Co-Author: Hanneke van den Dop, Veterinarian at Til-Vet International.

Is 50 years of intensive Methyltestosterone (MT) use finally killing the tilapia industry?

“Tilapia were previously considered to have good disease resistance. While the report and the emergence of TiLV will likely not dent the species’ significance in global aquaculture it is a sign that greater efforts must be made to manage disease risks in tilapia farming. Research now needs to focus on finding solutions for this emerging challenge to the world’s tilapia farms.” (Dr Michael Phillips, Director of Science and Aquaculture, WorldFish, 17 March 2017)

The tilapia industry is affected faster and faster by rampant diseases: Francisella (Costa Rica, 2009), Streptococcus spp. (Worldwide), Tilapia Lake Virus (2017, confirmed in more and more countries and even high risk in importing countries in Europe like The United Kingdom) and most recently (2018) unexplained mortality in Ghana and China. This causes great panic among end consumers – affecting the total industry:

It is well-known since decades that treatment with hormones disrupts the development of the fish’ immune system (Harris and Bird, 2000, Haitham G. Abo-Al-Ela, 2017). It is the latest article of Mr. Abo-El-Ela which gives an excellent overview of the effects of hormones on the immunity of tilapia (Haitham G. Abo-Al-Ela, 2018, Hormones and fish monosex farming: a spotlight on immunity)

Methyltestosterone (MT) is widely used for monosex production in Tilapia. Haitham mentions several severe effects of this hormone on fish’ immunity, ecosystems, histopathology, genotoxicity, abnormal embryonic development and effects on non-target species. Also an effect on the human body cannot be ruled out; especially when considering that there is no regulation for mixing MT through the feed and that feeding this feed is nearly always done with bare hands. Absurd instruction videos can be found on the internet.

The effect on the fish’ health starts with the attack on the first line of defence; i.e. the skin. Mucus of the skin disappears and parasites have free access followed by bacterial and other secondary infections. The below video shows Trichodina parasites attacking hormone sex-reversed fry from a huge hatchery in Colombia (Huila, 2016).

However, it is the genotoxic effect that worries the most (in genetics genotoxicity describes the property of chemical agents that damages the genetic information within a cell causing mutations). It seems that after 50 years of intensive use of MT (and the huge increase in tilapia production) the robustness of tilapia is seriously weakened.

Hatcheries that apply Methyltestosterone treatments to create monosex tilapia batches, suffer very high mortality rates. Mortalities of 75(!) percent before reaching a weight of 3 gram are no exception on larger farms in f.i. Thailand, Colombia, Costa Rica (own observations). It appears that these farmers consider this mortality as “common” and cover these loses by simply increasing the production capacity.

OiE (World Organization of Animal Health) has published their Disease Card on the Tilapia Lake Virus in may 2017 and mentions the significantly lower mortality in genetically produced Tilapia compared with other strains. This is confirmed by recent infection trials with Til-Aqua Natural Male Tilapia.

Haitham (2018): ….. to conduct further studies to find alternatieve more safe ways to ensure all-male aquaculture production such as using YY males…..

Eric Bink is founder and owner of Til-Aqua International, world’s largest producer of YY-males in Oreochromis niloticus L.. Today, after decades of manual selection, their males produce upto 99.7% male offspring and can also be used with local female lines. More information about YY-Technology and their disease-free status, you can find at www.til-aqua.com

Hanneke van den Dop works at Til-Vet International as a veterinarian. She specializes in the well-being of tilapia and regularly provides training in hatchery management, biosecurity and (emerging) tilapia threats