Chutima Klingklib, Naraid Suanyuk, Tharanan Kongkapan, and Chutima Tantikitti

DOI: 10.14456/sjst-psu.2021.158

pp. 1212 - 1219

Abstract

The present study report on epizootiology, pathogenicity and haemato-immunological aspects of Streptococcus
agalactiae (Group B Streptococcus, GBS) serotype Ib (GBS-Ib) affecting climbing perch (Anabas testudineus) in southern
Thailand. Study on growth of GBS-Ib under various conditions indicated that this bacterium grew from 25 to 35°C, pH 5 to 9 and
0.5 to 4.0% NaCl. Climbing perch inoculated by intraperitoneally injected GBS-Ib at concentrations of 10¹
to 10⁴ CFU/mL
exhibited 60.00-96.67% mortality, with 60 h-LD₅₀ and 72 h-LD₅₀ at 4.5x10² CFU/mL and 6.3x10¹ CFU/mL inoculums,
respectively. Study of the haemato-immunological changes in the fish infected with GBS-Ib revealed declines of haematocrit,
haemoglobin, serum protein, red blood cells, and respiratory burst activity. On the other hand, white blood cells, lysozyme
activity, phagocytic index, and average beads per cell, were significantly increased in the infected fish. Study on the effect of
environmental factors on the susceptibility of fish to GBS-Ib infection indicated that high water temperature and low dissolved
oxygen levels proved to increase mortality of climbing perch. These findings indicate that GBS-Ib is a pathogenic bacterium
responsible for fish mortality in Thailand.