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Genomar develops streptococcosis-resistant tilapia

After five years of extensive research and breeding trials, Genomar introduces new disease-resistant strains of tilapia.

The Fish Site
by The Fish Site
1 February 2021, at 8:00am

After more than five years of R&D and systematic breeding work, GenoMar introduces new disease-resistant products addressing one of the most economically important diseases in Nile tilapia. Repeated laboratory tests and a field trial have demonstrated an increased survivability of approximately 30 percent for the tilapia selected for streptococcosis resistance. For the farmers, tilapia with genetic resistance will lead to a more sustainable and profitable production.

tilapia swimming in a tank
Using disease-resistant tilapia could improve welfare outcomes and profit margins

Selection based on genetic information

GenoMar Genetics, who manages the breeding and distribution of tilapia genetics under the brands GenoMar, Aquabel and AquaAmerica initiated research back in 2015 with the aim of exploring genetic variation to this deadly disease. Since 2016 resistance to streptococcosis has been routinely included in the selection index of the breeding programmes for Nile tilapia. Similar research to increase the survivability in other major diseases like columnaris and francisellosis is ongoing.

"Our geneticists can now accurately determine the genetic component in the DNA of tilapia that codes for increased survival towards streptococcosis, and we used this knowledge to optimise the selection decisions leading to animals with higher streptococcosis resistance without negatively affecting other important traits," says Rajesh Joshi, Senior Researcher in GenoMar Genetics.

Works from day one

The advantage of genetic resistance is that it protects the fish throughout the whole tilapia farming cycle from birth to harvest and does not have application cost.

"This is a particularly important innovation for the control of streptococcosis in the tilapia aquaculture industry which struggles with adoption of vaccination and use of antibiotics. We have managed to prove that genetic resistance is an efficacious and cost-effective new tool against streptococcosis," says Alejandro Tola Alvarez, CEO in GenoMar Genetics.

30 percent increased survivability for streptococcosis resistant fish

To validate the effectiveness of the genetic selection, laboratory tests and field trials were performed to compare the survival between the selected and non-selected tilapia fish. The relative survival after using two different routes of infection (IP and Cohab) with the bacterium Streptococcus agalactiae were 42 percent and 25 percent respectively, for the selected fish. Further, another experiment was performed in Malaysia under field conditions to see whether improved survival in laboratory challenges also applies in commercial farms or not. Results showed increased survival by around 30 percent for the selected fish (see Figure 1).

Figure 1. Daily, cumulative mortality in a field trial with tilapia selected for streptococcosis resistance and non-selected tilapia, 135 days post-transfer to grow out. Both groups consisting of around 2000 fish each, were mixed, individually tagged, and raised together in cages at a commercial farm in Malaysia.
Figure 1. Daily, cumulative mortality in a field trial with tilapia selected for streptococcosis resistance and non-selected tilapia, 135 days post-transfer to grow out. Both groups consisting of around 2000 fish each, were mixed, individually tagged, and raised together in cages at a commercial farm in Malaysia.

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