Aquaculture America 2021

August 11 - 14, 2021

San Antonio, Texas

ASSESSMENT OF BURBOT Lota lota maculosa IMMUNE RESPONSES FOLLOWING EXPERIMENTAL INFECTION WITH AEROMONAS SPP.

Timothy J. Bruce*, Luke P. Oliver, Jie Ma, Evan M. Jones, Brent M. Vuglar,  and  Kenneth  D. Cain
 
Department of Fish and Wildlife Science s
875 Perimeter Dr. MS1136
University of Idaho
Moscow, ID, 83844-1136
tbruce@uidaho.edu
 

Burbot ( Lota lota maculosa ),  also known as freshwater cod, have shown strong potential as a new aquaculture species in the western United States . Previous b urbot research at the Cain Fish Health Lab (University of Idaho ) has  found that this fish species is relatively refractory to pathogens present in rainbow trout production systems, such as  F. psychrophilum and  F. columnare ,  potentially providing an opportunity for polyculture in existing salmonid production systems. However, it has been found that burbot are susceptible to  infection with pathogenic Aeromonas sp , which cause Motile Aeromonas Septicemia  (MAS)  in many fish species.  As such, two recent trials were conducted to assess the virulence of  novel  Aeromonas  sp.  isolates, including  A. hydrophila .  In Trial A,  triplicate tanks of 25 fish per tank  (mean weight of 40g)  were challenged with a known virulent  Aeromonas  sp. isolate (A141), along with a newly  recovered  IR034  isolate at approximately 1 x 108 CFU mL-1 in a 100 µl IP-injection. Mock controls were also challenged using culture media ( tryptic soy broth).  Endpoint cumulative percent mortality  (CPM)  at 21 days post-challenge (dpc )  was 49.3± 22.0% for A141 and 4.0±0 .0% for  the less virulent  IR034. A similar trial was conducted with 55.0  g burbot, incorporating another recent isolate, IR004 (8 x 107 CFU mL-1) , along with a previously reported  (in warmwater species)  virulent strain of  A. hydrophila (ALG-15-097 ; 3 x 107 CFU mL-1). Both isolates were  found to be virulent, displaying a CPM of 85.3±6.1% for the IR004 and 97.3±4.6 % for the ALG-15-097 at 21 dpc. Through the initial infection period (0h, 48h and 120 h post-challenge) spleen and kidney samples were collected  from three fish per tank for  immune  gene expression analyses to monitor changes from the onset of infection. Additionally, phagocytic capacity of head kidney-derived leukocytes was assessed using flow cytometry.  Trial results indicate that burbot are susceptible an array of different  Aeromonas sp. isolates , including  A. hydrophila .  Based on the challenge outcomes , both A141 and IR004 will be used as candidate isolates to develop a killed vaccine for MAS infections and examine the vaccination response in this unique fish species.