Myxozoan pathogens in cultured Malaysian fishes. II. Myxozoan infections of redtail catfish Hemibagrus nemurus in freshwater cage cultures

Cage-cultured Asian redtail catfish Hemibagrus nemurus (Valenciennes, 1840), a popular food fish in Southeast Asia, proved to be infected by 3 myxozoan species. All the 3 species belonged to the genus Henneguya: 2 were identified as H. mystusia Sarkar, 1985 and H. hemibagri Tchang et Ma, 1993, while the other was described as H. basifilamentalis sp. n. All plasmodia were found in the gills and were characterised by a specific site selection. H. mystusia formed plasmodia in the multi-layered epithelium between the gill lamellae and in the non-lamellar edge of the gill filaments, while H. hemibagri developed in the capillary network of the lamellae. H. basifilamentalis sp. n. had large oval plasmodia located deep among the filaments just above the gill arch.     

Stocking density positively influences the yield and farm profitability in cage aquaculture of sutchi catfish, Pangasius sutchi

The sutchi catfish (Pangasius sutchi Fowler 1937) was cultured at 10 different densities in cages suspended in a river‐fed channel during the summer of 2000. Catfish fingerlings (mean length 9.14–9.74 cm; mean weight 5.92–6.7 g) were stocked at densities of 60, 70, 80, 90, 100, 110, 120, 130, 140, and 150 fish m^?3, which were equivalent to 397, 427, 488, 551, 604, 656, 710, 871, 981, and 899 g m^?3 respectively. At the end of 150 days, the growth and yield parameters were studied and a simple economic analysis was performed to calculate profitability. Gross yields were 15.6 ± 0.27, 17.1 ± 0.31, 19.5 ± 0.30, 21.9 ± 0.29, 26.8 ± 0.22, 28.6 ± 0.40, 30.0 ± 0.37, 31.1 ± 0.45, 32.7 ± 0.31, and 34.5 ± 0.44 kg m^?3; net yields were 15.2 ± 0.22, 16.7 ± 0.28, 19.0 ± 0.29, 21.3 ± 0.21, 26.2 ± 0.19, 27.9 ± 0.33, 29.3 ± 0.33, 30.3±0.37, 31.8 ± 0.29 and 33.5 ± 0.36 kg m^?3, respectively, with stocking densities of 60, 70, 80, 90, 100, 110, 120, 130, 140, and 150 fish m^?3. Mean weights of fish at harvest were inversely related to stocking density. Both gross and net yields were significantly different and were directly influenced by stocking density, but the survival rates and feed conversion were unaffected. Higher stocking density resulted in higher yield per unit of production cost and lower cost per unit of yield, with a net revenue being higher with increasing stocking density. It was concluded that the density of 150 fish m^?3 produced the best results among the densities tested in this experiment.     

苏氏圆腹鱼芒对6种常用饲料原料的表观消化率

鱼类只能利用饲料中可消化吸收的营养成分,使用易消化的原料配方可提高鱼类对配合饲料的利用效率.确定养殖鱼类对不同饲料原料的表观消化率(ADC)是评价饲料原料营养价值和合理配方的基础.     

High genetic diversity in cryptic populations of the migratory sutchi catfish Pangasianodon hypophthalmus in the Mekong River

The detection and conservation of spawning units is of crucial importance in highly migratory species. The sutchi catfish Pangasianodon hypophthalmus (Pangasiidae; Teleostei) is a common large-sized tropical fish, which migrates annually to several upstream spawning sites on the Lower Mekong River and feeds on the huge floodplain of the Lower Mekong and Tonle Sap for the other half of the year. We hypothesised that because of the relative size of the feeding and spawning habitat, genetic variability would be high and homogeneous in foraging populations, but that spawning stocks would be distinct in space and time. To test these predictions, 567 individuals from 10 geographic locations separated by up to 1230 km along the Lower Mekong River were genotyped at seven microsatellite loci. The level of genetic diversity was much higher than other freshwater fish and reached values comparable to marine species (mean H(e)=0.757). All samples collected at the potential spawning sites deviated from Hardy-Weinberg expectations, suggesting admixture. Individual-based clustering methods revealed genetic heterogeneity and enabled the detection of three genetically distinct sympatric populations. There was no evidence of recent reduction in effective population size in any population. Contrasting with the vast extent of the feeding grounds, the shortage of spawning grounds seems to have moved sutchi catfish towards diachronous spawning. Hence the sustainable exploitation of this natural resource hinges on the conservation of the limited spawning grounds and open migration routes between the spawning and feeding grounds.     

Intra-annual genetic variation in the downstream larval drift of sutchi catfish (Pangasianodon hypophthalmus) in the Mekong river

Larvae of the sutchi catfish Pangasianodon hypophthalmus were collected during peak downstream drift in the Lower Mekong river on four occasions over an 8-week period during the 2003 spawning season, and genotyped using seven microsatellite loci. We provide evidence for several heterogeneous groups within and among the temporally discrete larval peak samples. Strong evidence for a significant deficit of heterozygotes was observed for each larval sample and the pooled sample, possibly due to population admixture. Although individual-based assignment tests suggested that each larval peak sample was admixed, significant but low genetic differentiation was observed among larval samples ( F _ST = 0.0052, P  < 0.01). The lack of significant relatedness confirms the multifamily composition of each larval group, excluding family bias to explain the observed genetic heterogeneity. Both the entire larval peak and each temporally separated larval peak originated from spawning groups with heterogeneous allelic composition involving several distinct spawning events. We propose three explanations to account for our findings: (1) the ecological match/mismatch hypothesis; (2) the genetic 'sweepstakes' selection hypothesis; and (3) life-history-specific characteristics of the spawning populations. Finally, an intra-annual shift in the contribution of the spawning populations to the larval drift was detected on successive occasions.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 719–728.     

First identification of Flavobacterium columnare infection in farmed freshwater striped catfish Pangasianodon hypophthalmus

The bacterium Flavobacterium columnare was recovered and identified as the aetiological agent causing freshwater columnaris infection in farmed striped catfish Pangasianodon hypophthalmus (Sauvage) fingerlings that had suffered high mortality rates within commercial hatchery ponds in Vietnam. The gross clinical signs were typical of columnaris-infected fish. Histological examination found numerous Gram-negative, filamentous bacteria present on the skin, muscle and gill tissues of affected fish. The yellow-pigmented bacteria were isolated and identified as F. columnare using primary, biochemical and PCR methods. An experimental immersion-challenge study with 2 strains was also performed. It fulfilled Koch's postulates and showed a median lethal concentration (LC50) of 4.27 × 105 and 1.66 × 106 cfu ml-1 for the F. columnare strains FC-HN and FC-CT, respectively. To the best of our knowledge this is the first report of freshwater columnaris infection in P. hypophthalmus.     

Morphology and histology of the swimbladder and infrastructure of respiratory epithelium in the air-breathing catfish, Pangasius sutchi (Pangasiidae)

The swimbladder of Pangasius sutchi is made up of fibrosa, collagenic fibre walls and mucosa; its walls extend into the lumen to form dense respiratory alveoli, with the inner surface covered by a highly vascularized respiratory epithelium. The thin epithelial cells have the structural characteristics and function of type I and type II cells of lung alveoli in higher mammals. These cells and the endothelial cells compose the barrier through which gases must pass in the exchange between blood and air. The study shows that the swimbladder of P. sutchi is an important accessory respiratory organ.     

Comparative antioxidant enzyme study in freshwater fishes. I. Distribution of superoxide dismutase, peroxide-decomposing enzymes and lipid peroxidation in herbivorous fishes

The activities of Cu,Zn-superoxide dismutase, Mn-superoxide dismutase, catalase and glutathione peroxidase were comparatively studied in organ homogenates from two herbivorous fishes, viz., the grass carp and the silver carp. 2. The protein contents and lipid peroxidation of organ homogenates were also compared. The comparative measurements primarily provide control values for subsequent toxicological examinations. 3. The highest total superoxide dismutase activities were found in the kidney, spleen and liver in the grass carp, and in the kidney and liver in the silver carp. 4. The antioxidant enzyme activities and other parameters of the organ homogenates appear to be independent of the feeding mode, but are rather characteristic of the fish variety.     

Determinants of host-specificity in parasites of freshwater fishes.

Factors responsible for interspecific variability in host-specificity were investigated within 15 genera (including 176 species) of metazoan parasites found in Canadian freshwater fish. For each species in a genus, the parasite's number of known hosts was determined from published host-parasite records. The effects of the total number and mean size of potential hosts (i.e. all fish species belonging to the family or families that include a parasite's known hosts) on number of hosts of congeneric species were evaluated using multiple regressions. Since parasite species that have been recorded often tend to have greater numbers of known hosts than do seldom-recorded parasites, it was necessary to control for the confounding effect of study intensity. In all parasite genera, whether from highly specific taxa such as monogeneans or from less host-specific ones, there was a positive relationship between the number of potential hosts and the number of known hosts. However, no consistent relationships were observed between the mean size of potential hosts and number of known hosts. These results suggest that the availability of suitable host species may have been a key factor limiting the colonization of new hosts by fish parasites.     

Hypoxia tolerance and partitioning of bimodal respiration in the striped catfish (Pangasianodon hypophthalmus)

Air-breathing fish are common in the tropics, and their importance in Asian aquaculture is increasing, but the respiratory physiology of some of the key species such as the striped catfish, Pangasianodon hypophthalmus Sauvage 1878 is unstudied. P. hypophthalmus is an interesting species as it appears to possess both well-developed gills and a modified swim bladder that functions as an air-breathing organ indicating a high capacity for both aquatic and aerial respiration. Using newly developed bimodal intermittent-closed respirometry, the partitioning of oxygen consumption in normoxia and hypoxia was investigated in P. hypophthalmus. In addition the capacity for aquatic breathing was studied through measurements of oxygen consumption when access to air was denied, both in normoxia and hypoxia, and the critical oxygen tension, Pcrit, was also determined during these experiments. Finally, gill ventilation and air-breathing frequency were measured in a separate experiment with pressure measurements from the buccal cavity. The data showed that P. hypophthalmus is able to maintain standard metabolic rate (SMR) through aquatic breathing alone in normoxia, but that air-breathing is important during hypoxia. Gill ventilation was reduced during air-breathing, which occurred at oxygen levels below 8 kPa, coinciding with the measured Pcrit of 7.7 kPa. The findings in this study indicate that the introduction of aeration into the aquaculture of P. hypophthalmus could potentially reduce the need to air-breathe. The possibility of reducing air-breathing frequency may be energetically beneficial for the fish, leaving more of the aerobic scope for growth and other activities, due to the proposed energetic costs of surfacing behavior.     

Partitioning of oxygen uptake and cost of surfacing during swimming in the air-breathing catfish Pangasianodon hypophthalmus

Though air-breathing has probably evolved mainly as a response to hypoxia, it may provide an important oxygen supplement when metabolism is elevated, as for example during swimming. Due to the increased travelling distance involved when an air-breathing fish swims to and from the surface, and the increased drag when the surface is breached, it can be proposed that air-breathing results in a rise in the apparent cost of transport. In order to investigate this hypothesis, it is necessary to use a fish that is able to swim equally well with and without access to air. The striped catfish Pangasianodon hypophthalmus has been shown to have a sufficiently high capacity for aquatic oxygen uptake in normoxia, to allow for such a comparison. Here, we measured the partitioning of oxygen uptake ( $ \dot{M}{\text{O}}_{2} $ ) during swimming and recovery, and calculated the apparent cost of transport with and without access to air, under normoxic conditions. Aerial $ \dot{M}{\text{O}}_{2} $ constituted 25–40 % of the total $ \dot{M}{\text{O}}_{2} $ during swimming and less than 15 % during recovery. The net cost of transport was 25 % lower in fish that did not air-breathe compared to fish that did, showing that the cost of surfacing can be substantial. This is the first study to measure partitioning in an air-breathing fish during swimming at velocities close to the critical swimming speed.     

Parasitofauna of freshwater fishes in the Serbian open waters: a checklist of parasites of freshwater fishes in Serbian open waters

As a result of freshwater fish parasitofauna investigations, throughout the past 75 years, the number of parasitic species is presented. This paper reviews the history, current state, and tendencies of the fish parasitofauna studies in Serbian open waters. Up to now, in total 170 parasitic species have been reported. Systematic parasitofauna investigations have been carried out on 54 freshwater fish species in waters of the Danube River Basin in Serbia, also in hill-mountanious watercourses, lakes and salmonid fishpond of Sjenicko-Pesterska plateau (south-west region of Serbia), Homolje area (east Serbia), and in Vlasina lake (south-east Serbia). This data review pointed that it is necessary to continue the investigation on fish parasites in Serbia. The data on freshwater fish parasites are important for evaluation of general influence on the community structure.     

小儿下呼吸道感染痰培养标本病原菌构成分析

目的了解小儿下呼吸道感染病原菌的分布及对常用抗菌药物的耐药状况。方法对2710例小儿下呼吸道感染患者痰标本进行培养,用VITEK-2Compact微生物鉴定系统鉴定菌种和药敏试验,WHO-NET5．4软件对数据进行分析。结果共分离病原菌675株,革兰阴性杆菌457株,占67．7％,主要为大肠埃希菌、肺炎克雷伯菌;革兰阳性球菌159株,占23．5％,主要为金黄色葡萄球菌、肺炎链球菌;真菌59株,占8．7％,主要为白色假丝酵母菌。结论小儿下呼吸道感染病原菌以革兰阴性杆菌为主,耐药性较为严重,应不断加强耐药性监测,合理使用抗菌药物。     

Seasonal distribution of Vibrio parahaemolyticus in freshwater environs and in association with freshwater fishes in Calcutta.

The seasonal distribution of Vibrio parahaemolyticus in freshwater environs and in association with freshwater fishes was studied in 1982 and 1983. The occurrence of this organism in water and sediments at the three sites studied was very infrequent and was restricted to the summer months, although it was not always isolated during these months. The association of V. parahaemolyticus with plankton was chiefly confined to the summer months and progressively declined with the onset of monsoons, remaining below detectable levels during the postmonsoon and winter months. The incidence and counts of V. parahaemolyticus were consistently higher in association with plankton than with water and sediment samples. V. parahaemolyticus could be recovered throughout the period of investigation from freshly caught and market samples of freshwater fishes. The highest recovery rate of this halophile from fishes was invariably from fecal samples. Most of the strains isolated in this study were untypable, and those which could be typed were predominantly serotypes encountered in the environment. All the isolates were Kanagawa negative. From this study, it could be concluded that the survival of V. parahaemolyticus in freshwater ecosystems is transient and dependent on a biological host.     

Pesticides induced changes in circulating thyroid hormones in the freshwater catfish Clarias batrachus.

1. Effects of endosulfan, malathion and carbaryl on circulating T4, T3 and T3/T4 ratio in the freshwater catfish, C. batrachus have been studied during reproductively active phases, i.e. vitellogenic and post-vitellogenic phases of its annual reproductive cycle. 2. Endosulfan provoked a significant increase in T4 and a decrease in T3 as well as the T3/T4 ratio. 3. Malathion decreased T3 and T3/T4 ratio without altering the level of T4 in circulation. 4. Carbaryl caused a decline in the level of T4 and an elevation in T3 and T3/T4 ratio.     

Oxidative enzymes in the urinary apparatus of several freshwater fishes

Synopsis The distribution and activities of several oxidative enzymes in the urinary apparatus of five freshwater fish species (river lamprey, lobe finned eel, Prussian carp, rainbow trout and three-spined stickleback) have been studied. Species were selected from three main taxonomic groups: Cyclostomata, Polypterini, Teleostei. Distinctly positive enzyme reactions were only found in the tubular elements of the kidney and the collecting duct-archinephric duct system, with the exception of the generally weak staining intensities of lactate dehydrogenase. The distal tubule normally showed strong to very strong reactions for most of the enzymes investigated. In the epithelial cells of the collecting tubule-collecting duct system, stronger reactions were observed for most of the mitochondrial-bound enzymes, especially succinate dehydrogenase and NADH-diaphorase. For these enzymes, the cells of the archinephric duct reacted strongly positive in Lampetra, Carassius and Gasterosteus.The enzyme patterns of various types of urinary tubules and ducts are compared with results of several morphological studies. In addition, the histochemical findings are discussed in relation to kidney function in different vertebrate groups.     

Pattern and process in the geographical ranges of freshwater fishes

North American freshwater fishes were studied to determine whether they displayed the same relationships between log (geographical range size) and log (body size) and the same pattern of range shape as found among North American birds and mammals. The forces that produce these patterns were also investigated. The log (geographical range size) : log (body size) relationship was analysed for 121 North American freshwater fish species. Thirty‐two imperilled species were compared with 89 non‐imperilled species to determine if the overall relationship could result from differential extinction. Range geometries were analysed, within and among habitat guilds, to determine if general patterns could be detected. The log (geographical range size) : log (body size) pattern among freshwater fish species was triangular and qualitatively similar to that found for North American birds and mammals. The results suggest that below a minimum geographical range, the likelihood of extinction increases dramatically for freshwater fishes and that this minimum range size increases with body size. The pattern of fish species’ range shapes differs from that found for other North American vertebrate taxa because, on average, fish possess much smaller ranges than terrestrial species and most fish species’ geographical ranges extend further on a north–south axis than on an east–west axis. The log (geographical range size) : log (body size) pattern reveals that fish species’ geographical ranges are more constrained than those of terrestrial species. The triangular relationship may be caused by differential extinction of species with large bodies and small geographical ranges as well as higher speciation rates of small‐bodied fish. The restricted geographical ranges of freshwater fishes gives them much in common with terrestrial species on oceanic islands. Range shape patterns within habitat guilds reflect guild‐specific historical and current ecological forces. The overall pattern of range shapes emerges from the combination of ecologically different subunits.