The effects of temperature on the physiological response to low oxygen in Atlantic sturgeon

Atlantic sturgeon (Acipenser oxyrhynchus), which are bottom dwelling and migratory fish, experience environmental hypoxia in their natural environment. Atlantic sturgeon, acclimated to either 5 or 15°C, were subjected to a 1 h severe (<10 mm Hg) hypoxia challenge in order to document their physiological responses. We measured hematological parameters, including O₂ transport (hemoglobin, hematocrit), ionic (chloride, osmolality), and metabolic (glucose, lactate) variables under normoxic conditions (~160 mm Hg), immediately following a 1 h exposure to hypoxic water, and following a further 2 h of recovery from this challenge in normoxic water. In a second experiment, we assessed the opercular beat frequency before, during, and after hypoxic exposure. Hemoglobin concentrations and hematocrit were significantly different between fish held at 5°C vs. 15°C and also significantly different between normoxia prior to hypoxia and following recovery. Plasma lactate concentrations increased following hypoxia at both temperatures, indicative of an increase in anaerobic metabolism. In contrast, a significant increase in plasma glucose concentrations in response to hypoxia only occurred at 5°C, suggesting different fuel demands under different temperatures. Changes in opercular beat frequency (OBF) were dependent on temperature. At 5°C, OBF increased upon exposure to hypoxia, but returned to pre-exposure levels within 35 min for the remainder of the experiment. During hypoxia at 15°C, OBF increased very briefly, but then rapidly (within 20 min) decreased to levels below control values. Following a return to normoxia, OBF quickly increased to control levels. Overall, these findings suggest that Atlantic sturgeons are relatively tolerant to short-term and severe hypoxic stress, and the strategies for hypoxia tolerance may be temperature dependent.     

Differences in activity level between cownose rays (Rhinoptera bonasus) and Atlantic stingrays (Dasyatis sabina) are related to differences in heart mass, hemoglobin concentration, and gill surface area

Aquatic animals are faced with the challenge of extracting oxygen from water, a medium that is metabolically expensive to ventilate and that contains just a fraction of the oxygen concentration relative to air, yet the physiologies of fishes have evolved to support a wide range of activity levels in nature. Oxygen delivery components, including gill surface area (oxygen uptake), blood chemistry (oxygen transport), and the heart (system pump), have been positively correlated to activity level in teleost fishes, yet relatively little is known about how these components are related to activity in elasmobranches. The current study addresses this question by examining heart mass, hemoglobin concentration, hematocrit level, and gill surface area in wild-caught representatives of the benthic Atlantic stingray (Dasyatis sabina) and active cownose ray (Rhinoptera bonasus). Allometric scaling exponents are similar for all four measures between the study species. Heart mass, gill surfaces areas, and hemoglobin concentrations were 2.1 times, approximately 7.1 times, and 2.0 times higher, respectively, in active cownose rays, when compared to benthic Atlantic stingrays, after correcting for differences in body mass. When considered in the context of functional plasticity within the oxygen delivery systems of benthic and active species, data from the current study indicate that higher activity levels in cownose rays are supported by modifications that, at least in part, are likely to enhance oxygen uptake.     

低氧胁迫对鲻幼鱼生长、能量代谢和氧化应激的影响

为研究低氧胁迫对鲻幼鱼生长、能量代谢和氧化应激的影响,实验将其放在溶解氧(DO,mean±SE)含量分别控制在(1.66±0.41)、(4.35±0.53)、(7.03±0.36)mg/L的条件下养殖10 d,然后恢复至接近饱和溶解氧含量7.0 mg/L的条件下养殖30 d,研究其特定生长率、排氨率、耗氧率、氧氮比和血浆、肌肉、肝脏及鳃组织的总抗氧化能力(T-AOC)、过氧化物歧化酶(SOD)活力、抗超氧阴离子活力(ASOR)、丙二醛(MDA)含量、乳酸(LD)含量、总谷胱甘肽(T-GSH)、还原型谷胱甘肽(GSH)和氧化型谷胱甘肽(GSSG)含量。结果表明:低氧胁迫对鲻幼鱼的生长、能量代谢影响显著,较严重缺氧组鲻的体质量、特定生长率(SGR)、耗氧率和排氨率显著低于其他处理,不具有补偿生长的能力;而轻微缺氧组获得完全补偿生长。低氧胁迫对鲻氧化应激指标影响显著,胁迫结束时鲻通过提高某些抗氧化酶的活力来增强抗氧化能力,以提高其应对恢复正常溶解氧环境可能带来的氧化应激的能力,同时在恢复溶氧后鲻氧化应激反应也较强烈。在恢复溶解氧阶段,肝脏中GSH显著增加,说明鲻体内的保护机制被激活。肝脏和鳃中MDA的含量在低氧胁迫后与溶解氧含量呈明显的负相关性,在复氧30 d后仍然高于对照组,表明低氧胁迫加强鲻肝脏和鳃组织脂质过氧化反应。     

溶解氧对团头鲂耐低氧新品系F5代的鳃组织形态及各组织酶活性的影响

为研究不同浓度溶解氧(DO)对团头鲂(Megalobrama amblycephala)耐低氧新品系F5代鳃组织形态以及各组织酶活性的影响,本研究将团头鲂在低氧[DO为(1.7±0.2) mg/L]和高氧[DO为(19.3± 0.5) mg/L]条件下分别处理0、4和7 d,恢复常氧[DO为(7.8±0.3) mg/L] 7 d后,通过石蜡切片观察鳃组织的形态,并测定了鳃、肝胰腺、肠道、肌肉中过氧化氢酶(CAT)、琥珀酸脱氢酶(SDH)及乳酸脱氢酶(LDH)活性和丙二醛(MDA)含量。石蜡切片结果显示,随着低氧处理时间的延长,团头鲂新品系鳃丝的层间细胞团体积减小,鳃小片表面积增加,恢复常氧7 d后又有所恢复。高氧条件下,层间细胞团体积增大,鳃小片表面积减小,恢复常氧7 d后也会恢复。酶活性检测结果显示,在低氧和高氧2种条件下,随着处理时间的延长,CAT活性和MDA含量在各组织中的变化无明显规律,但均有显著差异(P<0.05)。低氧条件下,LDH活性显著增高,SDH活性显著降低(P<0.05)。高氧条件下,LDH活性显著降低,SDH活性显著增高(P<0.05)。本研究可为溶解氧对团头鲂的鳃组织以及各组织酶活性的影响提供基础资料,并为团头鲂新品系的养殖与选育奠定基础。     

Comparison of NADH-dependent cytochrome b5 reductase activity and in vitro methemoglobin induction by sodium nitrite in Oncorhynchus mykiss, Salmo salar, and Salvelinus fontinalis

Methemoglobin is hemoglobin containing ferric iron. Methemoglobin cannot bind to oxygen and at high concentrations causes tissue hypoxia. Brook trout (Salvelinus fontinalis) develop significantly greater methemoglobinemia than Atlantic salmon (Salmo salar) or rainbow trout (Oncorhynchus mykiss) following general anesthesia with benzocaine or tricaine methanesulfonate. The objective of this study was to compare the activity of the major methemoglobin reducing enzyme, NADH-dependent cytochrome b5 reductase (CB5R), in brook trout erythrocytes to the activity of CB5R in Atlantic salmon and rainbow trout erythrocytes. Methemoglobin levels were compared using co-oximetry following in vitro incubation of erythrocytes with sodium nitrite (NaNO₂). The CB5R activity was measured using a ferricyanide assay. There was significantly greater methemoglobin at time 0 in brook trout erythrocytes than in rainbow trout or Atlantic salmon erythrocytes (2.79 ± 0.29 %, 2.19 ± 0.23 %, 2.08 ± 0.14 %), (P < 0.001). There was significantly greater methemoglobin induction by NaNO₂ in brook trout erythrocytes (33.14 ± 3.32 %) than in rainbow trout or Atlantic salmon erythrocytes (28.73 ± 2.92 % and 24.85 ± 1.40 %, respectively), (P < 0.001). The CB5R activity was significantly less in brook trout erythrocytes (median of 3.05 μmol/min/μl) than in rainbow trout erythrocytes (median of 6.73 μmol/min/μl). The CB5R activity in Atlantic salmon erythrocytes (median 4.09 μmol/min/μl) was not significantly different than in brook or rainbow trout erythrocytes. Total methemoglobin at any one time is a balance between induction by oxidants and reduction by antioxidants. Lower CB5R activity in brook trout erythrocytes may contribute to a species-specific sensitivity to methemoglobin induction; however, there are likely additional factors.     

Air-breathing behavior and physiological responses to hypoxia and air exposure in the air-breathing loricariid fish, Pterygoplichthys anisitsi

Hypoxic water and episodic air exposure are potentially life-threatening conditions that fish in tropical regions can face during the dry season. This study investigated the air-breathing behavior, oxygen consumption, and respiratory responses of the air-breathing (AB) armored catfish Pterygoplichthys anisitsi. The hematological parameters and oxygen-binding characteristics of whole blood and stripped hemoglobin and the intermediate metabolism of selected tissue in normoxia, different hypoxic conditions, and after air exposure were also examined. In normoxia, this species exhibited high activity at night and AB behavior (2–5 AB h^?1). The exposure to acute severe hypoxia elicited the AB behavior (4 AB h^?1) during the day. Under progressive hypoxia without access to the water surface, the fish were oxyregulators with a critical O₂ tension, calculated as the inspired water O₂ pressure, as 47 ± 2 mmHg. At water O₂ tensions lower than 40 mmHg, the fish exhibited continuous apnea behavior. The blood exhibited high capacity for transporting O₂, having a cathodic hemoglobin component with a high Hb–O₂ affinity. Under severe hypoxia, the fish used anaerobic metabolism to maintain metabolic rate. Air exposure revealed physiological and biochemical traits similar to those observed under normoxic conditions.     

Diel cyclic hypoxia alters plasma lipid dynamics and impairs reproduction in goldfish (<Emphasis Type="Italic">Carassius auratus</Emphasis>)

Diel cyclic hypoxia occurs with varying frequency and duration in freshwater habitats, yet little is known about its effects on reproduction of freshwater fishes. The present study shows that long-term exposure of goldfish (Carassius auratus) to cyclic hypoxia (0.8 ± 0.2 mg/l dissolved oxygen) for 9 h or more, per day, altered plasma lipid and sex steroid profiles, which in turn directly or indirectly suppressed ovarian growth and viable spermatozoa production. Hypoxia decreased total cholesterol and high density lipoprotein (HDL p < 0.05) and elevated triglycerides (TG; p < 0.05) in both sexes. Plasma steroid concentrations particularly of 17α-hydroxyprogesterone (17-HP), estradiol (E2), testosterone (T) in females, and T and 11-ketotestosterone (11-KT) in males were attenuated under diel hypoxic conditions. Intriguingly, both diel and continuous hypoxia elevated plasma E2 and vitellogenin levels in males. However, neither lipid nor steroid profiles recorded any variation in a dose-dependent manner in response to diel hypoxia. The reduced GSI, decreased number of tertiary oocytes, and motile spermatozoa in hypoxic fish clearly indicate suppression of gametogenesis. Thereby, prolonged diel cyclic hypoxia may affect valuable fishery resources and fish population structure by impairing reproductive performances and inducing estrogenic effects in males.     

Effect of Sublethal Hypoxia on the Immune Response and Susceptibility of Channel Catfish, Ictalurus punctatus, to Enteric Septicemia

The effect of sublethal hypoxia exposure on stress and immune responses and susceptibility to Edwardsiella ictaluri infection in juvenile channel catfish, Ictalurus punctatus, was investigated. Fish were monitored for temporal changes in glucose and cortisol concentrations before, during, and after 2 h exposure to sublethal hypoxia (<2 mg/L dissolved oxygen [DO]) and when maintained under normoxic conditions (6.0 ± 0.3 mg/L DO). Both blood glucose and plasma cortisol increased significantly in response to hypoxic conditions. Fish exposed to hypoxic or normoxic conditions were challenged with a high dose (1.3 × 10⁷ colony‐forming units [CFU]/mL) or a low dose (1.3 × 10⁵ CFU/mL) of E. ictaluri or sterile culture broth by 30‐min immersion bath. Approximately 1% of fish in both the normoxic and the hypoxic groups died when challenged with the low dose of E. ictaluri. However, when challenged with the high dose of E. ictaluri, catfish exposed to hypoxic conditions had significantly higher cumulative mortality (36 ± 12.1%) than those maintained under normoxic conditions (12 ± 1.1%). Total hemolytic complement and bactericidal activities and antibody response were lower in hypoxia‐exposed channel catfish, indicating that increased susceptibility of channel catfish to E. ictaluri may be the result of the immunosuppressive effects of the stress response to hypoxia.     

Effects of calcium and copper exposure on lipogenic metabolism, metal element compositions and histology in Synechogobius hasta

The present study was conducted to evaluate the effects of calcium (Ca) and copper (Cu) exposure on growth performance, metal element composition, enzymatic activities and histology in Synechogobius hasta and tested the hypothesis that Ca could protect against Cu-induced toxicity in the fish species. Three hundred sixty S. hasta (initial mean weight 22.6 ± 0.2 g, mean ± SEM) were stocked in 18 circular fiberglass tanks (water volume: 300 l), 9 of which were pre-exposed to Ca at a rate of 600 mg Ca/l for 10 days and then exposed to concentrations of 0, 77 and 154 μg Cu/l for 30 days. Another 9 tanks were cultured in natural seawater (no extra Ca addition) for 10 days and then exposed to concentrations of 0, 77 and 154 μg Cu/l for 30 days. Both Ca exposure and then waterborne Cu exposure influenced the accumulation of metal elements (Cu, iron, zinc and manganese) in several tissues (muscle, intestine, gill, liver and spleen), changed hepatic lipogenic metabolism and induced histological alterations in liver, gill and spleen. In general, Ca exposure seemed to mitigate the severity of Cu-induced mortality and histopathological injuries, indicating that Ca exposure had the capacity to decrease Cu toxicity in S. hasta. To our knowledge, it is the first study involved in the effects of Ca and Cu exposure on hepatic lipogenic metabolism and metal element compositions in a wide range of tissues and organs in fish, which provides new insight into the protective effect of Ca on toxic metal elements in fish.     

Acclimation to a low oxygen environment alters the hematology of largemouth bass (Micropterus salmoides)

One of the most severe impacts of urbanization on aquatic systems is the increasing presence of low oxygen environments caused by anthropogenic sources of pollution. As urbanization increases nationally and globally, it is becoming exceedingly important to understand how hypoxia affects aquatic fauna, especially fish species. In an effort to better understand the impacts of prolonged hypoxia on fishes, largemouth bass were held at 3.0 and 9.0 mg L^?1 for 50 days, which has previously shown to be temporally sufficient to impart plastic phenotypic changes. Following the holding period, fish from each group were subjected to a low dissolved oxygen (DO) challenge of 2.0 mg L^?1 for 6 h, and their physiological and hematological parameters were compared with control fish held for 6 h with no change in DO. There were no differences in the physiological stress responses between the two holding groups; however, the low oxygen holding group had increased hemoglobin and hematocrit levels following the 6-h low oxygen challenge compared with the high oxygen group. These results suggest largemouth bass exposed to chronic low oxygen conditions, either naturally or anthropogenically, may possess a beneficial advantage of increased oxygen uptake capacity during periods of low oxygen.     

Survival, growth and biochemical parameters of silver catfish, Rhamdia quelen (Quoy & Gaimard, 1824), juveniles exposed to different dissolved oxygen levels

Silver catfish, Rhamdia quelen (Quoy & Gaimard, 1824), is an endemic species from Latin America that is raised in cultivation ponds, and consequently may be exposed to low oxygen levels. Therefore, the objective of this study was to verify the lethal concentration (CL_{50?96 h}) of dissolved oxygen levels for silver catfish juveniles. In addition, the effects of different dissolved oxygen levels (1.96±0.08, 3.10±0.10, 4.14±0.09, 5.20±0.07 and 6.16±0.03 mg L^?1) on growth and metabolic parameters (glycogen, glucose, protein, lactate levels and catalase activity) were also investigated. CL_{50?96 h} was 0.52 mg L^?1 (CI 0.42–0.61 mg L^?1) or 6.7% oxygen saturation. After exposure of silver catfish to hypoxia for 30 days, there were no changes in biochemical parameters indicating the use of an anaerobic pathway by the fish. However, the dissolved oxygen levels influenced silver catfish juvenile behaviour, survival and growth, and under the experimental conditions 5.2 mg L^?1 (or 65.6% oxygen saturation) is the minimum oxygen level recommended for the growth of this species.     

The effects of long-term 20 mg/L carbon dioxide exposure on the health and performance of Atlantic salmon Salmo salar post-smolts in water recirculation aquaculture systems

Previous research and experience has linked elevated dissolved carbon dioxide (CO₂) to reduced growth performance, poor feed conversion, and a variety of health issues in farm-raised fish, including Atlantic salmon Salmo salar. Supplemental control measures in water recirculation aquaculture systems (RAS) to reduce CO₂ accumulation, however, such as increased water pumping to decrease tank hydraulic retention time, can represent significant costs for operators. We exposed post-smolt S₀ Atlantic salmon (197 ± 2 g, 423 days post-hatch) to either high (20 ± 1 mg/L) or low (8 ± <1 mg/L) dissolved CO₂ in six replicated freshwater RAS for 384 days to investigate differences in performance and health as the salmon were grown to harvest size. All RAS were operated at moderate water exchange rates (1.0% of the total recirculating flow), a 24-h photoperiod was provided, fish were fed to satiation, and densities were maintained between 40 and 80 kg/m³. Over the study period, dissolved oxygen was kept at saturation, mean water temperature was 14.1 ± 0.1 °C, and alkalinity averaged 237 mg/L as CaCO₃. At study’s end, no significant differences in fish weight (high CO₂ mean weight = 2879 ± 35 g; low CO₂ mean weight = 2896 ± 12 g), feed conversion ratio (1.14 ± 0.12 vs. 1.22 ± 0.13, respectively), or thermal growth coefficient (1.45 ± 0.01 vs. 1.46 ± 0.01, respectively), were observed. No significant differences in survival (high CO₂ mean survival = 99.1 ± 0.4%; low CO₂ mean survival = 98.9 ± 0.3%) or culls due to saprolegniasis (3.5 ± 1% vs. 3.0 ± 1%, respectively) were determined, and no nephrocalcinosis was observed through histopathological evaluation. Blood gas and chemistry evaluation revealed higher pCO₂, bicarbonate, and total CO₂, and lower chloride and glucose, in the high CO₂ cohort. Molecular analyses of gill enzyme regulation showed significantly higher expression of Na⁺/K⁺ ATPase α1a in high CO₂ fish at 3-weeks post-challenge, indicating physiological adaptation to the higher CO₂ environment without any noticeable long-term impacts on health or performance. Overall, the results of this study suggest that, at 237 mg/L as CaCO₃ mean alkalinity, post-smolt Atlantic salmon can be raised in freshwater RAS to harvest size with up to 20 mg/L CO₂ without significantly impacting fish health and performance.     

Long-term effects of intraperitoneal injection of estradiol-17β on the growth and physiology of juvenile stellate sturgeon Acipenser stellatus

Juvenile stellate sturgeon Acipenser stellatus were intraperitoneally injected with estradiol-17β (E₂; 0 and 5 mg/kg fish) to investigate the possibility of sex reversal and also determine the changes in biochemical parameters. Five-month-old fish (40.9 ± 1.1 g) were injected every 3-week interval during a 190-day trial. At the termination of the experiment, final weight and other growth parameters including weight gain and specific growth rate, hepatosomatic and viscerosomatic indices were not affected by repetitive injection of E₂. Hematological features of E₂-treated fish showed significant reductions in number of red blood cells, hemoglobin concentration, hematocrit value and mean corpuscular hemoglobin (P < 0.05), but no significant changes were observed in number of white blood cells, mean corpuscular volume and mean corpuscular hemoglobin concentration (P > 0.05). Calcium, phosphorus, glucose, triacylglycerol, cholesterol, total protein and estradiol concentrations were significantly increased in fish injected with E₂ (P < 0.001). Plasma progesterone and testosterone levels were noticeably lower in fish injected with 5 mg/kg E₂ rather than the control fish (P < 0.001). Histological observations of gonads showed that all fish injected with 5 mg/kg E₂ apparently feminized, while 66.6 % of the control group was female. These results revealed that the injection of E₂ is an effective method for feminization of stellate sturgeon without having significant inhibitory effects on growth and survival.     

Determining the tranquilization dose and residue of tricaine methanesulfonate (MS-222) in sea bass <Emphasis Type="Italic">Lates calcarifer</Emphasis> tissue

Although tricaine methanesulfonate (MS-222) is often used to tranquilize fish, the guidelines for its use in sea bass, a brackish species, have not been established. The aim of the study reported here was to establish the tranquilizing concentration of MS-222, based on the time required for MS-222 residue elimination and withdrawal. Thirty-six fish (6/group) were immersed in different concentrations of MS-222 (0, 30, 50, 60, 70 and 90 mg/l) to evaluate the fish physiological behavior. After 200 fish were anesthetized at 90 mg/l, the fish achieved a healthy recovery within 72 h after the administration of saline. The 10 fish in the control group were subject to the same treatment without anesthesia, 3 out of 10 died. After 108 fish (54/group) were immersed in 30 or 60 mg/l of MS-222, the sedated fish were healthy during and after the 8 h of transport. However, all the 10 fish in the control group died within 3 days. By high-performance liquid chromatography, the residue of MS-222 was assessed. In the skinned muscle and liver, the elimination half-life was 5.54 and 5.27 h (30 mg/l) and 8.72 and 7.15 (60 mg/l), respectively, and the withdrawal time was at least 4.5 days at 30 mg/l and 7.5 days at 60 mg/l.     

溶氧水平对黄颡鱼稚鱼摄食、生长及呼吸代谢的影响

在(28±0.5)℃循环水环境中设置4种溶氧水平,分别为2.92 mg/L(G1组)、4.71 mg/L(G2组)、6.77 mg/L(G3组)、9.68 mg/L(G4组),研究初始体重为(1.62±0.02)g的黄颡鱼(Pelteobagrus fulvidracoR.)稚鱼的生长、摄食及呼吸代谢规律。结果显示:G3组特定生长率(SGR)、饲料效率(FE)均显著高于其它各试验组(P<0.05)。试验鱼的耗氧率、排氨率与溶氧水平无正相关性,G3组的耗氧率、排氨率始终显著高于其它三组。第6周测定发现:摄食后1~4 h内耗氧率和排氨率均呈现迅速上升,到达最大值后再缓慢下降,二者均在09∶00和21∶00出现高峰,G3组的耗氧率高峰值分别为0.345、0.331 mg/g.h,G3组的排氨率高峰值分别为24.194、17.770μg/g.h。结果表明:不同溶氧条件下,黄颡鱼稚鱼的耗氧率、排氨率变化过程具有类似的特征,二者在能量代谢机制上相互关联;在6.77 mg/L的溶氧水平下,黄颡鱼稚鱼生长最快、呼吸代谢最为旺盛。     

Effect of acid environments on cortisol and cortisol receptor activity in Atlantic salmon,Salmo salar

The cytosol and nuclear extract of gill tissue obtained from laboratory held Atlantic salmon,Salmo salar manifested saturable cortisol binding of high affinity and low capacity (cytosol: K_a = 0.198 ± 0.024 × 10⁹/M, N_max = 116.8 ± 20.8 fmol/mg protein; nuclear extract: K_a = 0.823 ± 0.057 × 10⁷/M, N_max = 1563 ± 330 fmol/mg protein; n = 4). The cytosol receptor activity displayed high steroid and tissue specificity and a single binding peak at 191,000 Da following gel permeation chromatography. Atlantic salmon exposed for 3 or 8 months to waters from the Medway River (pH about 5.1), the Westfield River (pH about 4.8) and calcium carbonate treated Westfield River (pH about 5.6) showed no gill cytosol receptor activity. Cortisol receptor activity in the gill nuclear extracts from fish in limed Westfield River water in December (3 months) was less than half the activity in the fish treated with Medway River water (p < 0.05) although the plasma cortisol values were not different. In May (8 months), the plasma cortisol of fish in limed water was almost twice that of the fish held in acid Westfield River water (p = 0.058).     

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.     

Hematological and gill histopathological changes in iridescent shark,Pangasius hypophthalmus (Sauvage, 1878) exposed to sublethal diazinon and deltamethrin concentrations

The effect of two insecticides, diazinon and deltamethrin, was investigated on hematological parameters and gill morphology in iridescent shark, Pangasius hypophthalmus. Fish were exposed to 0.5 and 1 ppm diazinon as well as 0.015 and 0.020 ppm deltamethrin over a 7-day period. Both insecticides caused leukocytosis, lymphopenia, neutrophilia as well as increases in red blood cell (RBC), hematocrit (Ht), hemoglobin (Hb) and mean corpuscular volume (MCV). Morphological gill damages were observed in fish exposed to both pesticides. It is suggested that diazinon and deltamethrin changed immune function and induced gill damages which could be the reason of increase in RBC, Ht, Hb and MCV in iridescent shark.