Additive genetic variation in resistance of Nile tilapia (Oreochromis niloticus) to Francisella orientalis and its genetic (co)variation to both harvest weight and resistance to Streptococcus agalactiae Ib

Authors: Shoemaker, Craig; LOZANO, CARLOS - Benchmark Genetics; Lafrentz, Benjamin; Mumma, Wendy - Paige; VELA-AVITUA, SERGIO - Benchmark Genetics; OSPINA-ARANGO, JOSE FERNANDO - Spring Genetics; YAZDI, M. HOSSEIN - Benchmark Genetics; RYE, MORTON - Benchmark Genetics

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2022
Publication Date: 8/17/2022
Citation: Shoemaker, C.A., Lozano, C.A., Lafrentz, B.R., Mumma, W.P., Vela-Avitua, S., Ospina-Arango, J., Yazdi, M., Rye, M. 2022. Additive genetic variation in resistance of Nile tilapia (Oreochromis niloticus) to Francisella orientalis and its genetic (co)variation to both harvest weight and resistance to Streptococcus agalactiae Ib. Aquaculture. 561:738736. https://doi.org/10.1016/j.aquaculture.2022.738736.
DOI: https://doi.org/10.1016/j.aquaculture.2022.738736

Interpretive Summary: Global tilapia aquaculture is valued at about $11 billion, annually. Francisellosis caused by a gram-negative bacterium (Francisella (F.) orientalis) and streptococcal disease caused by a gram-positive bacterium (Streptococcus (S.) agalactiae Ib) result in billion-dollar losses to the tilapia industry. Collaborative research was undertaken with commercial partners to confirm the potential to selectively breed tilapia for resistance to F. orientalis and to examine the relationship between economically important traits of disease resistance (to francisellosis and streptococcal disease) and growth. Significant additive genetic variation was found for F. orientalis survival across four generations (estimated heritability = 0.31 ± 0.05). Results of assortative mating groups confirmed that genetic gain could be obtained for F. orientalis survival since offspring of fish selected with high estimated breeding values (EBV) exhibited higher F. orientalis survival. The genetic correlation between harvest weight and F. orientalis survival was low and not different from zero. The genetic correlation between F. orientalis survival and S. agalactiae Ib survival was positive but not significantly different from zero (rg= 0.14 ± 0.11; Log-likelihood-ratio test p > 0.05). The genetic correlation between harvest weight and S. agalactiae survival was negative but also not significantly different (rg= - 0.19 ± 0.10; Log-likelihood-ratio test p > 0.05). Lack of significant favorable genetic relationships between economically important traits favors multi-trait selection since selection for growth alone does not improve F. orientalis survival or S. agalactiae survival.

Technical Abstract: An understanding of the genetic relationship between traits of economic importance for a widely cultured species such as Nile tilapia (Oreochromis niloticus) is important, in particular the relationship between disease resistance and growth. Francisellosis results in economic losses for the industry, and we confirmed that Francisellosis resistance is under additive genetic control in our population. Analysing four generations, significant additive genetic variation was found for Francisella (F.) orientalis survival (P<0.001; Log-likelihood-ratio test) with an estimated heritability of h2 = 0.31 ± 0.05 across all generations. The random effect common to full-sibs was also significant, but of lower magnitude (c2 = 0.075 ±0.02) (P<0.001; Log-likelihood-ratio test). Results of assortative mating groups confirmed that genetic gain could be obtained for F. orientalis survival since offspring of fish selected with high estimated breeding values (EBV) exhibited higher F. orientalis survival. The genetic correlation between harvest weight and F. orientalis survival was very low (rg= -0.02 ± 0.13) and not significantly different from zero (Log-likelihood-ratio test p > 0.05). The genetic correlation between F. orientalis survival and S. agalactiae Ib survival was positive but not significantly different from zero (rg= 0.14 ± 0.11; Log-likelihood-ratio test p > 0.05). The genetic correlation between harvest weight and S. agalactiae survival was negative but also not significantly different (rg= - 0.19 ± 0.10; Log-likelihood-ratio test p > 0.05). Lack of significant favourable genetic relationships between economically important traits favours multi-trait selection since selection for growth alone does not improve F. orientalis survival or S. agalactiae survival.