Volume 71, 2019

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    Molecular Cloning, mRNA Expression, and Nutritional Regulation of a Fatty Acyl Δ6-Desaturase-like Gene of the Manchurian Trout, Brachymystax lenok (Pallas)
    ( 2019) Jian-hua Y ; Shu-guo L ; Hua-xin N ; Jie C ; Zong-fu H ; Ying H
    The fatty acyl delta-6 desaturase (Δ6-desaturase) is a key rate-limiting enzyme in the biosynthesis of long-chain polyunsaturated fatty acids (LCPUFAs). To study the effects of different oil sources in the feed on the nutritional regulation of Δ6-desaturase-like gene mRNA expression, the fulllength cDNA of the Δ6-desaturase-like gene was cloned from the liver of Manchurian trout (Brachymystax lenok). A 9-week feeding trial was performed, and the fish received diets with three different oil sources: fish oil (FO), sunflower oil (SO), and linseed oil (LO). The results showed that the 2448 bp long full-length cDNA contained an open reading frame (with a length of 1365 bp), encoding 454 amino acids. Gene expression analysis indicated that Δ6-desaturase-like gene mRNA is widely distributed throughout different tissues, with highest expression levels in both the liver and the brain. The linolenic acid (ALA) and linoleic acid (LA) compositions were highest in LO and SO diets, respectively. The eicosapentaenoic acid and docosahexaenoioc acid composition in LO and SO diets were significantly lower than in the FO diet. Fish fed with SO and LO showed significantly higher liver expression levels of Δ6-desaturase-like gene mRNA than those fed with FO. This indicates that SO and LO in the diet affected the nutritional regulation of the Δ6-desaturase-like gene mRNA in the liver of the Manchurian trout. In addition, these data suggest that the Manchurian trout has the ability to synthesize long-chain unsaturated fatty acids (LC-PUFAs) from ALA and LA.
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    Withdrawal Period of Oxolinic Acid in Cobia (Rachycentron canadum): Validation of an LC-MS/MS Method
    ( 2019) Chen RS ; Sheu SY ; Xue YJ ; Wang CY ; Liu CH ; Kuo TF ; Wang JH ; Chou CH
    Oxolinic acid (OXO) has been routinely used in aquaculture as both prophylactic and chemotherapeutic agents, principally against systemic bacterial infections. The residue depletion of OXO was investigated in cobia following multiple (5 days) in-feed dosing (30 and 60 mg/kg body weight/day) at 25°C; we assessed OXO concentrations of liver and muscle (+skin) samples post-treatment for three weeks. The OXO residues were quantified using a validated ultra-high-performance liquid chromatographytandem mass spectrometry (UPLC-MS/MS) method and the results indicated recoveries of 86.6-95.8%, with relative standard deviations (RSD) less than 8.5% for intra- and inter-day precisions. Within the range of 10−500 ng/g, the calibration curves for all matrices presented a determination coefficient greater than 0.99. Limit of detection and quantification were estimated at 6 and 10 ng/g, respectively. In order to account for the high variability of the residue data, a safety span corresponding to 50% of depletion time could be seen as appropriate. Considering a maximum residue limit (MRL) of 50 ng/g established by the Taiwan FDA for OXO in muscle with skin in natural proportions, a withdrawal period of 15 days was calculated for the sum of 10day depletion time and 5-day safety span. These results revealed that the analytical method is developed for residue OXO and that the withdrawal period is appropriate.
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    Expression Response Profiles of Toll-Like Receptor Family Members in Cyprinus Carpio after Lipopolysaccharide Stimulation, and Implication for Disease Control in Aquaculture
    ( 2019) Lin B ; Chen L ; Zhang J ; Zhang X ; Wang H ; Li G ; Wang Q ; Deng J
    In this study, response profiles of 17 Toll-like receptors (TLRs) to lipopolysaccharide (LPS) stimulation were studied at mRNA levels in the liver of the common carp Cyprinus carpio. Three types of gene response profiles were observed in TLR family. The first pattern was that the expressions of some TLRs were initially up-regulated and then decreased with time. This finding indicated that the responses of these TLRs were sensitive to LPS stimulation, and it was suggested that these TLRs were involved in responding and coping with LPS, implying that these TLRs were important in immune defense from Gram-negative bacteria. The second pattern was that some TLR expressions showed no obvious change after LPS stimulation, demonstrating that they were not sensitive to LPS and probably did not recognize LPS, implying that these TLRs should not be regarded as the major receptors to be regulated to prevent disease caused by Gram-negative bacteria. The third pattern was that gene expressions of partial TLRs were significantly downregulated after a period of LPS stimulation, indicating that their gene expressions were inhibited by LPS action, and implying that these TLRs did not initiate the signal pathway for inflammation reaction to clear Gramnegative bacteria. This study is based on the different response patterns of TLRs to LPS, that imply that the sensitive response TLR genes to LPS might be selected as target genes regulated by drugs that control inflammation reaction of diseased fish in aquaculture.
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    Nitrite-Induced Oxidative Stress, Histopathology, and Transcriptome Changes in the Mud Crab (Scylla paramamosain)
    ( 2019) Cheng C-H ; Su Y-L ; Ma H-L ; Deng Y-Q ; Feng J ; Chen X-L ; Guo Z-X
    Nitrite in the aquatic environment is highly toxic to aquatic animals. However, the mechanism by which the mud crab responds to nitrite-induced stress remains unclear. In this study, we investigated the physiological response and molecular mechanism in the mud crab (Scylla paramamosain) exposed to the acute nitrite exposure (20 mg/L) for 24h. The results showed that nitrite exposure induced significant changes in antioxidant enzyme activity and MDA content. Severe cytological damage was observed in the hepatopancreas. After 24h exposure to nitrite, 11,638 differentially expressed genes (DEGs) were identified by transcriptome analysis. These DEGs were involved in many pathways related to oxidative stress and immune responses. Our results also found that FoxO signaling pathway, p53 signaling pathway, and NF-kB signaling pathway participated in the anti-stress defense against nitrite stress. The study provides new insight into the understanding of nitrite-induced toxicity in the mud crab.
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    Effect of Dietary Iron Levels on Tissues, Intestinal Digestive Enzyme Activity, and Muscle Nutrient Compositions of Juvenile Bighead Carp (Aristichthys nobilis)
    ( 2019) Feng W ; Hu X ; Wang F ; Huang F ; Liu L ; Li H ; Liu H ; Yang W
    A 60-day feeding trial was conducted to estimate the effects of dietary iron (Fe) levels on iron concentration in tissues, intestinal digestive enzyme activities, and muscle nutrient composition of bighead carp (Aristichthys nobilis). Six experimental diets were formulated to contain different Fe levels (0, 43.1, 84.2, 123.3, 162.2 and 203.1 mg/kg of dry diets) using ferrous sulfate (FeSO4) as the source. When Fe dietary content increased to 43.1 mg/kg, trypsin activity in the intestine significantly increased and thereafter decreased. Lipase and amylase activity in the intestine significantly increased with increasing dietary Fe levels up to 123.3 mg/kg diet and thereafter decreased. With lipase and amylase activity in the intestine as the main indicators, Fe content of 123.3 mg/kg was the most suitable dietary Fe level for A. nobilis. Crude protein content in the muscle of the 84.2 mg/kg Fe group was the highest in all groups. Results indicated that the appropriate levels of dietary Fe alter muscle nutrient composition of A. nobilis. Fe content in the muscle and vertebrae significantly increased with increasing dietary Fe levels up to 203.1 mg/kg diet. Fe contents in different tissues were as follows: Vertebra >intestine >muscle.
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    Differences in Total Carotenoid Content in Tissues of the Pearl Oyster Pinctada fucata with Regard to Cuticle Shell Color
    ( 2019) Wei H ; Chen M ; Deng Z ; Li Y ; Ma Z ; Wang Y
    The aim of this study was to compare total carotenoid content (TCC) in tissues, and its correlation with shell color between four different shell color strains of Pinctada fucata. A total of 120 individuals (30 golden shells, 30 red shells, 30 black shell and 30 white shells) of P. fucata of similar size were evaluated. In this study, stomach, gill, adductor, and mantle were used for measuring the determination of TCC. The color measurements were taken from both the nacre shells and cuticle shells. The results showed that TCC varies significantly among four different tissues and the four different shell color strains (P < 0.05). A significant difference between the cuticle shell colors of the four different shell color strains of P. fucata was observed (P < 0.05), while the nacre shell colors of four shell strains were similar (P > 0.05). In the present study, results indicated that the TCC of P. fucata was significantly related to tissue and cuticle shell colors (P < 0.001), but not related to nacre shell colors (P > 0.05). TCC relating to the cuticle shell color suggested that increasing or decreasing TCC in P. fucata through selective breeding of cuticle shell color was feasible, and it could be significant both for food for humans, and the cultivation of high-quality pearls.
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    Inhibitory Effects of Galla chinensis, Tannic Acid, and Gallic Acid on Saprolegnia parasitica
    ( 2019) Zhang QQ ; Li AH ; Liu LH
    The inhibitory effects of Galla chinensis and its two main ingredients, tannic acid and gallic acid, on Saprolegnia parasitica were examined, using the method of agar plate assay and liquid dilution assay. The results showed that all the three tested drugs had different degrees of inhibitory activity on mycelial growth and zoospore germination of Saprolegnia parasitica, with tannic acid showing the most significant inhibition. The mycelial growth of S. parasitica was completely inhibited by tannic acid at the concentration of more than 32 mg/L, and the germination rate of S. parasitica zoospores decreased by 66% at a concentration of 5 mg/L. Considering the low cost of tannic acid together with its inhibitory effect on S. parasitica, tannic acid showed the most significant potential in the prevention and control of fish saprolegniasis.
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    Discontinuous Administration of β-glucan is Effective for Preventing Immune Fatigue in Litopenaeus vannamei
    ( 2019) Luo Z ; Guo J ; Hao S ; Zhang Z ; Tang H ; Wu H ; Jiang J ; Ye G ; Feng S ; Bai X
    β-glucan is an effective, available immunostimulant that has been successfully used to improve the immune defense of shrimp against pathogenic infection. However, the long-term continuous use of β-glucan can lead to immune fatigue, and intermittent feeding may be an effective way of avoiding this phenomenon. A 60-day growth trial was conducted to compare the effects of different feeding strategies of diets containing 200 mg/kg β-glucan on the growth and immune system of the Pacific white shrimp Litopenaeus vannamei. The results showed that either continuous feeding or intermittent feeding of diets containing 200 mg/kg β-glucan did not promote the growth of L. vannamei. However, the levels of superoxide dismutase, alkaline phosphatase, and acid phosphatase in the hepatopancreas of L. vannamei in the intermittent feeding group were significantly higher than those in the control and continuous feeding groups. Expression levels of the genes encoding LPS/β-glucan binding protein, superoxide dismutase, lysozyme, penaeid in-3a, and catalase were also significantly upregulated in the intermittent feeding group, whereas most of the immune parameters in the continuous feeding group were not significantly different from those of the control group. After artificial infection with Vibrio parahaemolyticus, the average mortality rates in the control group, the continuous feeding group, and the intermittent feeding group were 76.67%, 78.89%, and 45.56%, respectively. The results indicated that the addition of 200 mg/kg β-glucan to the diet did not promote the growth of L. vannamei, but the strategy of intermittent feeding effectively prevented immune fatigue and enhanced disease resistance, perhaps by increasing nonspecific immunity in L. vannamei.
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    Streptococcal Infection Caused by Enterococcus casseliflavus in Cultured Meagre (Argyrosomus regius)
    (The Israeli Journal of Aquaculture - Bamidgeh, 2019) Urku C ; Timur G
    Gram Positive Streptococci (GPS) have become increasingly important fish pathogens. In this study, 170 moribund marine fish (sea bass, gilthead sea bream, meagre, sharp snout sea bream, and marine rainbow trout), obtained from 30 fish farms in the Black Sea and Aegean Sea regions of Turkey, were investigated for the presence of GPS. Streptococci were recovered from fifteen moribund young meagre (Argyrosomus regius) from an inland fish farm located in the Aegean region. The isolates were identified as Enterococcus casseliflavus using a Polymerase Chain Reaction-based (PCR) method. This result was confirmed with 16S rRNA gene sequencing and serological methods, including slide agglutination and IFAT. The diseased meagre showed unilateral or bilateral exophthalmia, loss of eyes, and hemorrhagic ulcerative skin lesions on the body surface. Histopathologically, tubular degeneration and congestion in the kidney, myopathy in the heart tissue, discharge of the white pulp in the spleen, extensive vacuolation of hepatocytes, and congestion in the liver were observed. Intraperitoneal challenge with one of the isolates in healthy European sea bass (Dicentrarchus labrax) in resulted mortalities 8 days post-injection.
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    Effect of Ammonia Exposure on the Non-Specific Immunity of Fresh Water Pearl Mussel Hyriopsis cumingii
    (The Israeli Journal of Aquaculture - Bamidgeh, 2019) Xia H ; Yang P ; Liu L ; Luo Y ; Sun Y ; Wang W ; Yuan M ; Liu W
    Ammonia-N, the principal end-product of protein catabolism, is an important environmental toxic factor in ponds. Elevated environmental ammonia-N is very toxic to aquatic animals and has a deleterious effect on their immune system. However, its effect on their immune system remains unclear. In this study, the effects of ammonia-N (0, 5, 10 and 30 mg/L) on immune responses of Fresh Water Pearl Mussel Hyriopsis cumingii were determined. When exposed to 5 mg/L ammonia-N lysozyme activity increased significantly. Superoxide dismutase activity was highest in the 5 mg/L group followed by the 10 mg/L group. The marked decrease of Lysozyme activity of Fresh Water Pearl Mussel Hyriopsis cumingii in 10 mg/L and 30 mg/L ammonia-N groups suggests that the higher concentrations of ammonia-N reduces or inhibits their non-specific immunity. Compared to the control group, superoxide dismutase activity in 30 mg/L ammonia also decreased significantly. When exposed to 5mg/L ammonia-N, catalase, acid phosphatase and alkaline phosphatase activity enhanced. In the 10 mg/L and 30 mg/L group, ammonia-N decreased significantly The lysozyme, catalase, acid phosphatase and alkaline phosphatase activity showed a similar tendency. This suggests that in H. cumingii immunostimulatory response is enhanced at low ammoniaN concentrations. The results of this study provide a theoretical basis for disease prevention in the freshwater pearl mussel.