Phytoplankton biomass in relation to nutrients and zooplankton in thirty subtropical lakes adjacent to the Yangtze River, China

A total of 30 shallow lakes, located along the middle and lower reaches of the Yangtze River, were studied to assess the relative importance of nutrients and zooplankton biomass in determining the phytoplankton biomass in subtropical China. Zooplankton biomass and nutrients both varied greatly in these lakes. Factor analysis and multiple linear regression showed that phytoplankton biomass was positively correlated with TN, NH4+, NO3- and TP, while it did not show any negative relationship to zooplankton biomass. Meanwhile, the phytoplankton biomass showed contrary relationships to the mass ratio of TN/TP in spring and summer, suggesting that in nutrient-richer lakes the dominant phytoplankton species have different preferences for TN/TP ratio. The insignificant top-down control of phytoplankton biomass may be attributed to the dominance of small-sized crustaceans and low crustacean biomass resulting from cyanobacterial dominance and planktivorous fish predation as well as other factors. Thus, it is likely that nutrients were more important than zooplankton biomass in explaining the total variance of phytoplaDkton biomass in these subtropical lakes.

In situ study on the control of toxic Microcystis blooms using phytoplanktivorous fish in the subtropical Lake Taihu of China: A large fish pen experiment

Three large fish pens (0.36 km(2) of each) stocked with silver and bighead carp were set up in Meiliang Bay for controlling toxic Microcystis blooms. The responses of plankton communities and food consumption of silver and bighead carp were studied. Crustacean zooplankton were significantly suppressed in the fish pens. Total phytoplankton biomass, Microcystis biomass and microcystin concentration were lower in the fish pens than in the surrounding lake water, but the difference was not statistically significant. The present stocking density of silver plus bighead carp (about 40 g/m(3) in July) was likely too low to achieve an adequate control of Microcystis. Silver carp fed mainly on phytoplankton but bighead carp mainly on zooplankton: mean zooplankton contribution in the gut was 31.5% for silver carp and 64.7% for bighead carp. Compared with previous studies, both carp species preyed upon more zooplankton because of the abundant food resource. Daily rations of silver and bighead carp were estimated by Egger's model in the main growing season. Filtration rate was calculated from the daily ration and the density of plankton in the lake. During May-October, filtration rates of silver and bighead carp for phytoplankton were 0.22-1.53 L g(-1) h(-1) and 0.02-0.68 L g(-1) h(-1), respectively, and filtration rates for zooplankton were 0.24-0.44 L g(-1) h(-1) and 0.08-1.41 L g(-1) h(-1), respectively. Silver carp had a stronger ability of eliminating phytoplankton than bighead carp. To achieve a successful bioniampulation with a minimum effect of ichthyoeutrophication, the stocking proportion of bighead carp should be controlled in the future practice. (c) 2007 Elsevier B.V All rights reserved.

Studies on temporal and spatial variations of phytoplankton in Lake Chaohu

Temporal and spatial variations of the phytoplankton assemblage in Lake Chaohu, a large shallow eutrophic lake in China, were studied from September 2002 to August 2003. A total of 191 phytoplankton species was identified, among which Chlorophytes (101) ranked the first, followed by Cyanophytes (46) and Bacillariophytes (28). On average over the entire lake, the maximum total algal biomass appeared in June (19.70 mg/L) with a minimum (5.05 mg/ L) in November. In terms of annual mean biomass, cyanobacteria contributed 45.43% to total algal biomass, followed by Chlorophytes (27.14%), and Bacillariophytes (20.6%). When nitrate (NO3-N) and ammonium (NH4-N) concentrations dropped in spring, fixing-nitrogen cyanobacterium (Anabaena) developed quickly and ranked the first in terms of biomass in summer. It is likely that dominance of zooplanktivorous fish and small crustacean zooplankton favored the development of the inedible filamentous or colony forming cyanobacteria. The persistent dominance of cyanobacteria throughout all seasons may indicate a new tendency of the response of phytoplankton to eutrophication in Lake Chaohu.

An in situ estimate of food consumption by icefish in Lake Chaohu, China

The icefish (Neosalanx taihuensis) of Lake Chaohu, China, foraged almost exclusively on crustacean zooplankton in both spring and summer. The icefish showed diurnal feeding periodicity, with peak feeding in the morning. No food was observed in icefish guts collected at night. Our results indicate that that the icefish was a particulate feeder and light intensity greatly affected its foraging on zooplankton. Daily consumption of zooplankton by icefish varied significantly both diurnally and among seasons, which ranged from 0.22 to 2.23 g (wet weight) per 100 g wet fish weight at temperatures between 16.3 degrees C (spring) and 28.8 degrees C (summer).

The precocious Chinese mitten crab: Changes of gonad, survival rate, and life span in a freshwater lake

Changes of the gonad. survival rate, and life span of the precocious (i.e., sexually mature in their first October-November, at the age of 5 or 6 months) Chinese mitten crab (Eriocheir sinensis) were studied in a small, shallow, macrophytic, freshwater lake along the middle reaches of the Changjiang River, China. The gonosomatic index (GSI) reached peak during the next March when the female GSI was 12.32 +/- 1.75 SD% and the male GSI A as 4.24 +/- 0.19%. The sexual glands degraded from then on. In the first ten-day period of the following July, there was no complete ovum in the ovary. and the sperm became thin and lost adhesion. The population declined sharply from November to July, and the last one (a female) died in the middle of July, which indicated that the life span of the precocious crab was about 12 months (from larval hatching in June to death in July of next year). The survival curve might be expressed as Y = 1.09exp(-0.018x) (Y survival rate; x: days) for the precocious crabs stocked in experimental cages.

Enhancement of planktonic rotifers by Microcystis aeruginosa blooms: An enclosure experiment in a shallow eutrophic lake

Enclosure experiments with three treatments (sediment addition, sediment + nitrogen enrichment, sediment + phosphorus enrichment) and unfertilized controls were performed in shallow hypereutrophic Lake Donghu during the summer of 2000. Dense Microcystis aeruginosa blooms occurred in all the enclosures during the experimental period but not in the surrounding lake water. Generally, the dominant rotifers were Polyarthra vulgalis, Filinia longiseta, Proales sp. and Asplanchna sp. at the beginning of the experiment, followed by a shift to Brachionus calyciflorus, Trichocerca similis, Cephalodella catellina and Anuraeopsis fissa, and finally to F. longiseta, Proales sp. and Keratella cochleris. M. aeruginosa blooms strongly suppressed the larger Diaphanosoma brachyurum but enhanced the development of the smaller cladocerans and rotifers that probably efficiently utilized organic matter from M. aeruginosa through the detritus food chain. The smaller cladoceran and rotifers coexisted successfully throughout the experimental period.

Studies on the effects of silver carp (Hypophthalmichthys molitrix) on the Phytoplankton in a shallow hypereutrophic lake through an enclosure experiment

The responses of nutrients, water transparency, zooplankton and phytoplankton to a gradient of silver carp biomass were assessed using enclosure methods. The gradient of four silver carp biomass levels was set as follows: 0, 116, 176 and 316 g m(-2). Nutrients did not show any statistically significant differences among the treatments. An Outburst of Daphnia only occurred in fishless enclosures where phytoplankton biomass was the lowest and water clarity significantly increased. While among fish enclosures, the small-sized Moina micrura dominated throughout the experiment and both zooplankton and phytoplankton biomasses decreased with increased fish biomass. No large colonial cyanobacterial blooms occurred in the fishless enclosures as predicted. This might be due to low water temperature. short experiment time and the occurrence of large bodied Daphnia in our experiment. Cryptophyta was the most dominant group in most of the enclosures and the lake water throughout the experiment. The fishless enclosure had much lower proportion of Cyanophyta but higher proportion of Trachelomonas sp.

Experimental and field studies of Mesocyclops notius (Copepoda : Cyclopoida) from a subtropical Chinese lake, Lake Donghu

This paper reports experimental and field studies on the cyclopoid Mesocyclops notius from subtropical Lake Donghu close to the Yangtze river. Mesocyclops notius, a dominant crustacean Zooplankter throughout tropical Australia, was previously considered to be endemic to Australia, but recently, Mesocyclops leuckarti in Lake Donghu was re-identified as M. notius. Laboratory culture experiments were conducted to reveal the effect of temperature (15, 20, 25 and 30 degreesC) on the development, growth and reproduction of M. notius. Temperature was inversely related to development times of eggs, nauplii and copepodites, body length and physiological longevity of adults, and brood size. Body length and physiological longevity of females were greater than those of males at the same temperature. No reproduction took place at 15 degreesC. Production and seasonal cycles of M. notius during 1980-1982 were studied at two sampling stations of Lake Donghu. At the mid-lake station, the annual production and production/biomass (P/B) ratio of M. notius varied between 6.0 and 18.0 g dry wt m(-2) year(-1) and 74.6 and 95.5, respectively. Mesocyclops notius reached their highest density peaks in the warm months (July-October), with a maximum density of 1256 individuals l(-1) at a littoral site. No reproduction and recruitment by AL notius took place during the cold months (December March) when the temperature of the lake water was < 15 degreesC. Mesocyclops notius were more abundant at a littoral station than at a pelagic station, possibly due to different food availability. The higher male:female sex ratio of M. notius at the littoral station was most likely caused by size-selective fish predation on larger females.

A preliminary phylogenetic analysis of Metapenaeopsis (Decapoda : Penaeidae) based on mitochondrial dna sequences of selected species from the Indo-West Pacific

Phylogenetic relationships within Metapenaeopsis remain largely unknown. The modern revision of the genus suggests that the shape of the petasma, followed by the presence of a stidulating organ, are the most important distinguishing taxonomic features. In the present study, phylogenetic relationships were studied among seven Metapenaeopsis species from the Indo-West Pacific based on partial sequences of mitochondrial 16S rRNA and cytochrome c oxidase I (COI) genes. Mean sequence divergence was 6.4% for 16S and 15.8% for COI. A strikingly large nucleotide distance (10.0% for 16S and 16.9% for COI) was recorded between M. commensalis, the only Indo-West Pacific species with a one-valved petasma, and the other species with a two-valved petasma. Phylogenetic analyses using neighbor-joining, maximum parsimony, and maximum likelihood generated mostly identical tree topologies in which M. commensalis is distantly related to the other species. Two clades were resolved for the remaining species, one with and the other without a stridulating organ, supporting the main groupings of the recent taxonomic revision. Results of the present study also indicate that the deep-water forms represent a relatively recent radiation in Metapenaeopsis.

The construction of a cDNA library enriched for immune genes and the analysis of 7535 ESTs from Chinese mitten crab Eriocheir sinensis

Chinese mitten crab Eriocheir sinensis is one of the most important aquaculture crustacean species in China. A cDNA library was constructed from hemocytes of E. sinensis challenged with the mixture of Listonella anguillarum and Staphylococcus aureus, and randomly sequenced to collect genomic information and identify genes involved in immune defense response. Single-pass 5' sequencing of 10368 clones yielded 7535 high quality ESTs (Expressed Sequence Tags) and these ESTs were assembled into 2943 unigenes. BLAST analysis revealed that 1706 unigenes (58.0% of the total) or 4593 ESTs (61.0% of the total) were novel genes that had no significant matches to any protein sequences in the public databases. The rest 1237 unigenes; (42.0% of the total) were closely matched to the known genes or sequences deposited in public databases, which could be classed into 20 or 23 classifications according to "molecular function" or "biological process" respectively based on the Gene Ontology (GO). And 221 unigenes (7.5% of all 2943 unigenes, 17.9% of matched unigenes) or 969 ESTs (12.9% of all 7535 ESTs, 32.9% of matched ESTs) were identified to be immune genes. The relative higher proportion of immune-related genes in the present cDNA library than that in the normal library of E. sinensis and other crustaceans libraries, and the differences and changes in percentage and quantity of some key immune-related genes especially the immune inducible genes between two E. sinensis cDNA libraries may derive from the bacteria challenge to the Chinese mitten crab. The results provided a well-characterized EST resource for the genomics community, gene discovery especially for the identification of host-defense genes and pathways in crabs as well as other crustaceans. (C) 2009 Elsevier Ltd. All rights reserved.

Molecular characterization and mRNA transcript profile of vitellogenin in Chinese shrimp, Fenneropenaeus chinensis

A full-length cDNA encoding vitellogenin (Vg) was cloned from Chinese shrimp, Fenneropenaeus chinensis using RACE method. The full-length cDNA consist of 7,942 nucleotides including a 7,761 bp open reading frame, which encodes 2,587 amino acid residues. The deduced amino acid sequence showed high (from 94% to 37%) identity with other known crustacean Vgs. In addition, a consensus cleavage site (R-X-K/R-R) recognized by an endopeptidase and a member of subtilisin family of serine protease were identified in the deduced Vg precursor. RT-PCR analysis shown that Vg mRNA can be detected in both ovary and hepatopancreas of vitellogenic females but not in other experimental tissues including muscle, heart, lymph organ, gill, haemocytes and intestine. These results suggest that the Vg gene may be expressed exclusively in mature females, and both ovary and hepatopancreas are the possible tissues for Vg synthesis in F. chinensis. In addition, Vg gene is detected in genomic DNA of both females and males.

Discovery of genes involved in defense/immunity functions in a haemocytes cDNA library from Fenneropenaeus chinensis by ESTs annotation

Crustacean haemocytes play important roles in the host immune response including recognition, phagocytosis, melanization, cytotoxicity and inter-cellular signal communication. Expressed sequence tags (ESTs) analysis is proved to be an efficient approach not only for gene discovery, but also for gene expression profiles performance. In order to further understand the innate immune system and defense mechanisms of Chinese shrimp at molecular level, complementary DNA library is constructed from the haemocyte tissue of Fenneropenaeus chinensis. A total of 2371 cDNA clones are successfully sequenced and the average sequence length is 460 bp. About 50% are identified as orthologs of known genes from other organisms by BLASTx and BLASTn program. By sequences comparability and analysis, 34 important genes including 177 ESTs are identified that may be involved in defense or immune functions in shrimp based on the known knowledge. These genes are categorized into five categories according to their putative functions in shrimp immune system: 13 genes are different types of antimicrobial peptides (AMP, penaeidin, antilipopolysaccharide factor, etc.), and their proportion is about 3 8%; 11 genes belong to prophenoloxidase system (prophenoloxidase, serine proteinase, serine proteinase inhibitor, etc.), and their proportion is about 32%; five genes have high homology with clotting protein (lectin, transglutaminase, etc), and their proportion is about 15%; three genes may be involved in inter-cell signal communication (peroxinectin, integrin), and their proportion is about 9%; two genes have been identified to be chaperone proteins (Hsc70, thioredoxin peroxidase), and their proportion is about 6%. These EST sequences enrich our understanding of the immune genes of F chinensis and will help farther experimental research into immune factors and improve our knowledge of the immune mechanisms of shrimp. (c) 2007 Elsevier B.V. All rights reserved.

Identification of a novel DNA methyltransferase 2 from the brine shrimp, Artemia franciscana

DNA methyltransferase 2 (Dnmt2) is a dual-specificity DNA methyltransferase, which contains a weak DNA methyltransferase and novel tRNA methyltransferase activity. However, its biological function is still enigmatic. To elucidate the expression profiles of Dnmt2 in Artemia franciscana, we isolated the gene encoding a Dnmt2 from A. franciscana and named it as AfDnmt2. The cDNA of AfDnmt2 contained a 1140-bp open reading frame that encoded a putative Dnmt2 protein of 379 amino acids exhibiting 32%similar to 39% identities with other known Dnmt2 homologs. This is the first report of a DNA methyltransferase gene in Crustacean. By using semi-quantitative RT-PCR, A)Dnmt2 was found to be expressed through all developmental stages and its expression increased during resumption of diapause cysts development. Southern blot analysis indicated the presence of multiple copies of AfDnmt2 genes in A. franciscana. (C) 2007 Published by Elsevier Inc.

Molecular cloning, characterization and expression analysis of a putative C-type lectin (Fclectin) gene in Chinese shrimp Fenneropenaeus chinensis

Lectin is regarded as a potential molecule involved in immune recognition and phagocytosis through opsonization in crustacean. Knowledge on lectin at molecular level would help us to understand its regulation mechanism in crustacean immune system. A novel C-type lectin gene (Fclectin) was cloned from hemocytes of Chinese shrimp Fenneropenaeus chinensis by 3' and 5' rapid amplification of cDNA ends (RACE) PCR. The full-length cDNA consists of 1482 bp with an 861 bp open reading frame, encoding 287 amino acids. The deduced amino acid sequence contains a putative signal peptide of 19 amino acids. It also contains two carbohydrate recognition domains/C-type lectin-like domains (CRD1 and CRD2), which share 78% identity with each other. CRD1 and CRD2 showed 34% and 30% identity with that of mannose-binding lectin from Japanese lamprey (Lethenteron japonicum), respectively. Both CRD1 and CRD2 of Fclectin have I I amino acids residues, which are relatively invariant in animals' C-type lectin CRDs. Five residues at Ca2+ binding site I are conserved in Fclectin. The potential Ca2+/carbohydrate-binding (site 2) motif QPD, E, NP (Gln-Pro-Asp, Glu, Asn-Pro) presented in the two CRDs of Fclectin may support its ability to bind galactose-type sugars. It could be deduced that Fclectin is a member of C-type lectin superfamily. Transcripts of Fclectin were found only in hemocytes by Northern blotting and RNA in situ hybridization. The variation of mRNA transcription level in hemocytes during artificial infection with bacteria and white spot syndrome virus (WSSV) was quantitated by capillary electrophoresis after RT-PCR. An exploration of mRNA expression variation after LPS stimulation was carried out in primarily cultured hemocytes in vitro. Expression profiles of Fclectin gene were greatly modified after bacteria, LPS or WSSV challenge. The above-stated data can provide us clues to understand the probable role of C-type lectin in innate immunity of shrimp and would be helpful to shrimp disease control. (c) 2006 Elsevier Ltd. All rights reserved.

Molecular cloning, expression of a peroxiredoxin gene in Chinese shrimp Fenneropenaeus chinensis and the antioxidant activity of its recombinant protein

Peroxiredoxin (Prx) is known to be an antioxidant protein that protects the organisms against various oxidative stresses and functions in intracellular signal transduction. A Prx gene was firstly isolated in the crustacean, Chinese shrimp Fenneropenaeus chinensis. The full-length cDNA consists of 942 bp with a 594 bp open reading frame, encoding 198 amino acids. The molecular mass of the deduced amino acid is 22041.17 Da with an estimated pI of 5.17. Sequence comparison showed that Prx of F. chinensis shares 76%, 73% and 72% identity with that of Aedes aegypti, Branchiostoma belcheri tsingtaunese and Drosophila melanogaster, respectively. Northern blot analysis revealed the presence of Prx transcripts of F chinensis in all tissues examined. Real-time PCR analysis indicated that the Prx showed different expression profiles in shrimp hemocytes and hepatopancreas after artificial infection with Vibrio anguillarum. In addition, a fusion protein containing Prx was produced in vitro. LC-ESI-MS analysis showed that four peptide fragments of the recombinant protein were identical to the corresponding sequence of F. chinensis Prx. And the purified recombinant proteins were shown to reduce H2O2 in the presence of dithiothreitol. (c) 2007 Elsevier Ltd. All rights reserved.