Effect of Water Temperature on Hematology and Virulence of Aeromonas hydrophila in Hybrid Catfish (Clarias gariepinus Burchell x C. macrocephalus Gunther)

Abstract

Water temperature was set up at 2 levels; high (Ht, 29.5±0.5oC) and low temperature (Lt, 19.5±0.5oC). Experimental catfish body weight and total length were 12.07±1.41 g and 11.57±0.62 cm respectively. Catfish were divided into 4 groups: high temperature with 0.1% sodium chloride (NaCl) (HtWs), high temperature without 0.1% NaCl (HtW/s), low temperature with 0.1% NaCl (LtWs), and low temperature without 0.1% NaCl (LtW/s). Catfish hematocrit (Hct) and clinical chemistry including serum glutamic oxaloacetic transminase (SGOT), serum glutamic pyruvic transaminase (SGPT), alkaline phosphatase (ALP), blood urea nitrogen (BUN), and creatinine (Cr) were measured. The results showed that water temperature, Ht (HtWs and HtW/s) and Lt (LtWs and LtW/s), disturbed homeostasis. The Hct values showed that fish from LtW/s and LtWs group potentially were anemic fish much more than fish from HtWs and HtW/s group. The BUN to Cr ratio reveals that all fish in HtWs and LtWs group were dehydrated when compared to fish in HtW/s and LtW/s group. Ten isolates Aeromonas hydrophila (A. hydrophila)
were intra-peritoneal injection to catfish which exposed to HtW/s and LtW/s. All A. hydrophila were isolated from kidney and liver of sick fresh-water fish in Thailand from 2005 to 2008. The virulence of A. hydrophila to catfish exposed to LtW/s and HtW/s were 100% and 40% respectively. The results demonstrated water temperatures play a
major role to catfish hematology and A. hydrophila virulent levels. The evaluation of blood chemistry parametersprovide a baseline and as a tool in fish health management.