The bacterial flora of rainbow trout, Salmo gairdneri Richardson, and brown trout, Salmo trutta L., eggs and its relationship to developmental success

Abstract. The bacterial flora of rainbow, Salmo gairdneri Richardson, and brown trout, Salmo trutta L., eggs was studied during incubation. Few bacteria were considered to exist internally, although Pseudomonas species and Aeromonas hydrophila were isolated. During incubation, large numbers of bacteria approaching 500 colony forming units/mm² accumulated around egg surfaces. Both rainbow and brown trout eggs placed in a through-flow system were colonized mainly by Pseudomonas sp. and A. hydrophila , whilst rainbow trout eggs in a separate recycling system were dominated by a Cytophaga species. Glass beads were also incubated (as an inert surface) and found to support significantly lower numbers of bacteria. Egg mortalities were recorded daily and found to differ significantly between both fish species and water conditions. Statistical analysis indicated a potentially significant correlation between hatching success and numbers of surface bacteria.     

Lysozyme from rainbow trout, Salmo gairdneri Richardson, as an antibacterial agent against fish pathogens

Abstract. The antibacterial effect of two lysozyme variants purified from rainbow trout, Salmo gairdneri Richardson, kidney was investigated as part of a project directed towards increasing the disease resistance of fish by the transgenic technique. Seven bacterial strains from five Gram-negative species, of which one was considered non-pathogenic, were examined. One of the rainbow trout lysozymes was surprisingly potent, having substantial antibacterial activity on all strains tested. Hen egg-white lysozyme was bactericidal only against the one species considered non-pathogenic. The data suggest that lysozyme does play a role in the disease defence of rainbow trout and that the gene for the most active lysozyme may be suitable for testing the transgenic strategy.     

Enhancement of resistance to bacterial infection in rainbow trout, Oncorhynchus mykiss (Walbaum), by oral administration of bovine lactoferrin

Abstract Bovine lactoferrin was evaluated for its ability to enhance resistance of rainbow trout, Oncorhynchus mykiss (Walbaum), to infection with Vibrio anguillarum. Oral administration of lactoferrin (100 mg kg⁻¹) to fish daily for 3 days prior to an intraperitoneal challenge with V. anguillarum resulted in increased survival rates, and enhanced resistance against Streptococcus sp., although to a lesser extent. In lactoferrin-treated fish, an increase in phagocytic and chemiluminescent (CL) activities of pronephros cells against V. anguillarum was observed. The phagocytic and CL activities of cells against Streptococcus sp. were also significantly increased. However, no in vitro bactericidal activities of lactoferrin against V. anguillarum or Streptococcus sp. were observed. This suggests that the lactoferrin enhanced the resistance of the rainbow trout against bacterial infection through the activation of phagocytes.     

Morphological, physiological and biochemical parameters characterizing the over-ripening of rainbow trout eggs

In rainbow trout (Oncorhynchus mykiss) freshly ovulated eggs and over-ripened eggs which had been retained in the coelomic cavity for 7, 14 and 21 days were investigated in aspects of morphology, physiology and biochemistry. Egg viability was significantly reduced from 85.9±16.4% in freshly ovulated eggs to 25.1±21.9% in over-ripened eggs which had been retained in the coelomic cavity for 21 days. Further during over-ripening in the ovarian fluid the pH significantly decreased, while the levels of proteins, of esterified and non esterified fatty acids and the activities of aspartate aminotransferase and acid phosphatase significantly increased. Also egg parameters changed: the wet weight of the unhardened eggs increased, the weight increase during hardening and the levels of esterified and of non esterified fatty acids significantly decreased. In freshly ovulated eggs the yolk consisted of a homogenous mass and the perivitelline space was small, but in over-ripened eggs the yolk was non homogenous with numerous vesicular inclusions and the perivitelline space was enlarged. When freshly ovulated eggs were incubated in water the cortical reaction was detectable within 5 min, in over-ripened eggs hardly no extrusion of cortical vesicles was visible and the width of the perivitelline space was very irregular.For the investigated freshly ovulated and over-ripened samples the egg viability significantly correlated with ovarian fluid parameters (pH, protein, non esterified fatty acids, esterified fatty acids, aspartate aminotransferase, acid phosphatase) and egg parameters (weight increase during hardening, weight of the hardened eggs).     

The disease status of Australian salmonids: bacteria and bacterial diseases

Abstract. Eleven freshwater salmonid hatcheries in southern Australia were surveyed for bacterial pathogens and diseases between 1981 and 1985, Twenty-five populations of fish were examined in the study, representing a total of 2755 fish, from which kidney, liver, spleen, and in some cases peritoneum, blood and faeces were cultured. Bacteria of pathogenic significance isolated included Aeromonas hvdrophila, Streptococcus sp., Lactobacillus piscicola, Yersinia ruckeri, Mycobacterium fortuitum, M. chelonei and a filamentous acid-fast organism of uncertain taxonomic position. Lacto-bacillus piscicola and Streptococcus sp. were associated with clinical and subclinical peritonitis. Mycobacterium chelonei was isolated from visceral granulomas in an externally normal fish. Aeromonas salmonicida, Renibacterium salmoninarum and Edwardsiella tarda were not isolated, indicating that the diseases furunculosis, bacterial kidney disease and edwardsiellosis are exotic to Australian salmonids. Similarly, while Y. ruckeri was isolated, enteric redmouth disease had not been recorded and is considered an exotic disease.     

Atypical growth of Renibacterium salmoninarum in subclinical infections

Two growth types of Renibacterium salmoninarum were isolated from subclinically infected rainbow trout, one producing the smooth colonies typical of R. salmoninarum and the other forming a thin film on the surface of the agar with no separate colonies. The atypical growth was present on kidney disease medium agar in primary cultures of the kidney but not on selective kidney disease medium (SKDM). Fluorescent antibody staining of the fresh isolate and polymerase chain reaction amplification were the most reliable techniques to identify the atypical growth of R. salmoninarum. The condition was reversible, with growth reverting from atypical to the smooth colony form in experimentally infected rainbow trout and under laboratory conditions. There was no mortality, or any clinical signs of bacterial kidney disease (BKD) in the fish challenged with the atypical growth, although small numbers of smooth colonies of R. salmoninarum were isolated from 8% of these fish. The atypical growth reported here may explain some of the failures of culture, when SKDM agar alone is used for the detection of BKD in subclinically infected fish.     

Does chromic oxide (Cr2O3) affect faecal lipid and intestinal bacterial flora in Arctic charr. Salvelinus alpinus (L.)?

Abstract. Arctic charr. Salvelinus alpinus (L.), were fed a commercial diet with or without a supplement of 1% chromic oxide (Cr₂O₃) in fresh water at 8°C for 70 days. Supplementation of the diet with 1% chromic oxide did not affect the lipid composition of stomach contents, but did affect that of the faeces.
Highest total lipid content in faeces was observed when fish were fed on the diet supplemented with chromic oxide. The proportion of triacylglycerols and free fatty acids increased in the neutral lipid fraction. The level of the dietary fatty acids 16:0, 16:1 and 18:1 increased, while 20:1 (n-9), 22:1 (n-11) and 18:2 (n-6) decreased significantly (P < 0·05) compared to the unsupplemented diet.
Total viable counts (TVC) of aerobic microorganisms were somewhat higher in stomach contents when the charr were fed on the unsupplemented diet. In faeces from charr fed the unsupplemented diet, TVC were higher, by a factor of 10 compared to fish fed diet supplemented with chromic oxide. Bacterial composition in stomach content of both rearing groups were dominated by Pseudomonas sp. and Agrobacterium sp., but the number of Lactobacillus sp. and Streptococcus sp. enhanced in stomach content when the fish were fed on the chromic oxide enriched diet. The faecal bacterial flora were also different between the rearing groups. The predominant bacterial species present in the faeces of fish fed unsupplemented diet were identified as Pseudomonas sp. and Aeromonas sp. Other bacterial species isolated included Lactobacillus sp., Streptococcus sp., Agrobacterium sp., Flavobacterium sp. and Vibrio sp. In contrast, the bacteria flora in faeces of fish fed the chromic oxide diet was dominated by the Gram-positive bacteria Streptococcus and Lactobacillus.
It is suggested that the use of chromic oxide as a marker in digestibility studies in Arctic charr may not be ideal.     

An immune-complex glomerulonephritis of Chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Chinook salmon from New Zealand were shown to have a generalized membranous glomerulonephritis that was most severe in large fish. Marked thickening of the glomerular basement membrane was the most consistent lesion, with the presence of an electron-dense deposit beneath the capillary endothelium.Severely affected glomeruli also had expansion of the mesangium and loss of capillaries,synechiae of the visceral and parietal epithelium and mild fibrosis of Bowmans capsule. Chinook salmon from British Columbia, Canada with bacterial kidney disease caused by Renibacterium salmoninarum had similar histological lesions. They also had thickened glomerular basement membranes that were recognized by rabbit antiserum to rainbow trout immunoglobulin. This was true only when frozen sections of kidney were used and not formalin-fixed tissue. An attempt to experimentally produce a glomerulopathy in rainbow trout by repeated immunization with killed R. salmoninarum was not successful. Case records from the Fish Pathology Laboratory at the University of Guelph over a 10-year period revealed that a range of species were diagnosed with glomerulopathies similar to those seen in Chinook salmon. The majority of these cases were determined to have chronic inflammatory disease. This report has identified the presence of immunoglobulin within thickened basement membranes of Chinook salmon with glomerulonephritis and supports the existence of type III hypersensitivity in fish.     

Proliferative kidney disease in Switzerland: current state of knowledge

This study presents an overview of the distribution of proliferative kidney disease (PKD) in wild and farmed fish in Switzerland based on two sources: (1) the results of routine diagnostic work at the National Fish Disease Laboratory, and (2) the results of a country‐wide survey for PKD. The first case of PKD in Switzerland was diagnosed in 1979 and since 1981, a few cases have been found every year. Affected species were rainbow trout, brown trout and grayling from rivers and fish farms. Most of the diseased fish were found in the lower altitude regions of the country (Swiss midlands). A seasonal distribution of the cases was evident: PKD‐positive fish occurred only from June to November withprominent peaks in August and September. Among infected fish all length classes were present, but the highest numbers of affected fish were found in the length classes <10 cm and 16–20 cm. The evaluation of the samples from a survey of the occurrence of PKD in 2000/2001 revealed a much broader geographical distribution of the infection than expected from routine diagnostic observations. Fish from 56 of 139 rivers analysed by histological examination were positive for parasites. Fish from 131 of these sites were examined macroscopically. Of these, trout from 45 sites showed gross alterations indicative for PKD. Most of the positive fish were found in the Swiss midlands north of the Alps. Fish from six of 65 fish farms investigated were found to be PKD‐positive by histopathological analysis, and in four of these cases fish could be identified as infected on the basis of gross examination.     

Distribution and prevalence of T. bryosalmonae in Austria: A first survey of trout from rivers with a shrinking population

The first evidence of proliferative kidney disease (PKD) in an Austrian river (the River Kamp) was documented in 2016, and no information on the PKD infection status of trout in other rivers was available. Since then, brown trout (Salmo trutta fario) and rainbow trout (Oncorhynchus mykiss) have been collected from rivers in Upper and Lower Austria for different diagnostic purposes. In this study, we summarize the recent findings of a first survey concerning the distribution of Tetracapsuloides bryosalmonae, the causative agent of proliferative kidney disease (PKD), from these samples. Between September 2015 and October 2017, a total of 280 brown trout and 39 rainbow trout were collected from 21 rivers in the provinces of Upper and Lower Austria. T. bryosalmonae was detected by PCR of kidney tissue in 17 of 21 sampled rivers and in 138 of 280 brown trout as well as in 11 of 39 rainbow trout. Pathological signs of PKD (e.g., hypertrophy of the kidney) were observed in 33 analysed brown trout and six rainbow trout samples. No correlations between fish infected by T. bryosalmonae and the parameters size and age class, condition factor, geological origin of the streams and distribution within the river course were found, while positively tested fish are significantly increased at sampling sites exceeding water temperatures of 15°C for median periods of 115 days. The prevalence within the affected streams or stream sections is highly variable, and in single rivers, infection rates of up to 90% are confirmed.     

Suppression of Saprolegnia infections in rainbow trout (Oncorhynchus mykiss) eggs using protective bacteria and ultraviolet irradiation of the hatchery water

Since formalin is widely used in prevention of Saprolegnia infections in salmonid fish hatcheries, there is a need for more environmentally safe treatment methods. Therefore, we screened 360 bacterial isolates against their ability to antagonize the growth of Saprolegnia parasitica hyphae in vitro, and best strains were selected according to their antagonistic properties and colonization capability on rainbow trout egg surface. Protective bacterial cultures of Pseudomonas sp. M162, Pseudomonas sp. M174 and Janthinobacterium M169 were tested for prevention of Saprolegnia sp. infections during incubation trials of rainbow trout (Oncorhynchus mykiss) eggs with UV irradiated (400 mWs cm^?2) and non‐treated inlet water. UV irradiation of inlet water significantly decreased mortality during the incubation. Lowest mortalities were observed in protective culture treated groups incubated with UV‐irradiated inlet water. UV irradiation increased the dominance of the main bacterial colonizers and variation in the bacterial species diversity between the experimental units.     

The occurrence of proliferative kidney disease (PKD) in cultured and wild fish: further investigations

Abstract. In an investigation of the occurrence of proliferative kidney disease (PKD) in freshwater fish other than rainbow trout, 18 species of wild fish and seven species of fish raised in cultivation wore sampled from waters where the disease occurred annually in rainbow trout, Oncorhynchus mykiss (Richardson). Results revealed that certain wild stocks of brown trout. Salmo trutta L., grayling, Thymallus thymallus L., and pike, Esox lucius L., were infected with PKD, as were cultivated Atlantic salmon, Salmo salar L., parr, brown trout and char, Salvelinus alpinus (L.). Microscopical examination revealed the presence of the PKX cell in these species and also intraluminal protozoa possibly related to the PKX cell, which were not found in the rainbow trout. Other species of freshwater fish had myxosporidan infections but, unlike PKD infection, there was little host/parasite tissue response. The PKX cell as a myxosporidan stage is discussed and the presence of the disease in wild fish is reported.     

Relevance of Renibacterium salmoninarum in an asymptomatic carrier population of brook trout, Salvelinus fontinalis (Mitchill)

Abstract. These studies were done to determine the prevalence of infection, over time, of progeny from a population of 1988 year class brook trout, Salvelinus fontinalis (Mitchill), that was asymptomatically infected with Renibacterium salmoninarum , the causative agent of bacterial kidney disease. This population and its progeny from the 1991 and 1992 spawnings were monitored for approximately 3 years for prevalence of R. salmoninarum and development of bacterial kidney disease. Ovarian fluid samples from the 1991 and 1992 spawnings, and from a 1993 spawning of the 1991 progeny, were analysed for R. salmoninarum by enzyme linked immunosorbent assay (ELISA) and the membrane filtration fluorescent antibody technique. Kidney and spleen tissues of the 1988 year class were assayed by ELISA following the 1992 spawning. The progeny of the 1991 and 1992 spawnings were followed for increased prevalence of R. salmoninarum by the ELISA. Kidney tissues were assayed and sampling began once the fish were large enough. Each population of progeny was sampled quarterly for one year. Overall, the progeny displayed decreasing prevalence of R. salmoninarum and all ovarian fluids of the 1991 progeny (in 1993) were negative. Brood fish and progeny remained asymptomatic during the course of the study.     

Proliferative kidney disease: cellular aspects of the rainbow trout, Oncorhynchus mykiss (Walbaum), response to parasitic infection

Proliferative kidney disease (PKD) is an immunopathological condition of salmonid fish, caused by the hyperplastic response of their principal lymphoid tissues to infection with the spores of Tetracapsula bryosalmonae , a myxozoan parasite formerly designated proliferative kidney organism – unknown (PKX). In order to investigate the nature of cells involved in this host response and possible alterations of their functions during parasitic infection the course of PKD was studied by flow cytometry (FCM) techniques, using blood, pronephros and spleen leucocyte populations from rainbow trout infected by intraperitoneal (i.p.) injection with parasitic cells from infected donor fish. The parameters of the cellullar response studied were: cytogram of cell population, lymphoproliferation, phagocytosis, oxidative burst, and non-specific cytotoxicity. The modifications of cell population distribution and function in the PKD-infected fish mainly affected the pronephros cell populations and were coincident with the clinical phase of disease. During this phase, the lymphocytes constituted the major leucocyte cell population and underwent proliferation and were thus responsible for the renal tissue hyperplasia. Meanwhile, phagocytosis and oxidative burst were depressed. These data are in agreement with the patho-epidemiological background of PKD where the enhancement of the fish sensitivity to bacterial infections reflects the impairment of certain cellular defence mechanisms of innate immunity.     

A systemic protozoal disease of cultured salmonids

Abstract. Sporadic cases of a systemic protozoal infection with cells resembling Dermocystidium sp. are described from cultured rainbow trout, Salmo gairdneri Richardson, from France and brown trout, Salmo trutta L., and Atlantic salmon, Salmo salar L., from Ireland. Classical proliferative kidney disease was additionally found in the rainbow trout and PKX-like cells were also seen in the brown trout and salmon.     

Proliferative kidney disease in brown trout, Salmo trutta L., and Atlantic salmon, Salmo salar L., parr: histopathological and epidemiological observations

Abstract Proliferative kidney disease (PKD) has been described in cultivated rainbow trout but major outbreaks have not been recognized in other fish species. This paper describes light and electron microscope studies and presents epidemiological data of a disease condition in first summer Salmo salar parr and S. trutta , which is associated with an organism apparently identical to the aetiological agent of PKD. The pathology was found to be similar to that described for PKD in rainbow trout. The epidemiology in the brown trout suggests that exposure after May does not result in infection. The data from the outbreaks in two salmon hatcheries appear complex and suggest different susceptibilities to PKD among salmon originating from different sources.     

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.     

Viral haemorrhagic septicaemia (VHS) in grayling, Thymallus thymallus L.

Abstract. Two outbreaks of viral haemorrhagic septicaemia (VHS) have been detected in grayling, Thymallus thymallus L., in Switzerland, The affected fry showed a septicaemic haemorrhage. Due to their similar biotopes, the susceptibility of grayling and rainbow trout to the VHS virus has been compared. The mortality rates varied between 56 and 100% depending on the age of the fish and the infection dose, but no distinct loss-associated difference occurred between grayling and rainbow trout when comparing the same age group and infection dose. Anaemia, scattered subcutaneous and intermuscular haemorrhages and enteritis were frequent macroscopic findings. The major histopathological changes included necrotic foci in the liver, spleen, intestinal mucosa and haematopoietic part of the kidney, whereas a severe tubulonephrosis was detectable in the urinary part of the kidney.     

东北地区虹鳟IHN和IPN流行病学的初步研究

本文报道了虹鳟鱼病毒性疾病IHN和IPN的流行与危害情况，对这二种病毒性疾病的症状和病理变化作了初步的研究，并进行了病原学鉴定。文中建议严格地把住进口鱼卵或鱼苗的检疫工作，采取更严格的防疫措施，多层次地防止疫病的传播和蔓延。     

国际虹鳟育种产业简介及其对我国的借鉴意义

虹鳟Oncorhynchus mykiss原产于北美地区,为典型的冷水性鱼类,是世界性重要经济养殖鱼类之一和水产遗传育种领域的重要研究对象。虹鳟是最早采用数量遗传学理论指导遗传选育的水产动物之一,BLUP育种值估计和配合力分析等遗传评定方法以及家系选育、杂交和配套系育种等技术均在虹鳟育种实践中广泛应用。淡水鱼类养殖中,必须使用遗传选育的优良品种的行业共识,最早在虹鳟中确立。目前,在欧洲、北美以及智利等主要鲑鳟鱼养殖国家和地区,虹鳟良种覆盖率均已达到90%以上。鉴于虹鳟仍是我国养殖产量最高的鲑鳟鱼类,其育种工作在许多非原产国都取得了令人瞩目的成就,本文以全球化的视角,从虹鳟养殖与选育的历史概况、虹鳟种业的主要技术手段及产业格局、主要虹鳟育种机构的组织形式与类型特点等方面,简要介绍了国际虹鳟种业的发展及对我国虹鳟种业的借鉴意义。