中链脂肪酸及其酯对致病菌的抑菌作用

中链脂肪酸甘油酯已经成为抗生素替代物研究的新热点。文章旨在探究月桂酸、单辛酸甘油酯、单月桂酸甘油酯、辛葵酸甘油酯对大肠埃希菌、金黄色葡萄球菌、肠炎沙门氏菌和鸡白痢沙门氏菌的抑菌效果。结果显示:月桂酸、单月桂酸甘油酯、单辛酸甘油酯对大肠埃希菌有显著(P<0.05)抑制作用;月桂酸、单月桂酸甘油酯、单辛酸甘油酯、辛葵酸甘油酯对金黄色葡萄球菌有显著(P<0.05)抑制作用;月桂酸、单月桂酸甘油酯、单辛酸甘油酯、辛葵酸甘油酯对肠炎沙门氏菌有显著(P<0.05)抑制作用;月桂酸、单月桂酸甘油酯、单辛酸甘油酯对鸡白痢沙门氏菌有显著(P<0.05)抑制作用。其中,月桂酸、单月桂酸甘油酯、单辛酸甘油酯对4种致病菌的作用效果随时间延长而增强。     

Orange peel fragment improves antioxidant capacity and haematological profile of Nile tilapia subjected to heat/dissolved oxygen‐induced stress

This study evaluated the ability of orange peel fragment (OPF) to act as a functional feedstuff, influencing growth, haematological profile, and antioxidant enzyme activity of Nile tilapia subjected heat/dissolved oxygen‐induced stress (HDOIS). A group of 440 male Nile tilapia (31.7 g ± 0.34) was randomly distributed in 40 250‐L aquaria (11 fish/tank) and fed five practical diets with graded levels of OPF at 0%, 0.2%, 0.4%, 0.6%, and 0.8% for 70 days. The diets were formulated to contain 30% crude protein and 18 MJ/kg crude energy. After the feeding period, growth performance was evaluated and six fish per treatment were sampled for haematological profile and antioxidant enzyme activity, before and after HDOIS. Then, fish were subjected to HDOIS (32°C/2.3 mg/L dissolved oxygen) for three days and the same haematological profile and antioxidant enzyme activity were determined. There was no effect of OPF on the haematological profile, either before or after HDOIS. The polynomial regression model was used to express the relationship between antioxidant enzymes activity and OPF supplementation level. The maximum activity of superoxide dismutase, catalase, and glutathione peroxidase was reached at 0.66%, 0.63%, and 0.68% of OPF respectively. Results of the present study suggest that a dietary supplementation level of 0.63%–0.68% of orange peel fragment was appropriate to maintain Nile tilapia haematological profile and improve its antioxidant capacity under HDOIS.     

Aurantiochytrium sp. meal as DHA source in Nile tilapia diet,part II: Body fatty acid retention and muscle fatty acid profile

Nile tilapia juveniles (8.35 ± 0.80 g) were fed on four levels (0.0%; 0.5%; 1.0%; 2.0%, 4.0%) of Aurantiochytrium sp. meal (ALL‐G‐RICH?), a source of docosahexaenoic acid (DHA). The 1% Aurantiochytrium sp. meal diet was compared to a control diet, which contained the same amount of DHA as cod liver oil (CLO) at 1.7% diet. Groups of 25 fish were stocked in 100 L tanks and fed twice daily until apparent satiation, for 57 days, at 28°C. Increasing dietary Aurantiochytrium sp. meal reduced the body retention of DHA and n‐3 polyunsaturated fatty acids (n‐3 PUFA) but increased the body retention of alpha‐linolenic (α‐LNA), linoleic (LOA) and n‐6 polyunsaturated fatty acids (n‐6 PUFA). Fatty acid profile in tilapia muscle was affected by increasing dietary inclusions of Aurantiochytrium sp. meal, with an increase in DHA, α‐LNA, n‐3 PUFA and n‐3 long chain‐polyunsaturated fatty acids (n‐3 LC‐PUFA) but a decrease in monounsaturated fatty acids (MUFA), n‐6 PUFA and n‐6 long‐chain polyunsaturated fatty acids (n‐6 LC‐PUFA). There was a larger body retention of DHA, α‐LNA, LOA, n‐3 PUFA and n‐6 PUFA fatty acids and a higher percentage of DHA, n‐3 PUFA and n‐3 LC‐PUFA in muscle fatty acid profile in fish fed on CLO diets than in those fed on 1% Aurantiochytrium sp. Therefore, Aurantiochytrium sp. meal is an alternative source of DHA for Nile tilapia diets.     

Effects of dissolved oxygen on the growth performance,haematological parameters,antioxidant responses and apoptosis of juvenile GIFT (Oreochromis niloticus)

This study investigated the effects of different dissolved oxygen (DO) levels on the growth performance, antioxidant response and apoptosis of juvenile GIFT (genetically improved farmed tilapia, Oreochromis niloticus). GIFT were fed with five DO levels (1, 2, 3, 4 and 5 mg/L) for 60 days, and the results showed that the final body weight, weight gain rate, specific growth rate and crude protein and crude lipid contents of the fish muscle increased at 5 mg/L DO. The activities of the antioxidant and digestive enzymes were significantly up‐regulated with increasing DO levels. However, the haemoglobin content, number of red blood cells, malondialdehyde content, transaminase activities, glucose content and lactic acid levels decreased at higher DO levels. Furthermore, the cardiomyocyte apoptotic index was significantly decreased with increasing DO levels. Our results show that 5 mg/L DO improved growth performance, promoted antioxidant enzyme activities and reduced liver damage in GIFT.     

Effects of ferulic acid on growth performance,immunity and antioxidant status in genetically improved farmed tilapia (Oreochromis niloticus) fed oxidized fish oil

A study was conducted to characterize the effects of dietary oxidized fish oil on the growth performance, immunity and antioxidant status of genetically improved farmed tilapia (Oreochromis niloticus) and to determine the role of ferulic acid on the oxidative damage induced by the oxidized fish oil. The tilapia (13.73 ± 0.31 g) were fed four experimental diets containing untreated (peroxide value, POV: 2.2 meq/kg) and highly oxidized (POV: 120.6 meq/kg) fish oil either with or without ferulic acid (0 or 400 mg/kg) supplementation for 12 weeks. From the results, the oxidized fish oil treatments increased antioxidant enzyme activities and MDA values but decreased the weight gain and the immunological parameters in tilapia. Meanwhile, the serum biochemical indices were significantly affected by the oxidized fish oil. Besides, the addition of ferulic acid partially counteracted the free radical‐induced damage and improved the health status of tilapia. In conclusion, the oxidized fish oil may induce oxidative stress, destroy liver, dysregulate lipid metabolism as well as reduce non‐specific immunity, and eventually result in growth inhibition of tilapia. The ferulic acid supplementation partially offset the negative effects of the oxidized fish oil on tilapia.     

Effect of Bacillus cereus as a water or feed additive on the gut microbiota and immunological parameters of Nile tilapia

We evaluated the effects of Bacillus cereus, as an additive in water and feed, on the gut microbiota and immunological parameters of Nile tilapia (Oreochromis niloticus) fingerlings. Experiments were performed in tanks and net cages respectively. Experiment 1: Tilapia were housed in tanks for 42 days, and B. cereus was added to the water at 1.0 × 10⁴ cfu mL^?1 (Treatment 1) and 1.0 ×10⁵ cfu mL^?1 (Treatment 2) weekly. For the control, no probiotic was added. Experiment 2: Tilapia were housed in cages for 42 days, and the feed was supplemented with B. cereus at 1.0 × 10⁷ cfu g^?1 (Treatment 1) and 1.0 × 10⁸ cfu g^?1 (Treatment 2) weekly. For the control, no probiotic was added. Each treatment contained three replicates, with 50 male tilapias per replicate. The fish from the probiotic treatments in both tank and cage experiments had significantly higher serum lysozyme and peroxidase activities than the control. In the cage experiment, alkaline phosphatase and total superoxide dismutase activities in tilapia were significantly higher in probiotic treatments compared with the control. The results of polymerase chain reaction‐denaturing gradient gel electrophoresis showed that B. cereus supplementation in the feed and water affected the autochthonous gut bacteria community of tilapia and stimulated various potentially beneficial bacteria. Therefore, B. cereus, as a water or feed additive, could enhance the immune status and affect the gut microbiota of tilapia. Bacillus cereus was more effective as a feed supplement rather than a water additive for enhancing the immune status of tilapia.     

Effects of biofloc technology on reproduction and ovarian recrudescence in Nile tilapia

The objectives of this study were to evaluate the reproductive cycle, morphological changes of ovary and mobilization of energy reserves in Nile tilapia reared with biofloc technology (BFT). In general, the growth and reproductive performance were highly similar between BFT and Control system (clear water). Difference between the systems was found in the hepatosomatic index (using mixed‐effects models), which suggested that BFT can alter the energy mobilization in the post‐spawning period. The absolute and relative fecundity, fertilization rate, number of larvae produced per female, gonadosomatic index, proportion of oogenesis cells, number of post‐ovulatory and atretic follicles were similar between the two systems. We also did not detect a reduction in the reproductive cycle length in Nile tilapia reared in BFT. Because there was no evidence of the negative effects of BFT on Nile tilapia reproduction, we concluded that BFT might be used for breeder stocking of this species.     

Impact of sublethal di‐n‐butyl phthalate on the aquaculture fish species Nile tilapia (Oreochromis niloticus): histopathology and oxidative stress assessment

Phthalates such as di‐n‐butyl phthalate (DBP) and their esters are widely used plasticizers, their ubiquitous presence in daily life, inevitably leads to their restricted use due to important environmental pollution and health impacts and endocrine disruption potential. The aim of this study was to examine the effects of a sublethal concentration of 10 mg L^?1 DBP on haematocrit (HCT) values, gills and liver histology, malondialdehyde (MDA, 2‐thiobarbituric acid‐TBA reactivity) and reduced glutathione (GSH) levels in gills and liver tissue as oxidative stress biomarkers in the aquaculture fish species Nile tilapia (Oreochromis niloticus) after 24 (DBP‐24) and 96 (DBP‐96) h exposure. No differences were found between per cent HCT values in the 24 h exposure groups (P > 0.05). Response of antioxidant defence systems in liver and gill tissues of the fish were dependent on exposure duration and changed to a higher extent during 96 h. MDA levels in liver tissue increased in DBP treated fish in comparison to the control fish. However, the differences between the exposure and control groups were not significant (P > 0.05). A statistically significant decrease (P > 0.05) was recorded in gill MDA levels in the DBP‐96 group when compared to the control and DBP‐24 groups. The liver GSH levels were unchanged in the DBP treated fish. However, GSH levels were significantly lower in the gill tissue of the DBP‐96 group. Exposure to DBP caused several degenerative changes in the histology of gill and liver tissue. Gills displayed hyperaemia, epithelial lifting, oedema, talengiectasia, epithelial hyperplasia and fusion of secondary lamellae, whereas in liver several circulatory anomalies (hyperaemia, blood congestion and sinosoid dilatation) and vacuolization of hepatocytes were observed. Histopathological results demonstrated that the gills were more affected than the liver perhaps due to their direct contact with DBP.     

无乳链球菌LIP蛋白的截短表达及免疫保护性研究

为评价罗非鱼源无乳链球菌(Streptococcus agalactiae)BX2012株脂蛋白(lipoprotein)的免疫原性及其对奥利亚罗非鱼(Oreochromis aureus)和大菱鲆(Scophthalmus maximus)的保护效果,以无乳链球菌脂蛋白基因序列(GenBank序列号:CP000114.1,SAK_0321)的B细胞线性抗原表位区设计特异性引物进行扩增,构建重组表达载体,将截短表达的脂蛋白制备成亚单位疫苗,同时制备灭活疫苗进行免疫比对。结果显示:重组表达载体p ET-32a-LIP342在BL21(DE3)中获得了良好的可溶性表达,分子质量约为30 kDa,纯化使LIP342纯度由41.75%提至87.23%;Western blotting分析显示,LIP342可被兔抗无乳链球菌高免血清特异性识别;LIP342在目前已知不同种属来源或不同血清型的无乳链球菌分离株中同源性为90.35%~100%,在罗非鱼源分离株中同源性为100%;无乳链球菌LIP342蛋白和灭活疫苗均可显著提升奥利亚罗非鱼和大菱鲆血清抗体水平,而LIP342诱导的血清抗体水平均显著高于灭活疫苗;经0.1 mL 1×10~9cfu/mL的无乳链球菌攻毒后,LIP342蛋白和灭活疫苗对供试鱼的累积存活率均显著高于PBS对照组。结果表明,高度保守的LIP342具有较好的免疫原性,可作为无乳链球菌亚单位疫苗候选因子。     

巴氏杀菌乳中金黄色葡萄球菌的生长预测模型构建

巴氏杀菌乳中金黄色葡萄球菌污染可能会产生肠毒素,对人体健康造成危害。分别监测在4、10、16、20、24、28 ℃储藏条件下金黄色葡萄球菌在巴氏杀菌乳中的生长数据,采用Modified Gompertz模型、Logistic模型、Huang模型和Baranyi模型构建金黄色葡萄球菌动力学一级模型,采用平方根模型和Arrhenius模型建立二级模型以描述温度与相对最大生长速率(μ_max)的关系。结果显示,各温度下Modified Gompertz模型的拟合度更优,决定系数(R²)>0.98,均方根误差(RMSE)<4.6,为最合适的一级模型。二级模型中,Arrhenius模型的拟合度更优(R²=0.99,RMSE=0.60)。相较于平方根模型,外部验证显示Arrhenius模型的精确度因子(A_f)和偏差因子(B_f)分别为1.39和0.87,较接近于1,说明预测效果更好。研究结果可为巴氏杀菌乳中金黄色葡萄球菌的风险评估提供数据基础,为乳品货架安全期预测提供科学依据。