Antioxidative role of selenium against the toxic effect of heavy metals (Cd<Superscript>+2</Superscript>, Cr<Superscript>+3</Superscript>) on liver of rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis> Walbaum 1792)

The main purpose of this study is to discuss the effect of Cd⁺², Cr⁺³ and Se metals on biochemical parameters in liver tissue of Oncorhynchus mykiss. The rainbow trout were exposed to heavy metal stress (Cd⁺², Cr⁺³) at 2 ppm dosage. The present study was undertaken to determine the protective effect of selenium treatment at the same dosage (2 ppm) on some biochemical parameters. The activity of catalase (CAT), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and the changes in levels of malondialdehyde (MDA) from biochemical parameters were determined in liver tissue of the fish groups exposed to heavy metals, especially for the selenium-applied groups. Results of this study showed that the activities of CAT, GSH-Px and SOD in the tissues of fish exposed to the stress of Cd⁺² and Cr⁺³ were significantly lower than the control groups (P < 0.05). Meanwhile, the closer values to the control groups were obtained in selenium-added groups (Cr⁺³ + Se⁺⁴, Cd⁺² + Se⁺⁴). For the level of MDA, the last production of lipid peroxidation showed increases (P < 0.05) in the groups exposed to the metal stress, whereas significant decreases were obtained in selenium-applied groups. The result of the statistical evaluation showed that the negative effects occurring in the biochemical parameters of the applied groups exposed to the toxicity of heavy metal were significantly eliminated (P < 0.05) as a result of selenium treatment.     

Changes in metabolic enzymes,cortisol and glucose concentrations of Beluga (<Emphasis Type="Italic">Huso huso</Emphasis>) exposed to dietary methylmercury

In this paper, effects of dietary methylmercury (MeHg) on several blood biochemical parameters including GLU (glucose), LDH (lactate dehydrogenase), AST (aspartate aminotransferase), ALT (alanine aminotransferase), ALP (alkaline phosphatase) and cortisol were investigated in the Beluga sturgeon (Huso huso). Beluga juveniles were fed for 32 days on four diets containing MeHg (control: 0.04 mg kg⁻¹; low: 0.76 mg kg⁻¹; medium: 7.88 mg kg⁻¹; and high 16.22 mg kg⁻¹ treatment). Significant increases (P < 0.05) were observed in all biochemical parameters, except ALP levels, which decreased significantly (P < 0.05) compared to the control group with either dose- or time-dependent effects. These results suggest that long-term dietary MeHg exposure may affect metabolic enzyme activity and glucose levels in Belugas. These findings provide useful information for environmental and fishery officials to apply in future decisions for managing fish resources in Caspian Sea.     

Lack of arterial PO<Subscript>2</Subscript> downregulation in Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis> L.) during long-term normoxia and hyperoxia

Regulation of arterial partial pressure of O₂ (P_aO₂) in Atlantic salmon (Salmo salar) was investigated during resting conditions in normoxic and hyperoxic water. Dorsal aorta cannulated adult Atlantic salmon (1.2–1.6 kg, n = 8) were exposed to 2 week sequential periods of normoxia [16.7 ± 1.1 kPa (mean ± SD)] and hyperoxia (34.1 ± 4.9 kPa) in individual tanks containing seawater (33.7 ± 0.2 ppt) at stable temperature conditions (8.7 ± 0.7°C) and a light regime of L:D = 12:12. Tank design and sampling procedures were optimized to provide suitable shelter and current for the fish, and to allow repeated, undisturbed sampling of blood from free-swimming fish. Fish were sampled regularly through the experimental period. P_wO₂, P_aO₂, blood ion composition (Na⁺, K⁺, Cl⁻), acid–base status (pH, PCO₂, HCO₃ ⁻), haematocrit and glucose were measured. The most frequently observed P_aO₂ values were in the range of 60–80% of P_wO₂, both during normoxia and hyperoxia, and P_aO₂ values were significantly lower during normoxia than during hyperoxia. Blood pH, PCO₂ and HCO₃ ⁻ were significantly elevated during hyperoxia, while, Na⁺, Cl⁻ and Hct were significantly lower. K⁺ and glucose showed no significant differences. This study demonstrates a lack P_aO₂ regulation in Atlantic salmon to low partial pressures, in contrast to previous reports for many aquatic gill breathing animals. Both during normoxia and hyperoxia, P_aO₂ reflects P_wO₂, and alterations in external PO₂ consequently result in proportional arterial PO₂ changes. Physiological adaptation to hyperoxia, as illustrated by changes in several blood parameters, does not include down-regulation of P_aO₂ in Atlantic salmon. The lack of P_aO₂ regulation may make Atlantic salmon vulnerable to the oxidative stress caused by increased free radical formation in hyperoxic conditions.     

Use of vitamin C as an immunostimulant. Effect on growth,nutritional quality,and immune response of <Emphasis Type="Italic">Labeo rohita</Emphasis> (Ham.)

Teleost fish lack the enzyme for endogenous synthesis of ascorbic acid (AA), an essential micronutrient for fish. The aim of this study was to examine the effect of higher levels of dietary vitamin C on growth, nutritional quality, and immunomodulation in the Indian major carp, rohu (Labeo rohita). Four groups of L. rohita were fed experimental diets containing either no vitamin C (control) or supplemented with vitamin C at 500 mg kg⁻¹ (Exp-1), 1000 mg kg⁻¹ (Exp-2), or 1500 mg kg⁻¹ (Exp-3) for 60 days. Growth parameters (NWG, ADG, and SGR), serological parameters (TSP, TSA, TSG, and A:G), haematological parameters (TLC, TEC, Hct, MCV, and MCH), and different non-specific immunological parameters (PR, PI, respiratory burst activity, and bactericidal activity) were evaluated during the experimental trial. Fish fed a vitamin C-supplemented diet showed higher specific growth rate (SGR) up to 1000 mg kg⁻¹ compared with control fish. Different haematological and serological parameters along with non-specific immune parameters were influenced by vitamin C supplementation. Among the non-specific immune parameters phagocytic activity (PR and PI) and respiratory burst activity (NBT cells) were significantly (P ≤ 0.05) enhanced by increasing doses of vitamin C supplementation. Higher levels of dietary vitamin C significantly (P ≤ 0.05) enhanced protection against Aeromonas hydrophila (AH1) infection compared with controls. Results from this study help to establish the beneficial effect of vitamin C on growth and immunmodulation in rohu (L. rohita).     

Effect of dietary chromium picolinate on growth performance and blood parameters in grass carp fingerling, <Emphasis Type="Italic">Ctenopharyngodon idellus</Emphasis>

An experiment was conducted to investigate the effect of dietary chromium picolinate supplement on growth and haematology parameters of grass carp, Ctenopharyngodon idellus. Six diets with increasing dietary chromium picolinate levels 0, 0.2, 0.4, 0.8, 1.6 and 3.2 mg kg⁻¹ were fed to triplicate groups of 20 fish (initial weight of 12.78 ± 1.16 g, mean ± SD) in a flow water system for 10 weeks. Fish fed the diet supplemented with 0.8 mg Cr kg⁻¹ had significantly improved weight gain (WG), feed efficiency ratio (FER), protein efficiency ratio (PER) and protein retention (PR). Fish fed high-chromium diets exhibited lower whole-body crude lipid contents than fish fed low-chromium diets. Liver glycogen concentrations for fish fed the diet with 0.2 mg Cr kg⁻¹ was the highest (77.67 mg g⁻¹). Fish fed the diet supplemented with 1.6 and 3.2 mg Cr kg⁻¹ had significantly lower liver glycogen concentrations than other groups (P < 0.05). The highest serum insulin concentrations were observed in fish fed the diet supplemented with 0.8 mg Cr kg⁻¹, but serum insulin concentrations decreased (P < 0.05) when dietary supplementation of chromium was higher than 0.8 mg Cr kg⁻¹. Cholesterol concentrations decreased in direct proportion to dietary chromium level and achieved the lowest level when the fish were fed the 0.8 mg Cr kg⁻¹ diet, but increased when the fish were fed the diet with more than 0.8 mg Cr kg⁻¹ (P < 0.05). Fish fed the diet supplemented with 0.8 mg Cr kg⁻¹ had higher triglyceride and high-density lipoprotein cholesterol (HDL-C) concentrations compared to other treatments. The results of the present study suggested that chromium picolinate could modify serum carbohydrate and lipid metabolism profile, and that the optimal dietary chromium level was 0.8 mg kg⁻¹ for grass carp according to growth.     

Serum biochemical characteristics of Beluga, Huso huso (L.), in response to blood sampling after clove powder solution exposure

In order to investigate the effect of anesthesia on serum parameters, Beluga, Huso huso (L.) were blood-sampled immediately without anesthesia (control) or subjected to following anesthesia procedure: 40, 120, and 240 s exposure to 3,000, 700, and 500 mg l⁻¹ clove solution, respectively. Blood samples were collected after these periods, when fish were immobile and reached stage 4 anesthesia. Results showed that cortisol and glucose levels were significantly high in 700 and 500 but not 3,000 mg l⁻¹ group compared to control. Serum lactate levels were significantly high in 500 mg l⁻¹ group compared to control group. Lactate levels were not significantly differed between control, 3,000, and 700 mg l⁻¹ groups. There were no significant differences in serum levels of cholesterol, total protein, lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, Na⁺, Cl⁻, K⁺, and Ca²⁺. Results suggest that rapid anesthesia with higher dose is better than slow anesthesia with lower dose for blood sampling in Beluga.     

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.     

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.     

Effect of high phosphate fertilization rate on pond phosphate concentrations,chlorophyll <Emphasis Type="Italic">a</Emphasis>, and fish growth in carp polyculture

The effect of different application rates of triple superphosphate (22.4, 44.8, and 67.2 kg P₂O₅ ha⁻¹) was observed on total and available phosphorus concentrations in pond soil, total and filterable orthophosphate concentrations in pond water, chlorophyll a, and fish growth in a carp polyculture system during summer (22–32°C) months to determine the economical dose of P₂O₅. pH, hardness, calcium and alkalinity of soil and water did not differ significantly among treatments (P > 0.05) and were within the desired ranges. Average total phosphorus concentrations in pond soil were not significantly different between treatments but available phosphorus (P > 0.05) in pond soil, total phosphorus (P > 0.001), and filterable orthophosphate (P > 0.0001) concentrations in pond water, chlorophyll a (P > 0.0001), and net fish production (P > 0.01) were significantly higher in fertilized ponds than in controls. Overall, fish yield did not significantly differ among treatments, suggesting that a very high dose of P₂O₅ may not be necessary for high yields. Reducing the dose of P₂O₅ could reduce cost without reducing fish production.     

Molecular cloning of cDNA of mammalian and chicken II gonadotropin-releasing hormones (mGnRHs and cGnRH-II) in the beluga (<Emphasis Type="Italic">Huso huso</Emphasis>) and the disruptive effect of methylmercury on gene expression

Two gonadotropin-releasing hormone (GnRH) isoforms were identified in the beluga (Huso huso) brain by cDNA sequencing: prepro-mammalian GnRH (mGnRH) and prepro-chicken GnRH-II (cGnRH-II). The nucleotide sequences of the beluga mGnRH and cGnRH-II precursors are 273 and 258 base pairs (bp) long, encoding peptides of 91 and 86 amino acids, respectively. To investigate the effect of methylmercury (MeHg) on GnRH gene expression, animals were fed with four diets containing increasing levels of MeHg (0 mg kg⁻¹ [control]; 0.76 mg kg⁻¹ [low]; 7.8 mg kg⁻¹ [medium]; 16.22 mg kg⁻¹ [high]) for 32 days. The effects of MeHg on brain GnRH mRNA levels were evaluated by real-time PCR. A significant decrease in brain mGnRH and cGnRH-II mRNA levels were detected in fish receiving high dietary MeHg dose compared to controls on day 11 (P < 0.05). On day 18 and 32, all treatment groups had significantly lower brain mGnRH and cGnRH-II mRNA levels compared to the control group (P < 0.05). These findings demonstrate a disruptive role of MeHg on the level of brain mGnRH and cGnRH-II mRNAs in immature beluga.     

Dietary microbial levan ameliorates stress and augments immunity in Cyprinus carpio fry (Linnaeus, 1758) exposed to sublethal toxicity of fipronil

A 45‐day feeding trial was conducted to study the stress ameliorating and immunomodulatory role of microbial levan in Cyprinus carpio fry exposed to sublethal dose (1/10th LC₅₀) of fipronil [(±)‐5‐amino‐1‐(2,6‐dichloro‐α,α,α‐trifluoro‐p‐tolyl)‐4‐trifluoromethylsulfinylpyrazole‐3‐carbonitrile]. Two hundred and twenty‐five fry were randomly distributed in five treatments in triplicates. Four purified diets were prepared with graded levels of microbial levan. Five different treatment groups were levan control L₀P₀ (basalfeed + 0% levan without exposure to pesticide); pesticide control L₀P₁ (basalfeed + 0% levan with exposure to pesticide); L_0.25P₁ (basalfeed + 0.25% levan with exposure to pesticide); L_0.50P₁ (basalfeed + 0.50% levan with exposure to pesticide) and L_0.75P₁ (basalfeed + 0.75% levan with exposure to pesticide). Lactate dehydrogenase (LDH), malate dehydrogenase (MDH) and fructose‐1,6‐diphosphatase (FDPase) activites were significantly (P < 0.05) increased, whereas alkaline phosphatase (ALP), adenosine triphosphatase (ATPase) and acetyl choline esterase (AchE) activities were significantly (P < 0.05) reduced in higher levan‐fed groups. RBC, haemoglobin and WBC counts were significantly (P < 0.05) increased in the levan‐fed groups. Similar trends were also observed for the total serum protein, globulin, NBT and lysozyme activities. Blood glucose and serum cortisol exhibited a third order polynomial relationship with increasing level of dietary levan. Overall result showed stress ameliorating, immunostimulating and protective role of microbial levan against fipronil‐induced stress in C. carpio fry at 0.75% level of dietary levan supplementation.     

Diets with different n − 6/n − 3 fatty acid ratio in diets for juvenile Atlantic salmon, effects on growth, body composition, bone development and eicosanoid production

Vegetable oils, typically high in n − 6 fatty acids, are necessary alternatives in fish feed production. Such oils have been tested in salmonid diets with good growth results, but with major changes in lipid composition. The aim of this study was to provide information regarding the effect of the higher dietary n − 6/n − 3 fatty acid ratio caused by vegetable oil on growth, chemical composition and bone development, on eicosanoid production and on formation and mineralization of bone.A feeding experiment was carried out in juvenile Atlantic salmon (Salmo salar). Groups of fish (1.28 g) were fed diets added fish oil (FO) or soybean oil (SO) as the main lipid source through the 174 days long experimental period with sampling points at days 0, 31, 53, 96, 136 and 174 up to smoltification. Subsequently, fish performance was observed after 2, 8 and 18 months in sea water.Weight was significantly higher in the fish oil group (95.4 g) than in the soybean oil group (87.4 g) after the 174 days experimental period. This difference developed during short day treatment prior to smoltification, and the fish oil group had a significantly higher growth rate (TGC) during this period (1.62 vs 1.45). Whole body mineral analysis displayed low levels of Ca (2400 and 3500 mg kg−1) and P (3200 and 3900 mg kg−1) in all samples. The corresponding Ca:P ratio ranged from 0.74 to 0.91. On day 136 the level of Ca, and Ca/P ratio, were significantly higher in the fish oil group than in the soybean oil group. There was a significant increase in n − 6 fatty acids and decrease in n − 3 fatty acids in the soybean oil group compared to the fish oil group for both TAG and PL in vertebrae. Individual variation was large in plasma prostaglandin E₂ (PGE₂), and at day 174 the trend was towards a higher level in the soybean oil group. Radiography analyses demonstrated a distinctive pattern of development of spinal pathology with time and fish size, similar in both groups. Hyper dense vertebrae dominated at earlier stages, fusion-type malformations dominated at harvest size. The histological examination of the vertebrae revealed no differences between treatments.The results suggest that vegetable oil as a replacement for fish oil influence the arachidonic acid level in phospholipids of vertebrae, may slightly increase production of PGE₂ in blood, and reduce vertebrae mineralization around the sensitive smoltification phase. These trends did not lead to any detectable skeletal malformations. Differences in growth and vertebrae mineralization observed around smoltification disappeared during the seawater phase.     

Use of acceleration loggers in aquaculture to determine net-cage use and field metabolic rates in red sea bream <Emphasis Type="Italic">Pagrus major</Emphasis>

We investigated the usefulness of acceleration loggers in aquaculture by examining net-cage use and metabolic rates in red sea bream, Pagrus major. First, the fish’s metabolic rate (mg O₂ kg⁻¹ min⁻¹) was measured with the logger in a swim tunnel at designated water velocities. We found that metabolic rate could be expressed by using a linear regression model of the activity rate index (unitless min⁻¹) derived from acceleration data. Using this equation, the field metabolic rates of three fish in a net cage were monitored and were estimated at 14.1–15.0 kcal kg⁻¹ day⁻¹. The results suggested that 15–19% of energy from satiation feeding ration was consumed for metabolism and activity in the net cage. The loggers showed orderly net-cage use by the fish. Tagged individuals used the whole cage from surface to bottom, but individual fish that preferred the surface area rarely used the bottom, and vice versa. Metabolic rate increased significantly with distance of the fish from their preferred depths. The logger provided information on the physiological and behavioral responses of fish in a given breeding system, and its use should contribute to the design of practical aquaculture systems.     

Effects of dietary nucleotides supplementation on rainbow trout (Oncorhynchus mykiss) performance and acute stress response

This experiment was conducted to examine the effect of dietary nucleotides (NT) on fish performance and acute stress response on fingerling rainbow trout (23 g ± 0.01, mean weight ± SEM). Five experimental diets according to different levels of supplemented nucleotides (0, 0.05, 0.1, 0.15, and 0.2%) were assayed on experimental fish for 8 weeks. Growth, hematological parameters (hematocrit, hemoglobin, erythrocyte, lymphocyte, and neutrophil count), serum proteins (globulin, albumin), and plasma enzymatic activity (alkaline phosphatase, ALP; aspartate transaminase, AST; lactate dehydrogenase, LDH; alanine transaminase, ALT) were assayed. At the end of feeding trial, fish fed the control and 0.2% diets were subjected to handling and crowding stress. Modulatory effects of nucleotides on acute stress response (cortisol and glucose) and plasma electrolytes (Na⁺, Cl⁻, K⁺, and Ca²⁺) were studied. The percentage of body weight gain (WG) and feed efficiency (FE) of fish were better when the fish were fed 0.15–0.2% diets. Fish fed the nucleotide-supplemented diets tended to have lower levels of serum enzymes including ALP, AST, LDH, and ALT. Plasma cortisol levels of fish fed on 0.2% diet under handling and crowding stress were significantly lower than fish fed the control diet at all post-stress time intervals. In our study, fish fed nucleotide-supplemented diet had significantly lower concentrations of glucose compared to those fed the basal diet. The concentrations of sodium, chloride, calcium, and potassium of fish fed the control diet were significantly lower than in fish fed nucleotide-supplemented diet. Dietary nucleotides administration seems to promote growth and to enhance resistance against handling and crowding stress in fingerling rainbow trout.     

Pharmacokinetic model of florfenicol in turbot (Scophthalmus maximus): establishment of optimal dosage and administration in medicated feed

The pharmacokinetics of florfenicol (FF) in turbot (Scophthalmus maximus) was studied after single intravenous (10 mg kg⁻¹) and oral (100 mg kg⁻¹) administration. The plasma concentration–time data of florfenicol were described by an open one‐compartment model. The elimination half‐life (t_1/2) was estimated to be 21.0 h, and the total body clearance, Cl, was determined as 0.028 L kg h⁻¹. The apparent volume distribution (V_d) was calculated to be 0.86 L kg⁻¹ and the mean residence time (MRT_iv) was 30.2 h. Following oral administration, the maximum plasma concentration (C_max) of 55.4 μg mL⁻¹ was reached at 12 h (T_max). The absorption constant (k_a) was 0.158 h⁻¹. The bioavailability was estimated to be 57.1%. The low bioavailability observed at higher doses was explained by the saturation of the mechanisms of absorption. The drug absorption process was limited by its inherent low solubility, which limited the amount of available FF absorbed in the gastrointestinal tract. Based on the pharmacokinetic data, an optimal dosing schedule for FF administration is hereby provided. Based on the minimum inhibitory concentration found for susceptible strains of Aeromonas salmonicida, oral FF administration of first, an initial dose of 30 mg FF kg⁻¹, followed by 6 maintenance doses at 18 mg kg⁻¹/daily could be effective against furunculosis in turbot.     

Fluctuating salinity effect on Sphoeroides annulatus (Jenyns 1842) physiological responses

Euryhaline fish, such as the Bullseye puffer Sphoeroides annulatus (Jenyns 1842), experience sudden salinity changes in their natural environment, which is more common than the exception, so they must adapt to survive and cope with extreme salt conditions. Therefore, Bullseye puffer juveniles were exposed to short‐term stress (39 hr) by fluctuating salinity conditions (41, 35, 29, 23, 17, 11, 5, 11, 17, 23, 29, 35, 41 psu) with a 3‐hr interval between each point at 26 ± 1ºC in a respirometer chamber and acclimation reservoirs. Responses to oxygen consumption rate (OCR: 23–35 mg O₂ h^–1 kg^–1), ammonium excretion rate (AER: 1–1.85 mg NH4⁺ h^?1 kg^?1), oxygen‐nitrogen atomic ratio (O:N 17–30), osmoregulatory pattern (blood osmotic pressure from 342.4 to 332.8 mmol/kg) and changes in expression levels of Na⁺/K⁺‐ATPase in the gills (higher values at higher salinities) were measured. Although some signs of stress were detected below the iso‐osmotic point (11.4 psu), the puffer fish is a strong euryhaline fish that survives under these conditions. Nonetheless, it could recover when salinity returned to the initial acclimation point because Sphoeroides annulatus is able to live in a wide range of environments with wide natural salinity fluctuations; thus, a common practice in aquaculture has been to expose fish to low salinity for several reasons discussed in this study. This capacity reveals its high plasticity to saline adaptation from 41 to 5 psu an up from 5 to 41 psu, all in less than 2 days.     

Effect of the interaction between body weight and temperature on growth and maximum daily food intake in sharpsnout sea bream (<Emphasis Type="Italic">Diplodus puntazzo</Emphasis>)

In experimental culture conditions in tanks, the effect of weight (W: 11–452 g) and temperature (T: 14–29°C) on the growth rate (SGR, % bw day⁻¹) and maximum daily food intake (SFR, % bw day⁻¹) in sharpsnout sea bream (Diplodus puntazzo) was studied. The possible combined effect of both independent variables (W and T) was also analyzed by multiple regression analysis, fitting the data to the equation Ln Y = Ln a + b Ln W + cT + dT ² + eT Ln W. Both SGR and SFR, and therefore feed efficiency (FE = SGR/SFR), were significantly influenced by the interaction between temperature and weight and may be expressed by means of the following equations: Ln SGR = −6.1705 + 0.5809T − 0.0087T ² − 0.0249T Ln W ( R_\textadj² R_{\text{adj}}^{2}  = 0.949; ANOVA P < 0.0001); Ln SFR = −4.8257 + 0.4425T − 0.0063T ² − 0.0163T Ln W ( R_\textadj² R_{\text{adj}}^{2}  = 0.964; ANOVA P < 0.0001).The results suggest that the optimum temperature for SGR and FE (T _SGRopt and T _FEopt), and the temperature at which the maximum SFR (T _SFRmax) is reached, decreases with body weight, in accordance with the equations: T _SGRopt = 33.297 − 1.435 Ln W; T _FEopt = 29.332 − 1.890 Ln W; and T _SFRmax = 34.941 − 1.304 Ln W, respectively. In this way, T _SGRopt is 28.4, 26.7, and 24.7°C; T _SFRmax is 30.5, 28.9, and 27.1°C and T _FEopt is 22.9, 20.6, and 18°C for 30, 100 and 400 g body weight, respectively.     

Purified deoxynivalenol or feed restriction reduces mortality in rainbow trout,Oncorhynchus mykiss (Walbaum), with experimental bacterial coldwater disease but biologically relevant concentrations of deoxynivalenol do not impair the growth of Flavobacterium psychrophilum

Diets containing deoxynivalenol (DON) were fed to rainbow trout Oncorhynchus mykiss (Walbaum) for 4 weeks followed by experimental infection (intraperitoneal) with Flavobacterium psychrophilum (4.1 × 10⁶ colony‐forming units [CFU] mL⁻¹). Mortality of rainbow trout fed either 6.4 mg kg⁻¹ DON or trout pair‐fed the control diet was significantly reduced (P < 0.05) in comparison with trout fed the control diet to apparent satiation (<0.1 mg kg⁻¹ DON). In a second experiment, trout were fed one of three experimental diets; a control diet, a diet produced with corn naturally contaminated with DON (3.3 mg kg⁻¹ DON) or a diet containing purified DON (3.8 mg kg⁻¹); however, these fish were not experimentally infected. The presence of DON resulted in significant reduction (P < 0.0001) in feed intake as well as weight gain after 4 weeks. Respiratory burst of head‐kidney leucocytes isolated from rainbow trout fed diets containing purified DON (3.8 mg kg⁻¹) was significantly higher (P < 0.05) at 35 day post‐exposure compared with controls. The antimicrobial activity of DON was examined by subjecting F. psychrophilum in vitro to serial dilutions of the chemical. Complete inhibition occurred at a concentration of 75 mg L⁻¹ DON, but no effect was observed below this concentration (0–30 mg L⁻¹).     

Effect of starving and feeding on some haematological and physiological responses of the Nile catfish, <Emphasis Type="Italic">Clarias gariepinus</Emphasis> exposed to copper at extreme seasons

The lethal concentration for 50% of fish for 96h (96h LC₅₀) of copper (Cu²⁺) was estimated for the Nile catfish (Clarias gariepinus) in extreme seasons, winter and summer, 4.31 and 4.79 mg/l, respectively. The Nile catfish was exposed to 96h LC₅₀ of copper for 7 days in extreme winter and summer. The body indices, haematological parameters as well as some plasma and liver enzyme activities and metabolite level were significantly differed in fish exposed to copper over than those of the control fish. Most of the tested parameters were not significantly different between the control fish of winter and summer (winter, water temperature 18 ± 2°C and summer, 27 ± 2°C). The effect of two ration sizes on copper toxicity in two different seasons on C. gariepinus was justified. It was found that the haematological parameters and the tested plasma activities of enzymes were significantly valid due to season differences. The blood parameters as well as plasma activities of enzymes were significantly differed in fishes fed elevated ration (3%) and exposed to copper challenge. On the other hand, the exploit of low feeding ration (0.5%) along with copper exposure during the examined seasons induced non-significant differences of the tested parameters, from those of the corresponding control. Therefore, the low feeding ration provides some tolerance against the possible water-borne copper exposure.     

Effect of temperature on excess post-exercise oxygen consumption in juvenile southern catfish (<Emphasis Type="Italic">Silurus meridionalis</Emphasis> Chen) following exhaustive exercise

The effects of temperature on resting oxygen consumption rate (MO_2rest) and excess post-exercise oxygen consumption (EPOC) after exhaustive exercise (chasing) were measured in juvenile southern catfish (Silurus meridionalis) (8.40 ± 0.30 g, n = 40) to test whether temperature has a significant influence on MO_2rest, maximum post-exercise oxygen consumption rate (MO_2peak) and EPOC and to investigate how metabolic scope (MS: MO_2peak − MO_2rest) varies with acclimation temperature. The MO_2rest increased from 64.7 (10°C) to 160.3 mg O₂ h⁻¹ kg⁻¹ (25°C) (P < 0.05) and reached a plateau between 25 and 30°C. The post-exercise MO₂ in all temperature groups increased immediately to the peak values and then decreased slowly to a steady state that was higher than the pre-exercise MO₂. The MO_2peak did not significantly differ among the 20, 25 and 30°C groups, though these values were much higher than those of the lower temperature groups (10 and 15°C) (P < 0.05). The duration of EPOC varied from 32.9 min at 10°C to 345 min at 20°C, depending on the acclimation temperatures. The MS values of the lower temperature groups (10 and 15°C) were significantly smaller than those of the higher temperature groups (20, 25 and 30°C) (P < 0.05). The magnitude of EPOC varied ninefold among all of the temperature groups and was the largest for the 20°C temperature group (about 422.4 mg O₂ kg⁻¹). These results suggested that (1) the acclimation temperature had a significant effect on maintenance metabolism (as indicated by MO_2rest) and the post-exercise metabolic recovery process (as indicated by MO_2peak, duration and magnitude of EPOC), and (2) the change of the MS as a function of acclimation temperature in juvenile southern catfish might be related to their high degree of physiological flexibility, which allows them to adapt to changes in environmental conditions in their habitat in the Yangtze River and the Jialing River.