Antibacterial activity of sponge extracts against fish pathogens

The antibacterial properties of organic extracts of 15 species of sponges collected from a depth of 30 m in the coastal waters off Gopalpur (Bay of Bengal) were tested against six virulent fish pathogens. The extracts of 11 sponges showed species‐specific antibacterial activity. Four extracts exhibited broad antibacterial activity against three or more species. Epipolasis topsenti was active against all the six pathogens and showed the lowest minimum inhibitory concentration (MIC) value of 12.5 μg against three pathogens. Chromatographic fractionation of extracts yielded enriched fractions with increased activity and lower MIC values.     

Fish reproductive activity reveals temporal variations predominating spatial heterogeneity in maintaining high functional diversity of a Neotropical reservoir

The reproductive activity of the fish assemblage in a large Neotropical reservoir was evaluated by surveying the occurrence of ichthyoplankton in response to spatial and temporal variation in environmental factors. Fish reproduction was investigated by capturing larvae along representative spatial gradients in the main body (longitudinal) and arms (lateral) of the reservoir. After identification, the captured larvae were classified into different groups according to the functional traits of their parental stock. Sampling occurred monthly at night from October to March over five reproductive periods between 2009 and 2016, using conical-cylindrical plankton nets with flowmeter. Water samples were taken simultaneously allowing the measurement of environmental factors related to reproductive activity. The relationship between the environmental factors and the functional traits was assessed using RLQ and fourth-corner analyses. An evaluation of 51,995 larvae revealed there was greater larval abundance in the lacustrine and transition zones of both longitudinal and lateral gradients. Occurrences often correlated with temporal instead of spatial gradients. Higher rainfall correlated with abundances of detritivorous and migratory species. Higher water levels correlated with higher abundances of non-native species, species without parental care, with external fecundation, and partial spawning. Dry periods, with lower water and higher dissolved oxygen, correlated with higher abundances of insectivores and sedentary species. Although the presence of a dam-free stretch of river upstream of the reservoir had a positive influence on fish larvae in the fluvial zone, the results did not show differentiation along either gradient. Thus, the composition of the functional groups of fish species that reproduce in the Itaipu Reservoir appears to be predominantly influenced by the temporal variation in environmental factors rather than the formation of spatial gradients.     

北部湾西北部饵料浮游动物季节变化及其与鱼卵、仔稚鱼的关系

根据2012年在北部湾西北部广西近海冬、春、夏和秋4个季节的调查资料,探讨了该海域浮游动物总丰度的平面分布、季节变化及鱼卵仔稚鱼的丰度的季节变化,结果表明,调查水域浮游动物的丰度在春夏、秋冬季变化较大,而在冬春与夏秋季变化较小,浮游动物在冬、春、夏、秋四季的平均丰度分别为337.35 ind/m3、280.01 ind/m3、4.32ind/m3和14.78 ind/m3,冬春季明显高于夏秋季,浮游动物数量高峰季比东海提前了一个季节。冬春两季,浮游动物的数量分布特征相近,在湾内和沿岸水域数量高于近海水域。相反,在夏秋季,丰度在近海水域明显高于沿岸及湾内水域。浮游动物在各季节不同的分布特征与该海域沿岸水、外海水和混合水的季节性变化有关,优势种经历了由春季的沿岸暖温种到夏季和秋季的外海暖水种到冬季的沿岸暖水种更替的过程。该海域的主要优势种,冬季为鸟喙尖头溞(Penilia avirostris),春季为中华哲水蚤(Calanus sinicus),夏季和秋季同为肥胖软箭虫(Flaccisagitta enflata),主要优势种类的生态适应性决定了浮游动物总数量的分布特征。鱼卵、仔稚鱼在冬、春、夏、秋季的丰度为6.83 ind/m3、3.09 ind/m3、0.05 ind/m3、0.20 ind/m3,季节变化趋势与浮游动物一致,由高到低依次为冬季、春季、秋季、夏季,两者较强的正相关关系表明,食物饵料充足对鱼卵仔鱼的发育具有促进作用。     

Characterization of chymotrypsin activity during early ontogeny of larval red drum (Sciaenops ocellatus)

The temporal evolution of chymotrypsin activity during early ontogeny of laboratory reared red drum larvae was accomplished using a combination of biochemical assays and electrophoretic methods (substrate SDS-PAGE). Optimal functional conditions for chymotrypsin were also determined. Chymotrypsin activity was first detected prior to the onset of exogenous feeding. Total chymotrypsin activity increased with age and standard length. Specific activity was greatest on day 10 post-hatch. Maximal chymotrypsin activity was observed at 50 °C, pH 7.8, and Ca²⁺ concentration of 25 mM. Using substrate gel electrophoresis and specific inhibitors the molecular weight of red drum chymotrypsin was estimated to be 26–27 kD. Our results indicate that the digestive system of red drum larvae is capable of alkaline proteolysis before first feeding and suggest that chymotrypsin may have potential as an indicator of nutritional condition.     

Digestive enzyme activity at different developmental stages of blackspot seabream, Pagellus bogaraveo (Brunnich 1768)

Blackspot seabream, Pagellus bogaraveo (Brunnich), has been identified as a potential species to diversify European aquaculture production. Although rearing aspects have been widely investigated, little information exists on the nutritional requirements for this species. The aim of this study was to build up information on the activity of digestive enzymes at certain developmental stages of blackspot seabream in order to understand the nutritional needs of larvae and post larvae. Fish larvae were reared from hatching to 55 days after hatching (dah), and the feeding plan consisted in rotifers (5–35 dah), Artemia naupli (30–35 dah) metanaupli (35–45) and Gemma microdiet (45–55 dah). At 7, 11, 21, 45 and 55 days after hatching (dah), pooled samples of fish larvae were collected for analysis of trypsin, amylase, lipase, alkaline phosphatase and leucine–alanine peptidase activity. Up to 21 dah, the whole larvae body was used for enzymatic analysis, whereas in older larvae only the dissected abdominal cavity was used. Blackspot seabream body dry weight growth was exponential, increasing from 60 μg at 5 dah to 30±9.7 mg at 55 dah. Amylase specific activity decreased significantly during development, exhibiting at 11 dah (0.6 U mg^?1 protein) an average value 2.7 times lower than at 7 dah, and remaining stable between 45 and 55 dah (0.7 U mg protein^?1). Trypsin specific activity remained constant until 21 dah (between 38 and 44 mU mg protein^?1), which could be related to the larvae feeding regime. At later stages of development, lipase‐specific activity exhibited a significant increase (P<0.05), being three times higher at 55 dah (8 U mg protein^?1) than at 45 dah. The total activity of the studied digestive enzymes increased significantly during larval development (until 21 dah), whereas afterwards only lipase and leucine–alanine peptidase increased significantly between 45 and 55 dah. The pattern of digestive enzymes activity was related to organogenesis and the type of food used at different developmental stages.     

海水仔稚鱼的营养需求与微颗粒饲料研究进展

综述了近年来海水仔稚鱼对蛋白质、脂肪和维生素营养需求的研究状况,同时对其微颗粒饲料的特性和制作工艺进行探讨,以期为研制海水仔稚鱼的微颗粒饲料提供参考。     

大蒜对印度明对虾黑鳃病原耐药菌株哈维氏弧菌抗菌活性的研究

本研究针对大蒜提取物对印度明对虾(Fenneropenaeus indicus)黑腮病病原多重耐药哈维氏弧菌(Vibrio harveyi)体外和体内的抗菌活性进行了评价。先利用市售的几种抗生素记录致病性哈维氏弧菌的抗菌谱。然后,利用琼脂扩散法来研究大蒜对哈维氏弧菌的抗菌活性。将哈维氏弧菌接种在琼脂平板上,对每种大蒜提取物(鲜榨大蒜提取物—FSGE,冻干大蒜提取物—FDGE以及用甲醇提取的大蒜提取物—MGE)设计三种不同的浓度。结果表明,鲜榨大蒜提取物对哈维氏弧菌的抑菌活性明显优于冻干大蒜提取物和用甲醇提取的大蒜提取物。本研究分别在对虾基础饲料中添加0%(对照)、0.5%和1%浓度梯度的大蒜来评价大蒜治疗感染哈维氏弧菌的对虾的效果。结果表明,综合大蒜提取物的短期和长期防治(1%含量)的效果分析,对虾累积死亡率降低了75%。本研究探讨了鲜榨大蒜提取物替代抗生素在印度明对虾饲养防病上的优点。     

Bacteriocins and their applications for the treatment of bacterial diseases in aquaculture: a review

Aquaculture is one of the fastest growing food producing sectors in the world. The increase in the world population requires faster growth in aquaculture for better food availability and to overcome malnutrition. But this worldwide growth of aquaculture is overwhelmed by catastrophic fish diseases and spoilage during cultivation and preservation problems caused by pathogenic bacteria. Various remedies are available for food preservation and also from the bacterial diseases in the fish production. Due to the emergence of antibiotic resistance and adverse effects, an alternative to antibiotic is the need of the hour. The proteins such as bacteriocins, i.e. ribosomally synthesized antimicrobial peptides (AMPs) and possess antagonistic against closely related and other bacteria. These proteins are produced by most lineages of bacteria which are playing key roles in recognition and possess a cognate immunity system for self‐protection as well as host protection from infections. These proteins are potent immunomodulators with broad spectrum inhibition properties which are further used as novel therapeutic agents. In this review, we have tried to summarize the bacteriocins on the basis of their classifications, structural and functional attributes, mode of actions, bacteriocins isolated from fish and gut microbiota and presence of beneficiary bacteria in the fish gut. Further, this study highlighted where further research is a prerequisite to increase our basic understanding and search for novel bacteriocins to elucidate the proteins/peptides having antimicrobial properties for disease control in aquaculture as an alternative to antibiotics.     

Use of the microalga Nannochloropsis occulata in the rearing of newborn longsnout seahorse Hippocampus reidi (Syngnathidae) juveniles

The aim of this study was to evaluate the effect of microalgae on the rearing of newborn juveniles of the longsnout seahorse, Hippocampus reidi. Two treatments in three replicates were tested over a 15‐day period: with and without the addition of the microalgae Nannochloropsis oculata at a concentration of 2.02 ± 0.44 × 10⁶ cells mL^?1. At each replicate, beginning on the second day of life, 120 H. reidi juveniles (stocking density of 3 ind L^?1) were fed the offspring of the benthic copepod Tisbe biminiensis (100 copepod cm^?2) together with newly hatched Artemia nauplii (3.8 mL^?1). From the sixth day of life, enriched Artemia metanauplii replaced newly hatched Artemia nauplii. After 15 days, the H. reidi individuals were counted, measured and weighed. Mean survival was significantly greater in the microalgae treatment (76.42 ± 5.07%) than in the treatment with no microalgae (25.44 ± 6.91%). Moreover, total length, height and dry weight were significantly larger in the microalgae treatment. Thus, the addition of microalgae increases the growth and survival of H. reidi juveniles fed T. biminiensis and Artemia. The higher growth and survival of H. reidi juveniles was not related to the larger ingestion rates but probably to the nutritional improvement of the live feeds or to the probiotic effect. The protocol developed for rearing H. reidi juveniles resulted in a high survival, and represents an advance in the farming of this species.     

鱼类早期生活史研究与其进展

鱼类早期生活史的研究，主要涉及卵和仔鱼发育，仔鱼最佳饲养条件、饵料密度、营养、生长、临界期、饥饿、捕食、环境耐力和毒性反应等和渔业密切相关的诸因子，是鱼类自然资源繁殖保护和养殖业苗种培育的基础。近二、三十年来，鱼类早期生活史研究已成为水产科学的一个崭新领域，在国际上受到广泛重视并迅速发展。国际海洋开发理事会(ICES)曾三次举行鱼类早期生活史学术讨论会，     

养殖鱼类同类残食现象研究进展及其预防措施

残食行为被定义为同物种间相互杀戮与掠食的现象。在鱼类人工育苗阶段,同类残食行为普遍存在,是制约育苗阶段苗种存活率的主要因素之一。本文针对海水鱼类育苗期间出现的残食行为问题,结合笔者的前期研究发现,对鱼类残食行为的发生、形态学制约、摄食规格、生长优势和影响因子进行了概述。根据残食方式,鱼类的自残现象主要分为Ⅰ型残食现象和Ⅱ型残食现象。Ⅰ型残食中,残食者首先咬住被残食者的尾部,逐渐吞食至头部后将剩余部分丢弃,被残食个体通常会被部分吞食、消化;Ⅱ型残食中,残食者自被残食者的头部开始将其完全吞食,被残食个体通常会被完全吞食、消化。残食者口裂大小是自残行为发生的主要限制因子,而且越是在鱼类的早期阶段,口裂大小差异越明显。在鱼类残食行为中,残食者倾向于由小到大的顺序选择被残食者。残食现象对群体的影响取决于残食者的相对生长速度。本文还探讨了减少鱼类自残行为发生的措施,以期丰富海水仔稚鱼行为学理论,为建立优质苗种繁育技术提供理论依据。     

Phaeobacter grown in biofilters: a new strategy for the control of Vibrionaceae in aquaculture

Growth, biofilm formation, antagonism and residence time in green seawater tanks maintained under fish rearing conditions of Phaeobacter 27‐4 were studied in commercial biofilters made from plastic, sintered glass and ceramic. Phaeobacter reached 10⁸–10⁹ CFU cm^?3 and formed rosettes in all materials, but a multilayer biofilm was only observed in the ceramic biofilters. In sterile seawater, plastic and ceramic biofilters reduced Vibrio anguillarum and V. splendidus concentration in one‐two Log after 24–48 h, showing 10²–10³ CFU mL^?1. Sintered glass biofilters only inactivated V. anguillarum. In Marine Broth, sintered glass and ceramic biofilters inhibited V. anguillarum growth in two‐three Log, showing 10⁴–10⁵ CFU mL^?1 after 24 h. Plastic biofilters reduced V. anguillarum concentration in one Log after 48 h. V. splendidus growth was only inhibited by sintered glass and ceramic biofilters in one‐two Log, showing 10⁷ CFU mL^?1 after 24 h. Phaeobacter also diminished biofilters colonization by the pathogens, both in seawater and in MB. Phaeobacter residence time in green seawater tanks maintained under fish rearing conditions was longer with sintered glass and ceramic biofilters. The latest showed the lowest detachment and, after 11 days, Phaeobacter (10⁶ bacteria·cm^?3) covered more than 80% of biofilters total culturable bacteria. DGGE profiles showed that Phaeobacter biofilters stabilizes the green seawater bacterial microbiota.     

Effects of light intensity on growth,feeding activity and development in common sole (Solea solea L.) larvae in relation to sensory organ ontogeny

The effects of four light intensities (1000 lx, 500 lx, 50 lx, 3 lx) on growth, survival and feeding activity in common sole (Solea solea L.) larvae were studied from 4 to 51 days post hatching (dph). During the pelagic larval stage (4–12 dph), larvae reared at 3 lx showed a lower growth. From 19 onwards, the larvae reared under 3 lx displayed a significant (P ≤ 0.05) higher SGR than the other treatments and a higher final weight compared to 1000 lx and 500 lx. Survival rate was higher under intermediate light intensities (500 and 50 lx). Larvae reared at 3 lx displayed a significant delay in the degree of metamorphosis compared to the other treatments, while at 33 dph metamorphosis was completed under all treatments. Histological examination revealed the importance of vision and light in the first feeding of this species, while after metamorphosis, the full development of other sensory organs indicated that feeding activity is also mediated by chemosensory perception. Results indicate that high light intensity seems to be more suitable during the pelagic larvae, while the opposite would ensure better growth from the onset of metamorphosis to the benthic phase.     

Effect of probiotic (Bacillus spp.) addition during larvae and postlarvae culture of the white shrimp Litopenaeus vannamei

The effect of the addition of Bacillus probiotic during larvae and postlarvae culture of the white shrimp Litopenaeus vannamei was examined in three separate experiments: (I) Nauplius_4‐5 to Zoea₃, which were exposed to probiotic in the water (P_w), only in the microalgae (P_m), in the water and microalgae (P_wm) and a control with no probiotic (C); (II) Mysis₁ to Mysis₃, which were exposed to probiotic in the water (P_w), only in Artemia (P_a), in the water and Artemia (P_wa) and a control (C); (III) PL₁ to PL₁₀, which were exposed to similar treatments for mysis experiment. The use of probiotic Bacillus spp. resulted in an increase in the survival and growth of zoea and mysis phases, especially when the probiotic was added only in the water. For postlarvae, the use of the probiotic had no influence on the zootechnical parameters, however, there was a reduction in the count of presumptive Vibrio both for water and shrimp.     

Antibacterial abilities of intestinal bacteria from larval and juvenile Japanese flounder against fish pathogens

The present study was undertaken to examine the antibacterial abilities of intestinal bacteria isolated from juveniles and larvae of Japanese flounder Paralichthys olivaceus . Newly hatched larvae of flounder were held in a 100 L plastic circular tank and fed rotifiers, Artemia nauplii and commercial feeds, depending on the developmental stage of the fish. Genera Aeromonas , Moraxella and Vibrio were predominantly isolated from the intestinal tracts of Japanese flounder at larval and juvenile stages, whereas Aeromonas , Bacillus , coryneforms, Moraxella , Pseudomonas and Vibrio were detected at high densities in live diets and artificial feeds. Antibacterial bacteria accounted for 1.7–24.3% of the intestinal isolates against Lactococcus garvieae , Pasteurella piscicida , Vibrio anguillarum and V. vulnificus . In particular, as much as 53.3% of Vibrio spp. other than Vibrio -swarmer isolated from 197-day-old juveniles inhibited the growth of P. piscicida . These results suggest that intestinal bacteria having antibacterial activity play a role in the prevention of infectious diseases.     

黄边糙鸟蛤幼虫对9种单胞藻的摄食与消化研究

为确定黄边糙鸟蛤(Trachycardium flavum)幼虫生长发育时期的合适饵料,研究了幼虫对9种单胞藻的摄食与消化效果。用浓度为105个·m L-1的9种单胞藻分别饲喂2、6、10、14和18日龄幼虫,1 h后观察幼虫摄食情况,对已摄食单胞藻的幼虫过滤冲洗后转移至过滤海水中观察其消化效果。结果表明,幼虫在所有日龄都能摄食小球藻(Chlorella vulgaris)、微绿球藻(Nannochloropsis oculata)、绿色巴夫藻(Pavlova viridis)、湛江叉鞭金藻(Dicrateria zhanjiangensis)和球等鞭金藻(Isochrysis galbana),6日龄开始摄食杜氏盐藻(Dunaliella salina),14日龄摄食亚心形扁藻(Platymonas subcordiformis)和三角褐指藻(Phaeodactylum tricornutum),18日龄摄食牟氏角毛藻(Chaetoceros muelleri);但对小球藻和微绿球藻较难消化,水体中单胞藻投喂过多使单胞藻不消化或不完全消化。因此,在幼虫培育中应选择容易摄食和消化的绿色巴夫藻、湛江叉鞭金藻和球等鞭金藻作为开口饵料并遵循少量多次的投喂原则。     

黄连素对3种水产动物致病菌的抑制作用研究

文章研究了黄连素对副溶血弧菌（Vibrio parahaemolyticus）、溶藻弧菌（V.alginolyticus）和嗜水气单胞菌（Aeromonas hydrophila）等3种致病菌的最小抑菌浓度（MIC）和最小杀菌浓度（MBC）,检测了黄连素对病原菌菌体形态和生长曲线的影响,并以此解析黄连素对这3种致病菌的抑制特点和抑菌机制.结果显示,黄连素对副溶血弧菌、溶藻弧菌、嗜水气单胞菌的MIC和MBC分别为0.391 mg·mL^-1和0.391 mg·mL^-1、0.391 mg·mL^-1和0.781 mg·mL^-1、0.781 mg·mL^-1和1.563 mg·mL^-1,说明黄连素对3种致病菌均有明显的抑制作用,其中对副溶血弧菌的抑制效果最佳.同步结果显示,1.00 mg·mL^-1黄连素不仅会严重破坏致病菌的菌体形态,而且使致病菌的迟缓期延长2～7h,这暗示黄连素可能通过影响致病菌的细胞结构和生长繁殖来达到抑菌的效果.由此可见,黄连素在防治水产类细菌性疾病上有很好的应用潜力.     

Size-dependent predation on marine fish larvae by Ctenophores, Scyphomedusae, and Planktivorous fish

Size-dependent predation rates on marine fish larvae by the ctenophore Mnemiopsis leidyi , scyphomedusa Chrysaora quinquecirrha , and planktivorous fish Anchoa mitchilli were estimated via experiments in 3.2 m³ me-socosms. Predation rates on larvae of the goby Gobio-soma bosci were estimated in relation to 1) length of larval prey, 2) presence or absence of alternative < 1 mm zooplankton prey, and 3) a predator-prey interaction between the scyphomedusa and ctenophore. The consumption rate of larvae by the three predators generally declined as larval length increased. The ctenophore ate fewer (1.0 d^-1 per predator) larvae than did the medusa (7.8 d ^-1 per predator) or bay anchovy (4.0 d ^-1 per predator), but it consumed larvae in all size classes tested (3.0–9.5 mm SL). Predation by bay anchovy and the medusa was more size-dependent: 3.0–5.0 mm larvae were most vulnerable. Fewer larvae were eaten by the ctenophore and bay anchovy when zooplankton alternative prey was available, but predation on larvae by the medusa was not influenced by alternative zooplankton prey. Consumption rate of fish larvae by the medusa was reduced 20–25% when the ctenophore was present as its alternative prey. An encounter-rate model was developed and its parameters estimated from the experimental results. Model simulations indicated that the relationship between larval size and vulnerability is dependent on size, swimming speed, and behavior of both predators and larvae, and that bigger or faster-growing fish larvae are not always less vulnerable to predation.     

A new type of lordosis and vertebral body compression in Gilthead sea bream,Sparus aurata L.: aetiology,anatomy and consequences for survival

A new type of vertebral malformation is described, consisting of deformed cartilaginous neural and haemal processes and the compression and fusion of vertebral bodies. The malformation is designated as haemal vertebral compression and fusion (haemal VCF). We studied the aetiology of the malformations and described microanatomical histopathological alterations. The malformations were detected during routine quality control in one of six monitored Gilthead sea bream populations. Haemal VCF affected the posterior part of the vertebral column (haemal vertebrae). In 20% of the deformed specimens, haemal VCF was combined with lordosis. At 35 dph (days post‐hatching), early anatomical signs of the haemal VCF consisted of abnormal centrum mineralization, malformed cartilaginous neural and haemal processes and developing lordotic alterations. The histological examination of the deformed individuals revealed that haemal VCF is preceded by notochord abnormalities. The frequency of deformed individuals was three times higher at 35 than at 61 dph (50.3% vs. 17.2%, n = 157 and n = 250, respectively). No signs of repair or reversion of malformations have been observed. Thus, the steep decrease in deformities in older animals suggests that haemal VCF is linked to high mortality rates. The results are discussed in respect of the possible causative factors of haemal VCF.     

A method for the histochemical localization of digestive enzymes in whole freeze-substituted larval fish embedded in glycol methacrylate

In order to study the localization of digestive enzymes in larval walleye ( Sander vitreus vitreus), a novel method of low-temperature processing of whole, unfixed larvae and subsequent embedding in glycol methacrylate (GMA) was developed. Larval walleye aged 2–10 days post hatch were flash-frozen in liquid nitrogen and transferred into pre-chilled acetone for 12 h at a temperature of −25 °C. Acetone was gradually replaced with increasing concentrations of GMA resin monomer over a 6-h period. The polymer (100%) was further allowed to infiltrate the larvae for 36 h. Resin-embedded larvae were transferred to embedding moulds and polymerized overnight at −25 °C. Four micrometre sections were stained to identify either alkaline phosphatase, non-specific esterase, aminopeptidase M or dipeptidyl peptidase IV. All enzymes studied were readily detected and accurately localized, and no enzyme diffusion was observed. Therefore, freeze substitution combined with low-temperature GMA embedding allows the maintenance of excellent tissue morphology and accurate enzyme localization in whole larval walleye specimens from 2 to 10 days post hatch. It is recommended, however, that samples be frozen in pre-cooled fluorocarbon-based liquid coolants in order to assure optimal tissue preservation.