EFFECTS OF THERMAL SHOCK AND HIGH NITRITE LEVELS ON THE PATHOGENICITY OF INFECTIOUS BACTERIA IN ASIAN SWAMP EEL (Monopterus albus Zuiew, 1793)

Abstract

The study was conducted to evaluate the effects of environmental factors on the pathogenicity of Aeromonas veronii, Edwardsiella tarda and Flavobacterium columnare in juvenile Asian swamp eel (Monopterus albus). First, tolerance thresholds of the eels were determined at temperatures of 24, 26, 28, 30, 32, and 34°C, and two temperature shock ranges were selected: high (28 - 32°C) and low (24 - 28°C). Fourteen experimental treatments were then established, including single bacterial infection (Av, Et, Fc), thermal shock during bacterial infection (Lt-Av, Ht-Av, Lt-Et, Ht-Et, Lt-Fc, Ht-Fc), nitrite shock with and without bacterial infection (NO₂-Av, NO₂-Et, NO₂-Fc, NO₂) and a control group. The results showed that only the Ht-Av (20%), Lt-Fc (35%) and nitrite shock treatments (15-100%) exhibited mortality after the experimental setup. Clinical signs differed between thermal and nitrite shock treatments but did not differ among nitrite shock groups. These findings indicate that A. veronii and F. columnare cause disease in eels only under thermal shock conditions, while E. tarda contributes to increased mortality when juvenile eels are exposed to nitrite shock.