Induction of clinical aspergillomycosis by feeding contaminated diet to tilapia, Oreochromis niloticus (L.)

Abstract. Oreochromis niloticus maintained at 17°C and 26°C were fed a pelleted diet contaminated with cultures of Aspergitlus flavus fungus. Affected fish stopped feeding within one week, and became inactive, dark and oedematous. Exophthalmia, often accompanied by corneal or humoral changes, was common and mortalities commenced after 4 weeks. Surviving fish were sacrificed after 5 weeks and the fungus was isolated from all organs, including—irregularly—the eye. The histopathology was predominantly that of a necrotizing septicaemia, with fungal hyphae present in liver, peritoneum, kidney, intestinal wall and, distinctively, in the orbit and eye of affected fish.     

Ocular lesions associated with attachment of the parasitic copepod Ommatokoita elongata (Grant) to corneas of Greenland sharks, Somniosus microcephalus (Bloch & Schneider)

The eyes from six Greenland sharks, Somniosus microcephalus (Bloch & Schneider), infected with the parasitic copepod Ommatokoita elongata (Grant) were collected in the Arctic waters of Victor Bay, North-west Territories, Canada, for study. Transformed adult female copepods, one per eye, were firmly attached to the corneas by an anchoring structure (i.e. the bulla) and each bulla was associated with an opaque area on the cornea. Two eyes additionally had one O. elongata copepodid attached to the cornea via frontal filaments with bullas which were each associated with a small corneal opacity. In addition to opacities associated with copepods at the time of collection, there were several randomly distributed, small, round-to-irregular, full-thickness corneal opacities which were not associated with copepods. Two unfixed eye lenses grossly examined in the field were normal in appearance. Histologically, corneal epithelial ulceration and heterophilic keratitis, disruption, mineralization, and detachment of Bowman's membrane, thinning, disorganization, mineralization and fibrosis of the corneal substantia propria, and focal thinning and mineralization of Descement's membrane were observed. Mild heterophilic and mononuclear anterior uveitis was also present. Based on the present observations, it is concluded that parasitism by O. elongata could lead to severe vision impairment (possibly including blindness) in Greenland sharks. However, the otherwise healthy appearance of the infected sharks studied and the information contained in the literature suggests that O. elongata infections do not significantly debilitate the hosts.     

Evidence of enhanced bacterial invasion during Diplostomum spathaceum infection in European grayling, Thymallus thymallus (L.)

Farmed grayling, Thymallus thymallus (L.), are susceptible to atypical Aeromonas salmonicida (aAS) infections. Interactions between bacteria and parasites were studied using grayling subjected to concomitant exposure to aAS bacteria and the digenean parasite Diplostomum spathaceum. Atypical AS was detected from fish by a combination of bacterial cultivation and polymerase chain reaction techniques. A detection level of 17 aAS cells per 100 mg intestine tissue sample was obtained. Concomitant bacterial exposure did not enhance the severity of grayling eye rupture and nuclear extrusion induced by D. spathaceum, but D. spathaceum invasion into grayling increased the proportion of fish carrying aAS in their heart tissue. However, the number of aAS cells detected in heart tissue was low. Atypical AS did not cause acute disease or mortality during 15 days post-exposure. There was a higher prevalence of aAS in grayling heart samples than in intestinal samples, indicating that the intestine is not favoured by aAS. We suggest that heart tissue would be a good organ from which to isolate aAS when tracing latent carrier fish. We conclude that penetrating diplostomids can enhance bacterial infections in fish and that diplostomids can cause serious eye ruptures in grayling.     

Tolerance of lake trout, Salvelinus namaycush (Walbaum), sac fry to dissolved gas supersaturation

Abstract. The tolerance of sac fry of lake trout, Salvelinus namaycush (Walbaum), to the acute effects of gas supersaturation, from hatching to swim-up, was tested using six gas levels, ranging from ΔP 8 to 148. Although many fish were moribund by the time the yolk was nearly absorbed, mortality during the 40-day study was negligible; survival to swim-up was 96–99%, including 99% survival at ΔP 148. Of fish examined at ΔP 42, 40% showed bubble formation around the rim of the eye. Signs of trauma were greatest at ΔP 119 and 148, and included intestinal bubbles, a distended abdomen, and bubbles around the eye, in the mouth and in jaw tissues.     

Pathology associated with a viral erythrocytic infection in turbot, Scophthalmus maximus (L.)

Abstract. Since 1992, frequent erythrocytic viral infections have occurred in cultured turbot, Scophthalmus maximus (L.), on several fish farms in Galicia, Spain, causing important mortalities. Affected fish showed haemorrhages in the head, mouth and fins, exophthalmia and abdominal distension. The disease was also characterized by the presence of pale blue inclusions in affected erythrocytes. The examination of these erythrocytes by electron microscopy showed virus particles of 50–160 nm in size in the cytoplasm, budding av the cell membrane and extracellularly. The histopathological study revealed occasional necrosis of kidney haematopoietic tissue, an increase in the size and number of melanomacrophage centres of the spleen and kidney, and oedematous areas with hepatocytes containing eosinophilc bodies in the liver. Degeneration of muscle fibres was accompanied by an intense inflammatory oedema. Dermatitis as well as uveitis and corneal oedema were consistent lesions.     

Nutritional status assessed in groups off smolting Atlantic salmon, Salmo salar L., developing cataracts

There has been an increasing number of reports on cataracts in Norwegian and international salmon farming. The present study was undertaken to examine physiological and nutritional conditions during an outbreak of cataracts observed in rapidly growing Atlantic salmon, Salmo salar L., smolt with emphasis on zinc status. During this study, the cataracts were classified as irreversible. The outbreak of cataracts was positively related to fish growth and negatively related to the condition factor of the fish. Zinc concentrations in liver, eye and plasma were recorded in fish with cataract and in healthy fish from December to May. Lower zinc status (around 20%) was found in fish with cataracts compared to healthy fish, both over time and with regard to severity of the cataract. The decline in organ zinc concentrations seems to be explained by increased relative liver size, lower dry matters in liver and eye, and lower plasma protein. From the present data, the incidence of cataracts could not be directly related to zinc or any of the other nutrients (vitamin A, iron) examined, although relative deficiencies caused by other unknown rearing factors cannot be excluded. The lower condition factor and differences in organ water composition in fish with cataracts indicate that the cataracts may be related to the smoltification processes. Smoltification in the fish population was most probably accelerated by elevated water temperatures.     

Histopathology of experimental Streptococcus sp. infection in tilapia, Oroochromis niloticus (L.), and channel catfish, Ictafurus punctatus (Ratinesque)

Nile tilapia, Oreochromis niloticus (L.), and channel catfish, Ictalurus punctatus (Rafinesque), were experimentally infected by immersion with three isolates (Lake, DL8O5 and MS91452) of Streptococcus sp. from diseased fish. To enhance infection, the lateral body surface of each fish was scraped prior to bacterial exposure. The Lake and DL8O5 isolates caused exophthalmia, ocular opacity and ocular haemorrhage in some tilapia. Histopathology of these fish revealed; meningitis; polyserositis of heart, liver, spleen, ovary and kidney; splenitis; ovaritis; and myocarditis. Isolate MS91452 induced only mild granulomas in spleen, kidney and ovary of tilapia. The Lake and DL8O5 isolates induced endophthalitis, Channel catfish infected with the Lake and DL805 isolates developed similar eye lesions to tilapia. Histologic lesions caused by all three isolates in channel catfish consisted of meningoencephalitis, mild myocarditis, splenitis and ovaritis, but these lesions were not as severe as in Nile tilapia.     

7种观赏性剑尾鱼品种间杂交子代的体色及鳍形研究

7种观赏性剑尾鱼的自交、杂交,对其子代的体色(包括眼睛色彩)及鳍形等性状进行统计分析。试验结果表明,黑眼为显性基因控制,红眼为隐性基因控制,体色与眼睛颜色有一定的连锁关系;推测剑尾鱼体色遗传由数量性状基因参与控制;尾鳍燕尾相对于正常尾为显性,而且雄性尾鳍的燕尾和长臀鳍具有连锁性;高背鳍由显性基因控制,正常背鳍由隐性基因控制,拥有正常背鳍的个体,其基因型是隐性纯合,拥有高背鳍的个体,其基因型为杂合,初步推断显性纯合为致死基因型。     

A sensitive period during first feeding for the determination of pigmentation pattern in Atlantic halibut, Hippoglossus hippoglossus L., juveniles: the role of diet

Six groups of Atlantic halibut, Hippoglossus hippoglossus L., larvae were offered calanoid cope-pods at different periods from days 11 to 25 after first feeding (1.13-3.20 mm myotome height) in order to establish at which stage normal pigmentation was determined. Artemia nauplii enriched with an oil emulsion were used prior to and after the copepod period. Control groups were fed on copepods or Artemia only. The Artemia diet initiated an earlier intake of food and higher initial growth compared to the copepod diet. After 50 days of feeding, the average dry weights of the fish fed on Artemia and copepods were quite similar to the copepod-fed fish, while the Artemia-fed fish were the smallest in size. The lowest frequency of normally pigmented juveniles was found in the Artemia-fed group (66.4%), while the copepod group showed almost 100% normal pigmentation. A significantly higher frequency of pigmentation was found in juveniles given a copepod diet close to the initiation of metamorphosis than those provided with an earlier copepod period of equal duration. A high degree of eye migration was found in all groups, but was lowest in the Artemia-fed group. The initial stage of eye migration was found to occur at a larger body size in fish given Artemia and copepods, or a copepod diet than in fish fed on Artemia alone. There was no significant correlation between eye migration and growth rates prior to metamorphosis, although the largest individuals exhibited the most complete eye migration. High pigmentation frequencies were obtained in fish with a low 22:6n-3:20:.5n-3 (DHA:EPA) ratio (< 1.0).     

The histopathology of the eye of big head carp, Aristichthys noblis (Richardson), infested with Lernaea piscinae Harding, 1950

Abstract. The histopathological changes in the eye due to the penetration and growth of the parasite, Lernaea piscinae , in the host tissue of big head carp is described. Distinct pathological changes were hyperplasia of the corneal epithelium, severe inflammatory response mainly around the anchor of the parasite, in the anterior chamber, the corneal stroma and the vitreous body and detachment of the vitreous and retinal layers. Rupture of the lens capsule and fibrous tissue response around the process of the anchor structure of the parasite were also observed. The development of an immune response to the parasite within the body of the host is thought to have led to the infection of the cornea, an avascular site.     

基于计算机视觉的卵形鲳鲹眼部特征检测方法研究

鱼形态特征检测作为渔业信息化的一个重要课题,有着广泛地应用前景。现有的鱼眼特征检测主要依靠人工,操作复杂、效率低下、结果主观性强。因此提出一种基于图像处理及最小二乘椭圆拟合的鱼眼检测方法,首先在养殖场采集实验鱼例图像,再对鱼眼瞳孔和虹膜区域进行图像预处理,最后分别对鱼眼的瞳孔/虹膜轮廓进行椭圆拟合。实验结果显示,鱼眼瞳孔检测平均耗时325.96 ms,虹膜检测平均耗时364.57 ms,两者检测误差分别为7.247(1±11.82%)mm和12.179(1±14.05%)mm。研究表明,采用该方法不仅可以解决人工测量操作繁琐、主观性强等问题,而且能够避免测量过程耗时过长,为鱼眼的大批量非接触式测量提供了新途径。     

Isoenzymatic changes in grass carp, Ctenopharyngodon idellus Cuvier & Valenciennes, affected with haemorrhagic disease

Abstract. Electrophoretic analysis of six types of tissue (serum, erythrocyte, liver, kidney, muscle and eye) and seven different isoenzymes (LDH, MDH, Est, ADH, IDH, α-GPDH and SOD) from both healthy grass carp, Ctenopharyngodon idellus Cuvier & Valenciennes, and carp affected by haemorrhagic disease was performed. It was found that: (1) Enzymes from diseased grass carp showed the most drastic changes within each tissue. The absolute activity of LDH in serum from the diseased fish increased to approximately twice that of the healthy fish; whereas the relative activity of A₄ and A₃B₁, the main components of A sub-base in both serum and erythrocytes, was accelerated. (2) The isoenzymic changes in the control groups, diseased fish, artificially infected fish and healthy fish from diseased ponds indicated that biochemical changes occurred in the tissues before pathological change.     

Growth Rate, Maturation Level and Flesh Quality of Three Strains of Large Rainbow Trout (Oncorhynchus Mykiss) Reared in Estonia

Three all-female strains of large rainbow trout imported to Estonia (Danish, Finnish and Donaldson strain) were evaluated in a communal rearing experiment in tanks. The fish had been reared on different fish farms before the experiment started and they had an initial weight of 400–500 g. There were no significant genetic differences between the investigated strains on the basis of three allozyme loci. The total weight gain of the strains during the trial was similar but differences were revealed between seasons. The growth rate of the Finnish trout was high during the first autumn but decreased during the second summer of the trial, probably due to infestation by eye fluke Diplostomum sp. The strains differed in the percentage of immature fish and in the level of gonad development at the age of 2.5–3 years. The Donaldson strain had the highest number of immature fish of the studied strains. Mature females of the Finnish strain had the smallest gonads but also the lowest percentage of immature fish. The level of maturation was the main factor determining the quality – slaughter yield and flesh color.     

Development and characterization of cell lines derived from rohu, Labeo rohita (Hamilton), and catla, Catla catla (Hamilton)

Two new cell lines, designated RE and CB, were derived from the eye of rohu, Labeo rohita , and the brain of catla, Catla catla , respectively. The cell lines were maintained in Leibovitz's L-15 supplemented with 20% foetal bovine serum. The RE cell line was sub-cultured for more than 70 passages and the CB cell line for more than 35 passages. The RE cells are rounded and consist predominantly of epithelial cells. The CB cell line consists of predominantly fibroblastic-like cells. Both cell lines are able to grow at temperatures between 25 and 32 °C with an optimum of 28 °C. The growth rate of the cells increased as the foetal bovine serum concentration increased from 2% to 20% at 28 °C, with optimum growth at concentrations of 15% or 20% foetal bovine serum. The cells were successfully cryopreserved and revived at different passage levels. The cell lines were not susceptible to four marine fish viruses. Extracellular products from Aeromonas sp . were toxic to the cell lines. When the cells were transfected with plasmid eukaryotic green fluorescent protein (pEGFP [Clontech, Carlsbad, CA, USA]) vector DNA, a significant fluorescent signal was observed suggesting that these cell lines could be a useful tool for transgenic and genetic manipulation studies. Polymerase chain reaction amplification of mitochondrial 12S rRNA from rohu and catla confirmed that the cell lines originated from these fish species. The cell lines were further characterized by immunocytochemistry using confocal laser scanning microscopy.     

Liposarcoma in clownfish,Amphiprion ocellaris Cuvier,produced in indoor aquaculture

Clownfish, Amphiprion ocellaris Cuvier, produced and grown in an experimental indoor aquaculture facility, presented with lipomatous tumours. A total of 14 affected fish were examined. Based on the total number of fish at the aquaculture facility at the time of outbreak of this pathology, the scope of the incident is estimated to be 1 of 300 fish. The tumours were characterized by the presence of mature adipocytes of variable sizes, lipoblasts and by an invasive behaviour, which affected internal organs, muscle, central nervous system and, in one case, an eye. Detailed macroscopic and histopathological features are presented. The suggested diagnosis is that of a well‐differentiated liposarcoma, a diagnosis so far never applied to fish. The limited outbreak of the neoplasm lasted a few months in 2011 and did not recur. Possible factors leading to this phenomenon, notably the metastasis, are discussed.     

Field evaluation of live chilling with CO2 on stunning Atlantic salmon (Salmo salar) and the subsequent effect on quality

Atlantic salmon were slaughtered in three ways on a commercial slaughter line: (1) killed by a percussive stun after crowding; (2) killed by percussive stun after crowding, pumping and live chilling; (3) killed by exsanguination after crowding, pumping and live chilling. The live‐chilled fish were exposed to seawater (2°C) saturated with carbon dioxide (pH 5.5–5.7) for 40 min. The fish were calm after live chilling, but not unconscious, as eye rolling was observed in all individuals. Subsequent exsanguination of the unstunned fish resulted in death. Both rapid live chilling and the subsequent exsanguination appeared stressful to the fish, as a large and rapid pH drop coupled with earlier onset of rigor mortis, indicative of high muscle activity during the process were observed. The muscle core temperature during ice storage showed that live chilling only has an effect on carcass temperature during the first 6 h post mortem. After 6 h, no significant differences in temperature were detected between live‐chilled and traditionally ice‐chilled fish. We conclude that commercial use of live chilling in combination with high levels of CO₂ does not stun Atlantic salmon. Live chilling followed by exsanguination of the unstunned fish appears to be highly stressful and should be avoided.     

Establishment of cell lines from a tropical grouper,Epinephelus awoara (Temminck & Schlegel), and their susceptibility to grouper irido- and nodaviruses

Four tropical marine fish cell lines have been established from the eye, fin, heart and swim bladder of grouper, Epinephelus awoara (Temminck & Schlegel). Optimum media and temperature conditions for maximum growth were standardized. The eye and swim bladder cells were mostly epithelial, but the fin and heart cells were mostly fibroblastic. The viability of cells was 95% after 1 year of storage in liquid nitrogen (-196 degrees C). Besides these four cell lines, previously established grouper brain, kidney and liver cell lines were also used for a viral susceptibility study which showed that all the cell lines were sensitive to grouper iridovirus, whereas only brain, fin and liver cell lines were susceptible to the yellow grouper nervous necrosis virus (a nodavirus). Electron microscopy studies of the grouper irido- and nodaviruses in ultrathin sections of infected cells showed an abundance of viral particles in the cytoplasm of the virus-infected cells indicating the effective replication of these two viruses. It is suggested that these cell lines can be used for the isolation of putative fish specific viruses and provide a valuable tool to study the mechanisms of host-pathogen interactions. Furthermore, these cell lines upon transfection, using pEGFP-C1 and pEGFP-aMT2.5 (ayu metallothionein promoter), produced significant fluorescent signals indicating their utility for exogenous studies.     

Effect of eye fluke infection on the growth of whitefish (Coregonus lavaretus) —An experimental approach

Effect of the eye fluke Diplostomum spathaceum on fish growth has remained somewhat unclear because 1) the question has not been subjected to experimental examination with treatment-control setup and 2) growth has not been related to the coverage of parasite-induced cataracts in a quantitative manner. We examined effects of the parasite on growth and competitive ability of whitefish (Coregonus lavaretus) in experimental conditions resembling those at fish farms by maintaining groups of exposed and control fish, as well as mixed groups from both treatments, under optimal conditions for 8 weeks. Contrary to our expectations, we did not observe differences in fish growth between the treatments. However, at the level of individual fish, parasite-induced cataracts had a negative effect on weight of the exposed fish but this took place only when the cataract coverage reached 100% in both eyes. No effect of the infection on competitive ability of fish was observed in mixed treatments which may be related to patterns of food distribution in the tanks or cues received by the fish from less infected conspecifics. Overall, the results suggest that effects of D. spathaceum on fish growth become apparent only in cases of very high cataract coverage, and that feeding regimes and the shape of the cataract coverage distribution in a fish group are important determinants of the magnitude of these effects.     

Progressive panophthalmitis in chinook salmon, Oncorhynchus tshawytscha (Walbaum): a case report

Abstract. This report describes the gross and histopathological appearance as well as the bacteriological findings in an outbreak of panophthalmitis in farmed chinook salmon. In all cases, the bacteria were either Mycobacterium neoaurum or an unidentified Rhodococcus spp.; in some fish, both types were present in roughly equal numbers, while in others, one type dominated. Despite occasionally recovering the bacteria from kidney or spleen, no lesions were found in these or in any other organ, suggesting that the localization to the eye was not incidental, but a specific tropism. Nevertheless, the possibility of predisposing cause(s) must be considered and these are discussed.