Response of ATPases in the osmoregulatory tissues of freshwater fish Oreochromis niloticus exposed to copper in increased salinity

An increase in salinity of freshwater can affect the physiology and metal uptake in fish. In the present study, Nile tilapia Oreochromis niloticus were exposed to copper (1.0 mg/l) in increased salinities (2, 4, and 8 ppt) for 0, 1, 3, 7, and 14 days. Following the exposures, the activities of Na⁺/K⁺-ATPase, Mg²⁺-ATPase, and Ca²⁺-ATPase were measured in the gill, kidney, and intestine to evaluate the changes in osmoregulation of fish. Results showed that increases in salinity and Cu exposure of fish significantly altered the ATPase activities depending on the tissue type, salinity increase, and exposure durations. Salinity-alone exposures increased Na⁺/K⁺-ATPase activity and decreased Ca²⁺-ATPase activity. Na⁺/K⁺-ATPase activity decreased following Cu exposure in 2 and 4 ppt salinities, though the activity increased in 8 ppt salinity. Ca²⁺-ATPase activity decreased in the gill and intestine in all salinities, while the activity mostly increased in the kidney. However, there were great variations in Mg²⁺-ATPase activity following exposure to salinity alone and salinity+Cu combination. Cu accumulated in the gill and intestine following 14 days exposure and accumulation was negatively correlated with salinity increase. Data indicated that ATPases were highly sensitive to increases in salinity and Cu and might be a useful biomarker in ecotoxicological studies. However, data from salinity increased freshwaters should carefully be handled to see a clear picture on the effects of metals, as salinity affects both metal speciation and fish osmoregulation.     

Fish anesthesia: effects of the essential oils of Hesperozygis ringens and Lippia alba on the biochemistry and physiology of silver catfish (Rhamdia quelen)

The anesthetic activities of the essential oils (EOs) of Hesperozygis ringens (EOHR) and Lippia alba (EOLA) and their effects in silver catfish (Rhamdia quelen) after anesthesia and recovery were investigated. Fish (32.19 ± 1.24 g) were submitted to one of the following treatments for each EO: basal group, control, or anesthesia (150, 300, or 450 μL L^?1 EO). After that the anesthesia was induced or simulated and the biometric measurements were completed, fish were transferred to anesthetic-free aquaria to allow for recovery. Fish were sampled at 0, 15, 30, 60, and 240 min after recovery. At time 0 of recovery, the ventilatory rate was lower in the groups anesthetized with either EO. In comparison with the basal group, control fish showed an increase in plasma glucose, aspartate aminotransferase (AST), and Na⁺ levels and a reduction in Na⁺/K⁺-ATPase activity at 0 min of recovery. Plasma levels of ammonia and Na⁺ were lower in the fish anesthetized with EOLA (450 μL L^?1) and EOHR (all concentrations), respectively, than in the control fish. Additionally, lactate, AST, alanine aminotransferase, K⁺ plasma levels, and gill Na⁺/K⁺-ATPase and H⁺-ATPase activities were higher in the fish anesthetized with either EOHR or EOLA than in the control fish. The EOs promoted slight changes in silver catfish that enabled both an adaptive response and the recovery of most of the measured parameters after 240 min regardless of concentration or EO that was used. These findings support the use of EOHR and EOLA as anesthetics for fish.     

Lead accumulation and its effects on the branchial physiology of Prochilodus lineatus

The purpose of this work was to determine the tissue accumulation of lead (Pb) and its effects on osmoregulatory processes of the freshwater fish Prochilodus lineatus. Juvenile fish were exposed to Pb (from 1.7 to 0.7 mg of dissolved Pb L^?1) for 6, 24 and 96 h and Pb accumulation was analyzed in the gills, liver, kidneys, blood cells and muscle. The following parameters were also analyzed: hematologic (hemoglobin content, hematocrit and number of red blood cells), metabolic (blood glucose), endocrine (blood cortisol), osmo ionic (plasma osmolality and Na⁺, K⁺, Cl^? and Ca⁺² concentrations), gill enzymes (Na⁺/K⁺-ATPase and carbonic anhydrase), chloride cell (CC) density and CC location in the gills. Pb accumulated in all the analyzed tissues, with the kidneys showing the highest concentration, followed by the gills and liver. The lowest Pb concentrations were found in blood cells and muscle. Pb promoted an increase in blood glucose after 6 and 24 h exposure. Gill Na⁺/K⁺-ATPase was inhibited after 24 h of exposure, but its activity was restored at 96 h, probably due to the increase in CC in gill lamellae. Plasma Na⁺ was reduced after 6 and 96 h, while K⁺ concentrations increased at all the experimental times. Fish exposed to Pb showed reduced plasma Ca⁺² at all experimental periods. Hematologic parameters remained unchanged. Overall, this study demonstrated that Pb interferes in osmoregulatory processes of P. lineatus and the proliferation of CC in the gills is a response in order to reestablish adequate ion concentrations.     

In vitro and in vivo hepatoprotective and antioxidant effects of Astragalus polysaccharides against carbon tetrachloride-induced hepatocyte damage in common carp (Cyprinus carpio)

The present study is aiming at evaluating the hepatoprotective and antioxidant effects of Astragalus polysaccharide (APS) on the carbon tetrachloride (CCl₄)-induced hepatocyte and liver injury in common carp in vitro and in vivo. In vitro, APS (200, 400 and 800 μg/ml) was added to the carp primary hepatocytes before (pre-treatment), after (post-treatment) and both before and after (pre- and post-treatment) the incubation of the hepatocytes with CCl₄ at 8 mM in the culture medium. APS at concentrations of 200, 400 and 800 μg/ml significantly improved cell viability and inhibited the elevation of glutamate pyruvate transaminase (GPT), glutamate oxalate transaminase (GOT), lactate dehydrogenase (LDH) and malondialdehyde (MDA) and significantly increased the reduced level of superoxide dismutase (SOD). In vivo administration of APS at the doses of 1.5 and 3 g/kg in the diet for 60 days prior to CCl₄ intoxication significantly reduced the elevated activities of GPT, GOT and LDH and increased the reduced levels of total protein and albumin in the serum; meanwhile, the reduced levels of SOD, glutathione and total antioxidant capacity (T-AOC) were markedly increased and the MDA formation was significantly inhibited in liver tissue. Overall results proved the hepatoprotective action of APS, which is likely related to its antioxidant activity. The results support the use of APS as a hepatoprotective and antioxidant agent in fish.     

Thermal stress altered growth performance and metabolism and induced anaemia and liver disorder in Labeo rohita

Sudden fish deaths occurred during summer peaks in India and expected to be more in future. This study was conducted to explain the biochemical responses of Labeo rohita under extreme thermal condition (treated: 37–38°C against controlled: 28–30°C). Exposure of 14 days resulted in 30% of fish mortality. Glucose concentration was maintained in serum for both treated and controlled groups. However, triglycerides, protein, globulin, calcium, cholesterol and haemoglobin were declined and enzymes (glutamate‐pyruvate transaminase, GPT and glutamate‐oxalate transaminase, GOT) were elevated in serum in the treated group. Indicators of overall metabolism (biomolecules: glucose, triglycerides, protein, cholesterol; enzymes: GPT, GOT; and RNA: DNA) were diminished in liver, whereas these were less affected in muscle. Higher GPT, GOT and lower albumin in serum confirmed disturbance in hepatic panel. Simultaneously compromised growth (lower SGR, DNA content in liver) was observed in treated fish due to impaired metabolism. Extreme thermal stress induced by such catastrophic warmer water exposure caused liver problems and anaemia which ultimately caused fish death.     

iTRAQ proteomic analysis of salinity acclimation proteins in the gill of tropical marbled eel (<Emphasis Type="Italic">Anguilla marmorata</Emphasis>)

Osmoregulation plays an important role in the migration process of catadromous fish. The osmoregulatory mechanisms of tropical marbled eel (Anguilla marmorata), a typical catadromous fish, did not gain sufficient attention, especially at the molecular level. In order to enrich the protein database of A. marmorata, a proteomic analysis has been carried out by iTRAQ technique. Among 1937 identified proteins in gill of marbled eel, the expression of 1560 proteins (80 %) was quantified. Compared with the protein expression level in the gill of marbled eel in freshwater (salinity of 0 ‰), 336 proteins were up-regulated and 67 proteins were down-regulated in seawater (salinity of 25 ‰); 33 proteins were up-regulated and 32 proteins were down-regulated in brackish water (salinity of 10 ‰). These up-regulated proteins including Na⁺/K⁺-ATPase, V-type proton ATPase, sodium–potassium–chloride co-transporter and heat shock protein 90 were enriched in many KEGG-annotated pathways, which are related to different functions of the gill. The up-regulated oxidative phosphorylation and seleno-compound metabolism pathways involve the synthesis and consumption of ATP, which represents extra energy consumption. Another identified pathway is the ribosome pathway in which a large number of up-regulated proteins are involved. It is also more notable that tight junction and cardiac muscle contraction pathways may have correlation with ion transport in gill cells. This is the first report describing the proteome of A. marmorata for acclimating to the change of salinity. These results provide a functional database for migratory fish and point out some possible new interactions on osmoregulation in A. marmorata.     

Quality and biochemical properties of artificially hibernated crucian carp for waterless preservation

The aim of this study was to explore the artificial hibernation of crucian carp for?waterless preservation and to characterize the quality and biochemical properties during and after the hibernation. Anesthetized crucian carp using eugenol were stored at 8?°C with 90?% oxygen and 95–100?% relative humidity for 38?h and then transferred to fresh water to recover. Liquid loss and cooking loss had no significant changes (p?>?0.05). The total volatile basic nitrogen content and 2-thiobarbituric acid value in hibernated fish were significantly higher (p?<?0.05) than fresh and recovered groups. Serum cortisol, glutamic-oxaloacetic transaminase (GOT), alkaline phosphatase (AKP), and acid phosphatase (ACP) activities significantly increased (p?<?0.05) during hibernation, while glutamic-pyruvic transaminase (GPT) had no significant change (p?>?0.05). Both ACP and AKP activities decreased upon the fish recovered, but only the ACP activity returned to normal. However, there were increased serum glucose concentration, GOT and GPT activities in recovered fish. On the basis of these findings, it can be concluded that the artificially hibernated life of crucian carp was 38?h by the combination of anaesthetizing and low temperature. The muscle quality would not be influenced, and most of the stress responses would disappear after hibernated fish recovered.     

Salinity effects on osmoregulation and gill morphology in juvenile Persian sturgeon (<Emphasis Type="Italic">Acipenser persicus</Emphasis>)

The effect of abrupt and 5-day gradual salinity transfers from freshwater (FW) to 11 ‰ Caspian Sea brackish water (BW) was investigated in juvenile Persian sturgeon Acipenser persicus with three different weight groups: 1–2 g (1.62 ± 0.27 g), 2–3 g (2.55 ± 0.41 g) and 3–5 g (4.28 ± 0.76 g). Mortality rates, blood osmotic pressure, gill morphology and branchial Na⁺, K⁺-ATPase (NKA) activity were measured 4 and 10 days after abrupt transfer and 9 and 15 days after the initial gradual transfer (i.e. 4 and 10 days after reaching Caspian Sea salinity). Fish under 3 g could not survive increased salinity, and the blood osmotic pressure of the remaining surviving fish increased and remained elevated. However, heavier fish were able to survive and successfully acclimate, even to rapid salinity change with osmotic pressure reduced to Caspian Sea osmolality levels. At the gill level, the developmental increase in chloride cell volume and a higher NKA content most probably allow juveniles weighing more than 2 g to sharply increase NKA activity if the fish are transferred to BW. The rapid chloride cell proliferation occurring with increased salinity should strengthen this acclimation response. Therefore, a drastic physiological change occurs when fish weigh more than 2 g that allows migration to higher salinities. The triggering signal on chloride cells must be further investigated in order to optimize this functional step.     

Acclimation of brackish water pearl spot (Etroplus suratensis) to various salinities: relative changes in abundance of branchial Na+/K+-ATPase and Na+/K+/2Cl− co-transporter in relation to osmoregulatory parameters

The present study was conducted to elucidate the osmoregulatory ability of the fish pearl spot (Etroplus suratensis) to know the scope of this species for aquaculture under various salinities. Juvenile pearl spot were divided into three groups and acclimated to freshwater (FW), brackish water (BW) or seawater (SW) for 15 days. The fish exhibited effective salinity tolerance under osmotic challenges. Although the plasma osmolality and Na⁺, K⁺ and Cl^? levels increased with the increasing salinities, the parameters remained within the physiological range. The muscle water contents were constant among FW-, BW- and SW-acclimated fish. Two Na+/K+-ATPase α-isoforms (NKA α) were expressed in gills during acclimation in FW, BW and SW. Abundance of one isoform was up-regulated in response to seawater acclimation, suggesting its role in ion secretion similar to NKA α1b, while expression of another isoform was simultaneously up-regulated in response to both FW and SW acclimation, suggesting the presence of isoforms switching phenomenon during acclimation to different salinities. Nevertheless, NKA enzyme activities in the gills of the SW and FW individuals were higher (p < 0.05) than in BW counterparts. Immunohistochemistry revealed that Na⁺/K⁺-ATPase immunoreactive (NKA-IR) cells were mainly distributed in the interlamellar region of the gill filaments in FW groups and in the apical portion of the filaments in BW and SW groups. The number of NKA-IR cells in the gills of the FW-acclimated fish was almost similar to that of SW individuals, which exceeded that of the BW individuals. The NKA-IR cells of BW and SW were bigger in size than their FW counterparts. Besides, the relative abundance of branchial Na⁺/K⁺/2Cl^? co-transporter showed stronger evidence in favor of involvement of this protein in hypo-osmoregulation, requiring ion secretion by the chloride cells. To the best of our knowledge, this is the first study reporting the wide salinity tolerance of E. suratensis involving differential activation of ion transporters and thereby suggesting its potential as candidate for fish farming under different external salinities.     

Early biochemical biomarkers for zinc in silver catfish (<Emphasis Type="Italic">Rhamdia quelen</Emphasis>) after acute exposure

Contamination of aquatic ecosystems by metals causes various biochemical changes in aquatic organisms, and fish are recognized as indicators of environmental quality. Silver catfish were exposed to six concentrations of zinc (Zn): 1.0, 2.5, 5.0, 7.5, 10.0 and 12.5 mg/L for 96 h to determine the mean lethal concentration (LC₅₀). The value obtained was 8.07 mg/L. In a second experiment, fish were exposed to concentrations of 1.0 or 5.0 mg/L Zn and a control for 96 h. Afterward, the tissues were collected for biochemical analysis. Lipid peroxidation, as indicated by thiobarbituric acid-reactive substance (TBARS), decreased in the liver and brain for all Zn concentrations tested, while in the gills TBARS levels increased at 1.0 mg/L and declined at 5.0 mg/L. Zn increased protein carbonyls in the muscle of silver catfish and decreased it in the other tissues. The enzyme superoxide dismutase increased in both exposed groups. However, catalase did not change. Glutathione S-transferase decreased in the liver and increased in the gills (1.0 mg/L), muscle (5.0 mg/L) and brain (1.0 and 5.0 mg/L). Nonprotein thiols changed only in brain and muscle tissue. Zn exposure inhibited acetylcholinesterase (AChE) activity in the brain at both concentrations tested, but did not change it in muscle. Exposure to Zn inhibited the activity of Na⁺/K⁺-ATPase in the gills and intestine at both concentrations tested. Our results demonstrate that Zn alters biochemical parameters in silver catfish and that some parameters such as AChE and Na⁺/K⁺-ATPase could be considered as early biomarkers of waterborne Zn toxicity.     

Photoperiod and temperature effects on growth and maturation of pre- and post-smolt Atlantic salmon

The present study was undertaken to examine the long-term effect of continuous light and constant temperature and their interaction on growth, feed intake, gill Na⁺, K⁺-ATPase (NKA) activity and early sexual maturation in Atlantic salmon pre- and post-smolts. The fish (mean initial weight = 15.9 g ± 0.4 SE) were reared on two photoperiods (continuous light, LL and simulated natural photoperiod, LDN, 60°25′N) and on two constant temperatures (average 8.3 and 12.7 °C) from June to July the following year. This resulted in four experimental groups abbreviated as LL8, LL12, LDN8 and LDN12. Growth in freshwater was highest in the LL12 group and final weight of this group was 70–330 % higher than in the other experimental groups, and our findings further demonstrate that the growth-enhancing effect of continuous light alone corresponds to a 4.5° increase in temperature. Overall, the highest feed intake was registered in the LL12 group, whereas no differences in feed intake or growth were observed between the LL8 and LDN12 groups, and the lowest feed intake and growth in the LDN8 group. Both temperature groups on LL developed peak levels in gill NKA activity in October–November, 4–5 months prior to the natural season for the parr–smolt transformation. Fish at 12 °C showed peak levels in NKA activity 4–6 weeks before the fish on 8 °C. The proportion of mature males was higher at 12.7 °C (66 %) compared to 8.3 °C (11 %). Highest maturation was seen at LL12 (82 %). For the salmon industry, this means that long-term rearing at LL and 12.7 °C will improve growth but also leads to higher maturation proportion. By rearing fish at LL8, it is, however, possible to achieve high growth and low maturation simultaneously.     

盐度对条石鲷幼鱼Na+/K+-ATP酶活力的影响

研究了盐度变化对条石鲷幼鱼鳃、肾脏和肝脏中Na⁺/K⁺-ATP酶活力的影响。经不同盐度(8、18、28、38、48)的处理,条石鲷幼鱼3种组织Na⁺/K⁺-ATP酶活力均受到不同程度的影响。经低盐度(8和18)处理的幼鱼鳃Na⁺/K⁺-ATP酶活力在前6 h略微增加,然后逐渐降低,在处理24 h时下降到最低,之后又开始增加。经高盐度(38和48)处理时,鳃中Na⁺/K⁺-ATP酶活力在前6 h有所降低,然后迅速升高,并在处理24 h时达到最大,之后酶活力逐渐降低,并在处理96 h后与对照组无显著性差异(P>0.05)。所有盐度处理组幼鱼肾脏Na⁺/K⁺-ATP酶活力在处理开始6 h均稍有增加,而从处理6 h开始降低,在处理24 h下降到最低,此后酶活力又呈现增加的趋势。在盐度为8的处理组中,肝脏Na⁺/K⁺-ATP酶活力与肾脏中变化趋势相似,而其它3组则逐渐降低,在处理24 h时达到最低,之后又逐渐增加。结果表明,条石鲷幼鱼适盐范围广,具有较强的渗透压调节能力。3种组织的Na⁺/K⁺-ATP酶活力酶活性在盐度为18～38的范围内变化不明显,而在8和48的盐度下变化较大,最终酶活力均高于对照组。与肾脏相比,盐度变化对鳃和肝脏Na⁺/K⁺-ATP酶活力的影响较大。     

Biochemical and molecular differences in diploid and triploid ocean-type chinook salmon (<Emphasis Type="Italic">Oncorhynchus tshawytscha</Emphasis>) smolts

There is increasing evidence for complex dosage effects on gene expression, enzyme activity and phenotype resulting from induced ploidy change. In this study, ocean-type chinook salmon were bred using a 2 × 2 factorial mating design to create four families and test whether triploidization resulted in changes in growth performance and smolting. Eggs were pressure shocked after fertilization to create triploid fish from a subset of each family. In June, fish were sampled for size, plasma insulin-like growth factor 1 (IGF-1), gill Na⁺–K⁺-ATPase activity, and expression of two Na⁺–K⁺-ATPase α subunits in the gill. Diploids were significantly heavier than triploids, and there were significant differences due to family. Despite a significant positive correlation between plasma IGF-1 and fish size, plasma IGF-1 did not differ between diploid and triploid smolts. Diploids also had significantly greater gill Na⁺–K⁺-ATPase enzyme activities than triploids and there was a strong family effect. Gill Na⁺–K⁺-ATPase α1b isoform expression differed significantly by family, but not ploidy, and generally families with lower Na⁺–K⁺-ATPase enzyme activity had higher α1b isoform gene expression. Na⁺–K⁺-ATPase α1a isoform expression did not differ among any of the groups. Although diploids were larger and had higher specific activities of Na⁺–K⁺-ATPase in the gills, there was no difference in gene expression or circulating hormone levels. The strong family effect, however, suggests that strain selection may be useful in improving performance of triploids for aquaculture.     

Osmoregulation in juvenile Siberian sturgeon (Acipenser baerii)

The osmoregulation capabilities of juvenile Siberian sturgeon exposed to three experimental osmolalities (22, 250 and 387 mOsmol kg⁻¹) were studied over a 45-day period. Growth performance, haematological parameters, ion concentrations, gill and spiral valve Na⁺-K⁺-ATPase activities, as well as gill and spiral valve histology, were measured. At the end of the period, the plasma osmolality of fish kept in 250 and 387 mOsmol kg⁻¹ was higher than that of fish kept in 22 mOsmol kg⁻¹. Similar trends were observed in electrolyte concentrations. Spiral valve and gill Na⁺-K⁺-ATPase activity varied with exposure time and environmental salinity. Shortly after being transferred to hyperosmotic media, spiral valve Na⁺-K⁺-ATPase activity fell, while gill Na⁺-K⁺-ATPase activity remained constant. At the end of the experiment, gill Na⁺-K⁺-ATPase activities in fish kept in isosmotic and hyperosmotic media had increased in comparison to those of the control fish. Moreover, spiral valve Na⁺-K⁺-ATPase activities recovered and were similar to those recorded in fish kept in hyposmotic environments. Although some of the morpho-physiological mechanisms were operational in juvenile Siberian sturgeon in their adaptation to hyperosmotic media, fish cannot be considered hyperosmotic regulators as they were unable to maintain their plasma osmolality and electrolyte equilibrium in salinities higher than 250 mOsmol kg⁻¹. This suggests that the culture of juvenile Siberian sturgeon in brackish environments is unlikely to be successful. However, our data indicate that in natural environments, juvenile Siberian sturgeon in migratory populations (Ob and Lena Rivers) would be able to migrate successfully into estuarine brackish grounds with a salinity of up to 9%. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cloning and molecular characterization of cationic amino acid transporter y+LAT1 in grass carp (Ctenopharyngodon idellus)

The solute carrier family 7A, member 7 gene encodes the light chain- y⁺L amino acid transporter-1 (y⁺LAT1) of the heterodimeric carrier responsible for cationic amino acid (CAA) transport across the basolateral membranes of epithelial cells in intestine and kidney. Rising attention has been given to y⁺LAT1 involved in CAA metabolic pathways and growth control. The molecular characterization and function analysis of y⁺LAT1 in grass carp (Ctenopharyngodon idellus) is currently unknown. In the present study, full-length cDNA (2,688 bp), which encodes y⁺LAT1 and contains a 5′-untranslated region (319 bp), an open reading frame (1,506 bp) and a 3′-untranslated region (863 bp), has been cloned from grass carp. Amino acid sequence of grass carp y⁺LAT1 contains 11 transmembrane domains and shows 95 %, 80 % and 75 % sequence similarity to zebra fish, amphibian and mammalian y⁺LAT1, respectively. The tissue distribution and expression regulation by fasting of y⁺LAT1 mRNA were analyzed using real-time PCR. Our results showed that y⁺LAT1 mRNA was highly expressed in midgut, foregut and spleen while weakly expressed in hindgut, kidney, gill, brain, heart, liver and muscle. Nutritional status significantly influenced y⁺LAT1 mRNA expression in fish tissues, such as down-regulation of y⁺LAT1 mRNA expression after fasting (14 days).     

Mitochondrion-rich cells distribution,Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>-ATPase activity and gill morphometry of the Amazonian freshwater stingrays (Chondrichthyes: Potamotrygonidae)

Detailed measurements of gill area and constituent variables (total filament number, total filament length and mean filament length), and immunolocalization of the α-subunit of Na⁺/K⁺-ATPase and Na⁺/K⁺-ATPase activity were performed on both hemibranchs of all five arches of freshwater potamotrygonid stingrays (Paratrygon aiereba and Potamotrygon sp.). Both species exhibit similar mass-specific gill area, 89.8 ± 6.6 and 91.5 ± 4.3 mm² g⁻¹ for P. aiereba and Potamotrygon sp., respectively. The density of Na⁺/K⁺-ATPase-rich MRCs and Na⁺/K⁺-ATPase activity was higher in the 4th gill arch in both species. The Na⁺/K⁺-ATPase activity was positively correlated to the Na⁺/K⁺-ATPase-rich (Na⁺/K⁺-ATPase rich) mitochondrion-rich cell (MRC) distribution among the gill arches of P. aiereba but not in Potamotrygon sp. The levels Na⁺/K⁺-ATPase activity were not correlated to the gill surface area among the arches for both rays’ species. Considering that the Na⁺/K⁺-ATPase-rich MRC is the main site for active ion transport in the gill epithelia and Na⁺/K⁺-ATPase activity plays a crucial role in osmoionoregulatory function, we suggesting that 4th gill arch is more relevant for osmoregulation and ion balance in these potamotrygonids.     

Exploration of the mechanisms of protein quality control and osmoregulation in gills of Chromis viridis in response to reduced salinity

Fish gills are the vital multifunctional organ in direct contact with external environment. Therefore, activation of the cytoprotective mechanisms to maintain branchial cell viability is important for fish upon stresses. Salinity is one of the major factors strongly affecting cellular and organismal functions. Reduction of ambient salinity may occur in coral reef and leads to osmotic stress for reef-associated stenohaline fish. However, the physiological responses to salinity stress in reef-associated fish were not examined substantially. With this regard, the physiological parameters and the responses of protein quality control (PQC) and osmoregulatory mechanisms in gills of seawater (SW; 33–35 ‰)- and brackish water (BW; 20 ‰)-acclimated blue-green damselfish (Chromis viridis) were explored. The results showed that the examined physiological parameters were maintained within certain physiological ranges in C. viridis acclimated to different salinities. In PQC mechanism, expression of heat-shock protein (HSP) 90, 70, and 60 elevated in response to BW acclimation while the levels of ubiquitin-conjugated proteins were similar between the two groups. Thus, it was presumed that upregulation of HSPs was sufficient to prevent the accumulation of aggregated proteins for maintaining the protein quality and viability of gill cells when C. viridis were acclimated to BW. Moreover, gill Na⁺/K⁺-ATPase expression and protein amounts of basolaterally located Na⁺/K⁺/2Cl^? cotransporter were higher in SW fish than in BW fish. Taken together, this study showed that the cytoprotective and osmoregulatory mechanisms of blue-green damselfish were functionally activated and modulated to withstand the challenge of reduction in salinity for maintaining physiological homeostasis.     

Growth,body composition,intestinal enzyme activities and microflora of juvenile Jian carp (Cyprinus carpio var. Jian) fed graded levels of dietary valine

This study investigated the effects of valine on growth, intestinal enzyme activities and microflora in juvenile Jian carp (Cyprinus carpio var. Jian). A total of 1200 fish with an average initial weight of 9.67 ± 0.03 g were fed diets containing 5.3 (unsupplemented control), 8.7, 11.8, 14.9, 18.7 and 20.1 g valine kg^?1 diet for 60 days. Results indicated that the specific growth rate, feed efficiency, body protein and lipid content of fish were significantly improved by the dietary valine (P < 0.05). The hepatopancreas weight and activities of trypsin, amylase, lipase, chymotrypsin, glutamate oxaloacetate transaminase (GOT) and glutamate pyruvate transaminase (GPT) took the similar trends. Similarly, the optimum levels of dietary valine induced increases in the intestinal length, weight, folds height and activities of alkaline phosphatase, gamma‐glutamyl transpeptidase and creatine kinase. In contrast, the trends of muscle GOT activity and plasma ammonia content were opposite. Intestinal Aeromonas, Escherichia coli, Lactobacillus and Bacillus were changed by dietary valine supplementations. The dietary valine requirement for Jian carp (9.67–76.4 g) based on SGR was 13.7 g valine kg^?1 diet (4.0 g valine 100 g^?1 CP). Together, these results indicated that valine improved fish growth, digestive and absorptive ability.