The effect of feeding frequency on growth performance of juvenile cobia,Rachycentron canadum (Linnaeus, 1766)

The present study was carried out to investigate the number of daily feeding sessions that results in maximum growth of juvenile cobia under laboratory conditions. Groups of eight fish (110 g) were randomly distributed in twenty 500‐L tanks and hand‐fed a commercial diet for 60 days. The same amount of feed was offered daily, divided in 1, 2, 3, four or six meals. None of the parameters associated with growth performance (survival, weight gain, specific growth rate, feed intake, condition factor or size variation) showed any significant differences among treatments. Although under the present conditions feeding frequency had no effect on the growth performance of cobia larger than 110 g, in commercial farming operations where large numbers of fish are kept within a single rearing structure, fish may have aggressive interactions during feeding. Under these conditions, it is difficult to ensure that all cobia are fed to satiation and thus it is usual to provide two or more meals per day. The present results indicate that for an individual cobia the provision of more than one daily meal has no significant effect on growth performance.     

军曹鱼血液指标及血细胞发生的观察

测定军曹鱼的血液指标,红细胞密度为2．69±0．86×106个/mm3,白细胞密度为1．50±0．09×104个/mm3;血 红蛋白含量为7．42±0．22g/L,红细胞渗透脆性为0．43±0．07g％,红细胞沉降速率为1．18±0．46mm/h。观察军曹鱼 外周血液涂片,可区分出红细胞、血栓细胞、淋巴细胞、嗜中性粒细胞和单核细胞,但没有发现嗜酸性粒细胞和嗜碱 性粒细胞。在外周血液涂片观察中还发现了较多未成熟的红细胞和嗜中性粒细胞以及少量正在分裂的红细胞。 血栓细胞、淋巴细胞、嗜中性粒细胞和单核细胞在白细胞中所占比例分别为61．20±6．30％,16．60±3．28％,16．00± 3．61％和6．20±3．90％。对肝脏、脾脏、头肾和中肾等四种造血组织进行了涂片观察,军曹鱼的血细胞主要在头肾 和肾脏产生;脾脏是军曹鱼粒细胞发生的另一个场所,而肝脏也具有产生粒细胞和淋巴细胞的作用。       

军曹鱼营养需求与饲料研究进展

目前, 养殖鱼类已成为满足人类对水产品需求的主要来源。军曹鱼(Rachycentron canadum)具有生长速度快、肉质细嫩鲜美、营养价值高等特点, 已成为我国南方重要的海水网箱养殖鱼类。然而, 目前饲养军曹鱼仍主要依靠冰鲜杂鱼, 特别是大规格鱼的养殖, 这严重制约其养殖业的健康发展, 研发适合不同生长阶段需要的配合饲料非常必要。文章重点总结了军曹鱼对蛋白质、脂肪、氨基酸、脂肪酸、微量营养素等的需求, 饲料中鱼粉和鱼油替代研究, 饲料添加剂应用及其饲料产业发展现状, 以期为军曹鱼营养需求和配合饲料开发的深入研究提供参考。     

Genome-wide characterization of microsatellites in cobia Rachycentron canadum (Linnaeus, 1766): Survey and analysis of their abundance and diversity

The cobia Rachycentron canadum, mainly distributed in the warm waters of tropical and subtropical regions around the world, remains a fish of considerable economic importance. Detailed diversity and the number of microsatellite sequences in the cobia genome are still unintelligible. The primary aim of this work was to identify and quantify the miscellaneous SSR sequences in the cobia genome. More than 280,000 sequences were sequenced and screened using next-generation sequencing technology and microsatellite identification. Perfect mononucleotide repeats, dinucleotide microsatellites, and trinucleotide microsatellites contain (A)₁₀/(T)₁₀, (AC)₆/(TG)₆, and (AAT)_5–32 as the largest number of motifs in each type of microsatellite, respectively. The tetranucleotide and pentanucleotide microsatellites (TTM and PTM) consist of the largest number of motifs of both (ATCT)_5–32 and (TCAT)_5–31 in TTMs, and (CTCTC)_5–9 in PTMs, whereas the hexanucleotide microsatellites are rarely observed in the cobia genome. All c. 38000 sequences of composite microsatellites are extremely diverse, including compound (11.71%), interrupted compound (71.77%), complex (0.45%), and interrupted complex (16.07%). In this study, we developed a convenient and useful recording system for writing down and categorizing diverse composite microsatellite types. This system will provide great support for exploring repeat origins, evolutionary mechanisms, and the application of polymorphic microsatellites.     

Response to ocean acidification in larvae of a large tropical marine fish,Rachycentron canadum

Currently, ocean acidification is occurring at a faster rate than at any time in the last 300 million years, posing an ecological challenge to marine organisms globally. There is a critical need to understand the effects of acidification on the vulnerable larval stages of marine fishes, as there is potential for large ecological and economic impacts on fish populations and the human economies that rely on them. We expand upon the narrow taxonomic scope found in the literature today, which overlooks many life history characteristics of harvested species, by reporting on the larvae of Rachycentron canadum (cobia), a large, highly mobile, pelagic‐spawning, widely distributed species with a life history and fishery value contrasting other species studied to date. We raised larval cobia through the first 3 weeks of ontogeny under conditions of predicted future ocean acidification to determine effects on somatic growth, development, otolith formation, swimming ability, and swimming activity. Cobia exhibited resistance to treatment effects on growth, development, swimming ability, and swimming activity at 800 and 2100 μatm pCO₂. However, these scenarios resulted in a significant increase in otolith size (up to 25% larger area) at the lowest pCO₂ levels reported to date, as well as the first report of significantly wider daily otolith growth increments. When raised under more extreme scenarios of 3500 and 5400 μatm pCO₂, cobia exhibited significantly reduced size‐at‐age (up to 25% smaller) and a 2–3 days developmental delay. The robust nature of cobia may be due to the naturally variable environmental conditions this species currently encounters throughout ontogeny in coastal environments, which may lead to an increased acclimatization ability even during long‐term exposure to stressors.     

Ecological niche models reveal the potential zones of invasion of the cobia (Rachycentron canadum) in the Eastern Pacific Ocean

Hydrobiologia - Cobias (Rachycentron canadum) are large fish that live in all the tropical oceans of the world, except for the Eastern Pacific Ocean (EPO). During 2015, a cobia cage culture was...     

Effect of dietary fatty acids on the body tissues of larval and juvenile cobia and their prey

Polyunsaturated fatty acids (PUFAs) have been used as biomarkers in pelagic ecosystems although previous studies have failed to quantify the timing of conservation of dietary PUFAs in pelagic fishes and invertebrates. Here we investigated the influence of diet upon the timing of conservation of PUFAs throughout multiple trophic exchanges in larval and juvenile cobia (Rachycentron canadum) and their prey. Cobia, rotifers (Brachionus plicatilis), and Artemia (A. franciscana) were fed laboratory processed or natural diets resembling prey and dietary modification of fatty acid signatures was quantified using two-source mixing models. Specimens were collected throughout the experiment to track dietary influences over time. Cobia larvae underwent significant dietary modification of PUFAs after 24 h and conserved > 90% of dietary PUFAs after an average of 6 days. Similar results were identified in juvenile cobia as significant dietary modification of PUFAs took place after 3 days and > 90% were conserved after an average of 12 days. In addition, no significant ontogenetic changes in PUFA signatures were identified in juvenile cobia throughout the 30-day experiment. PUFA signatures in prey items (rotifers and Artemia) underwent significant dietary modification in 24 h, with over 90% incorporation after 5-7 days. Results from this study support the premise that fatty acids are promising dietary indicators and may be useful for future studies examining trophic relationships in marine ecosystems and habitat use of marine fishes.     

THE EFFECTS OF VALINE LEVEL ON PLASMA BIOCHEMICAL INDEXES,LIPID CONTENT AND GENE EXPRESSION INVOLVED IN LIPID METABOLISM IN COBIA (RACHYCENTRONCANADUM)

实验旨在研究饲料缬氨酸水平对军曹鱼(Rachycentron canadum)[初始体质量为(40.90.8) g]鱼体脂肪含量、血浆生化指标和肝脏脂肪代谢基因表达的影响。在基础饲料中梯度添加晶体缬氨酸, 配制出缬氨酸含量分别为1.26% (缺乏组)、2.21% (适量组)和2.62% (过量组)3种等氮等脂饲料, 饲喂养殖在海水浮式网箱的军曹鱼10周, 每天饱食投喂2次。结果表明, 缬氨酸缺乏组的军曹鱼鱼体和肌肉脂肪含量显著低于缬氨酸适量组和过量组(P0.05)。肝脏脂肪含量随着饲料中缬氨酸含量从1.26%升高到2.21%而显著升高(P0.05), 然后随之而逐渐下降(P0.05)。军曹鱼血浆总蛋白和总胆固醇含量在缬氨酸缺乏饲料组显著低于其他各处理组(P0.05)。饲料缬氨酸水平对军曹鱼血浆谷草转氨酶和谷丙转氨酶均无显著影响(P0.05)。军曹鱼肝脏固醇调节元件结合蛋白-1 (sterol regulatory element binding protein-1, SREBP-1)基因表达水平和肝脏脂肪酸合成酶(FAS)表达量, 均随着饲料缬氨酸水平增加而显著升高(P0.05)。军曹鱼肝脏过氧化物酶体增殖物激活受体(peroxisome proliferator activated receptor, PPAR)表达量在缬氨酸适量组, 显著低于过量组(P0.05), 而与缺乏组差异不显著(P0.05)。而随着缬氨酸含量升高, 肉毒碱棕榈酰转移酶-1 (CPT-1, Carnitine palmitoyltransferase-1)表达量逐渐下降(P0.05)。总之, 饲料缺乏缬氨酸可减少军曹鱼鱼体脂肪积累。饲料中缬氨酸水平对军曹鱼鱼体脂肪沉积的影响, 可能是通过调控脂肪合成和-氧化相关基因表达而实现的。     

Ubiquitous perivenous smooth muscle cords in viscera of the teleost Rachycentron canadum,with special emphasis on liver

The liver of the cobia, Rachycentron canadum, was examined by gross dissection, histological, and ultrastructural procedures. Other visceral organs were examined by histological techniques only. Unique perivenous smooth muscle cords are associated with veins in these systems, but they are particularly prominent in their association with the hepatic portal veins and their numerous intrahepatic branches. The perivenous smooth muscle cords accompany tributaries of the portal veins to the junction of the venules with the hepatic sinusoids. The reciprocal contraction and relaxation of various segments of the smooth muscle cords appear to result in pooling of blood in temporary reservoirs and in its transport to various regions of the organ. This process might apply to other organ systems as well. Possibly this unique relationship of the smooth muscle cords with veins functions in a diving reflex. Triads are occasionally encountered in the cobia liver. © 1992 Wiley-Liss, Inc.     

Purification of a toxic metalloprotease produced by the pathogenic Photobacterium damselae subsp. piscicida isolated from cobia (Rachycentron canadum)

The aim of the present study was to purify and characterize a toxic protease secreted by the pathogenic Photobacterium damselae subsp. piscicida strain CP1 originally isolated from diseased cobia (Rachycentron canadum). The toxin isolated by anion exchange chromatography, was a metalloprotease, inhibited by L-cysteine, ethylenediaminetetraacetic acid (EDTA), ethylene glycol-bis(beta-aminoethyl ether)N,N,N',N'-tetraacetic acid (EGTA), 1,10-phenanthroline, N-tosyl-L-phenylalanine-chloromethyl ketone (TPCK), and N-alpha-p-tosyl-L-lysine-chloromethyl ketone (TLCK), and showed maximal activity at pH 6.0-8.0 and an apparent molecular mass of about 34.3 kDa. The toxin was also completely inhibited by HgCl2, and partially by sodium dodecyl sulfate (SDS) and CuCl2. The extracellular products and the partially purified protease were lethal to cobia with LD50 values of 1.26 and 6.8 microg protein/g body weight, respectively. The addition of EDTA completely inhibited the lethal toxicity of the purified protease, indicating that this metalloprotease was a lethal toxin produced by the bacterium.     

Effects of dietary chitosan and Bacillus subtilis on the growth performance, non-specific immunity and disease resistance of cobia, Rachycentron canadum

The present study was performed to investigate the effects of various levels of dietary Bacillus subtilis and chitosan on the growth performance, non-specific immunity and protection against Vibrio harveyi infection in cobia, Rachycentron canadum. Fish were fed with the control diet and six different experimental diets containing three graded levels of B. subtilis at 2 × 10(10) CFU g(-1) (0.0, 1.0, 2.0 g kg(-1) diet) for each of two levels of chitosan (3.0 and 6.0 g kg(-1) diet). The results of 8 weeks feeding trial showed that the survival rate ranged from 81.3% to 84.0% with no significant difference (P > 0.05). The SGR (%) in the fish fed with dietary treatments was significantly higher than that of the control fish except diet 6 group with 2.0 g kg(-1)B. subtilis and 3.0 g kg(-1) chitosan. The serum lysozyme activities were significantly higher in 6.0 g kg(-1) chitosan groups and no significant differences were observed among B. subtilis levels. The serum ACP activities were significantly higher in 3.0 g kg(-1) chitosan groups at 0.0 and 1.0 g kg(-1)B. subtilis levels; at low chitosan level, the cobia fed diets with 1.0 g kg(-1)B. subtilis had significantly higher serum ACP activity, but at high chitosan level, the cobia fed diets with 2.0 g kg(-1)B. subtilis had significantly higher serum ACP activity. The phagocytosis and respiratory burst activity in the fish fed with dietary treatments was significantly higher than that of the control fish except diet 3 group with 6.0 g kg(-1) chitosan. Moreover, fish fed the diet containing 2.0 g kg(-1)B. subtilis and 6.0 g kg(-1) chitosan had significantly higher post-challenge survival on the 7th day following V. harveyi infection and post-challenge survival showed clearly the synergistic effect of chitosan and B. subtilis. Based on these results, the combination of 1.0 g kg(-1)B. subtilis and 6.0 g kg(-1) chitosan is optimal for the growth, innate immunity and disease resistance of cobia with an 8-week oral administration.     

Isolation and Characterization of Pathogenic Vibrio harveyi(V. carchariae) From the Farmed Marine Cobia Fish Rachycentron canadum L. with Gastroenteritis Syndrome

An outbreak of serious mortality among the cultivated juvenile cobia Rachycentron canadum L. (weighing 8–10 g) characterized by a swollen intestine containing transparent yellow fluid (ascites and gastroenteritis) occurred in August 2001 in Taiwan. Ten motile bacterial strains, C3d1–C3d10, were isolated from head kidney (an organ located near the head of the fish) and/or the intestinal yellow fluid on tryptic soy agar supplemented with 1% NaCl (TSA1) and/or thiosulphate citrate bile salt sucrose (TCBS) agar plates. These strains were characterized and identified as Vibrio harveyi(V. carchariae) on the basis of biochemical characteristics, and comparisons with those of three reference strains, originally identified as V. harveyior V. carchariae. The strain C3d1 was selected as a representative strain for virulence tests and was found lethal to the cobia with an LD₅₀ value of 7.48 × 10⁴ colony forming units g^–1 fish body weight. All the moribund/dead fish exhibited gastroenteritis as that observed in natural outbreak. The same bacteria could be reisolated from kidney and the transparent yellow fluid of swollen intestine of fish after bacterial challenge using TSA1 and TCBS plates. This is a first report showing that V. harveyi(V. carchariae) is the causative agent of gastroenteritis in the cobia.     

Elevated oxygen uptake and high rates of nitrogen excretion in early life stages of the cobia Rachycentron canadum (L.), a fast-growing subtropical fish

Physiological energetics of cobia Rachycentron canadum were quantified for 18 to 82 days post-hatch (dph) hatchery-reared juveniles to better understand energy transformation and its implications in growth and survival. Mean oxygen consumption rates ( ; mg O₂ h⁻¹) of fish fed ad libitum and fish that were starved significantly increased with increasing wet mass (M; g), = 1·4291 M ^0·8119 and = 1·1784 M ^0·7833, respectively, with a significant reduction in mean metabolic rates of starved fish (19 to 27% specific dynamic action; SDA). Total ammonia nitrogen excretion rates ( A _MM, μmol h⁻¹) also scaled with M and significantly decreased after starvation. Mean mass-specific A _MM and urea excretion rates are the highest reported in the literature, with urea accounting for approximately half the total nitrogen excretion measured in both fed and starved fish. Relatively high energetic rates may allow cobia to develop rapidly into pre-juveniles and be less susceptible to predation and starvation at a comparatively early age.     

饲料中不同水平鱼蛋白水解物对军曹鱼稚鱼生长及体组成的影响

设计4种等能等氮试验饲料,对照组以鱼粉为单一蛋白源,处理组分别以鱼蛋白水解物替代鱼粉蛋白的17%、34%和51%,军曹鱼(Rachycentron canadum)稚鱼的初始重为(3.79±0.22)g,实验在室内流水养殖系统中进行6周的饲养试验,每种饲料随机3个重复。试验结果显示不同水平鱼蛋白水解物对试验鱼的存活率没有显著影响(P>0.05),除了以鱼蛋白水解物替代鱼粉蛋白51%组外,其他各组的增重率(WG)和饲料摄入量(FI)都是随着饲料中鱼蛋白水解物替代鱼粉蛋白量的增加而增加。试验结果表明,在军曹鱼稚鱼饲料中用鱼蛋白水解物替代34%的鱼粉蛋白对于军曹鱼稚鱼的生长和饲料摄入量具有一定的促进作用。军曹鱼稚鱼血浆中胆固醇含量随着饲料中鱼蛋白水解物添加水平的升高而升高,而血浆中的总蛋白含量则无此规律,各处理组血浆中的甘油三酯无显著差异(P0.05)。       

军曹鱼催乳素受体PRLR1基因的克隆及其在不同盐度条件下mRNA表达差异

催乳素受体通过结合催乳素,能调节鱼体渗透压。为研究催乳素受体1(PRLR1)在高盐水体和低盐水体中对军曹鱼(Rachycentron canadum)的渗透调节作用,利用cDNA末端快速扩增(RACE-PCR)技术,获得了军曹鱼PRLR1全长cDNA序列。该基因全长为2629 bp,包含1953 bp的开放阅读框ORF,可编码650个氨基酸。氨基酸序列包含了2个纤维连接蛋白3型结构域(FN3)、保守的WS区和box1。采用qRT-PCR技术,检测不同盐度(10‰、30‰和35‰)条件下鳃、肠、体肾中PRLR1基因mRNA表达情况。结果显示,PRLR1基因在军曹鱼的各个组织中均有表达,其中鳃表达量最高,其次是肌肉、体肾和肠,而在胃、脾、脑和心脏中则微量表达。低盐组、正常组和高盐组中,PRLR1基因的表达量均为鳃最高;肠次之;体肾最低。随着盐度提高,PRLR1基因的鳃、肠和体肾组织表达量变化规律均呈逐步下降趋势。以上结果反映了军曹鱼PRLR1在渗透压器官中的功能差异性,说明PRLR1在军曹鱼渗透压调节上具有重要作用。     

Gonad maturation and spawning of cobia,Rachycentron canadum (Linnaeus, 1766) off the Dungun coast,Malaysia

The reproductive biology of cobia, Rachycentron canadum, from the coastal waters of Dungun, Malaysia was studied from June 2014 to May 2015. From commercial trawls, a total of 201 samples (combined sexes) were collected (fork lengths [FL] 37.5–124.0 cm; body weights 0.5–20.4 g). The overall sex ratio of females to males was 1:0.9, which was not significantly different (χ² = 2.12, df = 1; p < .05). Estimations of length at 50% maturity (L₅₀) showed that both sexes matured at approximately 75 cm FL; estimated spawning frequency was 6 days. Mean batch fecundity (BF) ranged from 0.55 to 4.32 million eggs. The average number of eggs per gram of ovary was from 2,100 to 5,400 eggs, and relative fecundity 147 eggs/g. There was a weak positive correlation (r² = .48) between BF and female FL as well as BF with an ovary‐free body weight (r² = .56), possibly due to females being in a continuous spawning condition and some possibly half‐spent, based on the histological examination of the female gonads. Despite cobia being asynchronous spawners, the gonadosomatic index in both males and females showed peaks in June, November, and particularly March. Based on histological examination, spawning‐capable males were encountered throughout the study period, whereas spawning‐capable females in the late developing subphase were found mostly in March and April. This is the first study on the reproductive aspects of cobia in Malaysian waters.     

Identification and expression analysis of cobia (Rachycentron canadum) Toll-like receptor 9 gene

Cobia culture is hindered by bacterial infection (Photobacterium damselae subsp. piscicida) and in order to study the effect of P. damselae subsp. piscicida challenge and CpG ODN stimulation on cobia Toll like receptor 9 (RCTLR9), we used PCR to clone RCTLR9 gene and qRT-PCR to quantify gene expression. The results indicated that RCTLR9 cDNA contains 3141 bp. It encodes 1047 amino acids containing 16 typical structures of leucine-rich repeats (LRRs) including an LRRTYP, LRRCT and a motif involved in PAMP binding was identified at position 240–253 amino acid. Broad expression of RCTLR9 was found in larval, juvenile and adult stages irrespective of the tissues. In larval stage, RCTLR9 mRNA expression decreased at 5 d and then increased at 10 dph. At juvenile stage cobia, the expression was significantly high (p < 0.05) in spleen and intestine compared to gill, kidney, liver and skin. However, at adult stage, the significant high expression was found in gill and intestine. Cobia challenged with P. damselae subsp. piscicida showed significant increase in RCTLR9 expression at 24 h post challenge in intestine, spleen and liver, while in kidney the expression was peak at 12 h and later it decreased at 24 h. The highest expression was 40 fold increase in spleen and the lowest expression was ∼3.6 fold increase in liver. Cobia stimulated with CpG oligonucleotides showed that the induction of these genes was CpG ODN type and time dependent. In spleen and liver, CpG ODNs 1668 and 2006 injected group showed high expression of RCTLR9, IL-1β, chemokine CC compared to other groups. Meanwhile, CpG ODN 2006 has induced high expression of IgM. The CpG ODNs 2395 have induced significant high expression of Mx in spleen and liver. These results demonstrates the potential of using CpG ODN to enhance cobia resistance to P. damselae subsp. piscicida infection and use as an adjuvant in vaccine development.     

Effect of dietary vitamin C on the growth performance and innate immunity of juvenile cobia (Rachycentron canadum)

This study was conducted to evaluate the effects of dietary vitamin C on growth performance, hematologic parameters and innate immune responses in juvenile cobia, Rachycentron canadum. Seven practical diets were formulated to contain 0.0 (as the basal diet), 13.6, 27.2, 54.4, 96.6, 193.4 and 386.5 mg ascorbic acid equivalent kg(-1) diet. Each diet was fed to triplicate groups of juvenile cobia with initial body weight of 5.5 g in 500-L cylindrical fiberglass tank. The results of 8 weeks feeding trial showed that typical vitamin C-deficient signs such as spinal deformation and body nigrescence were observed in the fish fed the basal diet. Fish fed the basal diet had significantly lower weight gain, specific growth rate (SGR), protein efficiency ratio (PER) and feed efficiency (FE) than those fed the diets supplemented with vitamin C, but no significant differences were observed among diets supplemented with vitamin C. However, survival rate was significantly affected by the dietary vitamin C levels, fish fed the basal diet had lower survival rate than those fed the diets supplemented with vitamin C. The ascorbic acid concentration in liver was correlated positively with the dietary vitamin C levels, however, the thiobarbituric acid reactive substances (TBARS) concentrations in liver was not significantly affected by the dietary vitamin C levels, although, fish fed the basal diet had the highest TBARS values among all treatments. The activities of serum lysozyme, superoxide dismutase (SOD), alkaline phophatase (AKP) and total immunoglobulin (Ig) were significantly influenced by the dietary vitamin C levels, fish fed the basal diet had lower lysozyme, SOD, AKP and total Ig than those fed diets supplemented with vitamin C. The serum glucose and triglyceride concentrations were significantly affected by the dietary vitamin C levels. Fish fed the basal diet had lower red blood cell and hemoglobin values than those fed the vitamin C supplemented diets. The challenge experiment with Vibrio harveyi showed that lower cumulative survival was in fish fed the unsupplemented diet, the cumulative survival were significantly increased with increase of the dietary ascorbic acid levels from 13.6 to 96.6 mg kg(-1), while the cumulative survival reached plateau when dietary ascorbic acid levels increased from 96.6 to 386.5 mg kg(-1). These results indicated that dietary vitamin C did significantly influence on growth performance and immune response of juvenile cobia.