Diversity and seasonal changes in lactic acid bacteria in the intestinal tract of cultured freshwater fish

The composition of intestinal lactic acid bacteria (LAB) in fish species in Lake Kasumigaura was analyzed. First, the LAB composition of four fish species, silver carp (Hypophthalmichthys molitrix), common carp (Cyprinus carpio), channel catfish (Ictalurus punctatus) and deepbodied crucian carp (Carassius cuvieri), were analyzed in July and December 2001. In all these species, the predominant LAB was Lactococcus lactis in July and Lactococcus raffinolactis in December, strongly suggesting that the predominant intestinal LAB of fish in Lake Kasumigaura is L. lactis in summer and L. raffinolactis in winter, irrespective of fish species. Next, a yearlong analysis of changes in LAB composition was performed in common carp from April 2002 to March 2003. The predominant LAB was L. lactis in summer when water temperatures were above 20 degreesC, and L. raffinolactis in winter, when temperatures ranged between 4 and 10 degreesC. The change in the predominate LAB occurred in spring and autumn when water temperatures were between 13 and 17 degreesC. During these intermediate periods, LAB composition was variable. The change in predominant LAB was revealed to be due to the difference in the growth profile of the two species: L. lactis grew faster at above 20 degreesC, but at lower temperatures, L. raffinolactis grew successfully. RAPD analysis of isolated strains revealed that L. lactis strains in common carp intestine were limited to a few strains throughout the seasons but L. raffinolactis strains were diverse. (C) 2004 Elsevier B.V. All rights reserved.