军曹鱼的胚胎发育及仔稚鱼形态观察

为了探明军曹鱼早期发育阶段的特征和规律,本实验通过连续显微观察,记录分析其胚胎及仔稚鱼发育各时期的形态特征和发育特点。结果显示,军曹鱼受精卵呈圆球形,为浮性卵,卵径(1.245±0.065) mm,油球1个,油球直径(0.325±0.027) mm。在水温(27.0±0.5)℃、盐度29、pH值8.3的条件下,军曹鱼卵从受精至孵化出膜约需26 h 30 min,经历合子、卵裂、囊胚、原肠胚、神经胚、器官形成和孵化出膜7个阶段,共24个时期。初孵仔鱼平均全长(3.254±0.096) mm,仔鱼在孵化后第3天开口摄食,眼囊变黑,卵黄囊被消耗约80%,第5天卵黄囊消失,第7天油球耗尽,转化为外源性营养。孵化后第14天全长(19.933±1.118) mm,各鳍鳍条形成,进入稚鱼期;22日龄稚鱼全长(41.140±3.779) mm,尾柄部开始出现鳞片,46日龄的后期稚鱼全长达(116.667±5.916) mm,体表完全覆盖鳞片,除尾鳍形状外,体形与成鱼相似。     

军曹鱼幼鱼对赖氨酸需要量的初步研究

选择体重为(14.7±0.3)g的军曹鱼(Rachycentron canadum)幼鱼,平均分成5组,分别饲喂含赖氨酸为2.30%、2.53%、2.76%、2.99%和3.22%的等氮等能精制饲料.以增重率为指标,一元二次回归分析表明,军曹鱼对饲料中赖氨酸的适宜需要量为6.06 g·(100 gCP)-1.通过鱼体的必需氨基酸模式推算出其它必需氨基酸需要量,分别是:精氨酸4.97 g·(100 gCP)-1;色氨酸0.83 g·(100 gCP)-1;亮氨酸5.49 g·(100gCP)-1;异亮氯酸3.12 g·(100gCP)-1;蛋氨酸 胱氨酸2.66 g·(100gCP)-1;苯丙氨酸 酪氨酸5.22g·(100 gCP)-1;丝氨酸2.96 g·(100gCP)-1;苏氨酸3.26 g·(100gCP)-1;纈氨酸3.26 g·(100 gCP).     

军曹鱼肠道及水体异养菌和弧菌的周年变化

采用总活异养菌2216E平板计数法和弧菌TCBS平板计数法对广东深圳大鹏养殖军曹鱼(Rachycentron canadum Linnaeus)养殖水体及鱼肠道细菌进行了周年监测。结果显示,育苗初期养殖水体异养菌和弧菌密度分别为0.63×104～6.2×104CFU/mL和0.30×102～1.03×104CFU/mL,鱼肠道异养菌和弧菌密度分别为0.80×106～7.5×107CFU/g和0～1.30×107CFU/g;网箱养殖监测期间,养殖水体异养菌和弧菌密度分别为4.20×103～5.40×105CFU/mL和0.70×102～1.14×105CFU/mL,鱼肠道异养菌和弧菌密度分别为1.50×107～8.78×108CFU/g和1.00×107～3.50×108CFU/g。周年监测结果显示,水体异养菌、弧菌的数量高峰均出现于8-9月份;肠道异养菌及弧菌的数量高峰均出现于6-7月份,分别又在12月份和2月份出现次高峰,弧菌变化趋势始终与异养菌一致。对分离得到的407株菌鉴定到属并进行多样性分析。结果显示,育苗期水体以假单胞菌(Pseudomonas)、黄单胞菌(Xanthomonas)和芽孢杆菌(Bacillus)为优势菌,三者约占水体异养菌总数的70%;养殖后期,弧菌(Vibrio)和发光杆菌(Photobacterium)的数量逐渐上升并占据一定优势,其中假单胞菌、黄单胞菌、弧菌和芽孢杆菌常年出现。鱼肠道异养菌以假单胞菌和芽孢杆菌为优势菌,其次是肠杆菌科(Enterbacteriaceae)细菌,也多次检测到弧菌、发光杆菌、气单胞菌(Aeromonas)和小球菌(Microccus)等。总之,养殖微生态系统的可持续稳定平衡与系统的种群多样性、群落组成及水质因子等因素相关,而整个环境生态系统的平衡直接影响到鱼类肠道的细菌生态系统。     

军曹鱼消化系统的形态及组织学研究

利用活体解剖和光镜技术对军曹鱼Rachycentron canadum消化系统进行形态及组织学研究。结果显示，军曹鱼消化道由口咽腔、食道、胃、幽门盲囊、前肠、中肠和后肠几部分组成。口咽腔大，粘膜上皮为复层鳞状上皮，内含少量杯状细胞。食道很短，但上皮包括复层鳞状上皮区和单层柱状上皮区。胃膨大，呈Y形，在贵门和幽门部可观测到杯状细胞，胃体粘膜层下有大量的胃腺细胞。幽门盲囊发达，肠短但分3部分，前肠、中肠和后肠，肠道系数为0．43，肠道由前向后杯状细胞和粘膜皱褶不断减少。消化腺包括肝脏和胰腺，肝小叶分界不明显，肝细胞内脂肪含量丰富，胰腺属于散在性的，其外分泌部有许多腺泡组成，胰岛分散于外分泌部间。     

Effects of dietary phospholipid level in cobia (<Emphasis Type="Italic">Rachycentron canadum</Emphasis>) larvae: growth,survival, plasma lipids and enzymes of lipid metabolism

A study was conducted to determine the effects of dietary phospholipid (PL) levels in cobia (Rachycentron canadum) larvae with regard to growth, survival, plasma lipids and enzymes of lipid metabolism. Fish with an average weight of 0.4 g were fed diets containing four levels of PL (0, 20, 40 and 80 g kg⁻¹dry matter: purity 97%) for 42 days. Final body weight (FBW), weight gain (WG) and survival ratio were highest in the 8% PL diet group and mortality was highest in PL-free diet group. We examined the activities of lipoprotein lipase (LPL) and hepatic lipase (HL) in liver, lecithin-cholesterolacyltransferase (LCAT) in plasma as well as plasma lipids and lipoprotein. LCAT activity showed a decrease of more than two-fold in PL-supplemented diet groups compared with the PL-free diet group. HL activity was highest in the 8% PL diet group and the other three groups showed no difference. LPL activity was significantly higher in the PL-supplemented diet groups than in the PL-free diet group. The dietary intervention significantly increased plasma phospholipids and total cholesterol (TC) levels, and the higher free cholesterol (FC) level contributed to the TC level. However, the fish fed PL exhibited a significantly decreased plasma triglyceride (TG) level. The lipoprotein fractions were also affected significantly by the PL. The PL-supplemented diet groups had significantly higher high-density lipoprotein (HDL) compared with the PL-free diet group, but showed a marked decrease in very low-density lipoprotein (VLDL). The results suggested that PL could modify plasma lipoprotein metabolism and lipid profile, and that the optimal dietary PL level may well exceed 80 g kg⁻¹ for cobia larvae according to growth and survival.     

Mass mortality associated with a Sphaerospora-like myxosporidean infestation in juvenile cobia, Rachycentron canadum (L.), marine cage cultured in Taiwan

Cultured cobia, Rachycentron canadum , of 45–80 g exhibited anaemia and ascites, and a mottled red and grey, extremely enlarged kidney with cream-coloured patches or spherical nodules. Cumulative mortality was about 90% within 1 month. Extrasporogonic or sporogonic stages of a myxosporean appeared in the blood, glomerulus, renal tubules and renal interstitium. The renal tubules were the main target tissue of the parasite and were completely occluded by sporogonic pseudoplasmodia at various degrees of maturity. Many sporogonic stages were attached to the brush border of the epithelium of the renal tubules. Mature spores were seen in the lumen of the tubules. They were elongated or spherical with numerous refractile granules in the cytoplasm. The polar filament formed 3–5 coils. No bacteria or viruses were isolated from the diseased fish. Based on the results of microbiological, histopathological and electron microscopical examinations, the cobia disease was believed to be caused by a Sphaerospora -like myxosporean. This is the first report of a myxosporean in cobia in aquaculture.     

军曹鱼稚鱼外周血细胞及其形态学观察

以出膜后第60天的军曹鱼外周血液为材料,利用光镜显微技术研究了其血细胞的种类和形态。外周血液包括5种类型的血细胞,红细胞、淋巴细胞、单核细胞、嗜中性粒细胞和血栓细胞。血细胞计数测得红细胞密度为(2.97±0.82)×109ind.mL-1,白细胞密度为(1.39±0.94)×106ind.mL-1,淋巴细胞、嗜中性粒细胞、单核细胞和血栓细胞在白细胞中所占的比例分别为(53.00±8.51)%、(17.59±4.28)%、(4.78±1.37)%和(24.63±4.08)%。未见到嗜酸性粒细胞和嗜碱性粒细胞。血细胞计数结果表明,红细胞数量远远大于白细胞,白细胞中淋巴细胞数量最多,单核细胞数量最少。实验还观察到处于分裂状态的红细胞、细胞表面有伪足样胞突的小淋巴细胞和细胞表面有许多微绒毛突起的大淋巴细胞、核呈多种形态的单核细胞和中性粒细胞及不同形态的血栓细胞等。     

Amending reduced fish‐meal feeds with marine lecithin,but not soy lecithin,improves the growth of juvenile cobia and may attenuate heightened responses to stress challenge

Sparing of marine resources in aquafeeds can be environmentally and economically advantageous; however, fish meal (FM) replacement can affect the production performance and physiological competence. Phospholipids are increasingly understood to be involved in maintaining growth and vigour in fish and may be deficient in reduced FM formulations. Accordingly, we evaluated the growth and stress tolerance of juvenile cobia fed typical (50% FM) or reduced FM feeds (12% FM) with or without phospholipid amendment [1% marine lecithin (12% FM + Marine PL) or soy lecithin (12% FM + Soy PL)] for 6 weeks in triplicate tanks (N = 3) in a recirculation aquaculture system. The 50% FM feed yielded significantly superior growth and growth efficiency in comparison with the 12% FM and 12% FM+ Soy PL feeds, but the 12% FM+ Marine PL feed yielded comparable results to 50% FM feed. A low‐water stress challenge induced elevated plasma glucose, cortisol and lactate levels in all treatments. However, a significant interaction (diet × stress) effect suggested a lesser cortisol response among fish fed the 12% FM+ Marine PL and 50% FM diets. These findings demonstrate that growth performance and, perhaps, resilience of cobia raised on reduced FM feeds may be improved by the addition of marine‐origin phospholipid to the diet.     

军曹鱼幼鱼维生素C需要量的研究

选用初体均重为25.85 g的军曹鱼幼鱼225尾随机分为5组,每组设3个重复,每个重复15尾.分别投喂添加5种不同剂量维生素C(添加量分别为0、37.5、75、150和300 mg/kg)的试验饲料,试验期为56 d,观察维生素c对军曹鱼幼鱼生长、组织维生素C积累量及非特异性免疫的影响.结果表明,随着饲料中维生素C添加量增加,军曹鱼幼鱼增重率和特定生长率呈现出上升后下降趋势,在75 mg/kg时达到最高值,显著高于0和300 mg/kg组(P<0.05).全鱼粗蛋白质含量随着饲料中维生素C添加量的升高亦呈现先上升后下降趋势,在75 mg/kg时达到最高值,全鱼干物质、粗蛋白质、粗脂肪、灰分含量在各组之间均无显著差异(P>0.05).血清维生素C积累量随着饲料中维生素C添加量的增加呈现先上升后下降趋势,在150 mg/kg时达到最高值且显著高于0 mg/kg组(P<0.05);脑和肝脏中维生素C含量在300 mg/kg时达到最高值.300 mg/kg组脑中维生素C含量显著高于0,37.5和75 mg/kg组(P<0.05),肝脏中维生素C含量显著高于0,37.5和150 mg/kg组(P<0.05).随着饲料中维生素C添加量的增加,溶菌酶活性呈现先上升后下降趋势,在75 mg/kg达到最高,显著高于0,37.5和300 mg/kg组(P<0.05);血清总抗氧化能力呈现上升趋势,75、150和300 mg/kg组显著高于0 mg/kg组(P<0.05);肾抗氧离子自由基在150 mg/kg组达到最高,但各组之间无显著差异(P>0.05).以鱼体增重率和血清溶菌酶含量为指标,经折线模型回归分析求得军曹鱼幼鱼饲料中维生素C的适宜添加量分别为70和80.72 mg/kg.     

Effects of dietary probiotic on the growth performance,non‐specific immunity and disease resistance of cobia,Rachycentron canadum

The present study was performed to investigate the effects of a commercially available probiotic product (compound probiotic) containing Bacillus subtilis 7.0 × 10⁹ CFU g^?1, Bacillus licheniformis 3.0 × 10⁹ CFU g^?1, Lactobacillus spp. 5.0 × 10⁸ CFU g^?1 and Arthrobacter spp. 1.0 × 10⁸ CFU g^?1 on the growth performance, non‐specific immunity and protection against Vibrio harveyi infection in cobia (Rachycentron canadum). Fish were fed diets containing six graded levels of compound probiotic (0.0, 1.0, 2.0, 3.0, 4.0 and 5.0 g kg^?1) for 8 weeks. The results showed that the survival rate ranged from 81.1% to 84.4% with no significant difference among dietary treatments (P > 0.05) after feeding experiment. Dietary compound probiotic significantly increased the specific growth rate (SGR), serum lysozyme, alternative complement pathway (ACP) activity, phagocytosis percentage (PP) and respiratory burst activity of head‐kidney macrophages of cobia. Moreover, feeding of supplemented diets containing compound probiotic resulted in significantly lower mortality against the pathogens Vibrio harveyi compared with the control group. To elevate the growth and immune resistance ability of cobia, an optimal dose of dietary compound probiotic administration determined by second‐order polynomial regression analysis was 3.3 g kg^?1, on the basis of the SGR and mortality after challenge with V. harveyi.