In the previous oceanographic survey conducted by HORIE et al .8) it was revealed that Biotype 1 organisms of Vibrio parahaemolyticus distribute in coastal sea area. It was also noted that Biotype 1 organisms can be more frequently isolated from plankton or marine mud than from sea water sample. The present study was undertaken to investigate the occurrence of Biotype 1 or 2 organ isms in the plankton or fish inhabiting in the pelagic ocean. The survey was carried out aboard the Umitaka-maru, a research vessel of Tokyo University of Fisheries in the sea off Southern Kanto and Tokai districts late in July 1963. The location of sampling stations is shown in Fig. 1. Plankton samples were obtained at all the 13 stations , whereas young fish were caught only at 3 stations. At the station 9, particularly , several samples of sizable fish and squid could be caught using flyingfish drift net , and the gastric contents of these organ isms were tested. A selective liquid medium, 3% NaCl containing arabinose ethyl violet broth (AE medium) , as shown in Table 1, was used. In order to get higher rate of detection of Biotype 1 organ isms, ME medium, 3% NaCl containing mannitol ethyl violet broth was employed , and the said medium of pH 7.8 was used in parallel with that of pH 9 .0. No bacteria belonging to Biotype 1 could be detected from the samples collected i n the pelagic ocean, whereas Biotype 2 were found to be widely distributed in the plankton samples. Bi otype 3 bacteria was not isolated from the plankton , but detected in the samples of young fish and in the gastric contents of fish and squid. Some strains isolated from the flying fish could be classified as Biotype 2 on account of the salt resistance , positive Voges-Proskauer reaction and sucrose fermentation, however , they were differentiated from the typical organ isms of Biotype 2 by other biological features.
The mechanism of black discoloration was investigated in lobsters by means of in vivo experi ments.Discoloration in iced lobster tails has been found to hold no relationship to lowering of quality. Traumatism in the alive state is a principal factor of discoloration and usually happens after one day of storage, as proved by DOPA and tyrosine reactions, found positive through enzymatic and histochemical tests. Further, the larger and the earlier the bruising, the more intensive the dis coloration which, however, never reached into the inner muscle. Absence of air-oxygen acted as an inhibiting factor with retarding effect, even if traumatism was present in the alive state.A relationship between molting cycle and melanosis is evident, as the old ventral cuticle of pre-molting phase showed intensive melanin formation, on the contrary to the new one which seemed to be resistant to that. When catechol and DOPA solutions were injected in the live lobsters, melanin formed ap pears to be DOPA melanin as identified in shrimp. The following treatment is recommended for lobster handling on board: after being taken out of the cage, lobsters should be put into a tank full of iced water for some time, before being tailed, washed and stored in ice. Sodium bisulfite (NaHSO3), commonly used as a preventing agent, has no effect against development of discoloration, once traumatism is already present.
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