Genetics

Risks Associated with Using Methyl Testosterone in Tilapia Farming

Despite widespread use of the androgen 17α-Methyl Testosterone (MT) in tilapia farming, the implications of tilapia hormone treatment in relation to human health and the environment have not been well articulated to the fish trade, or the general public. The purpose of this white paper is (a) to explain clearly why MT is widely used by the producers of farmed tilapia; and (b) to demonstrate why there are no risks to consumers, and no known risks to producers or the environment, provided the recommended best practices for MT use in aquaculture are followed. These best practices are described, so that tilapia dealers can ensure that their suppliers are taking the necessary steps to protect consumers, fish farm workers and the environment.

Click HERE to download and read the complete paper.

Introduction to the Genetics of Tilapia

By Thomas D. Kocher
Department of Zoology & Program in Genetics
University of New Hampshire
Basic tilapia genetics
We are at an early stage in the genetic domestication of tilapia. During the approximately 40 year history of intensive culture, the genetic resources of tilapia have been poorly managed. The genetic problems now manifesting themselves are of several kinds. First is the loss of pure species through mismanagement of interspecific hybridization (McAndrew 1993), a technique which has been used to produce all-male fry which have a higher growth rate in production systems (Hickling 1960; Hulata et al.1983). One popular commercial strain is thought to contain genes from as many as four species (McAndrew et al. 1988). A second problem is high levels of inbreeding depression. Primary collections of wild broodstock frequently consisted of a small number of individuals. These were serially distributed, so that genetic problems have been passed from country to country, and farm to farm. Eknath et al. (1993) compared four strains farmed in the Philippines with four strains newly isolated from wild populations in Africa. The best performing strains were those most recently isolated from nature, consistent with the idea that domesticated strains suffer from inbreeding depression (Tave and Smitherman 1980; Hulata et al. 1986; Teichert-Coddington and Smitherman 1988). A survey of 18 microsatellite DNA markers in several commercial strains found some strains with heterozygosities less than 10% of that found in wild strains (Kocher et al., unpubl.). In addition to inbreeding, it is likely that negative selection for growth rate has occurred during the propagation of many stocks. Finally, there is evidence for contamination of genetically improved strains by introgression from feral species (Macaranas et al. 1986).
In recent years attention has focused on a single [...]