Location: Aquatic Animal Health ResearchTitle: Resistance of Nile tilapia (Oreochromis niloticus) to Streptococcus iniae and S. agalactiae Ib is heritable but not correlated Author
|Lozano, Carlos - Akvaforsk Genetic Center As|
|Soto, Esteban - University Of California, Davis|
|Rye, Morton - Akvaforsk Genetic Center As|
Submitted to: Annual Eastern Fish Health Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 3/25/2018
Publication Date: 4/9/2018
Citation: Lafrentz, B.R., Shoemaker, C.A., Lozano, C.A., Garcia, J.C., Soto, E., Xu, D., Beck, B.H., Rye, M. 2018. Resistance of Nile tilapia (Oreochromis niloticus) to Streptococcus iniae and S. agalactiae Ib is heritable but not correlated. [abstract] Annual Eastern Fish Health Workshop. p. 35.
Technical Abstract: Tilapia (Oreochromis sp.) are an important source of protein with an economic value approaching US $8 billion yearly. Streptococcal disease, caused by Streptococcus iniae and S. agalactiae (both Gram positive bacteria), is an emerging or re-emerging disease negatively affecting tilapia aquaculture worldwide. Because of the difficulty controlling these pathogens in tilapia production, selective breeding for resistance S. iniae and S. agalactiae is a potential tool to limit the impact of streptococcal disease. The objectives were: 1) to verify additive genetic variation in resistance of Nile tilapia (Oreochromis niloticus) to S. iniae; 2) to determine if realized genetic gain in resistance and/or susceptibility to S. iniae is possible following positive assortative mating based on estimated breeding values (EBV); and 3) to determine if resistance to S. iniae and S. agalactiae Ib is genetically correlated. A total of 144 full and paternal half-sib families were challenged intraperitoneally with S. iniae using PIT tagged fish in a common tank. For S. agalactiae challenge, 130 full and paternal half-sib families were intramuscularly injected. Cumulative mortality was 46% for S. iniae and 68% for S. agalactiae. There was a high additive genetic component found for survival in fish injected with S. iniae (estimated heritability 0.52 ± 0.12) validating our previous results. The estimated heritability for S. agalactiae was 0.38 ± 0.11 based on the univariate linear animal model. Positive assortative mating further demonstrated resistance to S. iniae was heritable with mean survival of 88% (range 60 – 100%) for families produced on high EBV (S. iniae resistant parents) and mean survival of only 10% (range 0 -42%) for families produced using low EBV (S. iniae susceptible parents). No genetic correlation (rg = -0.3 ± 0.19) was noted amongst resistance to S. iniae and S. agalactiae Ib. Selective breeding of tilapia to improve survival to Streptococcus sp. will require knowledge of the pathogen(s) prevalent in the region so that custom genetic material may be formulated for individual farms.