Characterization of thermotolerant, fermentative yeasts from hot spring drainage

SUMMARY: Eight thermotolerant, ethanol-producing yeast strains were isolated from hot spring drainage at Rendaiji in Shizuoka Prefecture. The tolerance to elevated temperatures of three strains (RND13, 14 and 17) was studied in comparison with that of mesophilic yeasts. All three grew on a liquid culture at temperatures up to 42–45°C, with maximum growth rates at 37°C or 35°C, whereas the upper limit temperatures for fermentation were higher, ranging from 48 to 55°C. Above all, RND13 had higher ethanol productivity of 72.1% at 40°C for 24 h than that of 57.0% obtained by brewers' yeast at 25°C for 120 h. Regarding the taxonomy of RND13, 14, and 17, they were found to be Torulaspora delbrueckii , Dekkera sp., and Candida albicans , respectively. This is the first report on yeasts capable of fermentation over 51°C, as well as on the isolation of yeasts from a hydrosphere with elevated temperatures.     

Use of marine yeasts as an available diet for mass cultures of Moina macrocopa

A 4‐week feeding trial was conducted to test the use of marine yeasts purified from seawater and sediments as a dietary source in cultivating a cladoceran, Moina macrocopa, a potential alternative live food for fish larvae. Optimal growth conditions of two yeast strains were obtained for NaCl concentration, pH and temperature. Moina macrocopa was cultivated using different diets: marine yeasts (Debaryomyces hansenii Yeast‐14 and Candida austromarina Yeast‐16) and a commercial diet (Erythrobacter sp. Sπ‐I). The essential amino acids of both the yeast strains were nearly as great as those in M. microcopa. Further, the yeast‐fed M. macrocopa had essential amino acid profiles similar to the documented values for rotifers and Artemia enriched in microalgae and commercial diets. Erythrobacter sp. Sπ‐I lacked n‐3 polyunsaturated fatty acids, 20:5n‐3 and 22:6n‐3, which were also low but detected in both yeasts. An increase in the 20:5n‐3 [eicosapentaenoic acid (EPA)] and 22:6n‐3 [docosahexaenoic acid (DHA)] levels, compared with the levels in yeast strains themselves, was more pronounced in the 22:6n‐3 level of Moina fed the C. austromarina, resulting in a high DHA:EPA ratio. When the Moina diets were switched, their δ¹³C values shifted gradually towards the values of the switched diets. Diet switch from Erythrobacter sp. Sπ‐I to C. austromarina Yeast‐16 resulted in a more rapid turnover of Moina tissue carbon than that in the inverse case. When fed a mixed diet, the δ¹³C values of Moina tissue approached the value of marine yeasts immediately. These temporal changes in the δ¹³C values of Moina tissue indicate the preferential ingestion of marine yeasts and a selective assimilation of the carbon originated from marine yeasts. These findings suggest that marine yeasts, particularly C. austromarina Yeast‐16, are highly available to mass cultures of M. macrocopa, providing better nutritional and dietary values than the commercial diet (Erythrobacter sp. Sπ‐I).     

Marine yeast diet confers better protection than its cell wall component (1-3)-β-d-glucan as an immunostimulant in Fenneropenaeus indicus

A comparative study was performed to evaluate the immunostimulatory effect of yeast and yeast-derived glucan in white prawn Fenneropenaeus indicus (sub-adults of ∼20 gm). Feed with a whole cell biomass of marine yeast Candida sake S165 (CSY) at a concentration of 10% (w/w) and another feed with 0.2% glucan of C. sake S165 (CSG) were used in the study. Fenneropenaeus indicus were fed with these diets for 40 days and subsequently challenged with the white spot syndrome virus (WSSV). Haematological parameters such as the total haemocyte count, phenoloxidase activity, superoxide anion (O₂⁻) level, haemolymph peroxidase level and post-challenge survival against WSSV infection were determined to assess the immune status. In the present experiment, a higher immunity index and post-challenge survival were recorded in shrimps fed with the whole cell yeast diet. The better immunostimulatory performance of the whole cell yeast diet compared with the glucan diet could be attributed to the cellular constituents of yeast including the cell wall glucan, nucleotides, carotenoid pigments and vitamins. Here we observed that whole cell yeast performed better as an immunostimulant than the extracted cell wall glucans. Therefore, the use of yeast biomass in diets, rather than the yeast cell wall extract, glucan, would confer better protection against microbial infection besides reducing the cost of shrimp production.     

Short-term stress and mortality of juvenile school prawns, Metapenaeus macleayi, discarded from seines and trawls

Abstract  Two experiments were carried out to assess the short-term impacts to juvenile school prawns, Metapenaeus macleayi (Haswell) discarded from commercial seining and trawling in New South Wales, Australia, and the potential utility of modifications to operational and/or onboard handling practices designed to improve survival. For both gears, discards were handled according to two general categories of treatment (termed mild and extreme) chosen to represent the plausible limits of severity during existing commercial operations. A total of 600 trawled and 480 seined school prawns (from both treatments), along with appropriate numbers of controls (previously collected and housed in acclimation tanks), were placed into cages (in groups of 10). Subsets of each of these groups were then destructively sampled over periods of up to 5 days and examined for their mortality and physiological response (measured as levels of l -lactate in the haemolymph). In both experiments, the temporal mortalities in the treatment groups ranged between 0% and 15% and, for the most part, were not significantly different to controls. Prawns in the treatment groups had similar, significantly elevated levels of l -lactate approximately 40 min after being caught, but these returned to levels approaching baseline estimates within 48 h. Under the conditions examined, juvenile school prawns appear capable of withstanding a range of stressors associated with being discarded from active gears, and their fate is not greatly influenced by the duration of gear deployment and subsequent air exposure. However, further work is required to quantify other sources of unaccounted fishing mortality and, ultimately, the impacts that discarding has on stocks.     

Bacterial and parasitic pathogens in cultured common dentex, Dentex dentex L.

A bacteriological and parasitological study on cultured common dentex, Dentex dentex L., was conducted in a 2-year survey. Two different groups of fish were studied: (1) sampled only when mortalities occurred; and (2) sampled periodi-cally from 10days post-hatch until the juvenile stage. In both groups, peaks of mortalities coincided with high water temperatures. The same parasites were detected in both groups, except Ichthyophonus sp., which was identified only in the trunk kidney of fish from group 1. Two myxosporeans, Ceratomyxa sp. and Lepthotheca sp., were found in the bile and the trunk kidney, respectively. Epitheliocystis infection was also very frequent in the gills. An unidentified microsporidium, which was found in the liver, occurred very infrequently. Vibrio harveyi was dominant in samples from diseased animals (79%) and clearly associated with mortalities. It was not detected in water or larval homogenates. A high percentage (60%) of the isolates of this species were sorbitol positive. Other less frequently occurring bacteria were V. alginolyticus and Photobacterium (V.) damselae. The disease conditions found in common dentex were considered to be multifactorial in origin.     

Social control of growth in Macrobrachium rosenbergii: I. The effect of claw ablation on survival and growth of communally raised prawns

The effect of claw ablation on the growth and survival of juvenile Macrobrachium rosenbergii was tested; two sets of controls were used consisting of a group of intact prawns, and an additional group whose first pair of walking legs had been ablated so as to serve as controls for injury and regeneration. Survival among claw-ablated prawns was twice as high as that for the two control groups. Intact prawns weighed more than those with ablated appendages. During the experiment the coefficient of variation of mean weight decreased in the claw-ablated group. It increased in the intact prawns and was relatively stable in the group with ablated first pair of walking legs. The biomass of the claw-ablated group doubled within the test period while that of the controls was stable because the gain in mean weight and the mortalities counterbalanced each other.     

Chemiluminescent responses of striped bass, Morone saxatilis (Walbaum), phagocytes to strains of Yersinia ruckeri

Abstract. Seventeen strains of Yersinia ruckeri were examined for plasmid DNA by means of agarose gel electrophoresis of partially cleared lysates. All 10 serotype I strains examined contained a 70 Megadalton (Mdal) plasmid, whereas only one of the 7 serotype II strains examined contained a plasmid of about 2–3 Mdal. Yersinia ruckeri exhibited distinctive colonial morphology and serological reactivities which suggested a possible correlation with plasmid content. The luminol-enhanced Chemiluminescent (CL) responses of striped bass, Morone saxatilis (Walbaum), phagocytes to different strains of Y. ruckeri were also studied. Some variability was observed; however, the greatest phagocyte CL responses were elicited by serotype II strains without the plasmid while serotype I strains harbouring the plasmid consistently elicited weak CL responses from phagocytes.     

Production Comparison of Three Genetic Strains of Freshwater Prawn,Macrobrachium rosenbergii,Raised Under Two Pond Management Technologies

Three genetic strains (Texas [cultured], Hawaii [cultured], and Myanmar [wild]) of freshwater prawn, Macrobrachium rosenbergii, were characterized and compared under two pond grow‐out management technologies using a 3 × 2 factorial design. Juvenile prawns (45 d nursed juveniles) from each strain were stocked at individual average weights of 0.4 ± 0.3 g (Texas), 0.3 ± 0.2 g (Hawaii), and 0.3 ± 0.2 g (Myanmar). The low input management technology prawns were stocked at 24,700 /ha with no added substrate. The high input management technology prawns were stocked at 74,100 /ha with the addition of artificial substrate. Each of the six treatment combinations were replicated in three, 0.04 ha earthen ponds (total of 18 ponds). Prawns were fed a sinking pellet (32% protein) once daily at a standardized rate. After 112 d, prawns were harvested, bulk weighed, and counted. Survival of Texas strain (95%) was significantly higher (P ≤ 0.05) than Myanmar strain (77–80%) under both management technologies with survival of Hawaii strain (86–91%) intermediate and not significantly different (P > 0.05) from other strains. Under both management technologies, average weight, total production, and marketable percentage (>20 g) was significantly better (P ≤ 0.05) in Texas and Hawaii strains in comparison to the Myanmar strain. These data appear to indicate that the cultured strains evaluated in this study demonstrate positive impacts of domestication and do not indicate inbreeding depression.     

Genome-wide comparison of Carnobacterium maltaromaticum derived from diseased fish harbouring important virulence-related genes

Although Carnobacterium maltaromaticum has been used as a probiotic in fish, it was reported to cause disease for the first time in Korea. The objective of this study was to understand the differences between pathogenic and non-pathogenic strains. Pathogenicity was tested by challenging rainbow trout with C. maltaromaticum ATCC35586 and 18ISCm isolated from diseased fish, and DSM20342 isolated from a dairy product. We also compared 24 genomes of C. maltaromaticum strains plus the genome of our isolate 18ISCm sequenced in this study. Only the strains from diseased fish caused high mortality with severe histopathological changes. Although all strains shared more than 90% of Ko_id, wecC and xtmA were found only in strains from diseased fish. Interestingly, only strains from diseased fish harboured two wecC paralogs involved in the production of D-mannosaminuronic acid which is a major component of a well-known virulence factor, teichuronic acid. Two wecC paralogs of 18ISCm were increased when they were co-cultured with trout blood cells, suggesting that wecC genes might play a role in virulence. The results of this study show that strains isolated from diseased fish are different from strains derived from food in terms of pathogenicity to fish and the presence of virulence-related genes.     

异育银鲫致病性嗜水气单胞菌的分离鉴定与药敏特性研究

对江苏盐城某养殖场患出血病的异育银鲫(Carassius auratus gibelio)进行细菌分离鉴定和药敏试验,为该病的防控提供科学依据.从病死及濒死异育银鲫的肝脏、脾、肾中分离病原菌,经过形态观察、生理生化试验、16S rRNA序列分析,最终进行细菌鉴定,采用纸片扩散法进行药敏实验,通过人工回归感染试验确定分离菌株的致病性.分离的2株细菌(编号为WJ11-3和WJ11-4)均为嗜水气单胞菌(Aeromonas hydrophila),均能导致异育银鲫死亡,并出现与自然条件下基本一致的症状.药物敏感性试验结果显示,嗜水气单胞菌分离株WJ11-3对苯唑西林、林克霉素、万古霉素显示耐药性,对恩诺沙星等28种药物高度敏感;WJ11-4对苯唑西林、林克霉素、新生霉素显示耐药性,对氟苯尼考等28种药物高度敏感.本次异育银鲫的出血病由嗜水气单胞菌感染引起,可选用恩诺沙星、阿洛西林、氧氟沙星、苯唑西林、林克霉素、新生霉素等多种药物进行防治.     

Combined diet of yeast,fermented soybean meal,and microparticulate as larval feed in extensive rearing systems for seed production of the oriental river prawn <Emphasis Type="Italic">Macrobrachium nipponense</Emphasis>

The present study aims to evaluate the effects of several types of larval feed on seed production of the oriental river prawn Macrobrachium nipponense and water quality in extensive rearing systems. Healthy M. nipponense were distributed into fifteen 15-m² pond outdoors, and each pond was stocked with 90 prawns including 41 egg-bearing (berried) female prawns, 37 not bearing female prawns, and 12 male prawns for larval production. The experimental design was completely randomized, with four diet groups (diet A: soybean homogenate, diet B: yeast, diet C: yeast?+?fermented soybean meal, and diet D: yeast?+?fermented soybean meal?+?microparticulate diet) and one no feeding control and three replications. There are equal levels of the total protein content in diets A–D. Higher larvae and postlarvae number was obtained for diet C and diet D. Furthermore, the increase of M. nipponense larvae and postlarvae in diets B–D can result in the decrease of zooplankton and increase of phytoplankton in the pond during some periods, simultaneously improving the water quality. The Spearman correlation coefficient (r_M,N) between the amounts of larvae and postlarvae of M. nipponense per pond and zooplankton per pond during the entire experiment period was ??0.56. The highest juvenile M. nipponense production was obtained in the diet D group (3140.00?±?461.63), which was slightly higher than that in the diet C group (2940.33?±?382.60). The juvenile M. nipponense production in diet B (2303.00?±?449.23) was also significantly higher compared to diet A (1106.33?±?176.64) and the control group (1039.67?±?212.85). There were no significant differences in the amounts of juvenile M. nipponense between the control and diet A groups, which indicated that the soybean homogenate could not increase the amount of M. nipponense juveniles. Our results clearly showed that diet D significantly raised per unit yield of prawn seed comparing with no feeding and other diet group in extensive rearing systems and that the cost of producing prawn seed with diet D is low, which provide an important foundation for the expansion of oriental river prawn culture.     

Impact of marination,pre‐harvest salt acclimation and sodium chloride concentration on the sensory acceptability of freshwater prawn,Macrobrachium rosenbergii

This study was conducted to evaluate the consumer acceptability of post‐harvest freshwater prawns marinated in salt solutions (0.5%, 1%, 1.5% and 2% NaCl in the cooked product), and to compare the sensory acceptability of these treatments against prawns that had been salt acclimated pre‐harvest while still alive. The salt‐acclimated prawns were transferred to 250‐L tanks containing 10 ppt solar salt (NaCl with small concentrations of CaCl₂ and KCl). Salts were increased by 5 ppt in 2 h increments until 30 ppt was reached. After 18 h of salt acclimation, prawns were chill killed. Prawns that were used for post‐mortem marination treatments were transferred to 250 L tanks with freshwater for 18 h prior to harvest and post‐mortem marination. Two consumer‐based sensory tests were conducted (n = 102). Results indicate that flavour, texture and overall acceptability of prawns increased (P < 0.05) as the salt concentration increased from 0.5% to 1.5% in marinated prawns. In addition, marinated prawns that contained 1% sodium chloride after cooking did not differ (P > 0.05) in acceptability when compared to salt acclimated prawns which contained 0.5% sodium chloride in the cooked product. The salt‐acclimated product was preferred (P < 0.05) over the 0.5% salt marination treatment, although they did not differ in final salt concentration. This indicates that salt acclimation enhanced product acceptability through increased salt concentration as well as due to the salt acclimation process, thus lowering the amount of sodium chloride that was necessary to enhance product acceptability.     

Mass mortalities associated with viral nervous necrosis (VNN) disease in two species of hatchery-reared grouper, Epinephelus fuscogutatus and Epinephelus akaara (Temminck & Schlegel)

Mass mortalities of hatchery-reared juvenile groupers have occurred in southern Taiwan. The diseased fish swam in a darting, corkscrew fashion. Light microscopy revealed vacuolation in the brain tissue. Electron microscopy showed numerous non-enveloped, cytoplasmic viral particles (20–25 nm in diameter) in the brain cells, and many virions were enclosed in the membrane-bound organelles of the cells. Two structural proteins of the purified grouper virus, with molecular weights of 44 and 43 kDa, were revealed by SDS-PAGE. Moreover, the results of RT-PCR and nested PCR diagnosis using primers specific to the T2 and T4 target segments of striped jack nervous necrosis virus (SJNNV) RNA2 genes suggest that this virus is a fish nodavirus, and is designated as GNNV 9410 strain (grouper nervous necrosis virus strain 9410). This is the first case report of viral nervous necrosis among marine fish in Taiwan.     

Replacement of Fishmeal by Single Cell Protein Derived from Yeast Grown on Date (Phoenix dactylifera) Industry Waste in the Diet of Nile Tilapia (Oreochromis niloticus) Fingerlings

Isonitrogenous and isocaloric diets (32% protein, 4.3 Kcal/g) were formulated to replace fishmeal by single cell protein (SCP) from two yeasts, Saccharomyces cerevisiae and Candida utilis, grown on date (Phoenix dactylifera) processing waste in diets for two size groups (avg 15.39 g and 25.14 g) of juvenile Nile tilapia (Oreochromis niloticus). A control diet (T₁) with fishmeal and six experimental diets (S1, S2, and S3 with S. cerevisiae, and C1, C2, and C3 with C. utilis) each containing 11.6%, 23.2%, and 34.2% yeast as SCP were prepared to replace 25%, 50%, and 75% of fishmeal, respectively. Tilapia fed on the control and experimental diets (S1, S2, C1, C2) with 25% and 50% replacement of fishmeal showed better growth and feed utilization. Fish fed on diets S3 and C3 (75% fishmeal replacement) had significantly (p < 0.05) poorer growth suggesting that yeast SCP can replace up to 50% of fishmeal in juvenile tilapia diets.     

POLYCULTURE OF THE FRESHWATER PRAWN (Macrobrachium rosenbergii) WITH TWO COMBINATIONS OF CARPS IN MANURED PONDS

A study was conducted to 1) evaluate the compatibility of prawns (Macrobrachiurn rosenbergii) with carps, especially the effect of the common carp (Cyprinus carpio); and 2) measure the ability of prawns to utilize the foods available in manured systems. Carps used were the silver (Hypophthalmichthys molitrix), bighead (Aristichthys nobilis), grass (Ctenopharyngodon idella) and common carp (Cyprinus carpio). Four ponds (0.09 to 0.17 ha) were stocked with silver, bighead and grass carps while common carp were stocked in only two ponds. Total fish densities were 8,600/ha where four carps were stocked, but only 6,200/ha when common carp were omitted. Post-larval prawns (wt 0.116 g) were stocked at densities of 17/m². Swine (approximately 60/ha of pond surface area) were housed on pond dikes so that fresh manure continuously entered each pond. Two lots of swine were fattened during the experimental period and loadings of swine manure were calculated based on hog size and feed consumption. Growth periods were 163 days for fish and 107 and 121 days for separate stockings of prawns. Gains in biomass by prawns averaged 714 kg/ha in ponds without common carp and 364 kg/ha in ponds containing common carp. Gains in biomass for both fish and prawns were 3,619 kg/ha (19.8 kg/ha/day) in ponds with common carp and 2,924 kg/ha (18.0 kg/ha/day) in those without common carp. Prawn survival was higher (X = 84.5% vs X = 72.5%), but final average weight of prawns was lower (2.64 vs 5.86 g) in the presence of common carp due to competition for food between common carp and prawns. Competition from carp is believed to have exerted less influence on prawn survival than predation on small prawns by larger, faster-growing prawns.     

A test of two methods for marking larvae and postlarvae of the giant freshwater prawn, Macrobrachium rosenbergii

This paper describes the successful use of two tagging systems, both produced by Northwest Marine Technology Inc., on larval and postlarval giant freshwater prawns, Macrobrachium rosenbergii. Visible implant (VI) elastomer tags (a coloured liquid that solidifies under the epidermis) were used on stage XI larval prawns (mean weight 0.01 g) and postlarval prawns (mean weight 0.07 g). VI alphanumeric tags (small biocompatible plastic labels also inserted under the epidermis) were tested on postlarval prawns (from a weight of 0.5 g). Tags were inserted using clove oil as anaesthetic, and survival, mortality and growth rates of tagged animals were compared with those of controls that were handled but not anaesthetized or marked. Twenty per cent of the larval prawns (the smallest of the group) died just after tagging, but thereafter the remaining prawns survived well, as did all the tagged postlarval prawns. Visibility of the VI elastomer tags in larval prawns deteriorated with time, though 79% of marks were still visible to the naked eye 70 days after tagging. VI elastomer tags in the postlarval group remained clearly visible for up to 100 days. Visibility of the VI alphanumeric tags fell shortly after tagging, but remained adequate thereafter. Moult rates in control and tagged animals were the same in larvae with VI elastomer tags and postlarvae with VI alphanumeric tags, but the moult rate in the postlarval prawns given elastomer tags was slower than in controls. Rates of growth were similar in tagged (elastomer and alphanumeric) and control postlarval prawns, once the size‐dependent mortality of tagged larval prawns was taken into account. We conclude that VI elastomer tags could be used to mark small numbers of individual larval and immediately postlarval prawns for periods of several months, and that VI alphanumeric tags could be used to mark an unlimited number of individuals from a size of approximately 0.5 g.     

Characteristics of an Enterococcus-like bacterium from Australia and South Africa, pathogenic for rainbow trout, Oncorhynchus mykiss (Walbaum)

Abstract. Severe mortalities of up to 60% have occurred in Australian and South African farmed rainbow trout, Oncorhynchus mykiss (Walbaum), infected with Gram-positive cocci. Infected fish develop septicaemia and characteristic exophthalmos. Strains collected from outbreaks of disease appear to have attributes of the genus Enterococcus although no Lancefield group D antigen could be detected. All strains grew at 10°C but not at 45°C, grew in 6·5% NaCI, were bile-aesculin positive and hydrolysed L-pyrrolidonyl-β-naphthylamide. Isolates from both countries have similar phenetic characteristics and whole cell protein profiles.     

The Effects of Prophylactic Formalin Bath Treatment on Blood Glucose in the Giant Tiger Prawn Penaeus monodon

Abstract— Juvenile Penaeus monodon prawns were bathed in seawater-formaldehyde concentrations of 312, 625, and 1,250 ppm for up to 6 h. The tests were conducted at concentrations in excess of those previously published, in order to examine maximum tolerance levels to formaldehyde. Physiological stress was monitored by measurement of blood glucose levels. Under controlled laboratory conditions, 12 h food deprived juvenile prawns exposed to formaldehyde concentrations of 312 ppm did not exhibit signs of stress. However, bathing in formaldehyde concentrations of 625 and 1,250 ppm, caused significant increases ( P < 0.05) in blood glucose levels after 2 and 4 h, respectively. There were no mortalities in any treatment group. In contrast, juvenile prawns from grow-out ponds bathed in 625 ppm of formaldehyde immediately after 2.5 h of transport did not exhibit significant increases in blood glucose. This may be due to their nutritional status and these results are discussed. No significant change in blood glucose levels was observed in bilaterally eyestalk ablated prawns after exposure to 1,250 ppm formaldehyde. The increase of blood glucose due to formaldehyde treatment is presumably mediated by a stress response, which includes crustacean hyperglycemic hormone (CHH), and not a result of non-specific cell lysis and death.     

Development of hemolymph prostaglandins assay systems and their concentration variations during ovarian maturation in the kuruma prawn, Penaeus japonicus

Hemolymph prostaglandin (PGF₂ and PGE₂) measurement systems for the kuruma prawn Penaeus japonicus were developed and validated. In these systems, both PGF₂ and PGE₂ in hemolymph obtained from a single prawn were measured. PGs were extracted through reverse-phase C18 cartridge column, separated for isomers of each PG by high-performance liquid chromatography (HPLC), and quantified with a radioimmunoassay (RIA). Detectable range was 6.5–200 and 26–400 pg/tube for the PGF₂ and PGE₂ assays, respectively. Serial dilution of extracted and separated hemolymph PGs (RIA sample) produced a curve parallel to the standard curves in both assays. These assays were able to measure PGs in the RIA samples spiked with the authentic standard. Overall, results indicate that the presently established assay systems can accurately measure hemolymph PGs in female kuruma prawns.

When hemolymph PGF₂ and PGE₂ levels were determined and plotted against the gonado-somatic index (GSI), no correlation was found in either PGs. In terms of ovarian developmental stages, however, the concentration of PGF₂ significantly increased from 66.7 pg/ml at stage I (previtellogenic stage) to 303 pg/ml at stage II (primary vitellogenic stage) and decreased gradually thereafter. The concentration of PGE₂ also increased markedly (4037.7 pg/ml) at stage II and decreased at stage III (secondary vitellogenesis stage). These results indicate that PGs vary in concentration during ovarian development in kuruma prawns.     

梭子蟹酵母菌人工感染实验和组织病理学初步研究

近年,浙江省舟山市暂养梭子蟹(Portunus trituberculatus)连续暴发“乳化病”,发病蟹均分离到一种酵母菌。本实验以该株酵母菌通过肌肉注射方式,对三疣梭子蟹、红星棱子蟹、日本鲟3个品种的健康蟹进行了人工感染实验,以验证其致病性。结果发现,该菌株能感染试验蟹类,并出现与自然发病蟹类似的症状。从感染蟹的体液、肝胰腺、心脏等部位分离到了酵母菌,但未分离到细菌,也未发现寄生虫。酵母菌在病蟹的肝胰腺、鳃、心脏中大量侵袭,并引起这些组织发生以坏死为主的变质性病变,其病理特征主要表现为：细胞肿胀、变性、坏死,某些细胞的细胞核固缩、碎裂或崩解。初步确认该酵母菌是引发梭子蟹“乳化病”的病原。