Masachika Maeda

The concept of biological control methods in aquaculture

Microbial techniques of biocontrol using the interaction of microorganisms to repress the growth of deleterious bacteria and viruses were developed. The bacterial strain used in this work also improved the growth of fishes and crustaceans. Using the concept and procedures of the biocontrol method described here, the aquaculture production became stable and even increased.

Horizontal distribution of psammophilic ciliates in fine sediments of the Chichester Harbour area

The distribution of 28 species of psammophilic ciliates isolated from the fine sands of Chichester harbour was correlated with gradients of ecological factors running horizontally in a granulometrically uniform sediment. Six sampling stations were situated on a single transect that ran parallel to the shoreline for a distance of 987 metres. Sediment analysis indicated that the substrate was homogeneous with respect to grain size but detrital material increased from 0·01% to 1·15% in a continuous gradient around the headland. Gymnostome and hypotrich ciliates dominated the samples. Eight species were new records for the British coast, thus bringing the total for Britain to 178; each species displayed its own distribution pattern along the transect. Some species were encountered at every station while others were restricted to a short length of coastline. Species diversity was greatest at stations adjacent to saltmarshes where interactions between detrital deposition and wave exposure appeared particularly ...

Fluctuation of deoxyribonuclease activity from late spring to autumn in Tokyo Bay

Deoxyribonuclease (DNase) activity in seawater of Tokyo Bay was determined during 1972 and 1973. The activity was dependent on substrate (deoxyribonucleic acid) concentration within the range from o to io mg/l. During the summer the activity was high in the inner part of the bay and decreased on approaching the mouth of the bay. The intensity of activity was very high compared with the standing crop of particulate deoxyribonucleic acid (DNA) and this high activity corresponded with rapid decrease of the amount of nucleic acid with increasing depth in the water columns in the bay.During the investigation carried out in 1972 the activity fluctuated, being weak in May and November and high during the summer months. The profiles for activity did not coincide with those for chlorophyll-a, particulate DNA and seston, except in September. These non-parallel relations are discussed in terms of the distribution patterns of phytoplankton and bacteria.

Microbial ecology concerning to the degradation of nucleic acid in the marine environment

This article summarizes the authors current work on microbial degradation of nucleic acid. The aim of this work is to elucidate parts of the saprogenic process in the marine ecosystem through the study of the behavior of nucleic acid-hydrolyzing bacteria inhabiting seawater and sediments.Considerably large population of nucleic acid-hydrolyzing bacteria was found to occur in seawater and sediments. The main genera of these microbes areVibrio spp. in coastal seas, andPseudomonas spp. in the oceanic waters. As a result of microbial attack, nucleic acid components are released into seawater. The properties of extracellular nuclease produced by a marineVibrio sp. are well adapted to the seawater environment; consequently this enzyme has high activity and stability in seawater. By determining nuclease activity in seawater and sediments, the intensities of nucleic acid-hydrolysisin situ were evaluated.Distribution patterns of marine bacteria are also discussed in reference to the occurrence of phytoplankton in seawater.