Osmoregulatory Plasticity of Juvenile Greater Amberjack (Seriola dumerili) to Environmental Salinity

Osmotic costs in teleosts are highly variable, reaching up to 50% of energy expenditure in some. In several species, environmental salinities close to the isosmotic point (~15 psu) minimize energy demand for osmoregulation while enhancing growth. The present study aimed to characterize the physiological status related to osmoregulation in early juveniles of the greater amberjack, Seriola dumerili, acclimated to three salinities (15, 22, and 36 psu). Our results indicate that plasma metabolic substrates were enhanced at the lower salinities, whereas hepatic carbohydrate and energetic lipid substrates decreased. Moreover, osmoregulatory parameters, such as osmolality, muscle water content, gill and intestine Na+-K+-ATPase activities, suggested a great osmoregulatory capacity in this species. Remarkably, electrophysiological parameters, such as short-circuit current (Isc) and transepithelial electric resistance (TER), were enhanced significantly at the posterior intestine. Concomitantly, Isc and TER anterior-to-posterior intestine differences were intensified with increasing environmental salinity. Furthermore, the expression of several adeno-hypophyseal genes was assessed. Expression of prl showed an inverse linear relationship with increasing environmental salinity, while gh mRNA enhanced significantly in the 22 psu-acclimated groups. Overall, these results could explain the better growth observed in S. dumerili juveniles kept at salinities close to isosmotic rather than in seawater.

The Validity of Ultrasound Technology in Providing an Indirect Estimate of Muscle Glycogen Concentrations Is Equivocal

Researchers and practitioners in sports nutrition would greatly benefit from a rapid, portable, and non-invasive technique to measure muscle glycogen, both in the laboratory and field. This explains the interest in MuscleSound®, the first commercial system to use high-frequency ultrasound technology and image analysis from patented cloud-based software to estimate muscle glycogen content from the echogenicity of the ultrasound image. This technique is based largely on muscle water content, which is presumed to act as a proxy for glycogen. Despite the promise of early validation studies, newer studies from independent groups reported discrepant results, with MuscleSound® scores failing to correlate with the glycogen content of biopsy-derived mixed muscle samples or to show the expected changes in muscle glycogen associated with various diet and exercise strategies. The explanation of issues related to the site of assessment do not account for these discrepancies, and there are substantial problems with the premise that the ratio of glycogen to water in the muscle is constant. Although further studies investigating this technique are warranted, current evidence that MuscleSound® technology can provide valid and actionable information around muscle glycogen stores is at best equivocal.

Functional characterization and osmoregulatory role of the Na+-K+-2Cl− cotransporter in the gill of sea lamprey (Petromyzon marinus), a basal vertebrate

The present study provides molecular and functional characterization of Na+-K+-2Cl− cotransporter (NKCC1/Slc12a2) in the gills of sea lamprey ( Petromyzon marinus), the most basal extant vertebrate with an osmoregulatory strategy. We report the full-length peptide sequence for the lamprey Na-K-Cl cotransporter 1 (NKCC1), which we show groups strongly with and occupies a basal position among other vertebrate NKCC1 sequences. In postmetamorphic juvenile lamprey, nkcc1 mRNA was present in many tissues but was fivefold higher in the gill than any other examined tissue, and NKCC1 protein was only detected in the gill. Gill mRNA and protein abundances of NKCC1 and Na+-K+-ATPase (NKA/Atp1a1) were significantly upregulated (20- to 200-fold) during late metamorphosis in fresh water, coinciding with the development of salinity tolerance, and were upregulated an additional twofold after acclimation to seawater (SW). Immunohistochemistry revealed that NKCC1 in the gill is found in filamental ionocytes coexpressing NKA, which develop during metamorphosis in preparation for SW entry. Lamprey treated with bumetanide, a widely used pharmacological inhibitor of NKCC1, exhibited higher plasma Cl− and osmolality as well as reduced muscle water content after 24 h in SW; there were no effects of bumetanide in freshwater-acclimated lamprey. This work provides the first functional characterization of NKCC1 as a mechanism for branchial salt secretion in lampreys, providing evidence that this mode of Cl− secretion has been present among vertebrates for ~550 million years.

Water acidification causes death of marine ornamental fish (Perciformes: Pomacentridae) during transport: contributing to the conservation of wild populations

Pomacentridae is a common family in the aquarium fish trade. Most species are harvested from nature. Here we evaluate the following water parameters in the pomacentrid sergeant major, Abudefdufsaxatilis (Linnaeus, 1758), to assess their stress level during a 24, 48, and 72 hours transport: dissolved oxygen (DO), total ammonia, and pH. In addition, we evaluated the following physiological parameters: plasma osmolality, muscle water content, blood glucose, and the enzyme activities of the branchial carbonic anhydrase (CA), the hepatic glutathione S-transferase (GST), catalase (CAT), and superoxide dismutase (SOD). The mortality of fish measuring >6 cm total length was 22%, while no mortality was observed for fish measuring <6 cm. The pH of the water was significantly correlated with fish mortality, especially for the initial 24 hours of transport. Hypoxia after 24–48 hours also led to fish mortality, but build up ammonia was not a problem even after 72 hours. We suggest that a minimum water volume of 125 ml/g fish is necessary for safe and cost-effective transport of the sergeant major, preferably with <6 cm in total length.

Physiological tools to predict invasiveness and spread via estuarine bridges: tolerance of Brazilian native and worldwide introduced freshwater fishes to increased salinity

Non-native freshwater fishes may spread via estuaries, invading nearby basins. The Brazilian natives Rhamdia quelen and Geophagus brasiliensis, and the worldwide introduced Clarias gariepinus, Ictalurus punctatus, Oreochromis niloticus and Cyprinus carpio were acutely exposed (6 h) to salinities 15 and 30. Hypothetically, the introduced species display greater physiological plasticity than do the natives. Exposure to salinity 30 was lethal after 1.5–3 h to all species except for O. niloticus and G. brasiliensis. Increase in plasma osmolality was inversely related to muscle water content, mainly in salinity 30 for all species. R. quelen and C. gariepinus displayed increased expression of heat-shock protein 70 (HSP70) on salinity increase; differently, I. punctatus, O. niloticus and C. carpio showed high constitutive levels already in freshwater. Species with high constitutive expression of HSP and/or high degree of euryhalinity (cichlids) could potentially use estuaries as bridges, especially through areas of salinity <15.

Effect of extracellular osmolality on metabolism in contracting mammalian skeletal muscle in vitro

Extensive research has been conducted on hepatocyte metabolism perturbed under the influence of anisosmotic stress. However, much less is known about the behaviour of skeletal muscle metabolism under similar conditions. After establishing a working model to study anisosmotic stress in resting mammalian skeletal muscle, the current study tested the hypothesis that hyperosmotic (HYPER) stress would lead to increased creatine, lactate, and measured enzyme activity, whereas hypo-osmotic (HYPO) stress would lead to decreased metabolites and enzyme activity vs. iso-osmotic (ISO) stress post contraction. Rat soleus (SOL) and extensor digitorum longus (EDL) were isolated and incubated in an organ bath (95% O2, 5% CO2, pH 7.4, 25 °C) altered to targeted osmotic conditions (ISO, 290 osmol·L–1; HYPO, 180 osmol·L–1; HYPER, 400 osmol·L–1). Muscle samples were flash frozen after 10 min of contraction. Post contraction, muscle water content in the SOL HYPO condition was 18% greater than ISO, and HYPER had approximately 14% less water content than ISO (p < 0.05). In the HYPO condition, EDL had 21% greater water content than ISO, and HYPER had 17% less water content than ISO (p < 0.05). SOL HYPO resulted in higher phosphocreatine and lower lactate and creatine vs. HYPER (p < 0.05) but there were no differences in EDL between HYPO and HYPER. Pyruvate dehydrogenase activity increased in SOL HYPER vs. HYPO, whereas glycogen phosphorylase a increased in EDL HYPER vs. HYPO. In conclusion, fibre-type-specific responses exist after contraction such that when SOL muscle is perturbed in HYPER, as compared with HYPO, media, metabolic activity increases. Future work should focus on glucose uptake–regulation during anisosmotic conditions.

Metabolic substrates are not mobilized from the osmoregulatory organs (gills and kidney) of the estuarine pufferfishes Sphoeroides greeleyi and S. testudineus upon short-term salinity reduction

The marine-estuarine species of pufferfishes Sphoeroides testudineus and S. greeleyi are very efficient osmoregulators. However, they differ with respect to their tolerance of salinity reduction. During low tide S. testudineus remains in diluted estuarine waters, whereas S. greeleyi returns to seawater (SW). The hypothesis tested here was that the short-term mobilization of metabolic substrates stored in their main osmoregulatory organs would correlate with this differential tolerance. Fishes exposed to 5‰ (for 6 h) were compared to those kept in 35‰. Branchial and renal contents of triglycerides, protein and glycogen were evaluated, and total ATPase activity accounted for the tissues' metabolism. Plasma osmolality, chloride and glucose, hematocrit, and muscle water content were also measured. Total triacylglycerol content was higher in S. greeleyi than in S. testudineus in both salinities and in both organs. Kidney glycogen contents were higher in S. greeleyi than in S. testudineus in 5 and 35‰. Total ATPase activity was reduced in 5‰ when compared to 35‰ in the kidney of S. greeleyi, and was higher in the gills of S. greeleyi than in those of S. testudineus, in both salinities. Upon exposure to dilute SW, both species displayed a similar osmoregulatory pattern: plasma osmolality and chloride were reduced. Again in both species, stability in muscle water content indicated cellular water content control. Although the metabolic substrates stored in the osmoregulatory organs of both species were not mobilized during these short-term sea water dilution events, some differences could be revealed between the two species. S. greeleyi showed more metabolic reserves (essentially triacylglycerols) in these organs, and its gills showed higher total ATPase activity than those S. testudineus.

Physiological changes of sturgeon Acipenser naccarii caused by increasing environmental salinity

SUMMARY The possible repercussions of osmoregulatory processes on some indicators of classical and oxidative stress were examined during gradual acclimation of sturgeons (Acipenser naccarii) to full seawater (35% salinity) and after a period of 20∼days at this salinity. Erythrocyte constants and levels of cortisol, protein and glucose in the plasma were determined. In addition, plasma osmolality and muscle-hydration values, as well as liver and heart protein, were determined. Catalase, glutathione peroxidase and superoxide dismutase activities and lipidperoxidation levels were measured in blood (plasma and red blood cells) and tissue (liver and heart). A number of physiological responses, such as disturbance in body fluid, activation of osmoregulatory mechanisms, augmented antioxidant defences in blood and alteration of energy metabolites, were detected with increasing environmental salinity. After 20 days at 35% salinity, plasma osmolality, erythrocyte constants and muscle water content all returned to values usual for low environmental salinity, indicating that osmoregulatory processes have achieved their objective. However, cortisol values, antioxidant enzyme activities in the blood (plasma and red blood cells), lipid peroxidation in plasma, and hepatic proteins did not return to initial values, showing that osmoregulatory processes cause major physiological changes in the fish.