. Pike showed two main patterns of movements that were consistent within individuals across two years. Whereas some individuals stayed in the lagoon year-round, most pike left the lagoon for longer periods after spawning and returned to the lagoon prior to following year's spawning season. We found no evidence that probability of moving out of the lagoon co-varied with either length or condition factor. Despite the fact that the lagoon's salinity is close to the reported upper limit for pike egg development, results indicated that all pike spawned in the lagoon. Correspondingly, genetic data showed that all fish belonged to the same reproductive population unit. Movement patterns thus appear to reflect individual variation in home-range and/or resource optimisation following ideal free principles. [ABSTRACT FROM AUTHOR]

This study analyses fish data to understand how the gradual increase of salinity registered in a coastal lagoon and consequently, anthropogenic disturbance, affected the fish communities. For that, fish assemblages of the Ria de Aveiro were sampled monthly in 3 years from different decades (1988, 1997 and 2012). Dominant species were Atherina boyeri , A. presbyter , Sardina pilchardus , Dicentrarchus labrax , Liza aurata and L. ramada . Significant differences in fish communities were detected among years in both terms of density and biomass. Results pointed out to a taxonomic and functional homogenization of fish assemblages in 2012, when salinity was higher and its range of variation across the whole lagoon more uniform. Marine species were clearly associated with 2012, while some freshwater species only appeared in 1988, reflecting the gradual salinity increase in the lagoon. Overall, both the structure and function of fish assemblages of Ria de Aveiro have changed over the time, which was attributed to human activities to maintain the lagoon operational. [ABSTRACT FROM AUTHOR]

Anthropogenic disturbance of seleniferous soils can lead to selenium contamination of waterways. Although selenium is an essential micronutrient, bioaccumulation and maternal transfer of proteinaceous selenomethionine (SeMet) can result in embryo toxicity. Furthermore, as the climate changes, the salinity of spawning grounds in water-restrained estuaries is increasing. Although a small increase in salinity may not directly impact adult fish, it may alter the detoxification strategies of developing organisms. Previous research indicates that hypersalinity may potentiate SeMet embryo toxicity at an early developmental stage. However, embryonic development is a complex, spatiotemporal process with a constantly shifting cellular microenvironment. To generate thresholds and an adverse outcome pathway for the interactions between selenium and salinity, we sought to identify windows of susceptibility for lethality and deformities in the Japanese medaka ( Oryzias latipes). Embryos were treated in freshwater or saltwater for 24 h with 0.5 µM, 5 µM, and 50 µM SeMet at 6 different developmental stages (9, 17, 25, 29, 34, and 38). Survival, hatch, deformities (total, type, and severity), and days to hatch were quantified. Selenium embryo tissue measurements were performed. Selenomethionine exposures of 5 µM and 50 µM significantly decreased survival and hatch at all stages. However, SeMet uptake was stage-dependent and increased with stage. Stage 17 (early neurulation) was identified as the most susceptible stage for lethality and deformities. Selenomethionine in saltwater caused significantly greater toxicity than freshwater at stage 25 (early organogenesis), suggesting a role for liver and osmoregulatory organogenesis in toxicity. Environ Toxicol Chem 2016;35:1247-1256. © 2015 SETAC [ABSTRACT FROM AUTHOR]

Attempts at artificial propagation and rearing of juvenile galaxiids ('whitebait') have been hindered by low fecundities and survival. To circumvent these issues, we subjected wild and captivity-acclimated giant kokopu (Galaxias argenteus), a hitherto unexplored galaxiid, to captive breeding protocols and evaluated the effects of salinity and temperature on egg fertilisation, incubation duration and hatching. Eggs sourced over several spawning seasons were subjected to different salinity (0, 9, 15, 20 and 30-35 PSU) and temperature (4, 10, 15 and 17°C) combinations. Average fertilisation rates were highest (95%) when gametes were activated in fresh water (0 PSU) and declined as salinity increased. Average hatch rates were highest (71-68%) when eggs were incubated in fresh water (0 PSU) at 10°C and decreased as salinity and temperature increased. Sequential stages of embryonic development were documented and several year classes of offspring were produced to form a captive breeding colony. We conclude that the giant kokopu has notable reproduction-related qualities that may be useful for future aquaculture exploitation of this species. [ABSTRACT FROM AUTHOR]

The Gulf Killifish Fundulus grandis, a popular baitfish, is a euryhaline fish species native to coastal estuaries of the Gulf of Mexico and the eastern coast of Florida. Established culture methods have relied on a saline water source but such methods have not been widely adapted by the commercial sector. Since this species is highly euryhaline, there is potential for freshwater culture via the utilization of established inland facilities. In order to assess the feasibility of inland culture, changes in Gulf Killifish hypo‐osmotic tolerance throughout early growth were evaluated. Gulf Killifish were challenged with low salinity treatments of 0 (freshwater), 2.5, 5.0, and 7.5‰ at 2, 7, and 12 weeks posthatch for 4 weeks to determine growth, survival, gill Na+,K+‐ATPase activity, and whole‐body Na+ content. Gill Na+,K+‐ATPase activity and whole‐body ion samples were collected at 0, 2, 14, and 28 d posttransfer (dpt) for each age‐group. Results indicated Gulf Killifish at 2 weeks posthatch grew and survived at 2.5‰ as well as at higher salinities, but growth was reduced in freshwater. At 7 and 12 weeks posthatch, freshwater survival and growth rates at 0‰ salinity were comparable with other salinity treatments. Gill Na+,K+‐ATPase activity increased in Gulf Killifish that were transferred to freshwater at both 7 and 12 weeks posthatch. Whole‐body Na+ content was higher in freshwater 28 dpt in the 2‐week‐posthatch age‐group, and 14 dpt in the 7‐week‐posthatch age‐group. There were few differences in Na+,K+‐ATPase activity and whole‐body Na+ content between salinity treatments in the 12‐week‐posthatch age‐group. These results suggest Gulf Killifish develop hypo‐osmotic tolerance at less than 2 weeks of age posthatch and culture in low salinities including freshwater will be more successful with fish older than 7 weeks of age. [ABSTRACT FROM AUTHOR]

The anadromous Japanese Grenadier AnchovyCoilia nasusis a commercially important fish that is mainly distributed in the Yangtze River and its estuarine area. Two trials were performed to determine the effect of acute salinity stress on the survival of earlyC. nasuslarvae at 0 d posthatch (DPH) and 2 DPH. The salinity treatments for these two trials were 0.4, 5, 10, 15, 20, and 25‰. A third trial compared the growth of juveniles in 3, 6, 9, 12, 15, and 18‰ salinity. Larvae could only tolerate a limited range of salinity (<5‰). Salinity challenge significantly affected the survival of earlyC. nasuslarvae. When salinity was changed, even a low concentration of 2.5‰ could adversely affect earlyC. nasuslarvae. The growth of juveniles was also influenced by salinity. High salinity (>12‰) caused low survival, and low salinity (<6‰) caused poor growth. The optimum salinity for the survival and growth ofC. nasusjuveniles ranges from 6‰ to 12‰. Received November 30, 2014; accepted April 29, 2015 [ABSTRACT FROM PUBLISHER]

Odontesthes bonariensis is an inland water fish from the Pampas region, valued due to the quality of its flesh and its attractiveness as a game fish. Chasicó Lake located in the south of the pampean region is appreciated by fishermen due to O. bonariensis abundance. However, in the last year, a reduction in their catches was recorded. In this work, it was analyzed the changes of O. bonariensis biomass in relation to climate change and salinity in Chasicó Lake from 1997 to 2013. From 2004 to 2013, when a dry period began, a reduction in lake area (68.1-47.4 km) and an increase in salinity (18.9-41.5 g l) were observed. O. bonariensis catches showed a significant decrease in the same period as a result of salinity increments. Possibly, at high salinity, O. bonariensis may still develop but with an impaired reproduction and limited embryo and juvenile survival. In conclusion, after 2004, the fishery quality in Chasicó Lake showed a decreasing trend from the maximum registered in the Pampas lakes. This was in agreement with a marked decrease in the lake area which in turn increased water salinity up to levels close to the O. bonariensis tolerance limit. [ABSTRACT FROM AUTHOR]

Transient and resident habitat utilization patterns were described for juvenile striped bass Morone saxatilis in Albemarle Sound, North Carolina, using otolith elemental chronologies. As fish grew and migrated across the sound and into river habitats, influences from the ambient environment became dominant on elemental patterns. Otolith Ba:Ca was the most reliable element to discern fish movement across the salinity gradients in Albemarle Sound. Resident fish displayed faster growth (mean ± standard deviation: 1.3 ± 0.23 mm/d) than transients (1.1 ± 0.22 mm/d), indicating that residents may have located high quality habitats and remained there, while transient fish expended energy searching for more optimal habitat. Faster growth rates (1.31 ± 0.22 mm/d) and only resident fish were found in the Pasquotank River, which may be an important nursery habitat for juvenile striped bass. Slow growth (1.19 ± 0.26 mm/d), and more transients (53 %) were found in traditional nursery areas in Batchelor Bay at the mouth of the Roanoke River, indicating that these habitats may not be supporting high growth, causing fish to move out of these areas. This study discerns fine scale movements of juvenile striped bass and identified resident and transient contingents by combining otolith microchemistry with daily increment analysis to investigate the consequences of migratory behavior on fish growth. [ABSTRACT FROM AUTHOR]

Kidneys are important organs that play a role in ion and water regulation in different aquatic environments. The Van fish (Alburnus tarichi,Güldenstädt, 1814) has acclimated to the alkaline waters of the largest saline soda lake in the world. In this study, changes in kidney tissue were examined histologically in alkaline and freshwater as the fish entered freshwater for reproduction. In addition, immunological changes were examined for Na+, K+, ATPase (NKA), an important transmembrane protein in kidneys. A histological comparison of the kidneys of fish taken from both environments was made. The glomerular volume was larger in fish acclimated to freshwater, and the collecting tubules were larger in diameter and had thicker walls. The fish acclimated to alkaline lake water had reduced numbers of glomeruli of smaller size. NKA enzyme was present in tubules within kidneys in both environments. It was, however, observed more frequently in fish acclimated to freshwater. Although plasma osmolality and Cl−values decreased in the fish acclimated to freshwater, hematocrit values increased (p < 0.05). No changes were observed in the muscle water content between alkaline water- and freshwater-acclimated fish. We clearly demonstrate that histologic and immunochemical changes take place in the kidney of the Van fish acclimated to the different physicochemical characteristics of alkaline and freshwater environments. [ABSTRACT FROM AUTHOR]

Red SnapperLutjanus campechanusin the northern Gulf of Mexico are threatened by the combined influence of fishing pressures, the bycatch of juveniles in the shrimp trawl fishery, and the seasonal formation of hypoxic (≤2 mg/L O2) bottom water along the Louisiana–Texas continental shelf. Juveniles are especially at risk from hypoxia because they leave the plankton and transition from pelagic to demersal habitats en masse during summer, when hypoxic conditions peak. We explored the influence of hypoxia on juvenile Red Snapper by examining habitat suitability during years with low (areal extent, <10,000 km2), moderate (10,000–19,999 km2), and severe (≥20,000 km2) hypoxia through retrospective analyses of groundfish data from the Southeast Area Monitoring and Assessment Program. Significant interannual variability in the strength of juvenile recruitment was evident, and in general the weakest recruitment was observed during years of severe hypoxia. The relative abundance of juveniles in shallow (9–46 m) waters off central Louisiana was significantly reduced during years of severe hypoxia; this reduction was generally accompanied by an increase in relative abundance of Red Snapper longitudinally and in deeper waters. Patterns of habitat use during summer months varied in relation to hypoxia severity, with individuals occupying sites that were deeper, colder, and of higher salinity during years of severe hypoxia. Red Snapper also exhibited ontogenetic habitat shifts into deeper, cooler, and higher-salinity waters as fish size increased. In general, Red Snapper populations appear resilient to the broad-scale effects of severe hypoxia, although more localized effects may be in force but not evident because of the many factors affecting survival. Received June 19, 2014; accepted October 6, 2014 [ABSTRACT FROM AUTHOR]

Hwang, S.D.; Lee, T.W.; Choi, I.S., and Hwang, S.W., 2014. Environmental factors affecting the daily catch levels of Anguilla japonica glass eels in the Geum River estuary, South Korea. The Japanese eel, Anguilla japonica, is a catadromous fish whose recruitment stage glass eels enter estuaries and rivers after being born offshore in the ocean. The daily variation in glass eel catch was analyzed in relation to environmental factors that affect upstream migration. The first glass eels of the 2003 season were caught in the Geum River estuary in early March, when the water temperature exceeded 5°C. The catch rates peaked in mid-March, when the temperature reached 6-7°C. Few glass eels were caught when the temperature was above 14-16°C in early May. Water temperature may have triggered the timing of glass eel immigration. The catch fluctuated with tidal cycle, since the catch level was relatively high during each new and full moon throughout the sampling period. A generalized additive model indicated that the glass eel catch was significantly related to tidal range, temperature, and salinity. To estimate the effect of minor factors, such as salinity and wind speed, on catch rate, we calculated the standardized residuals of catch rate. The standardized residuals of catch rate did not show any correlations to freshwater inflow or cloud cover, but occasionally increases were seen as a result of drops in salinity and 2-3 days after strong winds, suggesting that these factors may also trigger upstream migration of glass eels in the estuary. [ABSTRACT FROM AUTHOR]

Abstract: The effects of salinity and temperature on growth, plasma ions, cortisol and immune parameters were investigated in two experiments. In the first experiment small, medium and large juvenile Atlantic cod Gadus morhua (initial average weights of 1.9, 8 and 83g, respectively) were reared at four constant salinities (6 to 32‰) for a short period (19–57days, depending on size), then returned to seawater (32‰) without acclimation and reared for another period (20–391days). The highest growth rates were found at 10‰ in all size-classes. After the fish were returned to seawater the growth rates were inversely related to the salinity change in all size-classes and long-term rearing of the medium-sized fish revealed that abrupt salinity increase from 6 and 10‰ to seawater may permanently reduce the growth capacity of juvenile cod. In another long-term experiment, there was no significant difference in the growth rate of cod (initial average weight 3.4g) reared at either 13.5 or 32‰ for 187days. Rearing at 13.5‰ neither enhanced growth rate at 6.3°C nor at 10°C in larger juveniles (>245g) compared with rearing in seawater. The study shows that rearing salinity and abrupt salinity changes have limited or no effects on stress and immune-related parameters, and there are no indications of ion regulatory disturbances at salinities as low as 6‰. This shows that the Atlantic cod is an extremely euryhaline marine teleost species, and indicates that commercial Atlantic cod aquaculture can just as well be carried out in locations with low as with high environmental salinity. [Copyright &y& Elsevier]

In order to determine the effects of fish size and weight on its salinity tolerance, the chloride cells (CCs) immunolocalization changes were examined in Caspian salmon (Salmo trutta caspius) parrs, with the same age (about 2 years old) but different types (type A: 4.88 g, 8.36 cm; type B: 14 g, 11.84 cm; type C: 24.05 g, 14.08 cm). Fish survival rate, blood osmolality, gills CCs histological and immunohistochemical changes were investigated following their transfer from freshwater (FW) to the Caspian Sea water (CSW). The survival rate increased in larger sizes and blood osmolality showed a tendency to increase in parallel with salinity. After 10 days in CSW, some abnormalities were observed in gill structure such as: lamellae cohesion, lamellae rupture and separated lamella from filament epithelium that were shown in all types. These abnormalities in type B were less than the other types. Gill CCs were observed on the gill filament and lamellae. In direct transfer of Salmon parrs to the CSW, changes in number, sectional area, and the surface occupied by CCs in the gill tissue were observed in all the three types. In the type B, the number of CCs did not change, however, in the type C, they decreased, while in the type A, there was significant increase. But in the CSW, the occupied surface by gill CCs in the type C, was reduced significantly compared to other types. According to the present results, among the Salmon parrs with the same age, the fish with type A lacked osmoregulation, while the type B had better compatibility with the CSW. However, after reaching the size of the type C and considering osmultification, it is probable that the type B fish would become compatible with the fresh water environment and they will not have osmoregulation ability in saline water for the long term. [ABSTRACT FROM AUTHOR]

ABSTRACT Knowledge of the interplay of abiotic factors and the invasive success of exotic fish is fundamental both to proper management and the ability to predict consequences for native communities., The highly invasive eastern mosquitofish ( Gambusia holbrooki) has been introduced worldwide; however, although salinity could limit its invasive success, the influence of variations in water salinity on its population biology has been scarcely studied., The present study aimed to analyse the effect of changes in water salinity on the life history and microhabitat use of a mosquitofish population inhabiting a hypersaline stream subjected to human-caused dilution stress., Dilution process and associated habitat changes, such as increased aquatic vegetation, available food and the spread of invasive riparian vegetation (the common reed Phragmites australis), seem to have favoured mosquitofish proliferation and colonization., Dilution caused an increased somatic condition for all individuals and a higher reproductive investment of males and larger females. This led to greater survival, recruitment rates, and abundance during the period of lower salinity., The species showed changes in microhabitat use which could be advantageous in less saline conditions; for instance, the species preferentially used areas with the presence of P. australis as a refuge, and this pattern increased during the dilution period., These results support the hypothesis that human activity is one of the main forces shaping the colonization and proliferation of exotic freshwater fishes. At least in a Mediterranean context, an increase in mosquitofish abundance and the improvement of its population status could be clear indicators of the degradation of natural saline systems., Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The physiological responses of Senegalese sole to a sudden salinity change were investigated. The fish were first acclimated to an initial salinity of 37.5 ppt for 4 h. Then, one group was subjected to increased salinity (55 ppt) while another group was subjected to decreased salinity (5 ppt). The third group (control group) remained at 37.5 ppt. We measured the oxygen consumption rate, osmoregulatory (plasma osmolality, gill and kidney Na,K-ATPase activities) and stress (plasma cortisol and metabolites) parameters 0.5 and 3 h after transfer. Oxygen consumption at both salinities was higher than for the control at both sampling times. Gill Na,K-ATPase activity was significantly higher for the 55 ppt salinity at 0.5 h. Plasma osmolality decreased in the fish exposed to 5 ppt at the two sampling times but no changes were detected for high salinities. Plasma cortisol levels significantly increased at both salinities, although these values declined in the low-salinity group 3 h after transfer. Plasma glucose at 5 ppt salinity did not vary significantly at 0.5 h but decreased at 3 h, while lactate increased for both treatments at the first sampling time and returned to the control levels at 3 h. Overall, the physiological response of S. senegalensis was immediate and involved a rise in oxygen consumption and plasma cortisol values as well as greater metabolite mobilization at both salinities. [ABSTRACT FROM AUTHOR]

We investigated the transepithelial potential (TEP) and its responses to changes in the external medium in Alcolapia grahami, a small cichlid fish living in Lake Magadi, Kenya. Magadi water is extremely alkaline (pH = 9.92) and otherwise unusual: titratable alkalinity (290 mequiv L, i.e. HCO and CO) rather than Cl (112 mmol L) represents the major anion matching Na = 356 mmol L, with very low concentrations of Ca and Mg (<1 mmol L). Immediately after fish capture, TEP was +4 mV (inside positive), but stabilized at +7 mV at 10-30 h post-capture when experiments were performed in Magadi water. Transfer to 250% Magadi water increased the TEP to +9.5 mV, and transfer to fresh water and deionized water decreased the TEP to −13 and −28 mV, respectively, effects which were not due to changes in pH or osmolality. The very negative TEP in deionized water was attenuated in a linear fashion by log elevations in [Ca]. Extreme cold (1 vs. 28°C) reduced the positive TEP in Magadi water by 60%, suggesting blockade of an electrogenic component, but did not alter the negative TEP in dilute solution. When fish were transferred to 350 mmol L solutions of NaHCO, NaCl, NaNO, or choline Cl, only the 350 mmol L NaHCO solution sustained the TEP unchanged at +7 mV; in all others, the TEP fell. Furthermore, after transfer to 50, 10, and 2% dilutions of 350 mmol L NaHCO, the TEPs remained identical to those in comparable dilutions of Magadi water, whereas this did not occur with comparable dilutions of 350 mmol L NaCl-i.e. the fish behaves electrically as if living in an NaHCO solution equimolar to Magadi water. We conclude that the TEP is largely a Na diffusion potential attenuated by some permeability to anions. In Magadi water, the net electrochemical forces driving Na inwards (+9.9 mV) and Cl outwards (+3.4 mV) are small relative to the strong gradient driving HCO inwards (−82.7 mV). Estimated permeability ratios are P/ P = 0.51-0.68 and $$ P_{{{\text{HCO}}_{3} }} /P_{\text{Na}} $$ = 0.10-0.33. The low permeability to HCO is unusual, and reflects a unique adaptation to life in extreme alkalinity. Cl is distributed close to Nernst equilibrium in Magadi water, so there is no need for lower P. The higher P likely facilitates Na efflux through the paracellular pathway. The positive electrogenic component is probably due to active HCO excretion. [ABSTRACT FROM AUTHOR]

Organisms that migrate between rivers and the sea inevitably pass through estuarine habitats. Despite the potential importance of salinity and temperature fluctuations for metabolic adaptation, little is known about the impact of environmental changes in estuaries on the survival of residents. Ayu ( Plecoglossus altivelis) is a migratory fish that inhabits estuarine brackish water in its early life stages. The recent decline in the abundance of populations ascending into rivers is of concern for local biodiversity. The present study aims to elucidate the ecological processes that determine the early success of Ayu larvae under variable environmental conditions. The effects of salinity and water temperature on the endogenous growth of newly hatched larvae from the same brood were examined experimentally based on morphological and metabolic characteristics. High salinity and high water temperature together appeared to require more energy for larval osmoregulation, resulting in the acceleration of yolk depletion and reduced growth of the notochord. Increasing the osmoregulative cost during the yolk-sac stage resulted in the faster induction of a state of starvation. Seawater is considered to have an adverse effect on the survival of newly hatched larvae, as it lowers the efficiency of foraging and predator avoidance due to an energetic tradeoff. More attention should be paid to the significance of estuarine environments involving brackish waters to ensure the early survival of amphidromous fish such as Ayu. [ABSTRACT FROM AUTHOR]

Alkalinity stress is common in cultured aquatic animals and considered to be one of the major stress factors for fishes when they are transferred to saline-alkali waters. To evaluate potential effects of alkalinity on the developmental biology of Oryzias latipes, fertilized eggs, larvae and breeding fish were exposed to different carbonate alkalinity concentrations of 1.5–64.5 meq l−1, for 9, 120, and 60 days, respectively. The mortality of embryos significantly increased when exposed to the high concentrations (16.5–64.5 meq l−1). Although more than 50% of survived embryos hatched in 16.5 and 31.4 meq l−1 concentrations of carbonate alkalinity, most were not able to swim up after hatching. Morphological abnormalities such as coagulated embryos, halted embryo development, and hatching failure were observed at stages 15, 29–33 and 38 in high concentrations (31.4, 64.5 meq l−1). Almost all larvae in 16.5 and 31.4 meq l−1 treatments died 70 d post-hatch. Growth of juveniles exposed to carbonate alkalinity of 5.3 and 8.8 meq l−1 was not significantly different at 70 d and 120 d post-hatch. The number of eggs released by breeders, the fertilization rate and the hatching rate of eggs were significantly lower in the 31.4 meq l−1 treatment than in other treatments. Although medaka are capable of surviving in high alkalinities (31.4, 64.5 meq l−1) for an extended period of time, these conditions are stressful to the fish, especially at the embryonic and reproductive stages. [ABSTRACT FROM AUTHOR]