Impact of polychaete infauna on enzymatic protein degradation in marine sediments affected by intensive milkfish farming

Marine sediments at intensive fish farming sites in Bolinao‐Anda, northwestern Philippines, are characterized by strong oxygen depletion and the widespread predominance of sulphidic conditions precluding macrobenthic infauna. In less affected areas, however, small macrobenthos (Spionide polychaetes) was present. Experimental sediment mesocosms containing burrowing polychaetes were set up to investigate the possible links between macrofaunal bioturbation of the sediment and its proteolytic capacity to recycle protein‐rich fish farming waste. Relative to polychaete‐free sediment, the addition of small Spionide polychaetes had no significant effect on the proteolytic capacity but caused an increase in the redox potential. On the other hand, the addition of large Eunicide polychaetes caused an increase in both the proteolytic capacity and the redox potential. The deposition of commercial fish feed particles increased the proteolytic activities but decreased the redox potential particularly at a higher deposition rate (250 g m^?2 day^?1). Accumulation of hydrogen sulphide increased at deposition rates above 83 g m^?2 day^?1 and limited the survival of large polychaetes.     

不同混养鱼类和投喂方式对鱼蚌综合养殖水体化学特征的影响

选用草鱼(Ctenoparyngodon idellus)、银鲫(Carassius gibelio)、鲢(Hypopthalmichthys molitrix)、鳙(Aristichthysnobilis)作为本研究的混养鱼类,通过围隔实验检验了不同混养鱼类组合(草鱼+鲫+鲢+鳙或鲢+鳙)和配合饲料投喂方式(投喂或不投喂)对三角帆蚌(Hyriopsis cumingii)养殖水体化学特征的影响,实验为期155 d。结果表明,实验设计的混养鱼类组合可显著影响鱼蚌综合养殖水体的Ca2+、总碱度(Alk)、总硬度(HT)和总磷(TP)水平;投喂配合饲料可显著影响Ca2+、Alk、HT、氨氮(TAN)、TP和化学耗氧量(CODMn)。采用混养组合(草鱼+鲫+鲢+鳙)且投喂配合饲料的围隔内溶氧(DO)水平和透明度(SD)较低,Ca2+、HT、TN、TP、TAN和CODMn水平较高;采用混养组合(鲢+鳙)且不投喂的围隔内DO和SD水平较高,而Ca2+、HT、TN、TP、TAN和CODMn水平较低。随养殖时间延长,各组围隔内Ca2+水平下降,TN、TP、TAN和CODMn水平升高。实验期间,DO与SD水平呈正相关;DO和SD与TAN、TN、TP、Ca2+和CODMn水平呈负相关。因此,鱼蚌综合养殖中,控制CODMn和TAN浓度,维持Ca2+稳定及较高的DO水平是水质管理的基本目标。     

Persistence of oxytetracycline in sediments from fish farms

The persistence of oxytetracycline, an antibacterial agent, in bottom deposits from fish farms was investigated. The drug was found in concentrations capable of causing antimicrobial effects up to 12 weeks after administration. A half-life of approximately 10 weeks was estimated through a pilot study. Possible effects on sulphide ion activity are suggested.     

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.     

Influence of fish food and faecal pellets on short‐term oxygen uptake,ammonium flux and acid volatile sulphide accumulation in sediments impacted by fish farming and non‐impacted sediments

Sediment cores were taken from impacted and non‐impacted areas and subjected to different incubations: (i) uninoculated, (ii) inoculated with fish feed and (iii) inoculated with gilthead seabream (Sparus aurata) faeces. After inoculation (or not), the cores were incubated for 8 h and the following biogeochemical fluxes were determined: sediment oxygen uptake (SOU), total ammonia nitrogen flux (TAN_f) and the production of acid volatile sulphides (AVS‐S_p). The results showed that the impacted sediments had a more pronounced benthic metabolism than non‐impacted sediments. Correlations between the variables and factorial analysis showed that oxygen consumption caused by the organic enrichment appeared as the trigger for subsequent biogeochemical alterations. The addition of faeces led to proportionally higher benthic rates of SOU, TAN_f and AVS‐S_p than those obtained in the feed incubations. Although the feed is relatively sterile and does not create an oxygen demand until colonized by bacteria, the faeces are already richly colonized with fish gut bacteria and could start to consume oxygen without the lag phase experienced in the incubations with feed. The TAN_f values measured after the addition of feed or faeces seem to be more related to the leaching velocity of TAN than with the benthic flux, given the short incubation time.     

Genotypic diversity among Shewanella spp. collected from freshwater fish

Different Shewanella species are isolated both from healthy and from diseased fish. To date, contemporary methods do not provide sufficient insight to determine species and detail differentiation between tested strains. Bacteria isolated from cultured (n = 33), wild (n = 12) and ornamental (n = 6) fish, as well as several reference strains, were tested by 16S rRNA gene sequencing, ERIC‐PCR and pulsed‐field gel electrophoresis (PFGE) assays. Our study indicates that isolates collected from freshwater fish were genetically diverse. Based on 16S rRNA gene sequences, bacteria were clustered into groups S. putrefaciens, S. xiamenensis and S. oneidensis. Some isolates were classified only to genus Shewanella; thus, 16S rRNA gene analyses were not enough to determine the species. ERIC‐PCR revealed 49 different genotype profiles indicating that the method might be useful for differentiation of Shewanella isolates irrespectively to species identification, contrary to PFGE which is not suitable for Shewanella typing.     

First isolation of hirame rhabdovirus from freshwater fish in Europe

A rhabdovirus was isolated in cell culture inoculated with tissue material from diseased grayling, Thymallus thymallus (L.), originating from a fish farm affected by a mortality episode in Poland. Diagnostics tests showed that the virus was not related to novirhabdoviruses known in Europe, nor to vesiculovirus‐like species, except perch rhabdovirus (PRhV) with which it shared moderate serological relations. However, RT‐PCR with PRhV probes gave negative results. To identify the virus, a random‐priming sequence‐independent single primer amplification was adopted. Surprisingly, two of the obtained sequences exhibited a high identity (>99%) with hirame rhabdovirus (HIRRV), a novirhabdovirus usually found in fish in marine Asiatic countries, for instance Japan, China and Korea. The full‐length sequence of the phosphoprotein gene (P) demonstrated a higher identity of the present isolate with HIRRV from China compared with the Korean isolate. An identical viral sequence was also found in brown trout, Salmo trutta trutta L., affected by mortalities in a second farm in the same region, after a likely contamination from the grayling farm. To our knowledge, this is the first report of HIRRV in Europe, and in two hosts from fresh water that have not been described before as susceptible species.     

电化水去除淡水鱼土腥味的研究

为改善淡水鱼土腥味严重导致品质下降的现状,实验从淡水鱼终端暂养环节出发,以电化水暂养淡水鱼,探讨去除土腥味效果和实用性。结果显示,电化水通过比常规水体更小的水分子团簇结构以及更低的粘度、更强的渗透性和溶解力等理化性质实现鱼肉土腥味物质的快速脱除,暂养淡水鱼24 h可去除64.66%以上土臭素(Geosmin)和24.45%以上二甲基异莰醇(2-Methylisoborneol),相比井水分别提高136.65%、196.13%以上。     

Serotyping of Vibrio anguillarum isolated from diseased freshwater fish in Japan

Abstract. During the period from 1965 to 1980, 263 Vibrio anguillarum strains from ayu, Plecoglossiis altivelis (Temminck & Schlegel), two from rainbow trout. Salmo gairdneri Richardson, and two from eel, Anguilla japonica (Temminck & Schlegel), were collected from fish suffering from vibriosis in various parts of Japan. On the basis of cross-agglutination and cross-absorption tests with thermostable (O) antigens, six distinct serotypes (A, B, C, D, E and F) were established among 12 selected strains of V. anguillarum . 241 strains isolated from ayu and two strains from rainbow trout belonged to serotype A, six strains from ayu and one strain from eel to serotype B, 12 strains from ayu to serotype C, three strains from ayu to serotype D, one strain from ayu to serotype E, and one strain from eel to serotype F. V. anguillarum strains belonging to serotypes D, E and F have not been detected from ayu, rainbow trout and eel since 1973; these serotypes appear to be minor types. V. anguillarum strain NCMB 6 and 1669 belong to our serotype A and V. anguillarum 813 to our serotype C.     

Bacterial community composition shifts in sediments influenced by fish feeds

This study investigated the influence of fish feed deposition on the microbial community of sediments in a coastal lake. Microcosms were designed to simulate the addition of fish feeds to the sediment, and physicochemical factors as well as composition of microbial assemblages were analysed. Although total organic carbon and total organic nitrogen did not significantly increase, redox potential and total sulphides showed a transition of sediment environments into anaerobic condition due to the addition of fish feeds. The bacterial community composition shifted with fish feed deposition as revealed by the band profiles of denaturing gradient gel electrophoresis, Sørensen's similarity indices and cell numbers of sulphate‐reducing bacteria. Occurrence of anaerobic bacteria (sulphate and nitrate reducers) and disappearance of strictly aerobic bacteria were observed with fish feed inputs. The results clarify the succession of the microbial flora and suggest negative impact of uneaten fish feeds on the microbial community in sediment and resultant environmental deterioration of fish‐farming areas.     

Natriuretic peptides and the control of catecholamine release in two freshwater teleost and a marine elasmobranch fish

Experiments were carried out in situ and in vivo to investigate the relationship between natriuretic peptides (NPs) and humoral catecholamine secretion in the American eel (Anguilla rostrata), rainbow trout (Oncorhynchus mykiss) and spiny dogfish (Squalus acanthias). In situ perfusion of the chromaffin tissue of A. rostrata with homologous atrial NP (ANP; 10–9 mol l–1) or ventricular NP (VNP; 10–9 mol l–1), or O. mykiss with either rat ANP (10–9 mol l–1), eel VNP (10–9 mol l–1), or trout VNP (10–9 mol l–1), did not significantly affect basal or carbachol-elicited (10–5 mol kg–1) catecholamine release. Bolus injections of homologous ANP (10–9 mol kg–1) or VNP (10–9 mol kg–1) in A. rostrata in vivo elicited a rapid and prolonged reduction in arterial blood pressure and an increase in heart rate (fH); circulating plasma catecholamine levels were unaffected. In O. mykiss, bolus injections of rat ANP (10–9 mol kg–1) or trout VNP (10–9 mol kg–1) elicited a significant bi-phasic pressor- depressor response and a marked increase in fH. Neither the acute pressor or the longer-term depressor effects of NPs in O. mykiss were associated with any change in circulating plasma catecholamine levels. In S. acanthias, bolus injections of homologous C-type natriuretic peptide (CNP; 10–9 mol kg–1) elicited a bi-phasic pressor-depressor response, an increase in systemic resistance, a decrease in cardiac output and stroke volume, but no change in fH. Plasma noradrenaline levels were elevated 15- fold after CNP injection while circulating adrenaline levels remained unchanged. These results show that NPs of systemic origin do not directly or indirectly affect basal or cholinergically-mediated catecholamine release in A. rostrata and O. mykiss and that the initial pressor response to NP's in trout cannot be attributed to an elevation of circulating catecholamines. Conversely, CNP appears to be a potent secretagogue (direct or indirect) of noradrenaline release in S. acanthias and thus there is likely to be a significant humoral adrenergic component to the cardiovascular effects of NPs in this species.     

Reduction of a native fish fauna by alien species: an example from Brazilian freshwater tropical lakes

The consequences of introducing Cichla cf. monoculus Spix & Agassiz, Astronotus ocellatus (Agassiz) and Pygocentrus nattereri Kner into lakes in the River Doce basin, Brazil, on richness, diversity and efficiency of aquatic macrophytes as natural refugia to native fishes was investigated. Samples were taken from lakes with and without alien fishes in areas with and without aquatic macrophytes. The presence of alien fishes reduced richness and diversity of the native fish community. The refugia function, which could be attributed to the clustering of aquatic macrophytes, does not exist in these lakes probably because the alien fishes exploit such habitats for reproduction. Since introductions threaten the native fish diversity of the region, studies on regional dispersion and factors that minimise the spread of alien fishes are needed.     

Phenotypical and genotypical characterization of Shewanella putrefaciens strains isolated from diseased freshwater fish

Between 2007 and 2012, a variety of disease outbreaks most often characterized by skin disorders were observed among different species of freshwater fish in Poland. In most cases, the clinical signs included focally necrotized gills, necrotic skin lesions or ulcers. Internally, haemorrhages, oedematous kidney and abnormal spleen enlargement were generally noted. The disorders were accompanied by increased mortality. Most of the problems concerned cultured common carp Cyprinus carpio L. and rainbow trout Oncorhynchus mykiss (Walbaum). Fish have been examined from a number of these farms, and additionally, the wild and ornamental fish with similar clinical signs of diseases were also tested. Bacteria were isolated consistently from lesions and internal organs. They had characteristic orange-pigmented colonies which grew in pure culture or constituted 55–95% of total bacterial flora. One hundred and eighteen isolates were collected and biochemically identified as Shewanella putrefaciens group, and this was confirmed by sequencing. Challenge tests confirmed the pathogenicity of these bacteria. This is the first report characterizing and describing S. putrefaciens as a pathogen of different species of freshwater fish in Europe.     

Evidence of fish spillover from freshwater protected areas in lakes of eastern Ontario

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Microbial decomposition process of organic matter in sinking particles,resuspendable particles,and bottom sediments at a coastal fish farming area

The possible impacts of resuspension of low-density bottom sediments on the microbial decomposition process of organic matter were investigated at a coastal fish farming area. Hydrolysis and mineralization rates were much higher in sinking particles, resuspendable particles, and bottom sediments than in seawater. The cell-specific mineralization rate of free-living bacteria in seawater was several times higher than that of particle-associated bacteria at the other three sites. Conversely, no significant difference was observed in the cell-specific ecto-enzymatic hydrolysis rate. These results indicated different strategies in the utilization of organic matter: free-living bacteria actively respire low-molecular-weight compounds produced from the high-molecular-weight compounds resulting from extracellular enzyme activity of particle-associated bacteria. Both hydrolysis and mineralization were higher in sinking particles than in the other three sites. Hydrolysis rates were higher in resuspendable particles than in bottom sediments. Furthermore, leucine aminopeptidase and mineralization rates tended to be highest during winter in all four sites within the water column. These results suggest that the microbial decomposition of organic matter is stimulated by the resuspension of bottom sediments, especially during winter, when vertical mixing is relatively strong.     

Towards sustainable freshwater prawn aquaculture – lessons from shrimp farming, with special reference to India

The annual increase in farmed freshwater prawn production in the world during the decade ending 2001 has been estimated as 29% and that during 1999–2001 as 48%, the production in 2001 being about 300 000 mt (all Macrobrachium species). Between 1999 and 2003 the annual increase in farmed Macrobrachium rosenbergii production in India was about 80%, production reaching 30 450 mt in 2002–2003. This log phase of production followed the rise and fall of shrimp farming in the country. Several shrimp farming ventures collapsed in the 1990s, owing to degraded environment and diseases, abetted by lack of awareness and inadequacy of information on the culture systems and their interactions with other human endeavours. This shrimp farming experience has made the aquafarmer and other stakeholders aware that while aquaculture has a high potential in ensuring food and nutritional security and livelihood, besides profit to the farmer and socio‐economic benefits to local communities, it is likely to slip from sustainable development pathways if adequate understanding, improved management practices, governmental policies and plans for implementation and regulation to ensure sustainability are not in place. The lessons learned from shrimp farming can help in steering the development of sustainable freshwater prawn aquaculture in India and elsewhere.     

A new high in fish production in India with record yields by composite fish culture in freshwater ponds

Composite fish culture of the Indian major carp, Catla catla, Labeo rohita and Cirrhinus mrigala together with the Chinese silver carp Hypophthalmichthys molitrix and grass carp Ctenopharyngodon idella and the Indonesian strain of common carp (Cyprinus carpio communis) was carried out in experimental ponds in 1971–1972 and 1973–1974. The management techniques adopted aimed at high yields of marketable fish (around 1 kg) in 1 year.In the first year, production varied from 3 889 to 5 600 kg/ha/year and this rose to an average of 8 200 kg/ha/year with a maximum of 9 389 kg/ha/year in the second year. The important changes made to the management schedule in 1973 were increased stocking density, greater use of feed and fertilizers, and provision of more weeds for grass carp.The experimental studies demonstrate the practicability of raising large crops of healthy marketable fish in India.     

Quantitative estimates of freshwater fish stocking practices by recreational angling clubs in France

Although freshwater fish stocking is widely used by managers, quantitative assessments of stocking practices are lacking in many countries. The general objective of the present study was to determine the quantity and characteristics of fish stocking in metropolitan France. Using a survey-based approach, stocking practices for 2013 by recreational angling clubs in France were quantified, which represented the bulk of fish stocking undertaken in that year. Stocking was found to be practiced by 88.6% of angling clubs in France, representing, on average, 65% of their annual budget. Overall, 22 species were stocked, including 13 native and nine non-native species, with strong variations among species in terms of life stages and body sizes used for stocking. Using Bayesian modelling, a total biomass of 2.029 t, representing approximately 90 million fishes, was estimated to be stocked in France in 2013. In terms of biomass, the most widely stocked species were rainbow trout Oncorhynchus mykiss (Walbaum), brown trout Salmo trutta L., roach Rutilus rutilus (L.), common carp Cyprinus carpio L. and northern pike Esox lucius L. A stocking volume of approximately 60 fishes or 1.5 kg of fish biomass per angler per year seems commonplace in industrialised countries for which data are available.