Effects of azithromycin on tilapia (Oreochromis niloticus): health status evaluation using biochemical,physiological and morphological biomarkers

Bacterial diseases cause tilapia's high‐mortality outbreak. This study investigated the toxicity of azithromycin (AZT), a macrolide antibiotic that has been considered a possible therapeutic drug for tilapia aquacultural use. The 48‐h acute toxicity (50% lethal concentration, LC50; 48 h) of AZT was determined for Oreochromis niloticus. Thereafter, fish were exposed to 0, 1, 50 and 100 mg L^?1 AZT during 14 days (chronic exposure) and measured the haematological variables, the activity of superoxide dismutase, catalase, glutathione peroxidase, glutathione‐S‐transferase (GST) and the concentration of glutathione (GSH), protein carbonyl and lipid peroxidation in the liver; histopathology was analysed the liver, gills and kidneys. The LC50; 48 h was >100 mg L^?1. No fish died during chronic exposure. Haematocrit and haemoglobin concentration increased in fish exposed to 50 and 100 mg L^?1, and the total number of leucocyte and thrombocyte increased after exposure to 100 mg L^?1 AZT, suggesting a stimulation of defence cell production. In the liver, the antioxidant enzyme activities did not change, but GST activity and the GSH level increased in fish exposed to 100 mg L^?1 AZT. Oxidative stress did not occur. Histopathological index (HI_L) indicates moderate liver damage; minor histological changes in the gill and no change in the kidneys. AZT was considered non‐toxic for O. niloticus after acute exposure and, although it causes moderated histopathology in the liver after chronic exposure, this antibiotic may be an alternative against bacterial infections, depending on its efficacy to control bacterial disease in fish.     

Gill damage to juvenile orange‐spotted grouper Epinephelus coioides (Hamilton, 1822) following exposure to suspended sediments

Juvenile Epinephelus coioides were exposed to three nominal concentrations (8, 32, 128 mg wet sediments L^?1) of suspended sediments (SS) from Port Shelter (PS), Mirs Bay (MB) and Victoria Harbour (VH) for 10 and 30 days using semi‐static system. Sediments from VH contained higher concentrations of Cu and polycyclic aromatic hydrocarbons (PAHs) than sediments from PS and MB. Gill damages including lamellar blood sinus dilation and vascular congestion were prevalent after just 10 days of exposure to SS. Fish exposed to SS at the highest concentration of 128 mg L^?1 showed higher incidence of lamellar aneurism. Hyperplasia in the base of lamellae was recorded in fish that had been exposed to contaminated SS from VH. Significant increases in the density of chloride cells and mucous cells were found on the gills of fish that had been exposed to 128 mg L^?1 of SS from PS. Clogging of gills by SS produced hypoxic‐like responses in fish. Polluted sediments from VH produced addictive or synergistic effects between SS and chemical contaminants on fish.     

Effects of dietary α‐ketoglutarate supplementation on the antioxidant defense system and HSP 70 and HSP 90 gene expression of hybrid sturgeon Acipenser schrenckii ♀ × A. baerii ♂ exposed to ammonia‐N stress

This study was conducted to determine the effects of dietary α‐ketoglutarate (AKG) supplementation on the antioxidant defense system and gene expression of heat shock protein (HSP) 70 and HSP 90 in hybrid sturgeons Acipenser schrenckii ♀ × A. baerii ♂ exposed to ammonia‐N stress. A 2 × 3 factorial experiment was arranged, in which each diet (0%, 1% AKG) was randomly assigned to 0.25 (control) 5 and 10 mg L^?1 ammonia‐N groups with three replicate aquaria for each 72 h. The 10 mg L^?1 ammonia‐N significantly increased serum ammonia concentrations and intestinal Gln concentrations and GS activity compared with the 0.25 or 5 mg L^?1 ammonia‐N groups. The intestinal Gln concentration and GS activity increased, and the serum ammonia concentration decreased, in fish given dietary supplementation of 1.0% AKG compared with fish given diets without AKG. Superoxide dismutase (SOD) and glutathione peroxidase (GPx) activity in serum, gills and intestines decreased when fish were exposed to 5 or 10 mg L^?1 ammonia‐N, and their activity increased in fish given diets with 1% AKG. Catalase in the serum and gills decreased when fish were exposed to 5 or 10 mg L^?1 ammonia‐N and increased in fish given diets with 1% AKG. The 10 mg L^?1 ammonia‐N or 1% AKG supplementation increased HSP 70 and HSP 90 gene expression in the liver. The increased activity of antioxidant enzymes, and increased HSP 70 and HSP 90 gene expression in fish fed diets containing 1% AKG suggested higher tolerance to ammonia‐N stress.     

Acute ammonia toxicity and gill morphological changes of Japanese flounder Paralichthys olivaceus in normal versus supersaturated oxygen

Ammonia toxicity and morphological changes in gills of juvenile Japanese flounder Paralichthys olivaceus (5.76 ± 0.12 g) were investigated when fish were separately exposed to normal dissolved oxygen (DO) at 6.5 ± 0.5 mg L^?1 and supersaturated oxygen at 16.0 ± 2.0 mg L^?1 at different ammonia concentrations. Under normal oxygen, ammonia concentrations were tested from 0.04 (control) to 93.3 mg L^?1 total ammonia nitrogen (TAN), whereas under oxygen supersaturation, ammonia concentrations ranged from 0.04 (control) to 226.7 mg L^?1 TAN in the trial. After exposure to ammonia for 96 h, the ammonia LC₅₀ for fish was 62.48 mg L^?1 TAN (0.50 mg L^?1 NH₃–N) at normal oxygen and 160.71 mg L^?1 TAN (0.65 mg L^?1 NH₃–N) at oxygen supersaturation. Light microscopic observations confirmed that gill damage in normal oxygen was more profound than in oxygen supersaturation when fish were exposed to the same level of TAN (93.3 mg L^?1). Furthermore, electron microscopic scanning also showed more crimple, retraction and fibrosis on the secondary lamella surface in fish exposed to normal oxygen than those in fish exposed to supersaturated oxygen at the same TAN (93.3 mg L^?1). This study suggests that supersaturated oxygen can increase ammonia tolerance in Japanese flounder through reducing gill damage by ammonia, which partially explains the merit of using pure oxygen injection in intensive fish farming.     

Immune responses of Litopenaeus vannamei to non‐ionic ammonia stress: a comparative study on shrimps in freshwater and seawater conditions

To investigate the effect of non‐ionic ammonia (NH₃‐N) stress (0.1 and 0.5 mg L^?1) on the immunity of Litopenaeus vannamei cultured in long‐term freshwater, the total haemocyte count (THC), the activity of phenoloxidase (PO), nitric oxide synthase (NOS), superoxidase dismutase (SOD) and the content of malondialdehyde (MDA) were determined and further compared with those of seawater shrimps. The results showed that NH₃‐N stress significantly reduced THC and the activity of PO and SOD (P < 0.05). Under 0.1 mg L^?1 NH₃‐N stress, NOS activity increased first and then decreased significantly, while it dropped dramatically under 0.5 mg L^?1 NH₃‐N stress (P < 0.05). During NH₃‐N stress, MDA content increased continuously, and the MDA content in hepatopancreas of freshwater shrimps was higher than that of seawater shrimps. It was concluded that NH₃‐N stress significantly influenced the non‐specific immunity and could also upset the balance of antioxidant system of L. vannamei in both freshwater and seawater shrimps. Compared with in seawater, the shrimps in freshwater were more vulnerable to NH₃‐N stress because of higher lipid peroxidation and lower immunity.     

Acute and chronic effects of aqueous ammonia on marbled spinefoot rabbitfish,Siganus rivulatus (Forsskål 1775)

Ammonia is a metabolite of aquatic organisms which might reach deleterious levels in intensive fish farms. The aim of the present study was to determine median lethal concentrations (96‐h LC₅₀) of total ammonia nitrogen (TA‐N) on marbled spinefoot rabbitfish (Siganus rivulatus) and chronic effects of TA‐N on survival, growth and behaviour of juvenile rabbitfish over a 50 day period. In the first experiment, fish were exposed to 0, 2, 4, 6, 8, 10, 12, 14, 16, 18 and 20 mg L^?1 TA‐N for 96 h and survival evaluated. In the second experiment, 12 fish were stocked per 50‐L tank and treated with one of 0, 2, 4, 6, 8, 10 and 12 mg L^?1 TA‐N with three replicate tanks per treatment. Survival and growth were determined and histopathological alterations of gills due to chronic ammonia exposure were studied by light and electron microscopy. The 96‐h LC₅₀ values were 16–18 mg L^?1 TA‐N. In the chronic exposure experiment, fish reared in water with 0 mg L^?1 TA‐N had 100% survival and had 50% weight increase in 50 days. Fish at 2 and 4 mg L^?1 TA‐N all died whilst fish in 6, 8, 10 and 12 mg L^?1 TA‐N survived and grew albeit less than in treatment 0 mg L^?1. Gills from ammonia treated fish displayed severe histological and ultrastructural alterations including hyperplasia, hypertrophy and fusion of secondary lamellae, aneurysms and presence of pleomorphic altered cells. Chronic exposure to ammonia is deleterious to marbled spinefoot rabbitfish and low concentrations of ammonia appear to kill the fish in <50 days whilst fish can survive for more than 50 days at concentrations between 6 and 12 mg L^?1 TA‐N.     

Effects of dietary cecropin on growth,non‐specific immunity and disease resistance of tilapia (Oreochromis niloticus × O. aureus)

An 8‐week feeding trial was conducted to evaluate the effect of dietary cecropin on growth performance, non‐specific immunity and disease resistance of hybrid tilapia (Oreochromis niloticus × O. aureus). A basal diet was supplemented with 0 (control), 75, 150 and 225 mg kg^?1 cecropin to formulate four experimental diets. The results showed that final body weight and specific growth rate obtained with diet 150 mg kg^?1 cecropin were significantly higher (P < 0.05) than that obtained with diets 0 and 75 mg kg^?1, whereas there was no difference between 150 and 225 mg kg^?1. Feed conversion efficiency was improved by increasing the dietary cecropin content (P < 0.05). However, feeding intake was reduced as dietary cecropin increased. Serum lysozyme, alkaline phosphatase, catalase and superoxide dismutase activity were significantly increased with the increased levels of dietary cecropin (P < 0.05), and reached a maximum at level of 150 mg kg^?1 cecropin, then those values no longer increased. Moreover, the dietary cecropin supplementation level also exhibited a decrease in the cumulative mortality rates compared with the controls when challenged with Aeromonas veronii. The results suggested that the dietary supplementation of cecropin could improve the growth, non‐specific immunity indicators and resistance of hybrid tilapia against A. veronii.     

Effects of hypoxia on lysozyme activity and antioxidant defences in the kidney and spleen of Carassius auratus

Assessing the responses of lysozyme activity and antioxidant defences to hypoxia is important to understand the adaptation and tolerance strategies of fish under hypoxia. This study investigated the effects of different dissolved oxygen (DO) levels on Carassius auratus, a natural triploid fish, from Qihe River. The content of malondialdehyde (MDA) and the activities of lysozyme and antioxidant enzymes were measured in the kidney and spleen after hypoxic exposure. At the DO concentrations of 1 and 2 mg L^?1, the activities of antioxidant enzymes and lysozyme significantly decreased and the content of MDA significantly increased (P < 0.01). This result suggests that hypoxia decreased antioxidant enzyme and lysozyme activities and caused MDA accumulation in a concentration‐dependent manner. The DO level of 4 mg L^?1 increased the activities of superoxide dismutase and catalase in the kidney and the activities of glutathione peroxidase and catalase in the spleen (P < 0.05). This result implies that slight hypoxic stress can enhance antioxidant defences to alleviate the damage of oxidative stress. The reduced activities of antioxidant enzymes and the accumulation of MDA at the DO level of ≤2 mg L^?1 implied the decrease in antioxidative ability and the occurrence of oxidative stress. The decrement in lysozyme activity indicated that the antibacterial ability was weakened to some degree. Therefore, hypoxic stress at DO levels ≤2 mg L^?1 should be removed by aeration to avoid the oxidative damage resulting from the reduced antioxidative ability and prevent the outbreak of diseases caused by weakened antibacterial effects.     

Dietary manganese requirement for juvenile cobia,Rachycentron canadum L

A 10‐week feeding trial was conducted to estimate the optimum dietary manganese requirement for juvenile cobia, Rachycentron canadum L. The basal diet was formulated to contain 501 g kg^?1 crude protein from vitamin‐free casein, gelatin and fish protein concentrate. Manganese sulphate was added to the basal diet at 0 (control group), 6, 12, 18, 24 and 36 mg Mn kg^?1 diet providing 5.98, 7.23, 16.05, 23.87, 28.87 and 41.29 mg Mn kg^?1 diet, respectively. Each diet was randomly fed to three replicate groups of cobia for 10 weeks, and each tank was stocked with 30 fish (initial weight, 6.27 ± 0.03 g). The manganese concentration in rearing water was monitored during the feeding period and was < 0.01 mg L^?1. Dietary manganese level significantly influenced survival ratio (SR), specific growth ratio (SGR), feed efficiency ratio (FER) and the manganese concentrations in the whole body, vertebra and liver of cobia. When the dietary manganese level rose from 5.98 mg kg^?1 to 23.87 mg kg^?1, the superoxide dismutase (SOD; EC 1.15.1.1) activities in liver also increased (P < 0.05). But there was no significant change in SOD activities for the groups fed with diets containing manganese level higher than 23.87 mg kg^?1. On the basis of broken‐line regression of SGR, manganese concentration in whole body and vertebra the manganese requirements of juvenile cobia were 21.72 mg kg^?1, 22.38 mg kg^?1 and 24.93 mg kg^?1 diet in the form of manganese sulphate, respectively.     

Effects of dietary folic acid on growth,antioxidant capacity,non‐specific immune response and disease resistance of juvenile Chinese mitten crab Eriocheir sinensis (Milne‐Edwards, 1853)

An 8‐week study was conducted to determine folic acid requirement and its effect on antioxidant capacity and immunity in juvenile Chinese mitten crab Eriocheir sinensis (Milne‐Edwards, 1853), followed by a challenge assay with the pathogen Aeromonas hydrophila for 2 weeks. Folic acid was added to a basal diet at seven levels (0, 0.5, 1.0, 2.0, 4.0, 8.0, 16.0 mg folic acid kg^?1 diet), and a diet free of folic acid and vitamin B₁₂ was also included as a control. Crabs were fed twice daily in 32 tanks with 7.76–8.17 mg oxygen L^?1, 25.0–31.0 °C and 7.5–8.3 pH. Growth and feed efficiency were significantly greater in crabs fed ≥2.0 mg folic acid kg^?1, but not significantly different between crabs fed diets >2.0 mg folic acid. The superoxide dismutase activity and glutathione S‐transferase activity were highest in crabs fed ≥2.0 mg folic acid kg^?1, followed by those fed 0.5 and 1.0 mg folic acid kg^?1, and the control diet. The malondialdehyde content was highest in crabs fed the control diet, followed by those fed 0 mg folic acid kg^?1, and the lowest value occurred in those fed ≥0.5 mg folic acid kg^?1. Phenoloxidase activity and total haemocytes were significantly higher in crabs fed ≥2.0 mg folic acid kg^?1 than other diets. Crabs fed 2.0 mg folic acid kg^?1 had the highest lysozyme, acid phosphatase and alkaline phosphatase activities but the lowest cumulative mortality. The optimum dietary folic acid requirement by E. sinensis was estimated at 2.29–2.90 mg kg^?1 diet.     

Dietary selenium requirement for on‐growing gibel carp (Carassius auratus gibelio var. CAS III)

A 12‐week growth trial was conducted in a flow‐through system to determine dietary selenium (Se) requirement for on‐growing gibel carp (initial body weight: 76.2 ± 0.05 g, mean ± SEM). Selenomethionine was supplemented to the basal diet to formulate seven semi‐purified diets containing 0.26, 0.58, 0.72, 1.14, 1.34, 1.73 and 2.09 mg Se kg^?1 diet. The results showed that plasma superoxide dismutase (SOD) activity significantly increased when fish were fed with 0.58 mg Se kg^?1 diet (P < 0.05) and then decreased at 2.09 mg Se kg^?1 diet (P < 0.05). Plasma T‐AOC activity was higher in fish fed with 0.72 mg Se kg^?1 diet (P < 0.05) and plasma malondialdehyde (MDA) was higher in fish fed with 0.26 mg Se kg^?1 diet (P < 0.05). When fish were fed 1.14 mg Se kg^?1 diet, hepatic GSH‐Px, T‐AOC, GSH and CAT activities were significantly higher than those fed with 0.26 mg Se kg^?1 diet (P < 0.05). Hepatic superoxide dismutase (SOD) activity was higher at 1.34 mg Se kg^?1 diet (P < 0.05). Fish liver Se concentrations were significantly higher when fed with 0.72 mg Se kg^?1 diet (P < 0.05) and then kept constant when Se ≥ 0.72 mg kg^?1 (P > 0.05). Whole‐body and muscle Se concentrations were higher when fed with 1.34 mg Se kg^?1 diet (P < 0.05) and kept a plateau when Se ≥ 1.34 mg kg^?1 (P > 0.05). In conclusion, based on broken‐line regression of hepatic Se concentrations, hepatic SOD activity and hepatic T‐AOC activity, dietary Se requirements for on‐growing gibel carp was 0.73 mg kg^?1, 1.12 mg kg^?1 and 1.19 mg kg^?1 diet respectively.     

Acute toxicity of ammonia in Pacu fish (Piaractus mesopotamicus,Holmberg, 1887) at different temperatures levels

Piaractus mesopotamicus juveniles (total length 12 ± 0.5 mm) were exposed to different concentrations of ammonia‐N (un‐ionized plus ionized ammonia as nitrogen), using the static renewal method at different temperature levels (15, 20 and 25°C) at pH 7. The 24, 48, 72, 96 h LC₅₀ values of ammonia‐N in P. mesopotamicus juveniles were 5.32, 4.19, 3.79 and 2.85 mg L^?1 at 15°C; 4.81, 3.97, 3.25 and 2.50 mg L^?1 at 20°C; and 4.16, 3.79, 2.58 and 1.97 mg L^?1 at 25°C respectively. The 24, 48, 72, 96 h LC₅₀ values of NH₃‐N (un‐ionized ammonia as nitrogen) were 0.018, 0.014, 0.013, 0.009 mg L^?1 at 15°C temperature; 0.023, 0.019, 0.016 and 0.012 mg L^?1 at 20°C; 0.029, 0.026, 0.018 and 0.014 mg L^?1 at 25°C. The temperature increase from 15 to 25°C caused an increase of ammonia‐N susceptibility by 21.80%, 9.55%, 31.92% and 30.87%, after 24, 48, 72 and 96 h exposure respectively. Furthermore, we found that exposure of fish to ammonia‐N caused an elevation in total haemoglobin and blood glucose with an increase of 2 mg L^?1 concentration. Ammonia levels tolerated, especially in different temperatures levels, have important implications for the management of aquaculture.     

Anaesthetic efficacy of clove oil,benzocaine, 2‐phenoxyethanol and tricaine methanesulfonate in juvenile marbled spinefoot (Siganus rivulatus)

Anaesthetics are used in aquaculture and fisheries to facilitate routine procedures, such as capture, handling, transportation, tagging, grading and measurements that can often cause injury or induce physiological stress. Two experiments were performed to assess the efficacies of four anaesthetic agents, clove oil, benzocaine, 2‐phenoxyethanol and MS‐222 on juvenile marbled spinefoot rabbitfish (Siganus rivulatus). In the first experiment we tested the lowest effective doses that produced induction and recovery times in 3 min or less and 5 min or less respectively. Dosages were 70 mg L^?1 for clove oil, 60–70 mg L^?1 for benzocaine, 400 μL L^?1 for 2‐phenoxyethanol and 100–125 mg L^?1 for MS‐222. In the second experiment, we determined optimal concentrations of the four anaesthetics if they were to be used to transport rabbitfish fry. Anaesthetic concentrations suitable for handling and transport were: 10–15 mg L^?1 of MS‐222, 5–10 mg L^?1 of benzocaine, 5 mg L^?1 of clove oil and 50–100 μL L^?1 of 2‐phenoxyethanol. All anaesthetic agents are acceptable for use on S. rivulatus, however, 2‐phenoxyethanol, MS‐222 and clove oil appear to be more suitable than benzocaine. Further studies need to be conducted on effects of high and low doses of anaesthetic agents on physiology of marbled spinefoot.     

Acute tolerance and histopathological effects of ammonia on juvenile maroon clownfish Premnas biaculeatus (Block 1790)

This study evaluated the median lethal concentration values (LC₅₀) and the histopathological effects of un‐ionized ammonia (NH₃^‐‐N) on juvenile maroon clownfish Premnas biaculeatus. After 96 h of exposure to different concentrations of ammonia, juveniles were sampled for histopathological evaluation. The 24 and 96 h LC50 values of NH₃^?‐N determined were 1.68 and 0.89 mg L^?1 respectively. Maroon clownfish exposed to different ammonia concentrations displayed histopathological alterations in the gills, kidney, liver and brain. Gill tissue damage included lamellar hyperplasia, lamellar shorting and hyperplasia and hypertrophy of mucous cells. The kidney showed hyperanaemia, enlarged sinusoids within an apparently decreased amount of haematopoietic tissue, oedema on tubular cells and tubular necrosis, and an enlarged Bowman's capsule. The liver presented dilatation of hepatic sinusoids, fatty deposition in hepatocytes and Mallory bodies. Examination of the brain revealed a proliferation of glial cells, and the Virchow‐Robin space indicated a severe perivascular oedema and signs of neuronal suffering with satellitosis. The results of this study indicate that juvenile maroon clownfish are relatively sensitive to ammonia and particular attention must be given to this toxic compound in culture systems.     

Effect of dietary lysozyme on growth,immune response,intestine microbiota,intestine morphology and resistance to Aeromonas hydrophilia in gibel carp (Carassius auratus gibelio)

A 75 days experiment was conducted in a flow‐through system on juvenile gibel carp (Carassius auratus gibelio) (3.43 ± 0.01 g) to evaluate the effects of dietary lysozyme on growth performance, intestine morphology, microbiota and immune response. Four isonitrogenous (crude protein: 367 g kg^?1) isolipid (62 g kg^?1) and isocaloric (gross energy: 17.92 kJ g^?1) diets were formulated to contain 0, 100, 500 and 1000 mg kg^?1 lysozyme, respectively. The results showed that specific growth rate (SGR) and feed efficiency (FE) increased at 1000 mg kg^?1 lysozyme. Blood leucocyte phagocytic activity (PA) and serum lysozyme (LZM) decreased with dietary lysozyme on day 25, 50 and 75. There were no significant differences in alternative complement pathway (ACP), respiratory burst (ROS), serum superoxide dismutase (SOD), glutathione peroxidase (GSHpx) or malonaldehyde (MDA). After Aeromonas hydrophilia challenge, higher survival was obtained at 500 mg kg^?1 group. PA, ROS, SOD, LZM and ACP increased with increasing dietary lysozyme, while MDA reversed. Goblet cells in mid‐intestine and microvilli height in distal intestine increased with dietary lysozyme on day 75. Dietary lysozyme reduced the diversity of intestine microbiota. In conclusion, oral administration of 500 mg kg^?1 dietary lysozyme for 75 days is recommended for the survival of gibel carp and 1000 mg kg^?1 dietary lysozyme for fast growth.     

Effects of iodized salt on the histopathology of the gills and liver in Rhamdia quelen and Metynnis maculatus

Table salt has been used as a reference substance in toxicological studies on fish and as an antiparasitic agent in aquaculture. The objectives of this work were to evaluate the sensitivity of Rhamdia quelen and Metynnis maculatus to iodized salt and to assess the possible changes in the gills and liver resulting from subchronic exposure of fish to this compound. The iodized salt toxicity levels after 96 h of exposure were 11.4 and 10.8 g L^?1 for R. quelen and M. maculatus. None of the observed changes in the livers of the studied fish could be unequivocally correlated with salt exposure. In turn, it could not be entirely ruled out that the changes found in the gills, including epithelial lifting, oedema formation and vascular congestion, were caused by exposure of fish to salt.     

Effects of ammonia exposure on stress and immune response in juvenile turbot (Scophthalmus maximus)

The aim of this study was to investigate the effects of ammonia exposure on stress and immune response in turbot. The species was exposed to five total ammonia nitrogen (TAN) concentrations: 0 (control), 1, 5, 20 and 40 mg L^?1 for 96 h. After 0, 24, 48 and 96 h of exposure, blood samples were collected to measure the levels of corticotropin‐releasing hormone (CRH), adrenocorticotropic hormone (ACTH), cortisol, growth hormone (GH), lysozyme (LZM), complement 3 (C3), complement 4 (C4) and immunoglobulinM (IgM); liver samples were taken to analyse oxidative stress parameters (superoxide dismutase, SOD; catalase, CAT; glutathione, GSH; malondialdehyde, MDA), and gene expression of heat shock proteins (HSP 70 and HSP 90) and insulin‐like growth factor‐1 (IGF‐1). The results showed that exposure to higher concentrations of TAN (20 and/or 40 mg L^?1) enhanced the levels of CRH, ACTH and cortisol and attenuated the levels of GH, LZM, C3, C4 and IgM in plasma of turbot after 48 and 96 h. In liver, TAN (20 and/or 40 mg L^?1) apparently increased the activities of antioxidative enzymes (SOD and CAT), mRNA levels of HSP (HSP 70 and 90) and formation of MDA, decreased the content of GSH and mRNA levels of IGF‐1 after 48 and 96 h of exposure. Overall, our results suggested that high ammonia exposure caused activation of hypothalamic–pituitary–interrenal axis, inhibition of GH/IGF axis and immunity, and occurrence of oxidative stress.     

Dietary thiamin could improve growth performance,feed utilization and non‐specific immune response for juvenile Pacific white shrimp (Litopenaeus vannamei)

This study evaluated the effect of dietary thiamin on growth performance, feed utilization and non‐specific immune response for juvenile Pacific white shrimp, Litopenaeus vannamei. Six isonitrogenous and isolipidic practical diets were formulated with graded thiamin levels of 6.9, 32.7, 54.2, 78.1, 145.1 and 301.5 mg kg^?1 of dry diet, respectively. Each diet was randomly assigned to triplicate groups of 30 juvenile shrimp and provided four times each day to apparent satiation. Weight gain (WG) and specific growth rate (SGR) of the shrimp were significantly influenced by the dietary thiamin levels, the maximal WG and SGR occurred at 54.2 mg kg^?1 dietary thiamin level. However, with further increase in dietary thiamin level from 54.2 to 301.5 mg kg^?1, the WG and SGR significantly decreased. Shrimp fed the 54.2 mg kg^?1 thiamin diet exhibited higher feed efficiency, protein efficiency ratio and protein productive value than those fed the other diets. Dry matter and protein content in whole body were significantly affected by the dietary thiamin levels. Thiamin concentration in hepatopancreas significantly increased when the dietary thiamin level increased from 6.9 to 145.1 mg kg^?1. The total protein, glucose, triacylglycerol and cholesterol contents in hemolymph were not significantly affected by the dietary thiamin levels. Dietary thiamin had significantly influenced superoxide dismutase, catalase and lysozyme activities in hemolymph. Results of this study indicated that the optimal dietary thiamin requirements estimated using a two‐slope broken‐line model based on WG and thiamin concentration in hepatopancreas were 44.66 and 152.83 mg kg^?1, respectively.     

Bioassay‐guided isolation and identification of active compounds from Macleaya microcarpa (Maxim) Fedde against fish pathogenic bacteria

Four alkaloids (Sanguinarine, 6‐Methoxyl‐dihydro‐chelerythrine, Cryptopine and β‐Allocryptopine) were isolated from aerial parts of Macleaya microcarpa (Maxim) Fedde using bioassay‐guided isolation method, and the inhibitory activity of ethanolic extract, various fractions and these four alkaloids against four fish pathogenic bacteria (Aeromonas hydrophila, Aeromonas salmonicida, Vibrio anguillarum and Vibrio harveyi) was assessed in vitro using the agar dilution method and the microdilution assay method respectively. A. hydrophila was the most sensitive strain to all the tested compounds. Minimum inhibitory concentration (MIC) values were lower for sanguinarine against all tested Gram‐negative strains than other three alkaloids, with MIC values of 12.5 mg L^?1 for A. hydrophila and 50 mg L^?1 to other pathogenic bacteria. Followed by 6‐methoxyl‐dihydro‐chelerythrine, which showed considerable antibacterial activity with MIC values of 80 mg L^?1 for A. hydrophila, 100 mg L^?1 for V. harveyi, and 125 mg L^?1 for both V. anguillarum and A. salmonicida. Cryptopine and β‐allocryptopine revealed similar inhibitory activity with MIC values of 100 mg L^?1 for A. hydrophila and 200 mg L^?1 for other three bacterial species. These finding provided evidence that extract, as well as isolated compounds from M. microcarpa might be potential sources novel antibacterial agents for the treatment of fish infectious diseases.     

Aloysia triphylla essential oil as food additive for Rhamdia quelen – Stress and antioxidant parameters

We examined the effects of dietary supplementation for 21 days with different levels (0, 0.25 and 2.0 ml/kg) of the Aloysia triphylla essential oil (EOAT) on silver catfish (Rhamdia quelen). Cortisol levels were lower in fish fed EOAT at 2.0 ml/kg diet, and lactate levels were lower in those fed at both doses. Glucose, alanine aminotransferase, aspartate aminotransferase and triglyceride levels did not vary between groups. The biomarkers of oxidative stress, thiobarbituric acid‐reactive substances, lipid hydroperoxide, superoxide dismutase, catalase and non‐protein thiols, were lower in the brain, liver and muscle of fish fed EOAT at 2.0 ml EO/kg diet. Glutathione‐S‐transferase, reduced glutathione, plasma Na⁺, Cl^?, and K⁺, and gill Na⁺/K⁺‐ATPase and H⁺‐ATPase did not vary between groups. Taken together, our results clearly indicate that the addition of EOAT at 2.0 ml/kg diet improves oxidative status and lowers the stress response in silver catfish.