Genetic variation of gross gill pathology and survival of Atlantic salmon (Salmo salar L.) during natural amoebic gill disease challenge

• Published in: Aquaculture
• Main Authors: Taylor, RS, Muller, WJ, Kube, PD, Elliott, NG
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier Science Bv 2009
• Subjects: Agricultural and Veterinary Sciences; Fisheries Sciences; Fish Pests and Diseases; Atlantic salmon; Salmo salar
• Online Access: https://doi.org/10.1016/j.aquaculture.2009.06.007; http://ecite.utas.edu.au/60959

Survival in an experimental disease challenge test or to natural disease challenge is utilised by aquaculturebreeding programs as the selection trait for disease resistance. However, these trials are expensive and do notoffer the ability to retest animals. The aim of this study was therefore to estimate genetic parameters forresistance to amoebic gill disease (AGD) measured by a categorical scale of gross gill signs (gill score) andsurvival in a field challenge in order to establish whether gill score provides adequate measurement ofgenetic variation for AGD resistance compared to an AGD challenge survival. A total of 1504 Atlantic salmonsmolt, representing 140 full-sib families, was transferred to a marine site in SE Tasmania. The gills wereassessed by gill score prior to freshwater bathing on the first two rounds of infection, and then the diseasewas allowed to develop until mortalities began. Gill score was reassessed after 50 days and mortality wasallowed to continue until it had reached a plateau at 100 days. The overall survival rate was 32.3% but variedfrom 0% to 69% between families. Estimated narrow sense heritability for AGD resistance assessed by gillscore varied between 0.23 and 0.48 over the three rounds of infection. Heritability of AGD survival challengewas 0.40 to 0.49 on the observed scale using binary and longitudinal measures. Gill score and survivalshowed a weak (−0.19) to strong (−0.96) negative genetic correlation which improved when assessedcloser to the survival challenge. Estimated genetic gains by selection of the top one hundred estimatedbreeding values for gill score indicated that up to 82% of the expected gain in survival can be achieved whencompared to estimated gain by selection upon survival (days to death), thus minimising selection costs andimproving fish welfare whilst allowing repeat measures to be made. The results show that genetic variationof gill score at the early onset of losses closely compares with survival results if the disease is allowed toprogress without subsequent freshwater bathing. Gill score may therefore be utilised as a nondestructive andrepeatable selection trait for breeding Atlantic salmon with greater resistance to AGD. 2009 Elsevier B.V. All rights reserved.