Physiology of seawater acclimation in the striped bass,Morone saxatilis (Walbaum)

Several experiments were performed to investigate the physiology of seawater acclimation in the striped bass, Morone saxatilis. Transfer of fish from fresh water (FW) to seawater (SW; 31–32 ppt) induced only a minimal disturbance of osmotic homeostasis. Ambient salinity did not affect plasma thyroxine, but plasma cortisol remained elevated for 24h after SW transfer. Gill and opercular membrane chloride cell density and Na⁺,K⁺-ATPase activity were relatively high and unaffected by salinity. Average chloride cell size, however, was slightly increased (16%) in SW-acclimated fish. Gill succinate dehydrogenase activity was higher in SW-acclimated fish than in FW fish. Kidney Na⁺, K⁺-ATPase activity was slightly lower (16%) in SW fish than in FW fish. Posterior intestinal Na⁺,K⁺-ATPase activity and water transport capacity (J_v) did not change upon SW transfer, whereas middle intestinal Na⁺,K⁺-ATPase activity increased 35% after transfer and was correlated with an increase in J_v (110%). As salinity induced only minor changes in the osmoregulatory organs examined, it is proposed that the intrinsic euryhalinity of the striped bass may be related to a high degree of “preparedness” for hypoosmoregulation that is uncommon among teleosts studied to data.     

Salt in the Food and Water as a Supportive Therapy for Ichthyophthirius multifiliis Infestation on Silver Catfish, Rhamdia quelen, Fingerlings

This study verified the efficacy of common salt (NaCl) in the food and water as a supportive therapy for Ichthyophthirius multifiliis and growth of silver catfish, Rhamdia quelen, fingerlings. After appearance of the first white spots following experimental exposure, indicating infestation by this parasite, fish were transferred to eighteen 40‐L polypropylene tanks and kept for 30 d. Experimental diets were prepared with five different levels of salt supplementation: 0.0, 1.2, 2.5, 5.0, and 6.0% for 30 d. In addition, another group of fish were fed a diet without salt supplementation but exposed to 4 g of salt/L of water. Fingerlings were collected at different times for analyses of whole‐body Na⁺, K⁺, and Cl^?. Dietary salt supplementation provoked a transitory increase in whole‐body Na⁺, K⁺, and Cl^? in infested catfish fingerlings, but the best stabilization of these ion levels was observed in specimens exposed to salt in the water. Silver catfish fed a diet containing 1.2% salt showed higher weight and biomass after 30 d compared to those fed with 6% salt. The use of 4 g of salt/L of water improved survival of infested silver catfish, but dietary salt supplementation was ineffective as a therapy for ichthyophthiriasis.     

Cobia Rachycentron canadum L. reared in low‐salinity water: does dietary sodium chloride affect growth and osmoregulation?

The effects of NaCl supplementation (0.0%, 2.5%, 5.0%, 7.5% and 10.0% dry weight of a basal diet) on growth, gill histological alterations and osmoregulation of juvenile cobia reared in low‐salinity water (5 g L^?1) were assessed. At the end of the experiment, gills were sampled for Na⁺, K⁺‐ATPase activity determination and histological evaluation. In all treatments, no mortality was observed. Results showed that dietary NaCl supplementation did not alter growth. At the highest supplementations (7.5% and 10.0%), juvenile cobia showed higher feed intake and feed conversion ratio. Na⁺, K⁺‐ATPase activity was higher in fish fed the diet without salt supplementation than in those fed with NaCl‐supplemented diets. The number of chloride cells significantly increased with increasing dietary salt level, being 2.5‐fold higher in fish fed with 10.0% NaCl supplementation (41 cells mm^?2) than in those from the non‐supplemented fed group (16 cells mm^?2). These findings indicate that dietary salt supplementation stimulated chloride cell proliferation paralleled with a reduction in the gill Na⁺, K⁺‐ATPase activity, suggesting a possible decrease in energy consumption associated with osmoregulation. However, the suggested energy sparing did not have a significant impact on juvenile cobia growth.     

Cortisol stimulates intestinal fluid uptake in Atlantic salmon (Salmo salar) in the post-smolt stage

The fluid uptake rate of the posterior intestine of salmonids increases during the parr-smolt transformation. Intestinal fluid uptake in post-smolt Atlantic salmon was investigated after treatment with cortisol and growth hormone (GH), alone or together. Two replicate experiments were conducted in August 1991 and August 1992. Cortisol was emulsified in vegetable shortening and vegetable oil (1:1) and implanted into the peritoneal cavity. GH was administered as intraperitoneal injections in a saline vehicle on days 0 and 2. On days 5 and 6, plasma cortisol levels, gill Na⁺,K⁺-ATPase activity, andin vitro measurements of fluid transport rate (J_v) across the posterior intestine were measured. Implants of cortisol elevated the plasma cortisol levels within a physiological range, and resulted in elevated gill Na⁺,K⁺-ATPase activity, as expected. The fluid uptake rate across the posterior intestine was roughly doubled by cortisol treatment. GH treatment did not affect intestinal fluid transport, gill Na⁺,K⁺-ATPase activity, or plasma cortisol concentrations. The seawater-adapting increase in the rate of fluid uptake by the posterior intestine of smolting salmon is probably stimulated by elevated plasma cortisol concentrations.     

Optimal dietary alpha‐linolenic acid/linoleic acid ratio improved digestive and absorptive capacities and target of rapamycin gene expression of juvenile grass carp (Ctenopharyngodon idellus)

Growth performance, digestive and absorptive capacities and target of rapamycin (TOR), ribosomal protein S6 kinase 1 (S6K1) and eIF4E‐binding protein (4E‐BP) gene expression in the hepatopancreas and intestine of juvenile grass carp (Ctenopharyngodon idellus) fed graded ratios of dietary alpha‐linolenic acid/linoleic acid (ALA/LNA) (0.01, 0.34, 0.68, 1.03, 1.41, 1.76 and 2.15) for 60 days were investigated. The results showed that ALA/LNA ratio of 1.03 significantly improved (i) per cent weight gain (PWG) and feed efficiency, (ii) hepatopancreatic trypsin, chymotrypsin, lipase, amylase and intestinal creatine kinase (CK) activities, (iii) hepatopancreatic trypsinogen‐2 and chymotrypsinogen mRNA levels. Meanwhile, fish fed with ALA/LNA ratio of 0.68 significantly enhanced, (iv) Na⁺/K⁺‐ATPase and γ‐glutamyl transpeptidase activities in whole intestine, and alkaline phosphatase activities in the proximal intestine (PI) and distal intestine, (v) amylase, intestinal Na⁺/K⁺‐ATPase alpha‐subunit isoform 1, Na⁺/K⁺‐ATPase alpha‐subunit isoform 8 and CK mRNA abundances, (vi) TOR and S6K1 gene expression in the hepatopancreas and intestine of juvenile grass carp. Based on the quadratic regression analysis of PWG, cholecystokinin and leptin contents in the PI, optimal dietary ALA/LNA ratio of juvenile grass carp (8.78–72.00 g) was estimated to be 1.08, 1.19 and 1.05, respectively.     

The effect of dietary sodium chloride on some osmoregulatory parameters of the teleost, Oreochromis niloticus, after transfer from freshwater to seawater

The aim of this work was to determine the effects of supplemental dietary sodium chloride on salt water acclimation of tilapia Oreochromis niloticus. Fish were fed a basal diet supplemented with NaCl (8%) during three weeks in fresh water (FW) and then transferred to salt water (SW) at 15 and 20. Changes in plasma osmolality, chloride ion concentration (Cl^–), plasma level of cortisol and gill Na⁺, K⁺-ATPase activity were measured at 6, 12, 24, 48, 72 and 168 h after transfer to 15SW, while the higher strength SW group (20) was only monitored up to 24 h. Morphological changes in the gill mitochondria-rich (MR) cells were examined in relation to environmental salinity. The changes associated with dietary NaCl were sporadic and of small magnitude. The plasma osmolality and Cl^– increased immediately after transfer up to 12–24 h, but fish fed dietary salt (S) showed lower values than the control group (C). The S group showed higher plasma levels of cortisol than the control, which maintained its initial levels during the experiment. Gill Na⁺, K⁺-ATPase activity of the S group began to increase in the first hours after transfer, reaching maximum at 12 h and returned to basal level at 24 h, while the control group maintained basal levels. The differences between gill Na⁺, K⁺-ATPase activity of S and C fish were significant (p < 0.05) at 12 h. Transmission electron microscopy (TEM) revealed that MR cells in SW show more mitochondria and a more developed tubular system arising from the basolateral membrane. The MR cells of both groups frequently formed a multicellular complex in SW, consisting of a main MR and one or more accessory cells. Such complexes are rarely observed in FW. Some MR cells of fish fed supplemented dietary salt displayed convex apical membrane in FW.     

Juvenile Lepeophtheirus salmonis (Krøyer) affect the skin and gills of rainbow trout Oncorhynchus mykiss (Walbaum) and the host response to a handling procedure

Infectious Lepeophtheirus salmonis (Krøyer) cause localized inflammation at the site of attachment on the host fish, while the greatest physiological impact occurs with the development of the subadult and adult stages. We exposed Oncorhynchus mykiss (Walbaum) to infectious copepods at 30, 25 and 14 days prior to a net confinement procedure, while a second group were sham infected. Fish were sampled at time zero, 2, 4, and 6 h of continuous net confinement, and at 24 h after 2 h confinement. Plasma Na⁺, Cl^–, gill Na⁺/K⁺‐ATPase activity and skin mucous cell numbers were measured, and skin and gill condition assessed microscopically. Exposure to copepods resulted in lower numbers of acidophilic mucous cells and poor condition of the skin and gill epithelia. Total numbers of mucous cells were decreased in net confined infected fish only. Plasma Na⁺ was elevated in all samples from non‐infected netted fish, without altered gill Na⁺/K⁺‐ATPase activity, while infected fish had higher plasma Na⁺ only at 2 h and increased gill ATPase activity at 4 h. The epithelia of infected fish were more severely affected by the confinement procedure. Exposure to juvenile lice can induce effects that become apparent only when a stressor is applied.     

Gill ATPase activities of silver perch, Bidyanus bidyanus (Mitchell), and golden perch, Macquaria ambigua (Richardson): Effects of environmental salt and ammonia

The Australian freshwater fish, silver and golden perch, are increasingly being used for aquaculture. Addition of salt to water is commonly used in commercial aquaculture to reduce stress attributed to high ammonia concentrations. The activities in gill homogenates of ouabain-sensitive Na⁺/K⁺-ATPase and NEM-sensitive ATPases (as a measure of H⁺-ATPases) of silver and golden perch were measured after maintaining the fish in water containing different salt and ammonia concentrations. Six treatments were applied in a 2 × 3 factorial design: two salt treatments, low salt (LS) of 2.5 g l^− 1 and high salt (HS) 5 g l^− 1, and three ammonia treatments, no added ammonia (NA), low ammonia (LA), 3 mg total ammonia nitrogen (TAN) l^− 1 and high ammonia (HA), 5 mg TAN l^− 1. In both species, activity of Na⁺/K⁺-ATPase was lowest in fish kept in the LSNA treatment (7.4 ± 0.4 μmol Pi mg protein^− 1 h^− 1 for silver perch and 3.1 ± 0.6 for golden perch) and highest in the HSHA treatment (15.2 ± 1.0 μmol Pi mg^− 1 protein h^− 1 for silver and 8.4 ± 1.2 for golden perch). In both species there was a significant increase (P < 0.001) in Na⁺/K⁺-ATPase activity with increase in salt concentration and with an increase in ammonia concentrations. A significant interaction (P < 0.036) between salt and ammonia on Na⁺/K⁺-ATPase activity was observed in silver but not in golden perch. In contrast, the lowest activity for NEM-sensitive ATPase was observed in the HSNA treatment (1.0 ± 0.2 μmol Pi mg^− 1 protein h^− 1 for silver and 1.5 ± 0.4 for golden perch) and highest in LSHA treatment (2.9 ± 0.4 μmol Pi mg^− 1 protein h^− 1 for silver and 3.6 ± 1.2 for golden perch). In both species there was a significant decrease in NEM-sensitive ATPase activity with increase in salt concentration and an increase in activity with increase in ammonia (P < 0.003). In silver perch, a significant interaction between the treatments was observed (P < 0.02). The results suggest that in these species of freshwater fish the Na⁺/K⁺-ATPase has a role in salt and ammonia homeostasis and that the NEM-sensitive ATPases are more active in fish kept in water with a lower salt content. It is possible that the increase in ammonia resistance when salt is added to the environmental water in commercial aquaculture systems may be due to the effects of salt on gill Na⁺/K⁺-ATPase activity rather than the NEM-sensitive ATPases.     

Potassium flux in juvenile striped bass (Morone saxatilis): influence of external concentrations of sodium chloride and calcium

Whole-body influx and efflux of K⁺ were determined for 25-day-old striped bass,Morone saxatilis, in conditions that simulated harvesting fish from ponds. During the first 5h in fresh water with combined high NaCl (80 mM) and low Ca²⁺ (0.12 mM) concentrations, a combination that is acutely lethal to this age of striped bass, K⁺ influx for fish in 0.07 mM K⁺ was 21±1.7 (SEM) compared to 3.4±0.33 nmol g^–1 h^–1 for fish in water with low Na⁺ (0.25 mM) or high Ca²⁺ (2.5 mM) concentrations. Influx of K⁺ was inhibited during the first few hours after fish were placed in flux chambers. Potassium efflux as percentage of⁴²K lost per hour was two-fold higher from fish in the high Na-low Ca treatment compared to fish in low concentrations of Na⁺ or high concentrations of Ca²⁺. Potassium efflux was probably much greater than influx, but exact values for efflux could not be calculated from the data available. Survival of fish in water with high Na-low Ca was not increased by addition of KCl to the water, indicating that the net loss of K⁺ was probably not the cause of death.     

Osmoregulation in juvenile Chinese sturgeon (<Emphasis Type="Italic">Acipenser sinensis</Emphasis> Gray) during brackish water adaptation

The osmoregulation capabilities of 7-month-old juvenile Chinese sturgeon (Acipenser sinensis Gray) (128.8 ± 15 g) transferred directly from fresh water (0‰, 46 mOsmol kg⁻¹) to brackish water (10‰, 273 mOsmol kg⁻¹) were studied over a 20-day period. Changes in serum osmolarity, chloride (Cl⁻), sodium (Na⁺), potassium (K⁺) and calcium (Ca²⁺) ion concentrations, as well as gill and spiral valve Na⁺,K⁺-ATPase activities were measured at 3, 12, 24, 72, 216 and 480 h after transfer to BW. The serum osmolarity and ion concentrations (Na⁺, Cl⁻ and Ca²⁺) increased immediately after the transference to BW, reaching maximum at 24 h and returned to a new steady state at 216 h, while the FW control group maintained basal levels which showed lower (P < 0.05) than the BW group. Gill Na⁺,K⁺-ATPase activity of BW group exhibited an abrupt decrease in the first 3 h after transfer, but began to increase at 3 h, reaching a peak value at 24 h, and returned to a new steady state at 216 h. The differences between gill Na⁺,K⁺-ATPase activity of BW and FW fish were significant (P < 0.05) after 12 h. In contrast, Na⁺,K⁺-ATPase activity of the spiral valve showed transient increase after transference from FW to BW, and then decreased rapidly at 3 h, reaching the lowest at 24 h after transference. At 216 h after exposure to BW, Na⁺,K⁺-ATPase activities of the spiral valve increased slowly to the levels of FW control. The results of our study indicate the existence of hyposmoregulatory adaptive mechanisms in 7-month-old juvenile Chinese sturgeon which enable this fish to acclimate itself successfully to brackish water.     

Responses of antioxidant enzymes,lipid peroxidation,and Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>-ATPase in liver of the fish <Emphasis Type="Italic">Goodea atripinnis</Emphasis> exposed to Lake Yuriria water

Lake Yuriria, located in the heavily populated and polluted Mexican Central Plateau, receives domestic sewage, industrial effluents, and municipal wastewaters that are still directly discharged without treatment into the tributaries and the lake. Pollutants in water and sediments include heavy metals, aromatic hydrocarbons, and organochlorine pesticides. Activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), as well as Na⁺/K⁺-adenosine triphosphatase (Na⁺/K⁺-ATPase) activity, and lipid peroxidation (LPO) were evaluated in the livers of the fish Goodea atripinnis after 96 h of exposure to water collected in March and June 2005 from three sites: Y (limnetic zone), L (Lerma tributary), and C (la Cinta tributary). Physical and chemical parameters of the lake water were also analyzed. Increases in CAT activity and LPO levels at all three sites were detected compared with control fish (P < 0.05), while GPx and SOD activities decreased significantly (P < 0.05). Na⁺/K⁺-ATPase activities were similar to the control in fish exposed to limnetic water from both March and June but were higher than control at the two tributary sites in March (P < 0.05); fish exposed to water from the Lerma tributary in June exhibited lower Na⁺/K⁺-ATPase than the control (P < 0.05). During March, CAT and Na⁺/K⁺-ATPase activities were increasing more than in June in Y and L, respectively, while in June, SOD and GPx were depleted more than March in L and Y and L, respectively. Despite the antioxidant defenses of the fish liver, exposure to all water samples from Lake Yuriria exerted alterations in hepatic LPO levels, antioxidant enzymes, and Na⁺/K⁺-ATPase activities that could substantially impair the mechanisms of fish defenses against oxidative stress.     

Deficiency of dietary niacin decreases digestion and absorption capacities via declining the digestive and brush border enzyme activities and downregulating those enzyme gene transcription related to TOR pathway of the hepatopancreas and intestine in young grass carp (Ctenopharyngodon idella)

To investigate the effects of niacin on growth, digestion and absorption capacity, and the potential mechanism for digestive and brush border enzyme activities, grass carp (Ctenopharyngodon idella) (256 ± 0.41 g) were fed diets containing 3.95 (basal diet group), 14.92, 24.98, 35.03, 44.97 and 55.01 mg niacin kg^?1 diet for 8 weeks. Results indicated that percentage weight gain (PWG), feed intake and feed efficiency were the lowest in basal group (P < 0.05). Similarly, niacin deficiency decreased hepatopancreas trypsin, chymotrypsin, lipase and amylase activities (P < 0.05), intestinal Na⁺, K⁺‐ATPase, alkaline phosphatase, γ‐glutamyl transpeptidase and creatine kinase (CK) activities, the cholecystokinin (CCK) content in proximal intestine (PI) and growth hormone content in serum (P < 0.05). Furthermore, niacin deficiency downregulated gene expression of hepatopancreas trypsinogen 1, trypsinogen 2, chymotrypsinogen and amylase, intestinal Na⁺, K⁺‐ATPase alpha subunit isoform 1, Na⁺, K⁺‐ATPase alpha subunit isoform 8 and CK, and target of rapamycin (TOR) and S6 kinase 1 (S6K1) of hepatopancreas and intestine (P < 0.05), whereas upregulated eIF4E‐binding protein (4EBP) gene expression (P < 0.05). The niacin requirement for young grass carp (256–689 g) based on PWG, hepatopancreas trypsin activity and Na⁺, K⁺‐ATPase in PI was 34.01, 35.10 and 42.08 mg kg^?1 diet, respectively.     

Physiological indices of seawater readiness in postspawning steelhead kelts

Management goals to improve the recovery of steelhead (Oncorhynchus mykiss) stocks at risk of extinction include increasing the proportion of postspawning fish that survive and spawn again. To be successful, postspawning steelhead (kelts) migrating downstream to the ocean must prepare physiologically and physically for a seawater transition. We sampled blood, gill filaments, and evaluated the external condition of migrating kelts from an ESA‐listed population in the Snake/Columbia River system over two consecutive years to evaluate their physiological readiness for transition to seawater. We chose attributes often considered as measures of preparation for seawater in juveniles, including gill Na⁺,K⁺ ATPase activity, plasma electrolytes and hormones to consider factors related to external condition, size and sex. We found kelts in good external condition had plasma profiles similar to downstream‐migrating smolts. In addition, we found more than 80% of kelts ranked in good external condition had smolt‐like body silvering. We compared measures from migrating kelts with samples obtained from hatchery fish at the time of spawning to confirm that Na⁺, K⁺ ATPase activity in kelts was significantly elevated over spawning fish. We found significant differences in gill Na⁺, K⁺ ATPase activity in migrating kelts between the years of sampling, but little indication of influence of fish condition. We conclude that the postspawning steelhead sampled exhibited a suite of behaviours, condition and physiology characteristic of fish prepared for successful transition to a seawater environment.     

Osmotic adaptation of Oncorhynchus kisutch walbaum. I. Seasonal variations of gill Na+K+ ATPase activity in coho salmon,O+-age and yearling,reared in fresh water

An eventual improvement in salmonid production in sea water will depend on a fundamental understanding of the natural osmotic behaviour, which demands, in turn, the seaward migration of young salmonids and the development of osmoregulatory processes. Seasonal changes in the gill Na⁺K⁺ ATPase of coho salmon, Oncorhynchus kisutch, were studied between February 1976 and August 1977, on two successive broods, O⁺-age and yearling, of the same origin and reared under natural conditions in a freshwater hatchery off the Brittany coast (France).The gill ATPase changes are of a rhythmical nature. The data show that a seasonal activation of the branchial Na⁺K⁺ ATPase affects one part of the population only. Both age groups, O⁺-age and yearlings, present two peaks of Na⁺K⁺ ATPase activity during the year, in the spring and in the fall, separated by a low activity period in summer and in winter. The peaks of ATPase activity in the fall (both groups) and spring (yearlings) correspond, roughly, with the equinox, whereas the spring rise of O⁺-age fish starts later on.The levels of gill ATPase activity are, probably, a function of the fish size for a given season, and the duration of Na⁺K⁺ ATPase activation may be affected by high temperatures of the late spring and thus may fluctuate from year to year. Yearly variations in branchial Mg²⁺ ATPase were evidenced in both groups; for the moment, these variations are impossible to correlate with the smolting process.Spring and autumn rises in the gill Na⁺K⁺ ATPase of coho salmon, in fresh water, indicate changes in the osmoregulatory physiology, that are preparatory to seaward migration.As a consequence, assays of gill ATPase activity can give aquaculturists some precise indications of the migratory tendencies in young fresh water salmon and thus the euryhalinity possibilities of the species at a given time.     

Effect of exposure to low salinity water on plasma ion regulation and survival rates in artificially wounded devil stinger <Emphasis Type="Italic">Inimicus japonicus</Emphasis>

We investigated the effect of exposure to low salinity water on plasma ion regulation and survival rates in artificially wounded devil stinger Inimicus japonicus. All fishes survived in 33% seawater (SW), while survival rate in 100% SW was 5.1% at 24 h. In 100% SW, plasma Na⁺, K⁺, Mg²⁺, and Ca²⁺ concentrations significantly increased to 238?±?49.9, 9.6?±?2.4, 15.1?±?3.5 and 5.0?±?0.7 mmol/l at 6 h, respectively; the gill Na⁺/K⁺–ATPase (NKA) activity was almost stable, although only one fish survived to 24 h. In 33% SW, plasma Na⁺ and K⁺ concentrations remained at the same level, and plasma Mg²⁺ and Ca²⁺ concentrations gradually increased to 16.2?±?0.7 and 4.5?±?0.2 mmol/l until 24 h, respectively. The NKA activity significantly increased to 5.1?±?1.1 µmol ADP/mg protein per h at 6 h. A positive correlation was observed between the wound surface area against body weight and the plasma ion concentrations, although no difference was observed in the restoration rate of the wounded area between 100 and 33% SW. These results indicate that exposure of wounded fish to low salinity water improves survivability by favoring plasma ion regulation without influencing the restoration rate.     

Osmoregulation in the mudskipper,Boleophthalmus boddaerti I. Responses of branchial cation activated and anion stimulated adenosine triphosphatases to changes in salinity

The mudskipperB. boddaerti, was able to survive in waters of intermediate salinities (4–27). Fish submerged in dechlorinated tap water suffered 60% mortality by the fifth day while 60% of those in 100% sea-water (sw) died after the third day of exposure. After being submerged in 50% or 80% sw for 7 days, the plasma osmolality, plasma Na⁺ and Cl^– concentrations and the branchial Na⁺ and K⁺ activated adenosine triphosphatase (Na⁺,K⁺-ATPase) activity were significantly higher than those of fish submerged in 10% sw for the same period. However, the activities of the branchial HCO₃ ^– and Cl^– stimulated adenosine triphosphatase (HCO₃ ^–,Cl^–-ATPase) and carbonic anhydrase of the latter fish were significantly greater than those of the former. Such correlation suggests that Na⁺,K⁺-ATPase is important for hyperosmotic adaptation in this fish while HCO₃ ^–-Cl^–-ATPase and carbonic anhydrase may be involved in hypoosmotic survival.     

Reduced fishmeal allowance with constant protein input for juvenile channel catfish Ictalurus punctatus

In this study, we evaluated different dietary fishmeal and protein levels on growth performance, intestinal structure and intestinal microbial community of juvenile channel catfish, Ictalurus punctatus. A total of 1800 fish distributed into 36 tanks were fed with nine different diets containing three protein levels (300, 330 and 360 g/kg) with three fishmeal (FM) levels (0, 30 and 60 g/kg) for 90 days. The results showed that significant interactions between the protein level and FM level were observed in final weight (FW), weight gain (WG), Na⁺, K⁺‐ATPase and alkaline phosphatase (AKP) activities. The significant lowest FW, WG, Na⁺, K⁺‐ATPase and AKP activities were observed in fish fed with no fishmeal and 300 g/kg protein dietary while the highest were shown in 60 g/kg fishmeal and 330 g/kg protein treatment. Additionally, the microvillar length of the mid‐intestine in catfish was significantly affected by the interaction between dietary protein level and fishmeal level. The intestinal samples were dominated by three major phyla, Firmicutes, Proteobacteria and Fusobacteria. Genera Romboutsia and Turicibacter accounted for probably 800 g/kg of the phylum Firmicutes; meanwhile, genus Cetobacterium represented more than 900 g/kg of the phylum Fusobacteria. In conclusion, this study indicated that channel catfish juveniles can be fed with a practical diet without fishmeal as long as the protein level increased to 360 g/kg; however, if the percentage of dietary protein was 300 g/kg, it seemed that fishmeal need to be supplied as a protein source.     

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.