The protective effect of lysozyme-galactomannan or lysozyme-palmitic acid conjugates orally administered to carp, Cyprinus carpio L. was investigated using a virulent strain of Gram-negative EdwardsieUa tarda isolated from an infected fish. Lysozyme-galactomannan conjugate was prepared through controlled Maillard reaction. Lysozyme-palmitic acid conjugate was prepared through base-catalyzed ester exchange using Nhydroxysuccinimide ester of palmitic acid. The conjugates provided substantial protection to carp infected with a Gramnegative bacteria f'Lsh pathogen E. tarda NG 8104. Lytic activities of lysozyme conjugates with galactomannan and palmitic acid were about 80 and 71% of native lysozyme using Micrococcus lysodeikticus as a substrate. Feeding with lysozyme conjugates, for 8 days, significantly enhanced fish protection against E. tarda infection. The survival rate was 30% for lysozyme-galactomannan conjugate treated fish and 20% for lysozyme-palmitic acid conjugate treated fish after 6 days cultivation while all control fish died within 3 days. On the other hand, a recovery rate of 40% after 6 days was observed in the fish group that were fed lysozyme-palmitic acid conjugate 3 and 2 h before and after E. tarda challenge, respectively, and for 6 consecutive days. The results of this work show the possibility of utilizing lysozyme conjugates with galactomannan or palmitic acid as a therapeutic for infection in fish.

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Kesayoshi HADANO and Takashi SAITO This paper discusses field observation and model results for temperature and salinity in Myojin-ike, a group of saline lake. Myojinike is itself composed of three smaller interconnected basins, the largest of which is connected to the sea of Japan. Water temperature and salinity observed 0.5m and 3.0m below water surface showed abrupt variations like a step function during November to December 1985. This phenomenon is investigated in relation to the water movement in the lake.