Development of a homologous radioimmunoassay for Mediterranean yellowtail (Seriola dumerilii, Risso 1810) LH

Purified Mediterranean (M.) yellowtail luteinizing hormone-like gonadotropin (MyLH) and its β-subunit (MyLHβ) served to develop a radioimmunoassay (RIA) for MyLH. The rabbit antisera against MyLH and MyLHβ used for this purpose were tested on pituitary sections by immunocytochemistry. Anti-MyLHβ specifically detected a single type of cells, which were located at the periphery of the proximal pars distalis (PPD) and surrounding the pars intermedia (PI). Anti-MyLH, however, also recognized two other cell types, thyrotropin β-immunoreactive (ir) cells and putative follicle-stimulating hormone-like (MyFSH)-producing cells. Labeling of the two latter cell types was prevented by preabsorption of anti-MyLH with M. yellowtail pituitary glycoprotein -subunit. The standard curve for the RIA was generated using purified MyLH, ¹²⁵I-labeled MyLHβ and anti-MyLHβ at a dilution of 1:70,000, which resulted in the binding of 30% of the tracer added. The standard curve ranged from 0.25 to 50 ng/ml. The midrange of the assay (ED50) was obtained with 5.48–7.87 ng LH/ml. The variation between assays was less than 15%. An average cross-reactivity of FSH in the LH RIA of 8.4% was found. Serial dilutions of M. yellowtail pituitary extracts displaced radiolabelled MyLHβ parallel to the MyLH standard. Application of the LH RIA to blood samples and pituitary cell culture medium provided physiological validation of the assay. Significant increases in LH levels were recorded after salmon GnRH treatments in vivo and in vitro. Serum LH levels from wild fish sampled at the spawning season were significantly higher than those from captive fish sampled in the same period.     

Encephalomyelitis associated with microsporidian infection in farmed greater amberjack, Seriola dumerili (Risso)

An outbreak of a disease characterized by a peculiar spiral movement in farmed greater amberjack, Seriola dumerili (Risso), occurred in Kagoshima Prefecture, Japan, in May 2008, immediately after importing the fish from China. Although neither bacteria nor viruses were detected in routine diagnostic tests, histopathological observations of the affected fish revealed severe inflammation in the tegmentum of the brain including the medulla oblongata and the anterior part of the spinal cord. In addition, a microsporidian parasite was observed in the nerve cell bodies or axons in the inflamed tissues. We identified a microsporidian small subunit rRNA gene (SSU rDNA) from the lesion, and the sequence showed 96.1% identity with that of Spraguea lophii. Subsequent in situ hybridization using probes presumably specific to the SSU rRNA confirmed that the parasite observed in histopathology harboured the identified SSU rRNA. Apparently degenerated microsporidian cells or spores were also frequently observed in tissue sections. Thus, the disease was most probably caused by the infection of a hitherto unknown microsporidian parasite that has a genetic affinity to the genus Spraguea, in the central nervous system of the amberjack.     

Increased melanomacrophage centres in the liver of reproductively dysfunctional female greater amberjack Seriola dumerili (Risso, 1810)

The greater amberjack Seriola dumerili is a new aquaculture fish that may display reproductive dysfunctions. During extensive follicular atresia, which is a common reproductive dysfunction in females during vitellogenesis, part of the reabsorbed yolk returns to the liver to be metabolized and recycled. Melanomacrophage centres (MMCs) are aggregates of macrophage-like cells that play a role in the destruction, detoxification and recycling of endogenous and exogenous materials, and have been associated with systemic stress. Wild and captive-reared greater amberjack were sampled in the Mediterranean Sea during two different phases of the reproductive cycle. The liver of reproductively dysfunctional captive-reared females sampled during the spawning season showed a high density of both MMCs and apoptotic cells. A weak liver anti-cytochrome P450 monooxygenase 1A immunoreactivity was observed, suggesting that the examined fish were not exposed to environmental pollutants. We propose that the observed increase in MMCs and apoptosis in captive-reared fish was related to the hepatic overload associated to the metabolism of yolk proteins reabsorbed during extensive follicular atresia. Since follicular atresia is a frequent physiological and pathological event in teleosts, we suggest that the reproductive state should be always assessed when MMCs are used as markers of exposure to stress or pollutants.     

Effect of temperature on growth performance of greater amberjack (SERIOLA DUMERILI Risso 1810) Juveniles

In order to successfully diversify Mediterranean aquaculture, it is necessary to determine optimum culture conditions of potential candidate species such as greater amberjack (Seriola dumerili). Among culture conditions, rearing temperature is a key factor for achieving optimum growth and maintaining fish welfare. However, little is known about the optimum culture conditions of greater amberjack (Seriola dumerili). Thus, the aim of this study was to determine the effect of three different rearing temperatures (17, 22 and 26°C) during 120 days on growth performance, body morphometry, biochemical composition, gut transit and liver morphology of greater amberjack (Seriola dumerili) juveniles. After 120 days of rearing, fish raised at 26°C showed higher (p < .05) body weight and specific growth rate than fish held at lower temperatures, as well as improved feed utilization, protein efficiency and nutrient retention percentages. Fish stomach emptying was faster (p < .05) in fish raised at 26°C than in fish held at 22°C and 17°C. Similar results were obtained for gut transit time, being gut emptying faster (p < .05) in fish reared at 26°C than in fish cultured at lower temperatures. Rearing temperature also induced changes in fish morphology which resulted in a higher (p < .05) caudal propulsion efficiency index for fish reared at 26°C. Based on these results, we conclude that greater amberjack fingerlings perform better at 26°C than at 22°C or 17°C.     

The reproductive biology of the amberjack, Seriola dumerilii (Risso 1810). I. Oocyte development in captivity

A study of the reproductive biology of the amberjack, Seriola dumerilii, held in captivity was carried out, describing oogenesis as well as the different stages of the ovarian cycle. Seven stages of oocyte development, as well as oogonia, were distinguished. Cortical alveoli were hardly detectable within the oocyte, as they were small, sparse and contained few mucopolysaccharides. It is suggested that their role in the fertilization process might be less important than in other teleost species. Fish aged 3 and 4 years were found to be sexually immature, with ovaries containing only previtellogenic oocytes. Vitellogenesis started in December in fish aged 4 + years. Late-developing ovaries showing deposition of yolk protein granules were found at the end of the 5th year of life (May) in specimens measuring 80.0 ± 3.5 cm standard length. This should be regarded as the minimum size at which sexual maturity is reached in S. dumerilii. Final vitellogenesis and oocyte maturation were, however, inhibited in captivity, and extensive follicular atresia took place as the natural spawning season approached. It is suggested that insufficient gonadotrophic stimulation because of confinement stress may be the cause of failed maturation and spawning in this species under culture conditions.     

Optimum digestible protein and energy levels and ratio for greater amberjack Seriola dumerili (Risso) fingerling

A study was conducted to determine optimum dietary digestible protein (DP) and digestible energy (DE) levels and DP DE⁻¹ ratio for growth of greater amberjack Seriola dumerili fingerlings. A 3 × 3 factorial design with duplication was used in this study. Nine experimental diets were formulated to contain three levels of crude protein (CP; 420, 470 and 530 g kg⁻¹) and three levels of crude lipid (CL; 130, 180 and 230 g kg⁻¹). Nine groups of fingerling (initial weight 51.8 g) were fed each experimental diet for 40 days. Final body weight, feed efficiency, specific growth rate and energy efficiency were significantly affected by dietary protein and lipid level. These parameters tended to improve with increasing dietary protein level. Conversely, an increase of lipid level negatively affected these parameters. High growth rate and feed efficiency were obtained from fish fed the diet containing 393 g kg⁻¹ DP and 14.2 MJ kg⁻¹ DE (27.7 g MJ⁻¹ DP DE⁻¹). The high DP DE⁻¹ (27.7 g MJ⁻¹) indicates that greater amberjack fingerling are highly dependent on dietary protein as an energy source.     

Epitheliocystis infection in wild and cultured sea bream (Sparus aurata, Sparidae) and grey mullets (Liza ramada, Mugilidae)

Heavy infection with epitheliocystis on gills caused mortality in hatchery-born Sparus aurata. Histopathological findings showed extensive proliferation of the gill epithelium around the epitheliocystis capsule. Such proliferation was not observed in benign infections. Epizootic infections thus occurred only in hatchery-born S. aurata. In S. aurata and mullets reared from natural stocks, infection remained benign and sporadic. Epitheliocystis infections were also found in juvenile mullets from the east Mediterranean waters as well as from the Gulf of Elat, Red Sea.     

黄条(鱼狮)染色体多种显带的形态特征分析

为详细了解黄条染色体带型的形态特征,实验采用体内注射植物血细胞凝集素(PHA)和秋水仙素的方法,取黄条全部头肾细胞经低渗处理、卡诺氏液固定、空气干燥法制备染色体分裂相。通过不同的研究方法,分别研究和探讨其中期染色体多种带型(C带核型、G带核型和Ag-NORs)的显带特征和形态特征。黄条的带型研究结果显示:(1)C带特征为48条染色体均有大小不一的C带,其中第2、4、5、16、18和19对染色体具有端部C带,其余均为着丝粒C带,无居间带和整体呈C带阳性深染染色体;计算异染色质含量约31.53%;(2)Ag-NORs带特征为第5对染色体末端具有Ag-NORs,为端部AgNORs;银染显现间期核中核仁的数目为1~2个,显现出2个核仁的细胞数目较多,达到60%;(3)G带特征为同源染色体G带带纹大小和位置基本吻合,非同源染色体G带带纹大小和带纹的位置不尽相同。每条染色体都有数量不等的深染带和浅染带,无整条染色体显示深染G带或浅染G带,24对染色体中在条带的数量、大小、位置、染色深浅等方面未发现完全相同的染色体G带。该研究结果可为黄条种质判定、染色体组学研究和遗传育种等提供基础资料。     

Susceptibility by amberjack (Seriola dumerili), yellowtail (S. quinqueradiata) and Japanese flounder (Paralichthys olivaceus) to Neobenedenia girellae (Monogenea) infection and their acquired protection

This study investigated: 1) susceptibility differences to infection by Neobenedenia girellae (Capsalidae) between amberjack Seriola dumerili (Carangidae), yellowtail S. quinqueradiata and Japanese flounder Paralichthys olivaceus (Paralichthyidae); 2) growth and egg production of N. girellae on each fish species; 3) acquired protection of each fish species against this parasite. The number of N. girellae on S. dumerili was significantly higher than on S. quinqueradiata and P. olivaceus when these fishes were exposed to oncomiracidia in the same aquarium. Neobenedenia girellae growth on S. dumerili was fastest and, thus the number of eggs laid by parasites on S. dumerili was greater than on the other two species. Seriola dumerili and P. olivaceus, which were previously infected with N. girellae and treated by freshwater bath, acquired partial protection against re-infection by N. girellae. The relative re-infection of three S. dumerili individuals out of eleven individuals was markedly low compared with the initial infection, and the relative initial infection and re-infection on two P. olivaceus out of eleven individuals was markedly low. The results of this study could be useful to control N. girellae infections when cultivating S. dumerili, S. quinqueradiata and P. olivaceus.     

黄条鰤幼鱼胃排空特征、消化酶活性及摄食调控基因表达

为阐明黄条鰤幼鱼摄食消化特性，构建最佳胃排空数学模型，确立最适摄食投喂间隔，实验检测了黄条鰤幼鱼[(63.96±5.63) g]胃排空过程中内容物质量、肝脏和肠道中消化酶活性变化，分析了垂体中摄食调控相关基因的表达，比较了线性模型、平方根模型、立方模型3种数学模型对胃排空曲线的拟合程度。结果显示，黄条鰤在摄食后瞬时胃内容物湿重呈阶段性降低，18 h后降为0，属于直线下降型胃排空类型。胃排空过程中，肝脏淀粉酶、脂肪酶和糜蛋白酶活性呈先上升后下降、随后又上升接着下降的“M”型变化趋势，淀粉酶活性在摄食后0～6 h显著上升，脂肪酶和糜蛋白酶活性在0～9 h显著上升。三种酶活性在9～12 h均呈显著下降趋势，在15～18 h显著上升，且在18 h活性达到最高；肠道中的淀粉酶在0～6 h显著上升，随后下降，9～12 h呈上升趋势，12 h活性达到最高，随后逐渐下降，其脂肪酶和糜蛋白酶活性则是在摄食后0～12 h显著上升，12 h活性达到最高，随后逐渐下降。神经肽Y (npy)和食欲素(ore) mRNA表达水平呈先上升后下降趋势，npy在摄食后12～15 h内表达水平显著上升，ore在9～15 ...     

Epitheliocystis in silver perch, Bidyanus bidyanus (Mitchell)

Cultured juvenile silver perch, Bidyanus bidyanus (Mitchell), were affected by epitheliocystis, with a prevalence of up to 75%. The condition affected 2–96% of gill filaments. Granular basophilic cysts ranged from 10 to 87 μm and had a round-to-oval shape. The infected cells were positioned centrally within a lamella, often close to its tip, and their identity was difficult to determine, but the involvement of pillar cells could not be precluded. The size of pathogen was within the range previously reported. The pathogen had two morphological forms, which were positioned differently within the cyst. The form located more in the centre was rod-shaped with an electron-dense core and electron-lucent vesicles on the sides of the core. Its mean length was 498.14 nm (SD = 47.68 nm), and its mean width was 145.14 nm (SD = 9.53 nm). The form present in a more peripheral position had an irregular shape, often did not show the electron-dense core and did not have the electron-lucent vesicles. Its mean length was 704 nm (SD = 170.29 nm) and its mean width was 152.4 nm (SD = 16.40 nm). Both forms were enclosed by a double trilaminar membrane. This is the first confirmed report of epitheliocystis in Australian freshwater fish.     

Investigation of the proximate composition,lipid quality,volatile and sensory profiles of wild vs. reared Greater amberjack (Seriola dumerili,Risso)

Greater amberjack is one of the major candidate species for aquaculture diversification; however, with the exception of sporadic data on the proximate (PC) and fatty acid (FA) composition, limited knowledge exists regarding the quality variations occurring between wild and reared Greater amberjack. To expand this knowledge, the current study examined, besides the PC and FA composition of raw tissue, the volatile compounds (VC) and sensory profiles of cooked tissue. The studied specimens originated both from the wild and from aquaculture and were of small commercial size (0.5–1 kg). The FA profiles varied with most profound differences being the lower n‐6/n‐3 ratio and the higher arachidonic (ARA) and docohexaenoic acid (DHA) proportions of wild counterparts. A superior lipid quality was found for reared fish, which was attributed, among other reasons to their significantly (p < .001) higher fillet lipid (wild: 0.27%; reared: 3.92%). The VC profiles differed with rearing origin. Reared Greater amberjack exhibited a significantly higher content in the majority of aromatic hydrocarbons and terpenes, while wild exhibited higher contents for the majority of compounds belonging to the alcohol, aldehyde and ketone groups. Minor sensory profile differences were observed, with reared and wild counterparts exhibiting higher butter and sardine flavour, respectively.     

High‐quality spontaneous spawning in greater amberjack (Seriola dumerili,Risso 1810) and its comparison with GnRHa implants or injections

Production of sufficient high‐quality eggs of greater amberjack (Seriola dumerili) still constitutes the main bottleneck for commercial production of this species. The main objective of this study was to compare the quality of spontaneous spawn of greater amberjack with those obtained by either GnRHa injection or GnRHa implant protocols. Captive amberjack broodstock were distributed in three circular tanks of 40 m³. Broodstock from Tank 1 were not hormonally induced and spawned spontaneously, whereas those of Tank 2 were intramuscularly injected with GnRHa (20 µg/kg body weight) and those of Tank 3 were given EV‐500 µg GnRHa implants. The number of eggs per spawn obtained in the broodstock without hormonal treatment was larger than in those obtained with injections or implants. Egg quality was best in broodstock with spontaneous spawn, followed by GnRHa‐injected fish and then GnRHa implants. Besides, size of larvae from control and injected broodstock was similar between them and significantly higher (p < 0.01) than those from GnRHa implant spawn. Overall, this study showed that it is possible to obtain very high‐quality spontaneous spawn in greater amberjack, providing the adequate conditions. Furthermore, GnRHa weekly injections lead to similar egg viability and hatching rates than spontaneous spawn and higher fertilization rates than GnRHa hormonal implants, which is better than in previous studies.     

Effects of docosahexaenoic acid on growth,survival and swim bladder inflation of larval amberjack ( Seriola dumerili, Risso)

The effect of docosahexaenoic acid (DHA) on the growth performance, survival and swim bladder inflation of larval Seriola dumerili during the rotifer feeding period was investigated in two feeding experiments. Amberjack larvae at 3 day post hatching were fed rotifers enriched with (1) freshwater C hlorella (Chlo), (2) a mixture (2:1, v/v) of Chlo and DHA‐enriched C hlorella (DHA‐Chlo), (3) DHA‐Chlo and (4) DHA‐Chlo and commercial DHA emulsion, in triplicate for 7 days. The average DHA contents of the rotifers were 0.0, 0.4, 1.0 and 1.9 mg g^?1 DM respectively. The survival rate was improved by the enrichment of rotifers with DHA‐Chlo alone, and DHA‐Chlo and emulsion. Growth and swim bladder inflation of fish fed rotifers enriched with DHA‐Chlo were significantly (P < 0.05) improved, however, with increased levels of DHA further improvement was not found. DHA content in the larval whole body proportionally increased with the DHA level in the rotifers. These results suggest that DHA enrichment of rotifers is effective to improve the growth, survival rate and swim bladder inflation of amberjack larvae. The DHA requirement of amberjack larvae is estimated to be 1.5 mg g^?1 on a dry matter basis of rotifers.     

Ontogenetic development of digestive enzymes in yellowtail kingfish Seriola lalandi larvae

The development of digestive enzymes was examined in laboratory-reared yellowtail kingfish larvae from hatching to 36 days after hatching (DAH). The specific activities of amylase, lipase, and alkaline phosphatase showed three distinct phases: a sharp increase in enzyme activity from hatching to the onset of exogenous feeding on 3 DAH, followed by a fluctuation and a general decline toward 18 DAH, and then a period of low activity from 18 to 36 DAH. The total activities of these three enzymes showed a gradual increase from hatching to 18 DAH, followed by a sharp increase toward 36 DAH. In contrast to other enzymes, the specific and total activities of trypsin reached the maximum on 15 DAH and 24 DAH, respectively, and then both activities declined to low levels toward 36 DAH. The dynamics of digestive enzymes corresponded to the anatomical development of the digestive system. The enzyme activities tend to be stable after the formation of gastric glands in the stomach on 15 DAH. The composition of digestive enzymes indicates that yellowtail kingfish is able to digest protein, lipid and carbohydrates at an early stage. However, due to the low level of amylase specific activity after 18 DAH, the carbohydrate component should remain at a low level in formulated diets for fish larvae.     

5-HMF对黄条鰤生长、肠道组织结构及生理特性的影响

为了分析在饲料中添加5-HMF (5-羟甲基糠醛)对黄条鰤(Seriola aureovittata)幼鱼生长、肠道组织结构、血清生化特性、消化道菌群结构等方面的影响,选用360尾平均体重(82.33±2.75)g的黄条鰤,随机分为4组(M0组、M1组、M2组、M3组),每组3个重复,每个重复30尾鱼,M0组为对照组,投喂基础饲料,M1组、M2组、M3组分别投喂添加5-HMF (添加量分别为0.25%、0.5%、1%)的基础饲料,实验持续6周。结果显示:体外Caco-2细胞(人结直肠腺癌细胞)增殖实验表明,本研究所用5-HMF浓度在安全范围内;M2和M3组实验鱼的增重率和特定生长率显著高于M0组(P<0.05),且M2组肥满度显著高于M0组(P<0.05);M2组实验鱼肠道肌层厚度和绒毛高度显著高于M0组(P<0.05); M2和M3组血清中谷胱甘肽过氧化物酶(GSH-Px)、超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性显著高于M0组(P<0.05),而丙二醛(MAD)水平显著降低(P<0.05); M2和M3组实验鱼血清免疫球蛋白M(IgM)和碱性...     

Osmoregulation and differential penetration of two grey mullets, Chelon labrosus (Risso) and Liza ramada (Risso) in estuarine fish ponds

Grey mullet ponds situated in Arcachon Bay on the western Atlantic coast of France, display contrasting mixohaline habitats.The pattern of osmoregulation of Chelon labrosus and Liza ramada exhibiting differential penetration of fish ponds has been investigated. Key variables of salinity and temperature have been considered. The tolerances to low salinities and to fresh water have been determined. The dynamics of variation in plasma osmotic pressure and major plasma electrolytes (Na⁺, Cl^?, K⁺) were studied in terms of: (1) gradual adaptation to a decreasing salinity gradient; (2) effects of a long-term adaptation in fresh water; (3) effects of low temperatures on sea water adapted fish.Both species can adapt to a wide range of salinities; however, while L. ramada show a good hypoosmotic regulation, with no alteration in plasma concentration over a wide range of salinity and after a long stay (5 months) in fresh water, C. labrosus cannot live for long periods of time in a wholly fresh water habitat. Both field samples obtained from thick-lipped grey mullets forced to stay in a freshwater pond and experimentally adapted fish showed, after 3 months, an unequivoqual decrease in plasma sodium and chloride, and plasma osmolality decreased to the same extent; this pattern of no compensation is bound, sooner or later, to end in death. The inability of C. labrosus to develop a long-term hypoosmoregulation in fresh water is referred to salinity preferences which probably limit the upstream penetration of this species.Plasma osmolality and major electrolytes (sodium and chloride) increased in cold (4 °C) sea water. This response might be due to a reduced ability of grey mullets to osmoregulate in cold waters. In the poly-mesohaline ponds, Winter drop in temperature (4–6 °C) causes grey mullets to migrate to the meso-oligohaline ponds where the mean temperature is more elevated (8 °C) and temperature changes less rapid (6–9 °C).