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.     

Enrofloxacin pharmacokinetics in Takifugu flavidus after oral administration at three salinity levels

The present study was designed to explore the pharmacokinetics of enrofloxacin in Takifugu flavidus at different salinity levels (10‰, 20‰ and 30‰). The concentrations of enrofloxacin in plasma and tissues (kidney, liver and muscle) of T. flavidus after a single oral dose of 10 mg kg^?1 were simultaneously determined using HPLC. The parameters of pharmacokinetics were calculated using non‐compartmental model based on statistic moment theory. The peak concentrations of enrofloxacin were higher and T_max values in plasma, liver and muscle tissues of T. flavidus were lower at the salinity of 20‰ and 30‰ than that of 10‰, except the kidney tissue. These demonstrated the absorption of enrofloxacin was more quickly and more quantity at the high salinity. The elimination half‐life (t_1/2z) of enrofloxacin in the plasma (45.22, 69.91 and 95.45 h) was increasing with the increase in salinity. And the t_1/2z values of enrofloxacin in liver (76.44, 44.21 and 33.48 h) and kidney (212.16, 157.43 and 35.61 h) both decline with the increase in salinity, indicating the elimination of enrofloxacin was faster in liver and kidney but slower in plasma at the high salinity. The content of enrofloxacin in liver was increasing with the increase in salinity, suggesting that salinity affects tissue distribution and metabolism in T. flavidus. In addition, the AUC_0–∞ data of enrofloxacin (kidney > plasma > liver > muscle) at different salinity levels were essentially consistent, and AUC_0–∞ data of kidney were declined with the increase in salinity, supporting that the kidney was the main organ and the role of extent of kidney on excretion was different in different salinity levels.     

Pharmacokinetics and physio‐metabolic response of single and multiple dose of fenbendazole in Labeo rohita (Hamilton, 1822) fingerlings

An experiment was carried to determine the plasma fenbendazole (FBZ) concentration and physio‐metabolic responses in juveniles of Labeo rohita (90 ± 4 g) after oral administration of single doses at 10, 20 and 50 mg, 20 mg FBZ/kg b.wt. in multiple times on 1st, 3rd and 7th day. The blood samples were collected at 0.5, 1, 2, 4, 8, 12, 24, 30, 48, 72, 96 and 120 hr, after single‐dose administration, and regularly (upto 15 day) in multiple dose. Plasma FBZ concentration was determined up to the limit of detection (LoD) of 0.09 µg/ml by HPLC. There was no parent drug detected in plasma for administration of 10 mg FBZ/kg b.wt. The drug attained the peak concentration (C_max) 1.85 and 3.09 µg/ml in plasma at 4 hr (T_max) after administration of 20 and 50mg FBZ/kg b.wt. respectively. Plasma FBZ was detectable up to 96 and 120 hr with concentration 0.09 ± 0.007 and 0.098 ± 0.006 µg/ml, respectively, after single‐dose administration of 20 and 50mg/kg b.wt. In case of multiple‐dose administration, the maximum concentration of FBZ was 1.01 ± 0.03 µg/ml on 7th day that was less than to the single dose at 50 mg/kg b.wt. However, FBZ was detected up to 11 day after multiple doses. The study revealed that the hepatic antioxidant enzymes activities like superoxide dismutase, catalase and glutathione‐S‐transferase were significantly affected by increasing FBZ in single and multiple doses. The results of the present study could reveal that single‐ or multiple‐oral administration of FBZ at 20 mg/kg b.wt. in feed as antihelminthic drug in L. rohita could be considered as the safe dose.     

Effects of dissolved oxygen and dietary lysine levels on growth performance,feed conversion ratio and body composition of grass carp,Ctenopharyngodon idella

In order to investigate the effects of lysine and dissolved oxygen on grass carp, the grass carp were fed with 13, 15 and 17 g kg ⁻¹ lysine diet at about 6 mg L⁻¹ (high dissolved oxygen, HO group) or 3.5 mg L⁻¹ (low dissolved oxygen, LO group) dissolved oxygen level, for 8 weeks. The fish were fed to apparent satiation by hand. The results showed that apparent digestibility of protein, energy and dry matter were decreased significantly when grass carp were fed at 3.5 mg L⁻¹ dissolved oxygen, and feed intake (FI) was also inhibited by low dissolved oxygen (P < 0.05). Weight gain, protein retention, protein efficiency, feed conversion ratio and amino acid retention of fish at 6 mg L⁻¹ dissolved oxygen level were significantly improved at 3.5 mg L⁻¹ dissolved oxygen level (P < 0.05). Weight gain, protein and amino acid retention, and feed efficiency of grass carp at the two dissolved oxygen levels were significantly improved by lysine supplementation (P < 0.05). The dietary lysine level and dissolved oxygen of water had an interaction effect on feed conversion ratios (P < 0.05). Grass carp fed at low dissolved oxygen level showed lower liver protein and fat contents. Plasma aspartate aminotransferase (AST) activity of grass carp fed at 3.5 mg L⁻¹ dissolved oxygen level was significantly increased compared to 6 mg L⁻¹ dissolved oxygen level (P < 0.05). Our results show that low dissolved oxygen level of water is harmful to the liver of grass carp.     

Effect of lactic acid on enrofloxacin pharmacokinetics in Eriocheir sinensis (Chinese mitten crab)

As a representative acidifier, lactic acid (LA) is widely used in the diets of aquatic animals. LA is the main supporter of energy metabolism and may be associated with drug metabolism. This study was designed to explore the pharmacokinetics of enrofloxacin (ENR) in Eriocheir sinensis (Chinese mitten crab) fed diets containing 0.1%, 0.2% and 0.3% LA (designated groups LA1, LA2 and LA3 respectively). The concentrations of ENR in the haemolymph, hepatopancreas and muscle were determined by HPLC after a single oral dose of 10 mg/kg. Our results showed that LA had a significant effect on the peak ENR concentrations in all the tissues (p < 0.05) by one‐way ANOVA analysis. There was a trend that C_max (peak concentration) of ENR was elevated with LA levels increasing up to 0.3% in haemolymph, hepatopancreas, muscle and T_max (time‐point of the peak concentration of the drug), t_1/2β (elimination half‐life) and AUC_(0‐∞) of ENR were shortened. Taken together, 0.3% LA might be effective in improving ENR pharmacokinetics in E. sinensis. Furthermore, it can be speculated that the enhanced biotransformation of ENR in the hepatopancreas mediated by LA is responsible for the differences in the pharmacokinetics of ENR in E. sinensis.     

Pharmacokinetics and tissue residues of vancomycin after oral administration in crucian carp

The pharmacokinetics and tissue residues of vancomycin in crucian carp (Carassius auratus) were studied after oral administration of a single dosage of 1 mg/kg body weight at water temperature of 18°C. The drug concentration‐time data were fitted using a two‐compartment open model with first‐order absorption. The vancomycin concentrations in plasma and tissues including muscle, liver and kidney were analyzed by means of liquid chromatography‐tandem mass spectrometry. As a result, the plasma absorption rate constant of vancomycin was 3.75/hr and the time point of maximum concentration in plasma was 3.0 hr respectively. The maximum concentration of vancomycin in plasma was 216.58 μg/L. The distribution half‐life and the elimination half‐life in plasma were 6.69 hr and 190 hr, as well as the absorption half‐life of plasma was 0.19/hr. The area under the plasma concentration‐time curve of plasma was 15.12 mg hr/L. The apparent volume of distribution of plasma was estimated to be 4.45 L/kg and the total body clearance was computed as 0.061 L hr^?1 kg^?1. In addition, the maximum tissue concentrations of vancomycin were in the order of liver > kidney > muscle. To guarantee the safety of tissue samples for consumption, it was suggested that the withdrawal time should not be less than 30 days at 18°C. All these results may provide guidance for future vancomycin treatment in aquaculture.     

Red blood cell indices of rainbow trout Oncorhynchus mykiss (Walbaum) in aquaculture

A direct non‐parametric method was used to calculate reference (physiological) haematology values for farmed 10–12‐month rainbow trout of the Kamloops strain (mean weight: 330±131 g) with respect to red blood cell counts (RBCc), haematocrit values (Hct), haemoglobin concentrations (Hb), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentrations (MCHC). The fish in the selected reference group (n=798) were given dry pelleted diets that contained 37–47% crude protein, 7–18% crude fat and 108–300‐mg vitamin E, 1.08–5‐mg folic acid, 0.018–0.05‐mg vitamin B₁₂, 48–64.5‐mg iron, 4.5–8.4‐mg copper and 0.18–0.24‐mg selenium supplied per kg of diet. Ethoxyquin and butylhydroxytoluol were used to protect the fat component against oxidation. The fish were kept at a stocking density of 50kg per cubic metre in tanks provided with running freshwater (dissolved oxygen 8.4–11.5 mg L^?1, with O₂ saturation of 77–98%) at an ambient temperature of 0.2–16°C. Blood was sampled between September and November at a photoperiod of 9–13 h:11–15 h (light:dark). Reference ranges for the preceding haematological indices were as follows in immature females (males): RBCc, 0.77–1.42T L^?1 (T – tera, 10¹²) (0.98–1.55T L^?1); Hct, 0.304–0.502 (0.34–0.546); Hb, 54–93 g L^?1 (59–97 g L^?1); MCV, 282–469 fL (279–434 fL); MCH, 51–86 pg (47–78 pg); MCHC, 0.15–0.22 (0.15–0.2). In males, values for RBCc, Hct and Hb were significantly higher (P=0.01 and 0.0000 respectively) and those for MCV, MCH and MCHC were significantly lower (P=0.01 and 0.0002 respectively) than in immature females. Nutritional and environmental factors affecting erythropoiesis in trout and some correlations between haematological (RBCc, Hb, Hct) and biochemical indices of the blood plasma (total protein, cholesterol) are discussed.     

Chlorogenic acid attenuates inflammation,oxidative stress,apoptosis and protects head kidney macrophage of yellow catfish from ammonia toxicity

Ammonia is the most common contaminants found in aquaculture water that seriously endangers fish health. However, there are few studies on the strategy and mechanism on alleviating ammonia toxicity in fish. The current study aimed to observe the cytotoxic effects of ammonia and the protective effects of chlorogenic acid (CGA) on head kidney macrophage of yellow catfish from the perspective of inflammation, oxidative stress and apoptosis. The cells were randomized into normal control, ammonia group (0.23 mg L^?1), CGA group (125 µmol L^?1), CGA (5, 25, 125 µmol L^?1) + ammonia (0.23 mg L^?1) groups. Cells were pretreated with CGA for 1 h followed by ammonia for 24 h. Findings suggested that ammonia treatment reduced cell viability, increased ROS production, up-regulated antioxidant (SOD, GPx) and pro-inflammatory (TNF-α, IL-1, IL-6, COX-2, NF-κB p65) genes expression, down-regulated the mRNA levels of M2-type macrophage marker (Arg-1) and anti-apoptosis (Bcl-2), and CGA attenuated the toxic effects of ammonia. The findings may provide insight into the underlying mechanisms of ammonia toxicity and suggest that CGA can be used as a potential natural supplement to alleviate ammonia toxicity in fish.     

Effect of acute and chronic toxicity of paraquat on immune system and growth performance in rainbow trout,Oncorhynchus mykiss

In this study, the impact of paraquat (1, 1‐dimethyl 4, 4‐bipyridiniumdicholoride) on rainbow trout immune system and growth parameters was evaluated. In acute exposure, fish were distributed into four groups and exposed to 0, 54, 90 and 150 mg L^?1 of paraquat for 96 h. In chronic trial, fish were allocated into six groups and exposed to 0, 1.25, 2.5, 5, 10 and 20 mg L^?1 of paraquat for 30 days. Growth performance (percentage weight gain, condition factor and specific growth rate) and innate immune parameters (lysozyme, haemolytic complement activity and total immunoglobulin) were evaluated. Experimental data showed a LD₅₀ about 48.2 mg of paraquat per litre. Immunotoxic proprieties of paraquat especially in higher doses were shown in both trials. Total weight was also significantly decreased in chronic exposure when fish was subjected to 10 and 20 mg L^?1 paraquat whereas other growth parameters were not affected in this experiment. In general, these results suggest that paraquat exposure in rainbow trout could suppress the immunological and growth parameters.     

Nutrient removal efficiency of Hydropuntia cornea in an integrated closed recirculation system with pink shrimp Farfantepenaeus brasiliensis

In this study, we have tested the effect of seaweed stocking density in an experimental seaweed biofilter using the economically important red seaweed Hydropuntia cornea integrated with the cultivation of the pink shrimp Farfantepenaeus brasiliensis. Nutrient removal efficiency was evaluated in relation to seaweed stocking density (2.5, 4, 6 and 8 g fw L^?1). Total ammonia nitrogen (TAN) was the main nitrogen source excreted by F. brasiliensis, with concentrations ranging from 41.6 to 65 μM of NH₄⁺‐N. H. cornea specific growth rates ranged from 0.8 ± 0.2 to 1.4 ± 0.5% day^?1 with lowest growth rates at higher seaweed stocking density (8 g fw L^?1). Nutrient removal was positively correlated with the cultivation densities in the system. TAN removal efficiency increased from 61 to 88.5% with increasing seaweed stocking density. Changes in the chemical composition of the seaweed were analysed and correlated with nutrient enrichment from shrimp effluent. The red seaweed H. cornea can be cultured and used to remove nutrients from shrimp effluents in an integrated multi‐trophic aquaculture system applied to a closed recirculation system. Recirculation through seaweed biofilters in land‐based intensive aquaculture farms can also be a tool to increase recirculation practices and establish full recirculation aquaculture systems (RAS) with all their known associated benefits.     

Characterization of a novel marine origin aerobic nitrifying–denitrifying bacterium isolated from shrimp culture ponds

A novel marine origin Bacillus subtilis strain H1 isolated from a shrimp culture pond effectively removed NH₄⁺‐N, ‐N and ‐N, with a maximum ammonium, nitrite and nitrate removal rate of 2.35 mg NH₄⁺‐N L^?1 hr^?1 per OD, 9.64 mg ‐N L^?1 hr^?1 per OD and 0.75 mg ‐N L^?1 hr^?1 respectively. The gas chromatography–isotope ratio mass spectrometry results indicated that N₂O was emitted when ¹⁵NH₄Cl, Na¹⁵NO₂ or Na¹⁵NO₃ was used. Additionally, N₂ was also produced when Na¹⁵NO₂ was used. Single‐factor experiments suggested that the optimal conditions for NH₄⁺‐N and ‐N removal were glucose as a carbon source, C/N 15, initial pH 7.5, 30 g/L NaCl, 28°C and a shaking speed of 160 rpm. Orthogonal tests showed that the optimal conditions for NH₄⁺‐N removal were C/N 15, pH 9, 10 g/L NaCl and shaking speed 160 rpm when ammonium chloride was used as the substrate. The optimal conditions for ‐N removal were C/N 10, pH 6, 10 g/L NaCl and a shaking speed of 160 rpm when sodium nitrite was used as the substrate. In summary, B. subtilis strain H1 had highly efficient aerobic nitrifying–denitrifying ability and high adaptability, suggesting that it is potentially valuable to marine aquaculture.     

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.     

Algal density alleviates the elevated CO2‐caused reduction on growth of Porphyra haitanensis (Bangiales,Rhodophyta), a species farmed in China

Growing of Pyropia haitanensis, a commercially farmed macroalga, usually increases their densities greatly during cultivation in natural habitats. To explore how the increased algal densities affect their photosynthetic responses to rising CO₂, we compared the growth, cell components and photosynthesis of the thalli of P. haitanensis under a matrix of pCO₂ levels (ambient CO₂, 400 ppm; elevated CO₂, 1,000 ppm) and biomass densities [low, 1.0 g fresh weight (FW) L^?1; medium, 2.0 g FW L^?1; high, 4.0 g FW L^?1]. Under ambient CO₂, the relative growth rate (RGR) was 5.87% d^?1, 2.32% d^?1 and 1.51% d^?1 in low, medium and high densities, and elevated CO₂ reduced the RGR by 27%, 25% and 12% respectively. Maximal photochemical quantum yield of photosystem II (F_V/F_M) was higher in low than in high densities, so were the light‐utilized efficiency (α), saturation irradiance (E_K) and maximum relative electron transfer rate (rETR_max). Elevated CO₂ enhanced the F_V/F_M in low density but not in higher densities, as well as the α, E_K and rETR_max. In addition, elevated CO₂ reduced the content of chlorophyll a and enhanced that of carotenoids, but unaffected phycoerythrin, phycocyanin and soluble proteins. Our results indicate that the increased algal densities reduced both the growth and the photosynthesis of P. haitanensis and alleviated the elevated CO₂‐induced negative impact on growth and positive impact on photosynthesis. Moreover, the elevated CO₂‐induced reduction on growth and promotion on photosynthesis indicates that rising CO₂ may enhance the loss of photosynthetic products of P. haitanensis through releasing organic matters.     

Effects of dietary vitamin B1 on growth performance,blood metabolites,body composition,intestinal enzyme activities and morphometric parameters of juvenile yellow catfish (Pelteobagrus fulvidraco)

The effects of vitamin B₁ on growth, blood metabolites, body composition, intestinal enzyme activities and morphometric parameters were evaluated by a 63‐day feeding trial in Pelteobagrus fulvidraco fed diets containing vitamin B₁ with 4.29, 6.02, 7.86, 11.94 and 19.05 mg/kg, respectively. Results showed that 7.86 mg/kg vitamin B₁ resulted in significantly higher weight gain (WG), specific growth rate (SGR) and protein efficiency ratio (PER) (p < .05). Serum triglyceride, cholesterol and whole‐body lipid were observed in 11.94 mg/kg vitamin B₁ group significantly higher than those in 4.29 mg/kg group, accompanied by the lower serum glucose content in the same group (p < .05). Significantly higher values of whole‐body protein, serum total protein, relative intestinal length, fold height, intestinal trypsin, amylase, alkaline phosphatase, Na+/K+‐ATPase, γ‐glutamyl transpeptidase, creatine kinase, muscular layer thickness and intestosomatic index were observed in 7.86 mg/kg vitamin B₁ group compared with those in 4.29 mg/kg group (p < .05). These results suggested that diets supplemented with vitamin B₁ improved growth performance, feed utilization, intestinal digestive and absorption capacity of juvenile yellow catfish. The optimal dietary vitamin B₁ requirements estimated using a two‐slope broken‐line model based on WG and PER of yellow catfish were 7.42 and 6.01 mg/kg, 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).     

Fatty acid,fat‐soluble vitamin and sterol contents in testis and semen,testis‐somatic index and spermatologic values of broodstock rainbow trout (Oncorhynchus mykiss) fed with different levels of omega‐3 fatty acids under regular stripping conditions

In this study, the testis and semen fatty acid, fat‐soluble vitamin and sterol levels, testis‐somatic index and spermatological values were investigated in the broodstock rainbow trout fed with the different levels of omega‐3 polyunsaturated fatty acid (PUFA) under the regular stripping conditions. For this purpose, a control and three test diets were prepared. The control, D1, D2 and D3 diets were contained the omega‐3 PUFA at 3.14%, 7.84%, 13.63% and 20.54% as a percentage of the total fatty acids respectively. The fish in the experimental groups were fed with these diets for 60 days. The testis‐somatic index (3.81–4.50), semen volume (9.30–18.5 ml) and pH (8.05–8.99), initial sperm motility (68.1%–93.7%), duration of 50% sperm motility (141.3–258.9 s), total duration of sperm motility (268.7–489.6 s) and sperm density (9.95–17.5 cells × 10⁹ ml^?1) values of the fish fed the control diet were significantly decrease (p < 0.05) depending on decline of the omega‐3 PUFA, fat‐soluble vitamin and sterol contents in the testis and semen. The omega‐3 PUFA (3.40%–14.76% and 3.96%–16.31%), vitamin A (33.9–61.2 ml/mg and 9.12–26.7 ml/mg), D₂ (0.10–0.19 ml/mg and 0.04–0.10 ml/mg), D₃ (0.75–1.30 ml/mg and 0.06–0.24 ml/mg), alpha‐tocopherol (30.1–60.4 ml/mg and 8.93–25.3 ml/mg), K₁ (0.30–0.94 ml/mg and 0.03–0.08 ml/mg) and K₂ (2.0–3.19 ml/mg and 0.25–0.34 ml/mg) vitamins, cholesterol (1,201–1,588 ml/mg and 330–596 ml/mg), ergosterol (3.12–6.40 ml/mg and 2.10–4.08 ml/mg), stigmasterol (5.57–10.4 ml/mg and 10.2–12.6 ml/mg) and beta‐sitosterol (0.20–0.60 ml/mg and 0.14–0.41 ml/mg) contents in the testis and semen of the fish were significantly affected (p < 0.05) by the dietary omega‐3 PUFA supplementation. The highest values for these parameters were provided from the fish fed the D2 and D3 diets (p > 0.05), followed by the fish fed the D1 diet (p < 0.05). These results showed that the dietary omega‐3 PUFA at 13.63% of the total fatty acids could increase the omega‐3 PUFA, fat‐soluble vitamin and sterol contents in the testis and semen, the testis‐somatic index and spermatologic values of the broodstock rainbow trout under the regular stripping conditions.     

Pharmacokinetics of minocycline in crucian carp (Carassius auratus) after intravenous and oral administration

The pharmacokinetic of minocycline was studied after a single intravenous as well as oral dose (5 mg/kg body weight) in crucian carp (Carassius auratus) reared in freshwater at 10°C. Plasma samples were randomly collected from six fish at each sampling time. Plasma concentrations were determined by high‐performance liquid chromatography and further subjected to noncompartmental analysis. Initial concentration of minocycline just after intravenous administration was calculated as 7.320 μg/ml, while the other parameters after intravenous injection were determined as flows: apparent elimination rate constant (λ_z) of 0.064 per hr, apparent elimination half‐life () of 10.82 hr, total body clearance (Cl) of 142.72 ml/hr/kg, volume of distribution (Vz) of 2,227.38 ml/kg and volume of distribution at steady‐state (Vss) of 1,937.08 ml/kg. While after oral administration, the λ_z, , mean absorption time (MAT), absorption half‐life (t_1/2ka) and bioavailability were determined as 0.059 per hr, 11.74, 5.55, 3.84 hr, and 81.98%, respectively, and the peak concentration was observed as 1.474 ± 0.362 μg/ml at 8 hr. It was shown that minocycline was slowly but relatively completely absorbed, extensively distributed, and slowly eliminated in crucian carp. Based on the ratios of AUC_0–24 hr/MIC90, a minocycline dosage of 5 mg/kg body weight administered intravenously or orally would be only effective to successfully treat crucian carp infected by bacterium with MIC values ≤0.25 μg/ml.     

Immunostimulatory effect of water soluble fraction of Nyctanthes arbortristis leaves on the immune response in Oreochromis mossambicus (Peters)

Use of immunostimulants as a prophylactic measure against diseases in fish is considered as an effective alternative to antibiotic use. Plant‐derived immunostimulants have recently received more attention, as most of them are cost‐effective and eco‐friendly. This study was carried out with the objective of evaluating the possible immunostimulatory activity of intraperitoneally injected water soluble fraction of Nyctanthes arbortristis (an Indian medicinal plant) leaves on (i) specific immunity (antibody response), (ii) nonspecific immunity (Lysozyme activity, ROS production) and (iii) functional immunity in terms of disease resistance against Aeromonas hydrophila in Oreochromis mossambicus. The results of the study showed that all the tested doses (i.e. 3.2, 16, 80 and 400 mg kg^?1) of water soluble fraction of Nyctanthes arbortristis leaves significantly enhanced both primary and secondary antibody responses to heat killed A. hydrophila. Significant enhancement in serum lysozyme activity by all the doses of water soluble fraction was observed on day 10. The lower doses of 3.2 and 16 mg kg^?1 of water soluble fraction alone enhanced intracellular ROS production. Fish treated with both single and double dose of water soluble fraction showed maximum disease resistance. The highest dose (400 mg kg^?1) of water soluble fraction exhibited highest relative per cent survival in both single dose and double dose groups.     

The in vitro efficacy of oxytetracycline against re‐isolated pathogenic Aeromonas hydrophila carrying the cytolytic enterotoxin gene through hybrid catfish,Clarias macrocephalus (Günther, 1864) × Clarias gariepinus (Burchell, 1822) in Thailand

Aeromonas hydrophila is a pathogen infecting farmed hybrid catfish, Clarias macrocephalus (Günther, 1864) × Clarias gariepinus (Burchell, 1822) which incurs substantial economic losses in Thailand. The study aimed at a genetic tracking of A. hydrophila infection and the in vitro assessment of the efficacy of antibiotics against its virulent strains. Five clinical strains from catfishes and Nile tilapia were employed. They were 3‐passage re‐isolated through healthy hybrid catfish and the cytolytic enterotoxin gene (AHCYTOEN) of individuals was traced. Each of the re‐isolates at a dose of ~6.67 × 10⁵ CFU/g was intraperitoneally injected into ~15 g‐healthy hybrid catfish and their pathogenicity were observed for 7 days. It was found that AHCYTOEN was carried over whereas typical signs of motile aeromonas septicaemia were found in the specimens. The bacterial strains of Nile tilapia origin did not induce mortality but those of catfish origins (80%–100% rate of mortality). The strains were susceptible to the tetracycline antibiotics, and oxytetracycline produced MIC₅₀ and MBC as low as 0.007–0.031 μg/ml and 1–8 μg/ml respectively. As oxytetracycline specifically inhibited pathogenic A. hydrophila in vitro, it is recommended that an appropriate dosage regimen of the drug should be established.     

Dietary copper requirement of fingerling Heteropneustes fossilis for formulating copper‐balanced commercial feeds

Dietary copper requirement of Heteropneustes fossilis (6.74 ± 0.03 g) was determined by feeding purified diets containing same protein (400 g/kg) and gross energy (17.89 kJ/g) but different levels of copper for 12 weeks. Graded amount of CuSO₄.5H₂O (0, 1.96, 3.93, 5.89, 7.86, 9.82, 11.79 mg/kg) was supplemented to basal diet to attain desired dietary copper levels (0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mg/kg). Analysed dietary copper concentrations were 4.28, 4.63, 5.28, 5.70, 6.19 and 6.69 mg/kg. Absolute weight gain, feed conversion ratio and protein gain improved with the increasing levels of dietary copper up to 5.28 mg/kg. Further inclusion of copper at a level of 5.70 mg/kg did not improve the above parameters. Significantly higher (p < .05) plasma ceruloplasmin, liver copper‐zinc superoxide dismutase, catalase activities and lower thiobarbituric acid reactive substances were evident in fish receiving diets with 5.28 and 5.70 mg/kg copper compared to other groups. Whole body and liver copper concentrations increased significantly (p < .05) with increasing dietary copper levels. Quadratic regression analysis of absolute weight gain, feed conversion ratio, protein gain and broken‐line regression analysis of plasma ceruloplasmin activity and liver TBARS value against the variable dietary copper levels depicted the dietary copper requirements for fingerling H. fossilis in the range of 5.24–5.68 mg/kg.