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The freshwater rotifer, Brachionus calyciflorus is one of the live food organisms used for the mass production of larval fish. In this study possibility of obtaining high density cultures of the freshwater rotifer B. calyciflorus were investigated. The two culture systems used differed in their air and dissolved oxygen supplies using three temperatures in each case: 24, 28 and 32 deg. C. Rotifers were batch-cultured using 5 l-vessels and fed with the freshwater Chlorella. The growth rate of rotifers significantly increased with an increase in temperature. The maximum density of the rotifers with air-supply at 24 deg. C, 6500 ind. ml-1, was significantly lower than those cultured at 28 and 32 deg. C, i.e. 8600 and 8100 ind. ml-1, respectively. Dissolved oxygen levels decreased with time and ranged from 0.8 to 1.4 mg l-1 when the density of freshwater rotifer was the highest at each temperature. The highest density (19 200 ind. ml-1) of freshwater rotifer was obtained in cultures with a supply of oxygen at 28 deg. C. Densities of 13 500 and 17 200 ind. ml-1 were found at 24 and 32 deg. C, respectively. Levels of NH3-N increased with time and a dramatic increase of NH3-N was observed at high temperatures. Levels of NH3-N at 24, 28 and 32 deg. C were 13.2, 18.5 and 24.5mg l-1, respectively. These levels coincided with the highest rotifer density at each of the three temperatures. When rotiferswere cultured with an oxygen-supply and pH was adjusted to 7, the maximum density of rotifer reached 33 500 ind. ml-1 at 32 deg. C . These results suggested that high density culture of freshwater rotifer, B. calyciflorus could be achieved under optimal conditions with DO value of exceeding 5 mg l-1 and NH3-Nvalues of lower than 12.0 mg l-1. [ABSTRACT FROM AUTHOR]

Abstract: The intertidal copepod Tigriopus japonicus has shown promising results in classical acute and chronic toxicity studies. Recently, a large number of genes have been identified from this species and their mRNA expression has been studied independently against exposure to marine environmental pollutants. T. japonicus is a promising organism for the study of mechanistic aspects of marine environmental pollutants using genomics. In this study, a 6K oligochip for T. japonicus that included mostly unique sets of genes from ∼26K ESTs, was developed. A total of 5463 spots (2313 mRNAs upregulated and 3150 downregulated) were identified to be significantly expressed on microarray by hierarchical clustering of genes after exposure to copper for different time durations (10μg/L for 6, 12 and 24h). However, mRNAs of only 138 and 375 genes were observed to be consistently upregulated and downregulated, respectively, at all time points. Most of the changes of mRNA expression were observed at the short exposure of 6h. It was observed that mRNA expression of several genes involved in growth, metabolism, reproduction and hormonal regulation was modulated in Cu-exposed T. japonicus. mRNA expression of genes involved in detoxification and antioxidant functions was also modulated. This indicates that Cu-induced gene transcription is complicated in T. japonicus similar to other crustaceans. Cu specifically upregulated mRNAs of genes of some isoforms of cytochrome P450 (CYP). On the other hand, a majority of downregulated mRNAs were of genes encoding for proteins important for growth and development. The expression profile of mRNAs of selected genes was verified by the quantitative real time RT-PCR. The mRNA expression profiles provide insight into the mechanism of action of copper in T. japonicus. These results demonstrate the suitability of a T. japonicus oligochip microarray for risk assessment of trace metals in the marine environment. As yet, major breakthroughs in invertebrate toxicogenomics have mainly been in Daphnia and Drosophila. Daphnia''s use is limited to freshwater ecotoxicogenomics. Here we propose an oligochip microarray-based approach for risk assessment of trace metals in a potential model marine test species. [Copyright &y& Elsevier]