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Research Project: Pathogen Characterization, Host Immune Response and Development of Strategies to Reduce Losses to Disease in Aquaculture

Location: Aquatic Animal Health Research

Title: Controlled laboratory challenge demonstrates substantial additive genetic variation in resistance to Streptococcus iniae in Nile tilapia

item Lafrentz, Benjamin
item LOZANO, CARLOS - Akvaforsk Genetic Center As
item Shoemaker, Craig
item Garcia, Julio
item Xu, Dehai
item LOVOLL, MARIE - Veso Vikan
item RYE, MORTEN - Akvaforsk Genetic Center As

Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: 12/21/2016
Publication Date: 2/20/2017
Citation: Lafrentz, B.R., Lozano, C.A., Shoemaker, C.A., Garcia, J.C., Xu, D., Lovoll, M., Rye, M. 2017. Controlled laboratory challenge demonstrates substantial additive genetic variation in resistance to Streptococcus iniae in Nile tilapia. In: Aquaculture America 2017 Conference, San Antonio, Texas, February 19-22, 2017. p. 234.

Interpretive Summary:

Technical Abstract: Streptococcus iniae is an etiologic agent of streptococcal disease in tilapia and is one of several Streptococcus spp. that negatively impact worldwide tilapia production. Methods for the prevention and control of S. iniae include vaccines, management strategies, and antibiotics. An alternative and complimentary approach may include selective breeding for increased disease resistance, but the potential for this is unknown in tilapia. Therefore, this study was initiated to phenotype Nile tilapia (Oreochromis niloticus) families for disease resistance to S. iniae and determine heritability estimates. Fish from the third generation of the Spring Genetics Nile tilapia breeding program with nucleus operations in Homestead, Florida, US, were used for this study. A total of 143 full- and half-sib families (avg. 176 g, sd = 50 g) were challenged with S. iniae, and fish were divided into two groups with each containing on average 9 individually PIT tagged fish per family. The challenge was designed with the intent to utilize fish injected with S. iniae (Group 1) as shedder fish to transfer the bacterium to cohabitated fish (Group 2) and determine the mortality of each family by both injection and cohabitation. To accomplish this, tilapia from Group 1 were challenged by intraperitoneal injection with a volume containing 1.15 × 108 cfu S. iniae per fish, and then cohabitated with tilapia from Group 2 in a single 5,550 L tank. Accumulated mortality at the end of the experiment was only 6.4% for fish challenged by cohabitation (Group 2) and was 60% for the fish challenged by injection (Group 1). The results revealed high variation between the mean survivals of the families injected with S. iniae (range from 0% to 100%, CV 69%). The estimated heritability of post-challenge survival in Group 1 was 0.42 on the observed binary scale and 0.58 on the underlying liability scale, derived from fitting a linear animal model and a sire-dam threshold model, respectively. The results demonstrated substantial additive genetic variation in resistance to S. iniae when fish are challenged by injection, and suggest promise in genetic improvement of tilapia for resistance to S. iniae by using selective breeding.