Morphology and distribution of granulomatous inflammation in freshwater ornamental fish infected with mycobacteria

Mycobacteriosis in fish is a chronic progressive ubiquitous disease caused by Mycobacterium marinum, M. gordonae and M. fortuitum in most cases. The aim of this study was to describe the morphology and distribution of lesions in 322 freshwater ornamental fish across 36 species. Granulomatous inflammation was diagnosed by gross examination and histopathology testing in 188 fish (58.4%); acid‐fast rods (AFR) were determined in only 96 (51.1%) fish from 19 species after Ziehl–Neelsen staining. The most often affected organs with AFR were the kidney (81.2%), digestive tract (54.1%), liver (48.2%), spleen (45.9%) and skin (21.2%); sporadically, AFR were found in the branchiae (9.4%) and gonads (4.7%). In 14 randomly selected fish originating from four different fish tanks, the distribution of mycobacterial infection was studied by culture examination of the skin, gills, muscle tissue, digestive tract, liver, spleen and kidney. In 12 fish, the species M. marinum, M. gordonae, M. fortuitum, M. triviale, and M. avium subsp. hominissuis (serotypes 6 and 8 and genotype IS901? and IS1245+) were detected; mixed infection caused by different mycobacterial species was documented in five of them.     

Relative prevalence of Mycobacterium marinum in fish collected from aquaria and natural freshwaters in central Europe

A survey was carried out on occurrence of Mycobacterium marinum in fish kept in aquaria and those living in their natural environment. Species‐specific qPCR targeting the erp and IS2404 genes together with the conventional culture method were used. The analysis of 72 ornamental fish (n = 216 samples: gills, muscle and intestine) collected from aquaria revealed the presence of M. marinum in 30 individuals (41.7%) of whom 17 (23.6%) were later culture positive. Culture‐independent detection revealed the presence of M. marinum in 16 of 83 environmental samples (19.3%) collected in aquaria. The presence of viable M. marinum cells was later confirmed in 5 samples (6.0%). No qPCR or culture positivity was observed when 123 groundwater fish and their corresponding environmental samples (n = 142) were analysed.     

Detection and identification of aquatic mycobacteria in formalin-fixed, paraffin-embedded fish tissues

The isolation of mycobacteria from field samples is problematic, and isolation of the bacterium is sometimes not even attempted. The detection of mycobacteria through traditional histology using formalin‐fixed, paraffin‐embedded (FFPE) tissues is neither sensitive nor specific. However, detection of mycobacterial DNA from FFPE specimens, suspected of being infected with mammalian mycobacteriosis, is a routine clinical procedure. In the present study, a polymerase chain reaction (PCR)‐based method was used to detect and identify mycobacteria in FFPE specimens sampled from fish suspected of being infected with fish mycobacteriosis. A total of 45 fish tissue samples, comprising of 12 tissue samples obtained from experimentally infected fish and the remainder from fish naturally infected with mycobacteria, were analysed using a PCR protocol which amplifies a fragment of the mycobacterial 65 kDa heat‐shock protein (hsp65) gene. PCR‐restriction enzyme analysis and/or sequencing were employed to further analyse the PCR amplicons. The PCR results were compared with those obtained by histology and culture. Mycobacterial DNA was detected in 34 of the 45 samples examined, of which 16 samples (47%) showed granulomatous reactions on histological examination. Using histology as the gold standard, no false‐negative PCR results were obtained. Also, considering the presence or absence of granulomas as a diagnostic criterion, the sensitivity and specificity of PCR in 42 of the FFPE tissues were 16/16 (100%) and 8/26 (～30.8%), respectively. Corresponding microbiological cultures were available for 15 cases, of which 13 were pure Mycobacterium cultures. Of these, 13 were PCR positive (100% sensitivity and 50% specificity). The PCR‐based methods used here proved sensitive, specific and rapid for the detection of mycobacteria in routinely processed paraffin wax‐embedded and formalin‐fixed histological samples, and the results of the study suggest that this method has potential use in retrospective epidemiological studies.     

Particle size distribution of wastes from freshwater fish farms

Waste water treatment on freshwater fish farms is problematic as waste material and water flows can vary greatly on a daily basis, and, in terms of effluent standards, fish farm effluent represents a dilute waste water output. A study was undertaken to investigate in detail the nature of the waste outputs under field conditions. Waste water samples were split by meshes into the following size ranges: >200μm, 200-100μm, 100-60μm, 60-30μm and <30μm. Waste water quality parameters, suspended solids (SS), biochemical oxygen demand (BOD₅) and total phosphorus (TP) were examined for each size range at two freshwater fish farm sites in Scotland, as part of a wider investigation into waste water quality of aquaculture operations. Results indicated that during periods of peak waste output i.e. tank cleaning, approximately 80% of BOD₅ and SS was present in a particle size range of 100-60μm, but only 66% of TP transport occurred in this size range. At other times, low levels (≤40%) of entrapment of wastes by the chosen meshes was observed, suggesting a reversion to predominantly dissolved material transport. Compared against a larger data set of outflow concentrations obtained from another section of the study, maximum removal rates of 46%, 48% and 30% for BOD₅, SS and TP respectively were determined. The implications for waste water treatment at fish farms are discussed.     

Distribution of mycobacteria in clinically healthy ornamental fish and their aquarium environment

Some mycobacterial species (particularly Mycobacterium marinum) found in aquarium environments may cause chronic diseases in fish and cutaneous infections in humans, the so-called 'fish tank granuloma'. The presence and distribution of mycobacterial species in clinically healthy aquarium fish and their environment has not been adequately explored. The present study analysed the occurrence of mycobacteria in a decorative aquarium (Brno, South Moravia) and in five aquaria of a professional fish breeder (Bohumin, North Moravia). After Ziehl-Neelsen staining, acid-fast rods (AFR) were observed in six (14.3%) and mycobacteria were detected by culture in 18 (42.9%) of 42 tissue samples from 19 fish. Sixty-five samples of the aqueous environment from all six aquaria were examined; AFR were found in 16 (24.6%) and mycobacteria were detected by culture in 49 (75.4%) samples. Forty-one (70.7%) of 58 selected mycobacterial isolates were identified biochemically as follows: M. fortuitum, M. flavescens, M. chelonae, M. gordonae, M. terrae, M. triviale, M. diernhoferi, M. celatum, M. kansasii and M. intracellulare. The clinically important species for humans and fish, M. marinum, was not detected. Mycobacterium kansasii was isolated from one sample of the aquarium environment from North Moravia, which is a region of the Czech Republic with endemic incidence of M. kansasii in water. The incidence of other conditionally pathogenic mycobacterial species in healthy fish and in all investigated constituents of the aquarium environment including snails and crustaceans used for fish feeding, was quite high. Accordingly, mycobacterial species from aquarium environments may serve as a possible source of infection for both aquarium fish and immunodeficient fish handlers.     

中国淡水鱼类寄生虫研究七十年

寄生虫是水产养殖中最主要的病原类群之一,对鱼类苗种直至成鱼各个阶段的危害都十分严重。我国的鱼病学即是从鱼类寄生虫的研究发端并逐步发展起来的。本文从病原生物学、生态学、药物学、免疫学四个方面回顾了我国淡水鱼类寄生虫自新中国建立初期至今70年间(1953年—2023年)的研究历程和已取得的成绩,并对未来的发展趋势和前沿热点进行了展望。本文为从事鱼类寄生虫学以及水产其他相关研究的读者提供了关于中国鱼类寄生虫研究的历史、现在发展水平和未来发展动向等较为全面的素材。     

Aquatic food security: insights into challenges and solutions from an analysis of interactions between fisheries,aquaculture, food safety,human health,fish and human welfare,economy and environment

Fisheries and aquaculture production, imports, exports and equitability of distribution determine the supply of aquatic food to people. Aquatic food security is achieved when a food supply is sufficient, safe, sustainable, shockproof and sound: sufficient, to meet needs and preferences of people; safe, to provide nutritional benefit while posing minimal health risks; sustainable, to provide food now and for future generations; shock‐proof, to provide resilience to shocks in production systems and supply chains; and sound, to meet legal and ethical standards for welfare of animals, people and environment. Here, we present an integrated assessment of these elements of the aquatic food system in the United Kingdom, a system linked to dynamic global networks of producers, processors and markets. Our assessment addresses sufficiency of supply from aquaculture, fisheries and trade; safety of supply given biological, chemical and radiation hazards; social, economic and environmental sustainability of production systems and supply chains; system resilience to social, economic and environmental shocks; welfare of fish, people and environment; and the authenticity of food. Conventionally, these aspects of the food system are not assessed collectively, so information supporting our assessment is widely dispersed. Our assessment reveals trade‐offs and challenges in the food system that are easily overlooked in sectoral analyses of fisheries, aquaculture, health, medicine, human and fish welfare, safety and environment. We highlight potential benefits of an integrated, systematic and ongoing process to assess security of the aquatic food system and to predict impacts of social, economic and environmental change on food supply and demand.     

Promotion and contribution of biota in low water exchange ponds farming blue shrimp Litopenaeus stylirostris (Stimpson)

An experimental study was conducted during 20 weeks in Bahia Kino, Sonora, Mexico, in order to evaluate the feasibility of promoting biota in low‐water exchange ponds farming blue shrimp, Litopenaeus stylirostris. The effect of that promotion on the production parameters of cultured shrimp as well as on the water quality parameters was evaluated. Treatments consisted of: (i) ponds fed formulated food (FF), and (ii) ponds fed formulated plus promoted natural food (NFF). Phytoplankton, zooplankton and benthos were effectively promoted during some weeks of the culture period. Growth and feed conversion ratio (15.16 g and 1.79 respectively) were significantly better in treatment NFF than in treatment FF (13.89 g and 2.02 respectively). Differences in some of the water quality parameters were observed among treatments. Phosphates (0.15 mg/L versus 0.53 mg/L), and total ammonia‐N (0.09 mg/L versus 0.12 mg/L) presented greater concentrations in treatment FF than in the NFF.     

耐盐红螺菌科细菌对淡水 池水质及细菌类群的影响

对耐盐红螺菌科光合细菌应用于淡水斑点叉尾Hui、彭泽卿养殖后，水化学环境因子、细菌类群及养殖生物的变化进行了研究。结果表明，鱼池泼施光合细菌后，水体NH4^+-N、NO2^--N、NO3^--N和COD下降，溶氧和pH上升；细菌类群及数量变化大致是：光合细菌提高3－50倍（多数在15－20倍）, 硝酸细菌提高3倍，硝酸细菌提高4－5倍；斑点叉尾Hui养殖池的主要异养细菌肠杆菌科细菌提高9．4％，气单胞菌属降低7．5％，彭泽鲫养殖池的主要异养细菌假单胞菌属降低16％，肠杆菌科提高21％；养殖生物的养殖效果是：斑点叉尾Hui鱼苗个体增重提高15．7％，彭泽卿苗个体增重提高12．8％。     

A review of mycobacteriosis in marine fish

Mycobacteriosis is a serious and often lethal disease of fish, affecting a wide range of species globally both in culture and wild settings. Caused by several species of the genus Mycobacterium , the disease has received considerable attention in recent years because of the discovery of new species in piscine hosts, epizootics in wild fisheries, and the ability of a few species to infect humans. The impact of this disease in aquaculture and the aquaria trade has been well reported and there is currently no widely accepted cure other than depopulation and facility disinfection. However, the impact on wild fisheries is poorly understood and may relate to species-specific interactions (host–pathogen) and possibly environmental stressors. In this review, much of what is known about mycobacteriosis in marine fish is summarized with particular attention to an epizootic in striped bass, Morone saxatilis , (Walbaum), in Chesapeake Bay, USA.     

Current forces on,and water flow through and around,floating fish farms

The wake generated by a screen or a net is analysed by the linear free-wake equations in conjunction with an eddy viscosity formulation. The behaviour of the near and far-field wake is investigated, and a relationship between the drag coefficient and the wake velocity is derived. A method for calculating the current forces experienced by the net structure and the resulting deformation is derived and compared with model tests. The effects of the wake behaviour and the deformation of the net cages, on the design and operation of floating fish farms are discussed and some recommendations are given.Nomenclature A Area of a net panel - dA Area of a portion of a net panel - A ^N Area of the net panel normal to the flow direction - A ^P Area of the net panel parallel to the flow direction - C_D,i Drag coefficient of thei ^th cylinder - C_D() Drag coefficient as function of the angle between the normal to the net and flow direction - C_L() Lift coefficient as function of the angle between the normal to the net and flow direction - D Diameter - D _i Diameter of thei ^th cylinder - DO Dissolved oxygen concentration - F _D Drag force - F _L Lift force - H Heaviside function - L Width of net panel - l _i Length of thei ^th cylinder - N Number of cylinders - N _i Number of cylinders in y-direction - N _j Number of cylinders in z-direction - N _N Number of cages in direction normal to the flow - N _C Number of cages in direction of the flow - r=u/U Velocity reduction factor - Rn=U*D/v Reynolds number - Sn Solidity ratio, defined as the ratio between the area covered by the threads and the total area of the net panel - t Time - U Current or free flow velocity - u ₁=U–u Velocity defect - u=U–u ₁ Wake velocity - x,y,z Cartesian coordinate system or field point for calculation of velocity - x _i ,y _i ,z _i Source point on screen element - Angle between the flow direction and the normal vector to the net, in the direction of the flow - Eddy viscosity - Mesh size - Kinematic viscosity - Density of water - Error function - Partial differential operator - Infinity     

Effect of fish species combinations on water chemistry and plankton composition in earthen fish ponds

Fish-environment relationships in ponds with several different combinations of fish species are analysed. The study was carried out in 18 earthen fish ponds in a farm at Lohamei HaGetaot, Israel, during the 1986 fish culture season. Water was analysed for temperature, dissolved oxygen, pH, ammonium, nitrite, nitrate, and phyto- and zooplankton. Factor analysis was applied to the physico-chemical and plankton datasets to identify respectively the main ecological processes and species groups in the ponds. The general linear model was applied to analyse the effect of fish species combination and month on the ecological and plankton factors identified. The main source of water quality variability was accounted for by three factors: pond loading (CHF1), oxygenation of the water (CHF2), and pH effect on the second step of nitrification (CHF3). The main source of variability in the plankton composition was due to presence or absence of a blue-green algal bloom (PLF1). Another four plankton factors were identified. Each factor was differently affected by the fish species combination in the pond and the month. The complex nets of interactions between common carp, tilapia and mullet, and how these fish in different cominations affect pond water quality and food webs are discussed.     

Application of Azotobacter enhances pond productivity and fish biomass in still water ponds

Two strains (derepressed-nitrogen fixing, Mac-27 and phosphate solubilizing, PS-21) of Azotobacter chroococcum were inoculated in fish culture ponds, singly and in combination with inorganic fertilizers (urea, single superphosphate–SSP). Physico-chemical parameters of pond waters, plankton production and fish biomass were studied. Inoculation of A. chroococcum (Mac-27) enhanced nitrogenase activity and rate of nitrogen fixation. A slight reduction in nitrogen fixation and nitrogenase activity was noticed when urea at 96 kg ha–1 y–1 was mixed with the biofertilizer (Mac-27). Inoculation of PS-21 enhanced phosphate solubilization, but Kjeldahl-nitrogen concentration values remained low in comparison with controls. On the other hand, inoculation of Azotobacter (either strain) enhanced the accumulation of ammonium-N, nitrite-N and nitrate-N. A significant (p < 0.05) reduction in dissolved oxygen (DO) concentration also took place when Azotobacter (both Mac-27 and PS-21) was inoculated in fish ponds. However, when used along with inorganic fertilizers, the reduction was not significant. The pH values were only slightly lowered when the phosphate-solubilizing strain (PS-21) of Azotobacter was inoculated. Inoculation of biofertilizer enhanced plankton production, net primary productivity and fish biomass. However, highest values in most of these parameters were noticed only in ponds that were treated with the higher doses of inorganic fertilizers (urea 192 kg and SSP 1500 kg ha–1 y–1). © Rapid Science Ltd. 1998     

Biochemical and physiological characteristics and plasmid profiles of Aeromonas hydrophila strains, isolated from freshwater fish and from fresh water

Abstract. Twenty-five Aeromonas hydrophila strains, isolated from freshwater fish and from freshwater samples were identified, using API 20NE and CH50. They were screened for the one plasmid (20 kb), and a third group (four strains) contained two or three plasmids. A 20 kb plasmid was common to all plasmid-positive strains. Although their plasmid profile differs, all groups are very similar with regard to their biochemical and physiological characterization. However, the differences observed using clustering can be explained by characteristics, some of which have been reported as virulence associated. No relationship between these factors and the presence of plasmids is found. The possibility of differentiating A. hydrophila strains on the basis of biochemical characteristics using a cluster analysis is considered.     

Feed preferences of Salminus brasiliensis (Pisces, Characidae) larvae in fish ponds

Feed preferences of dorado, Salminus brasiliensis, in the early stages of life was studied in larvae, stocked 5 days after hatching in three earthen commercial ponds (810 m², 900 m² and 1480 m²) at a density of 30 m^− 2. Larvae were fed on natural food from ponds supplemented with a commercial ration (40% crude protein), and for 12 days fish samples were taken daily in the morning and in the afternoon from each pond to analyze the food items present in the diet. Zooplankton available in the environment was also analyzed. Feeding was intensive since 94% of the larvae guts examined contained food. Since the commercial diet was not found in the dorado guts, the natural diet dominated the artificial food, but the cannibalistic behavior typically found in laboratory conditions was not observed. Insect larvae and cladocerans were the main prey items found in the gut of the larvae. In fish ponds dorado larvae can be considered a generalist feeder, since small amounts of different food items were consumed, but they tend to specialize in some items, according to their developmental stage.     

Generalist feeding strategies in Arctic freshwater fish: A mechanism for dealing with extreme environments

Generalist feeding strategies are favoured in stressful or variable environments where flexibility in ecological traits is beneficial. Species that feed across multiple habitat types and trophic levels may impart stability on food webs through the use of readily available, alternative energy pools. In lakes, generalist fish species may take advantage of spatially and temporally variable prey by consuming both benthic and pelagic prey to meet their energy demands. Using stomach content and stable isotope analyses, we examined the feeding habits of fish species in Alaska's Arctic Coastal Plain (ACP) lakes to determine the prevalence of generalist feeding strategies as a mechanism for persistence in extreme environments (e.g. low productivity, extreme cold and short growing season). Generalist and flexible feeding strategies were evident in five common fish species. Fish fed on benthic and pelagic (or nektonic) prey and across trophic levels. Three species were clearly omnivorous, feeding on fish and their shared invertebrate prey. Dietary differences based on stomach content analysis often exceeded 70%, and overlap in dietary niches based on shared isotopic space varied from zero to 40%. Metrics of community‐wide trophic structure varied with the number and identity of species involved and on the dietary overlap and niche size of individual fishes. Accumulation of energy from shared carbon sources by Arctic fishes creates redundancy in food webs, increasing likely resistance to perturbations or stochastic events. Therefore, the generalist and omnivorous feeding strategies employed by ACP fish may maintain energy flow and food web stability in extreme environments.     

Autotrophic and heterotrophic production of micro-organisms in intensely-manured fish ponds,and related fish yields

Intensely-manured ponds produce 15–30 kg fish ha^?1 day^?1 with cow or chicken manure and nitrogen- and phosphate-rich fertilizers as the only nutritional inputs. The manure as it is supplied to the ponds is not a good fish food and does not produce good fish growth. Quantitative analysis shows that the production of all organisms, autotrophic and heterotrophic, pelagic and benthic, large enough to be used directly by the fish (i.e., larger than 37 microns) is adequate to account for less than half of the measured fish growth. Production within the microbial community that flourishes on and rapidly digests the manure organic matter is adequate to produce the measured fish growth. The fish appear to harvest the microorganisms at the level of bacteria and protozoa, by ingesting the small straw-like particles which comprise much of the manure and serve as the substrate for the microbial growth.     

A sensitive FRET probe assay for the selective detection of Mycobacterium marinum in fish

Mycobacterium marinum is the causative agent of mycobacteriosis in wild and cultured fish and of atypical infection in humans. For the diagnosis of M. marinum , cultural and traditional polymerase chain reaction (PCR) methods are currently used. However, these protocols, although able to discriminate within Mycobacterium spp., have proved to be time-consuming or difficult to carry out. For this reason, the aim of this study was to obtain a rapid and specific diagnostic tool to quantify fish Mycobacterium spp. or to discriminate M. marinum from other mycobacteria. A primary PCR amplification with SYBR Green had a detection limit (dl) of 10² Mycobacterium DNA copies with a log-linear quantification range up to 10⁴ ( R ² = 0.99). The second PCR using FRET probes, flanking a region containing species specific nucleotide variations, was designed and validated with synthetic erp gene fragments corresponding to different mycobacterial species, different whole mycobacteria suspensions, experimentally infected fish tissues, tissues from experimentally infected fish, and samples of cultured fish. The results show that the FRET probes demonstrate a high specificity as the melting curve analysis allowed efficient discrimination of M. marinum from Mycobacterium chelonae , Mycobacterium fortuitum , Mycobacterium pseudoshottsii , Mycobacterium shottsii and Mycobacterium ulcerans . The kidney is the organ with the strongest detection signal and using fish tissues the method has a mean sensitivity of 50 DNA copies/PCR.     

Characterization of Mycobacterium salmoniphilum as causal agent of mycobacteriosis in Atlantic salmon,Salmo salar L., from a freshwater recirculation system

Thirty Atlantic salmon, Salmo salar L., with low corporal condition relative to other fish present in the culture system, were sampled from a freshwater recirculation pisciculture located in Chile. The most characteristic signs and lesions were cachexia and presence of multiple greyish‐white granulomas within internal organs. The external and internal lesions, along with the microscopic, histologic and biochemical findings, were consistent with mycobacteriosis. The identification of Mycobacterium salmoniphilum as the causal agent of the lesions was possible through the use of molecular analyses. This study represents the first report of Mycobacterium salmoniphilum in a freshwater recirculation system and the first case of fish mycobacteriosis described in Chile.