Response of rainbow trout gill (Na++K+)-ATPase and chloride cells to T3 and NaCl administration

With the aim of comparing the effects of oral T₃ and NaCl administration on trout hypoosmoregulatory mechanisms, three groups of rainbow trout (Oncorhynchus mykiss Walbaum) held in freshwater (FW) were fed a basal diet (C), the same diet containing 8.83 ppm of 3,5,3-triiodo-L-thyronine (T₃) (T) or 10% (w/w) NaCl (N) respectively for 30 d. They were then transferred to brackish water (BW) for 22 d and fed on diet C. Gill (Na⁺+K⁺)-ATPase activity and its dependence on ATP, Na⁺ and pH, number of gill chloride cells (CC), serum T₃ level as well as fish growth, condition factor (K) and mortality were evaluated. During the FW phase, as compared to C trout, T trout showed a two fold higher serum T₃ level, had unchanged gill (Na⁺+K⁺)-ATPase activity and increased CC number, whereas N trout showed higher gill (Na⁺+K⁺)-ATPase activity and CC number. At the end of the experiment the enzyme activity was in the order T>N>C groups and all groups showed similar CC number. Both treatments changed the enzyme activation kinetics by ATP and Na⁺. A transient increase in K value occurred in N group during the period of salt administration. In BW, T and N groups had higher and lower survival than C group respectively. Other parameters were unaffected by the treatments. This trial suggests that T₃ administration promotes the development of hypoosmoregulatory mechanisms of trout but it leaves the (Na⁺+K⁺)-ATPase activity unaltered till the transfer to a hyperosmotic environment.     

Fatty acid composition,osmolality, Na+, K+‐ATPase activity,cortisol content and antioxidant status of rainbow trout (Oncorhynchus mykiss) in response to various dietary levels of eicosapentaenoic acid and docosahexaenoic acid

This study was conducted to evaluate the effect of dietary eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) levels on the fatty acid composition, salinity tolerance and antioxidant status of rainbow trout (Oncorhynchus mykiss). Four diets were formulated with total EPA and DHA contents of 5.41, 9.55, 13.97 and 17.88 g/kg (abbreviated as ED‐5.41, ED‐9.55, ED‐13.97 and ED‐17.88 respectively). Rainbow trout (initial weight of 90.61 ± 9.25 g) were fed the experimental diets for 8 weeks to accumulate significant differences in fatty acid composition and subsequently underwent salinity acclimation. Our results indicated that high dietary EPA and DHA significantly improved the EPA and DHA content in fish tissues. The serum osmolality of fish returned to their freshwater values in the ED‐9.55, ED‐13.97 and ED‐17.88 groups. The Na⁺, K⁺‐ATPase (NKA) activity of fish in the ED‐13.97 group changed dramatically to adapt the fish to the hypertonic environment. Moreover, there was no significant difference in the serum cortisol concentration and liver catalase (CAT) activity of fish in the ED‐13.97 group during salinity acclimation. The liver superoxide dismutase (SOD) activity in the ED‐13.97 group was significantly higher than that in ED‐5.41 and ED‐9.55 groups at the end of salinity acclimation. The muscle malondialdehyde (MDA) content in the ED‐13.97 group was significantly lower than that in the ED‐17.88 group before salinity acclimation and significantly lower than the ED‐5.41 and ED‐17.88 groups on day 7 of acclimation. The results of this study indicate that the rainbow trout in the ED‐13.97 group exhibited optimal salinity acclimation performance.     

Effects of salinity and pH on ion-transport enzyme activities, survival and growth of Litopenaeus vannamei postlarvae

Effects of the salinity and pH on ion-transport enzyme activities, survival and growth of Litopenaeus vannamei postlarvae were investigated. Shrimp were transferred from salinity 31‰ and pH 8.1 to different salinity levels of 22, 25, 28, 31 (control), and to different pH levels of 7.1, 7.6, 8.1 (control), 8.6 and 9.1. The results showed ion-transport enzyme activities and weight gains of postlarvae were significantly affected by salinity and pH variation, which had no obvious effect on survival rate. The changing salinity affected the activities of total ATPase and Na⁺-K⁺-ATPase notably (F > F_0.05), meanwhile, non-significantly to the activities of V-ATPase, HCO₃⁻-ATPase. Within 48 h of salinity changing, the activities of ATPase, Na⁺-K⁺-ATPase in each treatment group gradually increased with the sampling time and reached their climax at 48 h, and then stabilized, showing negative correlation with salinity. The changing of pH affected greatly the activities of ATPase, Na⁺-K⁺-ATPase, V-ATPase and HCO₃⁻-ATPase (F > F_0.05), the activities of ATPase, Na⁺-K⁺-ATPase in each treatment group (pH = 7.1, 7.6, 8.6, 9.1) showed peak change within 72 h and stabilized afterwards, and the Na⁺-K⁺-ATPase activities came back to the level of the control group; Meanwhile the changing extent of V-ATPase and HCO₃⁻-ATPase activity corresponded with the grads of pH, and these ATPase activities showed negative correlation with pH changing, the activities of V-ATPase, HCO₃⁻-ATPase in postlarvae of each treatment group came to stable level after 24 h. The experiment also indicated the strength order of these ion-transport enzyme activities were as follows: Na⁺-K⁺-ATPase > V-ATPase > HCO₃⁻-ATPase. Na⁺-K⁺-ATPase was the chief undertaker of osmoregulation under the salinity effects, while V-ATPase and HCO₃⁻-ATPase were the chief osmoregulation undertakers under pH changing. In different salinity environment, the contributions of Na⁺-K⁺-ATPase, V-ATPase and HCO₃⁻-ATPase of L. vannamei postlarvae approximately accounted for 62.0-78.0%, 15.9-29.0% and 2.03-4.12% of ATPase activities in total, respectively. Meanwhile, in different pH medium, the contributions of these ATPases approximately accounted for 50.7-67.4%, 21.3-31.8% and 2.15-7.90% of total ATPase activities, respectively. Weight gain of shrimp transferred to salinity 31 (control) and 28‰ was significantly higher than that of shrimp reared at 25 and 22‰, and weight gain of shrimp transferred to pH 8.1 (control) and 8.6 was significantly higher that that of shrimp transferred to pH 7.1, 7.6 and 9.1. It was suggested that during the process of desalting and culturing of postlarvae, the salinity changing should not exceed 3 and pH variety not more than 0.5.     

Vitamin B6 supplementation increases the docosahexaenoic acid concentration of muscle lipids of rainbow trout (Oncorhynchus mykiss)

Fish fillet quality is influenced by feed quality. In particular, vitamin B₆ availability improves growth rate and nutritional value, because it is related to protein and lipid metabolism. The present study investigates the effect of increasing amounts of vitamin B₆ on growth, fatty acid composition and lipid peroxidation of muscle tissue of rainbow trout (Oncorhynchus mykiss). Quadruplicate groups of trout of a mean initial weight of 110 g were fed commercial diets supplemented with four different quantities of vitamin B₆ (0, 10, 25 and 50 mg kg^?1 diet). Over the experimental period, there were no significant differences in weight gain and feed intake, while vitamin B₆ concentration of muscle was affected by dietary intake, even though its increase was not proportional to the concentrations in the feed. The fatty acid composition of muscle lipid showed differences between the four groups. The percentage of long‐chain unsaturated fatty acids, in particular docosahexaenoic acid, increased significantly in vitamin B₆‐supplemented groups. However, despite the increased fatty acid unsaturation index, lipid peroxidation parameters such as vitamin E content, malondialdehyde production, glutathione reductase and glutathione peroxidase activities did not show significant differences, meaning that the higher level of long‐chain unsaturated fatty acid did not increase the muscle susceptibility to oxidative stress.     

Influence of cortisol, growth hormone, insulin-like growth factor I and 3,3′,5-triiodo-l-thyronine on hypoosmoregulatory ability in the euryhaline teleost Fundulus heteroclitus

The capacity of cortisol, ovine growth hormone (oGH), recombinant bovine insulin-like growth factor I (rbIGF-I) and 3,3,5-triiodo-l-thyronine (T₃) to increase hypoosmoregulatory capacity in the euryhaline teleost Fundulus heteroclitus was examined. Fish acclimated to brackish water (BW, 10 ppt salinity) were injected with a single dose of hormone suspended in oil and transferred to seawater (SW, 35 ppt salinity) 10 days post-injection. Fish were sampled 24 h after transfer and plasma osmolality and gill Na⁺, K⁺-ATPase activity were examined. Transfer from BW to SW induced significantly increased plasma osmolality but not gill Na⁺, K⁺-ATPase activity. Cortisol (50 g g^–1 body weight) improved the ability to maintain plasma osmolality and to increase gill Na⁺, K⁺-ATPase activity. oGH (5 g g^–1 body weight) also increased hypoosmoregulatory ability and gill Na⁺, K⁺-ATPase activity. A cooperation between oGH and cortisol was observed in increasing hypoosmoregulatory ability but not in increasing gill Na⁺, K⁺-ATPase activity. rbIGF-I (0.5 g g^–1 body weight) alone was without effect in increasing salinity tolerance or gill Na⁺, K⁺-ATPase activity. rbIGF-I and oGH showed a positive interaction in increasing salinity tolerance, but not gill Na⁺, K⁺-ATPase activity. Treatment with T₃ (5 g g^–1 body weight) alone did not increase salinity tolerance or gill Na⁺, K⁺-ATPase activity, and there was no consistent significant interaction between cortisol and T₃ or between GH and T₃. The results confirm the classical role of cortisol as a seawater-adapting hormone and indicate an interaction between cortisol and the GH/IGF-I axis during seawater acclimation of Fundulus heteroclitus.     

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。     

Effects of salinity acclimation on the growth performance,osmoregulation and energy metabolism of the oriental river prawn,Macrobrachium nipponense (De Haan)

In this study, we evaluated the growth, osmoregulation and energy metabolism of the oriental river prawn, Macrobrachium nipponense, reared during 6 weeks with different salinities (0, 8, 14 and 22 g/L). The results showed that the haemolymph osmolality of M. nipponense increased with an increase in ambient osmotic pressure; the isosmotic point was 490 mOs/kg H₂O. The prawns showed a higher survival rate, weight gain rate and hepatopancreas index in salinity 14 g/L. Digestive enzymes were all affected by salinity, and the highest activities were observed in the salinity 14 g/L. The mRNA expression of Na⁺‐K⁺‐ATPase in gills and p53 in hepatopancreas were the highest in salinity 22 g/L. The expressions of heat shock protein 90 and glutathione S‐transferase genes in hepatopancreas were significantly higher in the salinity 8 g/L. Lipid metabolism‐related genes in hepatopancreas were significantly expressed in the salinity 14 g/L. The glucose‐6‐phosphatase gene in hepatopancreas was highly expressed in the salinity 8 and 22 g/L, and the expression of the ecdysone receptor gene in hepatopancreas was significantly higher in the salinity 14 g/L. The results showed that salinity 14 g/L could promote the growth of M. nipponense. However, higher salinity conditions may cause physiological damage, which provides a theoretical basis for brackish water culture of M. nipponense.     

Effects of Salinity on Biogenic Amines,Hemolymph Osmotic Pressure,and Activity of Gill’s Na+/K+‐ATPase in Charybdis japonica (Crustacea,Decapoda)

The effects of salinity on hemolymph osmotic pressure, gill Na⁺/K⁺‐ATPase activity and dopamine (DA), norepinephrine (NE), serotonin (5‐HT) in the gills, and hemolymph of the adult Charybdis japonica were studied. DA levels increased significantly (P < 0.05), while the NE and 5‐HT revealed contrary change in hemolymph and gills. The iso‐osmotic point of C. japonica (911.4 mOsm/kg) was at salinity of 27.87 ppt. The Na⁺/K⁺‐ATPase activity of gill showed negative correlation with salinity in the hypotonic environment (<27.87 ppt). The results of this experiment indicated that C. japonica had great capability to acclimate to low salinity.     

盐度胁迫对三疣梭子蟹鳃Na+/K+-ATPase酶活的影响

通过钼蓝法测定三疣梭子蟹在3组实验盐度的胁迫过程中第2对和第6对鳃Na⁺/K⁺-ATPase酶活的变化,比较了3组实验盐度胁迫1 d时,鳃Na⁺/K⁺-ATPase的酶活大小。结果表明,在盐度胁迫初期,3组实验盐度下第2对和第6对鳃Na⁺/K⁺-ATPase的酶活下降;之后,各组实验盐度下第2对和第6对鳃Na⁺/K⁺-ATPase的酶活开始随胁迫时间增长而上升;最后,各组实验盐度下第2和第6对鳃Na⁺/K⁺-ATPase的酶活下降并趋于稳定。另外,胁迫1 d时,各组实验盐度下三疣梭子蟹前5对鳃Na⁺/K⁺-ATPase的酶活显著低于后3对鳃Na⁺/K⁺-ATPase的酶活。三疣梭子蟹对盐度变化的调节可分为被动应激期(酶活力下降)、主动调节期(酶活力逐渐上升)和适应期(酶活力稳定);三疣梭子蟹后3对鳃是离子转运、渗透压调节的主要部位。     

Partial substitution of fish oil with rapeseed, linseed and olive oils in diets for European sea bass (Dicentrarchus labrax L.): effects on flesh fatty acid composition, plasma prostaglandins E2 and F2α, immune function and effectiveness of a fish oil finishing diet

Triplicate groups of European sea bass (Dicentrarchus labrax L.), of initial weight 90 g, were fed four practical‐type diets in which the added oil was 1000 g kg^?1 fish oil (FO) (control diet), 600 g kg^?1 rapeseed oil (RO) and 400 g kg^?1 FO, 600 g kg^?1 linseed oil (LO) and 400 g kg^?1 FO, and 600 g kg^?1 olive oil (OO) and 400 g kg^?1 FO for 34 weeks. After sampling, the remaining fish were switched to the 1000 g kg^?1 FO diet for a further 14 weeks. Fatty acid composition of flesh total lipid was influenced by dietary fatty acid input but specific fatty acids were selectively retained or utilized. There was selective deposition and retention of docosahexaenoic acid (DHA; 22:6n‐3). Eicosapentaenoic acid (EPA; 20:5n‐3) and DHA were significantly reduced and linolenic (LNA; 18:3n‐3), linoleic (LA; 18:2n‐6) and oleic (OA; 18:1n‐9) acids significantly increased in flesh lipids following the inclusion of 600 g kg^?1 RO, LO and OO in the diets. No significant differences were found among different treatments on plasma concentrations of prostaglandin E₂ and prostaglandin F_2α. Evaluation of non‐specific immune function, showed that the number of circulating leucocytes was significantly affected (P < 0.001), as was macrophage respiratory burst activity (P < 0.006) in fish fed vegetable oil diets. Accumulation of large amounts of lipid droplets were observed within the hepatocytes in relation to decreased levels of dietary n‐3 HUFA, although no signs of cellular necrosis was evident. After feeding a FO finishing diet for 14 weeks, DHA and total n‐3 HUFA levels were restored to values in control fish although EPA remained 18% higher in control than in the other treatments. This study suggests that vegetable oils such as RO, LO and OO can potentially be used as partial substitutes for dietary FO in European sea bass culture, during the grow out phase, without compromising growth rates but may alter some immune parameters.     

The Effect of Bilateral Eyestalk Ablation on Signal Transduction Pathways of Ion Regulation of Litopenaeus vannamei

A study was performed on the effects of bilateral eyestalk ablation on signal transduction pathways of ion regulation of Litopenaeus vannamei. The study included three treatments (starvation group, bilateral eyestalk ablation, and starvation and bilateral eyestalk ablation) in addition to a control group. The shrimp were sampled at 0, 12, 24, and 48 h. Results showed that the ablation of bilateral eyestalk had significant effects on the contents of three kinds of biogenic amines (BAs), cyclic guanosine monophosphate (cGMP), and the activities of three kinds of ion‐transport enzymes (P < 0.05). According to these results, bilateral eyestalk ablation had significant effects on the ion signal pathway of L. vannamei. The same changes were observed in 5‐hydroxytryptamine (5‐HT) contents, Na⁺‐K⁺‐ATPase, and HCO₃^?‐ATPase activities, suggesting that crustacean hyperglycemic hormone (CHH) regulated the changes in ion‐transport enzymes, mediated by BAs and cGMP. The specific pathways may be 5‐HT → cGMP → Na⁺‐K⁺‐ATPase, HCO₃^?‐ATPase, and BAs → cGMP → V‐ATPase. 5‐HT contents, Na⁺‐K⁺‐ATPase, and HCO₃^?‐ATPase activities in the starvation group were ultimately higher than those in the bilateral eyestalk ablation group, while the cyclic adenosine monophosphate (cAMP) contents increased slightly. Study results suggested that under the situation of bilateral eyestalk ablation, the shrimp could also use feed or its metabolites to increase 5‐HT or cAMP contents to regulate the Na⁺‐K⁺‐ATPase and HCO₃^?‐ATPase activities in gills.     

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.     

Characterization of transport Na+-ATPases in gills of freshwater tilapia

Branchial plasma membranes from the freshwater cichlid teleostOreochromis mossambicus (tilapia) contain two Na⁺-dependent ATPases: Na⁺/K⁺ ATPase, and an amiloride-sensitive ATPase which is postulated to operate as a Na⁺/H⁺ (–NH₄ ⁺) ATPase. It is suggested that both enzyme activities are located in the basolateral membrane system of the chloride cells. K⁺ has opposing effects on the two enzymes: it stimulates Na⁺/K⁺ ATPase and inhibits Na⁺/H⁺ (–NH₄ ⁺) ATPase activity. Na⁺/H⁺ ATPase appears more sensitive to NH₄ ⁺ at low concentrations than Na⁺/K⁺ ATPase and the stimulatory effect by NH₄ ⁺ ions on the first enzyme could be important in facilitating NH₄ ⁺ excretion by tilapia gills under physiological conditions.In vitro maximum stimulation by NH₄ ⁺ is similar for the two enzymes (200%). In contrast to Na⁺/K⁺ ATPase, Na⁺/H⁺ ATPase activity is inhibited by supra-physiological (>20 mM) concentrations of NH₄ ⁺.     

A microplate technique to quantify nutrients (NO2−, NO3−, NH4+ and PO43−) in seawater

Many methods to measure nutrients (NO₂^?, NO₃^?, NH₄⁺, and PO₄^3?) in water are based on the formation of coloured complexes that are measured by spectrophotometry, frequently using large‐volume (10 mL) spectrophotometer cells. Miniaturization of the techniques using microplate readers and sample volumes as small as 250 μL is an affordable alternative for these determinations. This work describes the adaptation to microtechniques using a 96‐well microplate to measure nitrogen compounds and phosphate in seawater. They can be used as an inexpensive procedure for routine monitoring in aquaculture ponds because of the smaller sample, reagent requirements, and suitable ranges.     

Effects of dietary thyroid hormones on the red drum (Sciaenops ocellatus)

Four separate 8-week feeding trials were conducted to assess the effects of supplementing semipurified diets with either triiodothyronine (T₃) or thyroxine (T₄) at 0, 2, 10, and 50 mg/kg on growth and body composition of juvenile red drum (Sciaenops ocellatus) held in artificial brackish water (6‰) and artificial seawater (32‰). At both levels of salinity, increasing doses of T₃ resulted in fish with reduced weight gain, feed efficiency, condition factor (weight × 100/length³), and muscle ratio (muscle weight × 100/body weight), as well as a lighter body color. Significant (p < 0.05) effects of T₃ on the proximate composition of whole body, liver, and muscle were variable, generally reflecting decreased lipid and protein storage in liver and muscle, respectively. The two highest doses of T₃ given to seawater adapted fish increased survival. Dietary T₄ supplementation had no distinctive effects on appearance, growth or proximate body composition. These results indicate that whereas T₃ may function to regulate protein and lipid metabolism in red drum, dietary supplementation with T₃ leads to a hyperthyroidism-induced catabolic state. The elevated endogenous thyroid hormone levels found in fish fed optimal diets may thus adequately supply tissue needs during juvenile growth.     

Effect of soybean oil and soybean lecithin on intestinal lipid composition and lipid droplet accumulation of rainbow trout, Oncorhynchus mykiss Walbaum

Rainbow trout (Oncorhynchus mykiss Walbaum) were fed purified diets containing fish oil for six weeks and then soybean lecithin or soybean oil for 25 days. The gastrointestinal tract segments, stomach, midgut and hindgut were then sampled for lipid and fatty acid composition and electron microscopy. Membrane lipid class composition was fairly similar in all three segments of trout fed fish oil. Hindgut contained slightly more phosphatidylserine than stomach and midgut, while midgut contained more phosphatidylcholine and less lysophospatidylcholine/sphingomyelin. Feeding soybean products appeared to marginally decrease free cholesterol. The fatty acid compositions of the main lipid classes showed significant regional differences. In control fish, stomach had higher levels of arachidonic acid (20:4n-6) and n-6 polyunsaturated fatty acids than midgut and hindgut, and lower content of docosahexaenoic acid (22:6n-3) and n-3 polyunsaturated fatty acids. Midgut phosphatidylethanolamine also had higher levels of saturated fatty acids and less n-3 polyunsaturated fatty acids than the other tissues. Feeding soybean products decreased the n-3/n-6 ratio mainly due to increases in linoleic (18:2n-6) and 20:4n-6 and decreases in 22:6n-3 and eicosapentaenoic acid (20:5n-3). Phosphatidylcholine and to a lesser extent phosphatidylethanolamine adapted more readily to dietary changes by major increases in 18:2n-6 and C₂₀₋₂₂ n-6 polyunsaturated fatty acids. The composition of phosphatidyl-serine and -inositol appeared to be under more strict metabolic control. Linoleic acid hardly increased at all while the increase in other n-6 polyunsaturated fatty acids was less pronounced than for the other lipid classes. Regardless of lipid class, stomach resisted dietary changes more strongly than midgut and hindgut. Increases in n-6 polyunsaturated fatty acids were minor as were the loss of n-3 polyunsaturated fatty acids. The dead-end product 20:2n-6 accumulated to a higher degree in hindgut phosphatidyl-ethanolamine and -coline compared to midgut and stomach, suggesting that the activity of Δ₆ desaturation is higher in the anterior part of the intestine where most of the lipid is absorbed. Feeding soybean oil caused massive accumulation of free lipid droplets in midgut enterocytes while little lipid droplets were observed in trout fed fish oil or soybean lecithin. Since both soybean products influenced intestinal composition to the same degree, altered fatty acid profiles in membranes is not responsible for the observed lipid accumulation. This supports previous observations in Arctic charr (Salvelinus alpinus L.), suggesting that fish may require exogenous phospholipids in order to sustain a sufficient rate of lipoprotein synthesis. This revised version was published online in July 2006 with corrections to the Cover Date.     

Salinity increases total body prolactin and gill and skin prolactin receptor expression in the Chinese edible frog,Hoplobatrachus rugulosus,tadpole

Water salinity has effects on growth and metamorphosis of anuran species, including Hoplobatrachus rugulosus. Previously, we reported that cultured H. rugulosus tadpoles at low salinities (2–4‰) were of bigger size and grew faster than those in fresh water (FW). However, at a higher salinity level of 6‰, their sizes were reduced and the metamorphosis was delayed. It was therefore hypothesized that high salinity‐induced osmotic stress affected secretion of prolactin (PRL), which acts as osmoregulatory hormone and a regulator of metamorphosis in amphibians. In this study, transferring tadpoles into 4‰ and 6‰ brackish water increased the PRL levels by ~1.2‐ and ~twofold, respectively, as compared to FW group. These osmotic challenges also increased the total body fluid osmolality and levels of Na⁺, Cl^? and Ca²⁺. The contents of triiodothyronine (T₃) were significantly reduced in 4‰ and 6‰ groups, but not 2‰ group. Three sizes (49, 29 and 23 kDa) of H. rugulosus PRL receptors (PRLRs) were detected, and their protein expression was found in the skin, gill, tail fin, brain, intestine, heart, liver and kidney. The expression of PRLR‐49k protein was significantly higher in both skin and gills in 2–4‰ groups, whereas that of PRLR‐29k and PRLR‐23k were higher in gills and lower in skin of the 6‰ group than FW group. In conclusion, salinity challenge, particularly 4‰ and 6‰, increased the levels of PRL, while decreasing the T₃ levels, which could explain why salinity markedly modulated growth, metamorphosis and survival of tadpoles.     

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.     

Interactive effects of salinity on oxygen consumption,ammonium excretion,osmoregulation and Na+/K+‐ATPase expression in the bullseye puffer (Sphoeroides annulatus,Jenyns 1842)

A physiological study was performed to explore the effects in Sphoeroides annulatus (Jenyns 1842) juveniles of exposure to different salinities 10, 17, 23, 29, 35 and 41‰ on oxygen consumption rate (OCR), ammonium excretion rate (AER), the oxygen‐nitrogen atomic ratio (O:N), osmoregulation and Na⁺/K⁺‐ATPase expression. The OCR values ranged from 27.9 to 30.9 mg O₂ h^?1 kg^?1, displaying a Type 1 response pattern Kinne (1977). AER ranged from 0.60 to 0.69 mg h^?1 kg^?1, and O:N values were from 53.12 to 59.26, indicating that the puffers use proteins and lipids as an energy‐substrate. Osmoregulation in S. annulatus was hyposmotic in salinities of 23, 29, 35 and 41‰ and hyperosmotic in a salinity of 10‰. The isosmotic point of the bullseye puffer was 356 mmol kg^?1 (10.5‰). The enzyme expression analysis indicates that the fish acclimated to 41‰ had the highest Na⁺/K⁺‐ATPase expression level, whereas, the lowest expression level was found close to the isosmotic point. Na⁺/K⁺‐ATPase expression in the gills was found to have a U‐shaped relationship with environmental salinity. We conclude that the bullseye puffer is strongly euryhaline and can be cultivated in a wide range of environments that has important economic implications.     

Growth performance,osmoregulatory and metabolic modifications in red porgy fry,Pagrus pagrus,under different environmental salinities and stocking densities

The effects of two different environmental salinities [brackish water (BW), 12‰; sea water (SW), 39‰] and initial stock densities [low (LD), 1.0 g L^?1; high (HD), 2.0 g L^?1] on growth, osmoregulation, stress and energy metabolism of the fry Pagrus pagrus were investigated over a period of 45 days. Pagrus pagrus (n=80, 5.51 ± 0.25 g mean initial body weight) were randomly divided in eight groups. Growth, weight gain and specific growth rate increased in BW‐acclimated fish compared with SW‐acclimated fish. No differences were observed between the two stock densities tested at either environmental salinity. Plasma osmolality was lowest in BW‐acclimated specimens, but the stock density had no effect on this parameter. Branchial Na⁺,K⁺‐ATPase activity was positively correlated with environmental salinity, but unaltered at the renal level. Plasmatic parameters were enhanced by salinity and stocking conditions. At the hepatic level, triglyceride values were enhanced in BW‐acclimated fish maintained at LD. Muscle metabolites (glycogen, glucose and lactate) increased in BW‐ compared with SW‐acclimated fish; stock density had no influence. Our data suggest that changes in metabolic parameters could be correlated with the higher growth rates observed in P. pagrus acclimated to BW, while no significant effects due to the stocking density used were observed.