Longgen Guo

Effects of nitrogen and phosphorus from fish cage-culture on the communities of a shallow lake in middle Yangtze River basin of China

In recent decades, net-cage aquaculture has become one of the main patterns of the intensive fish-culture in the lakes, reservoirs and even rivers in China. This aquaculture pattern results in enriching exogenous nutrients in water and, consequently, accelerates the process of lake eutrophication. To ensure that normal environmental conditions and fisheries in a lake remain sustainable, qualitative estimations of nutrients in relation to ecosystem changes are essential. A study, mainly on nitrogen (N) and phosphorus (P) influences due to cage fish-culture was carried out in a shallow 35.5 ha bay in Niushanhu Lake, a shallow lake located in middle Yangtze Basin, during the period from March to December 2000. Net-cages in total covered an area of 1000 m(2) and the annual fish yield was 16.0 metric tons (MT). Fish feeding residue entering the water during the period was equivalent to 1532.9 kg of total N and 339.2 kg of total P. Sampling and analyses of the total N and total P concentrations, diversity and biomass of plankton and Chi a were made monthly, while data on zoobenthos were collected twice, respectively, at the beginning and the end of the study. Results showed that the Chi a content in water was correlated negatively to distance from the cage. The Chi a content that is converted into wet biomass of phytoplankton may be expressed by the regression: B = 2.673 - 0.0016D (B, biomass in mg/l; D, distance in km, r=0.9362; n=7). The biomass of rotifers inside or near the cages was higher than that in areas more distant, while that of the cladocerans was the opposite. No significant difference of copepod density or biomass was detected between cages and open water. Changes of zoobenthic community were remarkable. At the beginning of fish farming, there were nine zoobenthic taxa inside and 13 outside the cages. Only two saprophilous taxa, chiefly oligochaetes, were present in the cages at the end of the culture. Density and biomass of benthic animals decreased as well. Several bioindices, such as Shannon-Wiener index, Simpson index, and Margelef index, also exhibited a declining tendency. Through this study, the authors are of the opinion that mass-input of exogenous nutrients may cause negative effects on water quality in areas from the cage to a distance of 50 m outwards

Controlling factors of spring–summer phytoplankton succession in Lake Taihu (Meiliang Bay, China)

The spring–summer successions of phytoplankton and crustacean zooplankton were examined weekly in Meiliang Bay of the subtropical Lake Taihu in 2004 and 2005. During the study period, the ecosystem of Meiliang Bay was characterized by (i) clearly declined nitrogen compounds (nitrate, TN, and ammonium) and slowly increased phosphorus compounds (TP and SRP), (ii) increased total phytoplankton density and rapid replacement of chlorophyta (mainly Ulothrix) by cyanobacteria (mainly Microcystis), and (iii) rapid replacement of large-sized crustaceans (Daphnia and Moina) by small-sized ones (Bosmina, Limnoithona, and Ceriodaphnia). Results from the CCA and correlation analysis indicate that the spring-summer phytoplankton succession was primarily controlled by abiotic factors. Cyanobacteria were mainly promoted by increased temperature and decreased concentrations of nitrogen compounds. The pure contribution of crustacean was low for the variation of phytoplankton suggesting a weak top-down control by crustacean zooplankton in the subtropical Lake Taihu.

Factors Affecting Temporal and Spatial Variations of Microcystins in Gonghu Bay of Lake Taihu, with Potential Risk of Microcystin Contamination to Human Health

A field survey of the seasonal variation of microcystin (MC) concentration was performed in Gonghu Bay (a total of 15 sampling sites) of Lake Taihu from January to December 2008. Microcystis spp. biomass and intra-/extracellular MCs were significantly correlated with water temperature, suggesting the importance of temperature in cyanobacterial blooming in the lake. Higher MC concentration was found in summer and autumn, and peaks of Microcystis biomass and intra-/extracellular MC concentrations were all present in October. Spatially, risk of MCs was higher in littoral zones than in the pelagic area. There were significant correlations between N or P concentrations, and Microcystis biomass or MC content, suggesting that N and P levels affected MC production through influencing Microcystis biomass. Intra-/extracellular MCs and Microcystis biomass had negative exponential relationships with TN:TP, and the maximum values all occurred when TN:TP was <25. Multivariate analyses by pcca indicated that intra- and extracellular MC concentrations had better correlations with biological factors (such as Microcystis biomass and chl-a) than physicochemical factors. The maximum concentration reached up to 17 µg/L MC-Lreq, considerably higher drinking water safety standard (1 µg/L) recommended who. So it is necessary take measures reduce exposure risk of cyanobacterial toxins human beings.

Plasma biochemical responses of the planktivorous filter-feeding silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) to prolonged toxic cyanobacterial blooms in natural waters

The planktivorous filter-feeding silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) are the attractive candidates for bio-control of plankton communities to eliminate odorous populations of cyanobacteria. However, few studies focused on the health of such fishes in natural water body with vigorous toxic blooms. Blood parameters are useful and sensitive for diagnosis of diseases and monitoring of the physiological status of fish exposed to toxicants. To evaluate the impact of toxic cyanobacterial blooms on the planktivorous fish, 12 serum chemistry variables were investigated in silver carp and bighead carp for 9 months, in a large net cage in Meiliang Bay, a hypereutrophic region of Lake Taihu. The results confirmed adverse effects of cyanobacterial blooms on two phytoplanktivorous fish, which mainly characterized with potential toxicogenomic effects and metabolism disorders in liver, and kidney dysfunction. In addition, cholestasis was intensively implied by distinct elevation of all four related biomarkers (ALP, GGT, DBIL, TBIL) in bighead carp. The combination of LDH, AST activities and DBIL, URIC contents for silver carp, and the combination of ALT, ALP activities and TBIL, DBIL, URIC concentrations for bighead carps were found to most strongly indicate toxic effects from cyanobacterial blooms in such fishes by a multivariate discriminant analysis.

Field and Laboratory Studies on Pathological and Biochemical Characterization of Microcystin-Induced Liver and Kidney Damage in the Phytoplanktivorous Bighead Carp

Field and experimental studies were conducted to investigate pathological characterizations and biochemical responses in the liver and kidney of the phytoplanktivorous bighead carp after intraperitoneal (i.p.) administration of microcystins (MCs) and exposure to natural cyanobacterial blooms in Meiliang Bay, Lake Taihu. Bighead carp in field and laboratory studies showed a progressive recovery of structure and function in terms of histological, cellular, and biochemical features. In laboratory study, when fish were i.p. injected with extracted MCs at the doses of 200 and 500 μg MC-LReq/kg body weight, respectively, liver pathology in bighead carp was observed in a time dose-dependent manner within 24 h postinjection and characterized by disruption of liver structure, condensed cytoplasm, and the appearance of massive hepatocytes with karyopyknosis, karyorrhexis, and karyolysis. In comparison with previous studies on other fish, bighead carp in field study endured higher MC doses and longer-term exposure, but displayed less damage in the liver and kidney. Ultrastructural examination in the liver revealed the presence of lysosome proliferation, suggesting that bighead carp might eliminate or lessen cell damage caused by MCs through lysosome activation. Biochemically, sensitive responses in the antioxidant enzymes and higher basal glutathione concentrations might be responsible for their powerful resistance to MCs, suggesting that bighead carp can be used as biomanipulation fish to counteract cyanotoxin contamination.

Risk assessment of microcystins in silver carp (Hypophthalmichthys molitrix) from eight eutrophic lakes in China

Bioaccumulation and risk assessment of microcystins (MCs) in muscle of silver carp (Hypophthalmichthys molitrix) from eight eutrophic lakes along the Yangtze River of China were examined by using liquid chromatography electrospray ionisation mass spectrometry. MCs contents in seston collected from these eutrophic lakes ranged from 0.02 to 21.7 μg/L. MCs concentrations in silver carp muscle samples varied from 0.014 to 0.036 μg/g DW with an average of 0.028 μg/g DW. The total length of silver carp showed a significant negative correlation with MCs concentrations in their muscle (r=-0.85, p<0.05), suggesting that MCs accumulation in silver carp muscle seems to be size dependent. EDI values of MCs in fish muscle from these eight eutrophic lakes varied from 0.0027 to 0.0071 μg/kg day, which was much lower than the TDI value of 0.04 μg/kg day previously established by WHO, indicating that it is safe to consume silver carp muscle from eutrophic lakes in China.

The impact of fish predation and cyanobacteria on zooplankton size structure in 96 subtropical lakes.

Zooplankton are relatively small in size in the subtropical regions. This characteristic has been attributed to intense predation pressure, high nutrient loading and cyanobacterial biomass. To provide further information on the effect of predation and cyanobacteria on zooplankton size structure, we analyzed data from 96 shallow aquaculture lakes along the Yangtze River. Contrary to former studies, both principal components analysis and multiple regression analysis showed that the mean zooplankton size was positively related to fish yield. The studied lakes were grouped into three types, namely, natural fishing lakes with low nutrient loading (Type1), planktivorous fish-dominated lakes (Type 2), and eutrophic lakes with high cyanobacterial biomass (Type 3). A marked difference in zooplankton size structure was found among these groups. The greatest mean zooplankton size was observed in Type 2 lakes, but zooplankton density was the lowest. Zooplankton abundance was highest in Type 3 lakes and increased with increasing cyanobacterial biomass. Zooplankton mean size was negatively correlated with cyanobacterial biomass. No obvious trends were found in Type 1 lakes. These results were reflected by the normalized biomass size spectrum, which showed a unimodal shape with a peak at medium sizes in Type 2 lakes and a peak at small sizes in Type 3 lakes. These results indicated a relative increase in medium-sized and small-sized species in Types 2 and 3 lakes, respectively. Our results suggested that fish predation might have a negative effect on zooplankton abundance but a positive effect on zooplankton size structure. High cyanobacterial biomass most likely caused a decline in the zooplankton size and encouraged the proliferation of small zooplankton. We suggest that both planktivorous fish and cyanobacteria have substantial effects on the shaping of zooplankton community, particularly in the lakes in the eastern plain along the Yangtze River where aquaculture is widespread and nutrient loading is high.

Ecological degeneration of the Erhai Lake and prevention measures

The water quality of Erhai Lake is good as a whole, but its decreasing trend is not optimistic; the water ecosystem of Erhai Lake has changed dramatically, showing an obvious degenerating trend. The main reasons for the ecosystem degeneration are as follows: inflow pollution load exceeding the water environmental capacity, not favorable water habitat for the propagation of submerged plants, and the weak management for the lake basin. To prevent the degeneration of Erhai ecosystem, two key problems should be solved: one is to reduce the inflow pollution load to prevent the increase of nitrogen and phosphorus concentrations in the overlying water; and the other is to implement the ecosystem regulation, namely improve the stability and biodiversity of Erhai ecosystem by habitat improvement, ecological restoration and ecological regulation. In terms of the preventive measures against the Erhai ecosystem degeneration, the pollution source control in combination with ecosystem regulation should be taken as the focus. Pollution source control, habitat improvement, ecological restoration, ecological regulation and watershed management should be emphasized simultaneously. To be specific, the key tasks for preventing Erhai ecosystem degeneration include five points namely, the reduction of pollution loading into lake, adjustment of ecological fishery, restoration of submerged vegetation, watershed integrated management, and emergency treatment of water blooms.

Nephrotoxic effects from chronic toxic cyanobacterial blooms in fishes with different trophic levels in a large Chinese lake

Physiological and biochemical responses in kidneys of fishes with different trophic levels to toxic cyanobacterial blooms were studied. We sampled four fishes: the phytoplanktivorous Hypophthalmichthys molitrix and Aristichthys nobilis, the omnivorous Carassius auratus, and the carnivorous Culter ilishaeformis. Alterations of the antioxidant (GSH) and the major antioxidant enzymes (CAT, SOD, GPx, GST) were monitored monthly. Catalase and glutathione S-transferase were significantly higher during blooms than before and after blooms. All fishes showed ultrastructural alterations during blooms, which mainly are inosculation of foot processes in epithelial cell of glomeruli and mitochondria swelling in the proximal tubules. The results suggested that kidney impairment from chronic exposure of toxic cyanobacterial blooms might be the first step, and then followed by hepatic failure. Compared with livers in terms of physiological status, the weaker antioxidant ability of kidney made it more susceptible to chronic MCs exposure, besides its effective accumulation of MC metabolites.

Food Consumption by In Situ Pen-Cultured Planktivorous Fishes and Effects on an Algal Bloom in Lake Taihu, China

ABSTRACT Silver carp (Hypophthalmichthys molitrix) and bighead carp (Aristichthys nobilis) were used as a new pen-cultureed biomanipulation technique to control algal blooms in Meiliang Bay of Lake Taihu. In order to evaluate the capacity of these two fishes to decrease algal blooms, die1 feeding samplings were carried out in May (without algal blooms) and September (with algal blooms) in 2005. Based on estimated food consumption by the Elliott-Persson model, silver carp increased daily food consumption from 2.07 g dry weight per 100 g wet body weight in May before the outbreak of algal blooms to 4.98 g dry weight per 100 g wet body weight in September during algal blooms outbreak. However, no obvious variation of food consumption was observed in bighead carp during the study period. This species 1.88 and 1.54 g dry weight of plankton per 100 g wet body weight in May and September, respectively. Silver carp had a higher feeding capacity for plankton than bighead carp. Biotic factors (i.e., fish size and conspecific competition with natural species in the lake) may affect the feeding behaviors of both carps as well as seasonal variation of plankton communities in the pen.