Genome mapping in aquatic animals: Progress and future perspectives

The genome of aquatic animals is poorly understood and information from different taxonomic groups is sketchy. While there have been intensive genomic studies on some fish models, investigations on other fishes and invertebrates have been scarce. Yet there are recently some coordinated studies on genome mapping in a number of aquaculture animals of economic importance. This review summarizes information available on genome mapping of the important fish models and aquaculture animals. The future perspectives of this field of studies are discussed.

The restoration of aquatic macrophytes for improving water quality in a hypertrophic shallow lake in Hubei Province, China

This paper deals with a case study of the restoration of submerged macrophytes for improving water quality in a hypertrophic shallow lake, Lake Donghu of Wuhan, Hubei Province, China. Macrophyte restoration experiments were conducted in large-scale enclosures established in three sublakes of different trophic status, and the effectiveness for water quality improvement was tested by using the enclosure experiment in the hypertrophic sublake. Water quality was remarkably improved after the reestablishment of aquatic macrophytes. It is suggested that the submerged vegetation of less polluted sublakes could be capable of recovering spontaneously once the stocking of herbivorous fishes has been ceased, and the K-selected plants such as Potamogeton maackianus should be introduced into these sublakes to enhance the stability of aquatic vegetation. However, it may not be possible and economical to restore the submerged macrophytes in severely polluted basins unless external pollution has been cut off and internal nutrient loadings considerably reduced. In this case, the r-selected submerged plants should be used as the pioneer species for macrophyte recovery. (C) 2001 Elsevier Science B.V. All rights reserved.

Effects of the stocking density and body size of the mitten crab (Eriocheir sinensis) on aquatic plant biomass

Experiments in tanks and cages were conducted to examine the effects of stocking density and body size of the Mitten crab (Eriocheir sinensis) on transplanted submersed macrophyte biomass. The early juvenile crab with 7.0 +/-0.6 mm. carapace width (CW) had little effect on plant biomass, regardless of the stocking densities. However, larger crabs (CW: 18.0 +/-2.2,35.0 +/-3.6, and 60.0 +/-5.7 mm) significantly influenced plant biomass, especially at large stocking densities. Predictive models, using crab body size and stocking density, were generated to demonstrate effect of the mitten crab on the changes Of plant biomass. The results indicate that dense mitten crab populations may adversely affect aquatic plant communities, particularly when its animal food resources are scarce.

The distribution of monogenean parasites on aquatic vertebrates inhabiting Chinese inland waters

The general distribution of monogenean parasites of aquatic vertebrates inhabiting Chinese inland waters is summarised. Five hundred and seventy-two out of a total of 581 species of monogeneans were discovered on fish, while only nine species were found on Amphibia and Reptilia. Most dactylogyrids and diplozoids parasitise cyprinids, while ancyrocephalids occur on silurids and cyprinids, and gyrodactylids are found mainly on cyprinids and cobitids. Analyses of host-specificity and host-diversity suggests that the family Ancyrocephalidae should be divided into several families parallel with the Dactylogyridae. Of 12 subfamilies of the Cyprinidae, only the Gobiobotinae was found to be free of infection with monogeneans, and the genus Dactylogyrus has more species than any other monogenean genus associated with every cyprinid subfamily.

MOBILITY AND TRANSFER OF RESIDUAL HEXACHLOROCYCLOHEXANE (HCH) IN AQUATIC ENVIRONMENT

An investigation was carried out to study the mobility and transfer of HCH-residues in Yanjia lake, Hubei, China, from 1990-1993. By sampling at different locations, the horizontal distribution of HCH-residues was determined; by sampling at different depths in the same location, the vertical mobility of HCH-residues and its penetration were measured. The vertical profiles of HCH-residues in sediment showed a gradient distribution, which was reduced with the increase in depth. This was very similar in shape to the organic carbon and nitrogen content profiles. The penetration of HCH-residues was measured as 60cm approximately. Meanwhile, water, sediment (0-12cm), benthos and benthic fish collected from the lake were analyzed to determine the transfer of HCH-residues along aquatic food chain. The BCF values of HCH-residues indicated that the bioaccumulation of HCH-residues in freshwater food chain still exsisted in spite of the banning of HCH since 1983. The maxium BCF value of HCH-residues in the liver samples of 5-year-old common carp was up to 61966 (calculated by beta-HCH).

A colorimetric assay for screening microcystin class compounds in aquatic systems

Secondary metabolites produced by water-blooming cyanobacteria in eutrophic waters include some potent hepatotoxins, These compounds also have tumour-promoting properties, attributable to their inhibition and activation of protein phosphatases and kinases respectively. The inhibitory effect of these toxins on protein phosphatases have been employed in a commonly used radiometric assay, involving the use of a P-32-labeled substrate, for the detection and quantitation of these compounds. This paper investigates and describes a colorimetric method in which the activity of protein phosphatase 2A is determined by measuring the rate of colour production from the release of yellow p-nitrophenol using p-nitrophenyl phosphate as the substrate. Results of this study suggest that the colorimetric protein phosphatase inhibition assay is a simple, inexpensive tool for screening substances that may have tumour-promoting characteristics in aquatic systems. The detection limit of the colorimetric method is comparable to the radiometric assay. (C) 1998 Elsevier Science Ltd. All rights reserved.

Degradation of aquatic humic material by ultraviolet light

Natural humic water was treated with ultraviolet (UV) light and UV + hydrogen peroxide . The effects on the dissolved organic carbon content (DOC), the UV-absorbance at 254 nm (UV-abs.), the molecular size distribution, pH, and mutagenic activity were monitored, and the identity and concentrations of the most abundant gas chromatographable organic degradation products were determined. The DOC content and the UV-abs. of the water decreased substantially during treatment with. The decreases were dependent on the time of irradiation (UV dose) as well as on the H2O2 dose applied. The humus macromolecules were degraded to smaller fragments during irradiation. At higher UV doses, however, part of the dissolved organic matter (DOM) was found to precipitate, probably as a result of polymerization. Oxalic acid, acetic acid, malonic acid, and n-butanoic acid were the most abundant degradation products detected. These acids were found to account for up to 20% and 80% of the DOM in UV- and waters, respectively. No mutagenic activity was generated by the UV irradiation or the treatment. It is further concluded that the substantial mutagenic activity formed during chlorination of humic waters cannot be decreased by using UV irradiation as a pretreatment step.

Comparison of effectiveness of different ashing auxiliaries for determination of phosphorus in natural waters, aquatic organisms and sediments by ignition method

An improved method for the determination of phosphorus in natural waters, aquatic organisms and sediments by ignition method is proposed. The recoveries of phosphorus (P) from selected inorganic and organic P-containing compound standards after ignition with different auxiliaries, such as MgSO4, Mg(NO3)(2), MgO2, Mg(Ac-2) and CaCl2, were compared. We found that the phosphorus from most compound standards could not be completely recovered when these compounds were ignited (450-500degreesC) with the MgSO4 as auxiliary and the baked residue was extracted with 0.2 mol l(-1) HCl for 30min at 80degreesC or at room temperature. P recoveries, for example, were poor, less than 85%, if pyrophosphate and metaphosphate were ignited with the addition Of MgSO4 prior to the extraction of the baked residue with 0.2 mol l(-1) HCl at 80degreesC for 30 min. In contrast, MgO2, Mg(Ac)(2) and CaCl2, as well as Mg(NO3)(2), could all yield complete P recoveries at routine ashing temperatures (450-500degreesC). The results demonstrate that MgC12 is a more effective auxiliary agent for the determination of phosphorus in natural waters, aquatic organisms and sediments by ignition method than MgSO4 which is commonly used. (C) 2003 Elsevier Science Ltd. All rights reserved.

Partitioning, bioavailability and effects of oestrogens and xeno-oestrogens in the aquatic environment

This review provides insights into the distribution and impact of oestrogens and xeno-oestrogens in the aquatic environment and highlights some significant knowledge gaps in our understanding of endocrine disrupting chemicals. Key areas of uncertainty in the assessment of risk include the role of estuarine sediments in mediating the fate and bioavailability of environmental (xeno)oestrogens (notably their transfer to benthic organisms and estuarine food chains), together with evidence for endocrine disruption in invertebrate populations. Emphasis is placed on using published information to interpret the behaviour and effects of a small number of model compounds thought to contribute to oestrogenic effects in nature; namely, the natural steroid 17 beta -oestradiol (E2) and the synthetic hormone 17 alpha -ethinyloestradiol (EE2), together with the alkyl-phenols octyl- and nonyl-phenol (OP, NP) as oestrogen mimics. Individual sections of the review are devoted to sources and concentrations of (xeno)oestrogens in waterways, sediment partitioning and persistence, bioaccumulation rates and routes, assays and biomarkers of oestrogenicity, and, finally, a synopsis of reproductive and ecological effects in aquatic species.