Abstract
The need for improved aquaculture productivity has led to widespread pressure to introduce the Genetically Improved Farmed Tilapia (GIFT) strains of Nile tilapia (Oreochromis niloticus) into Africa. However, the physical and regulatory infrastructures for preventing the escape of farmed stocks into wild populations and ecosystems are generally lacking. This study characterized the genetic background of O. niloticus being farmed in Ghana and assessed the genetic effects of aquaculture on wild populations. We characterized O. niloticus collected in 2017 using mitochondrial and microsatellite DNA markers from 140 farmed individuals sampled from five major aquaculture facilities on the Volta Lake, and from 72 individuals sampled from the wild in the Lower Volta River downstream of the lake and the Black Volta tributary upstream of the lake. Our results revealed that two farms were culturing non-native O. niloticus stocks, which were distinct from the native Akosombo strain. The non-native tilapia stocks were identical to several GIFT strains, some of which showed introgression of mitochondrial DNA from non-native Oreochromis mossambicus. We also found that the non-native cultured tilapias have escaped into the wild and interbred with local populations, and also observed potentially admixed individuals on some farms. Our results highlight aquaculture as a vector in the spread of invasive non-native species and strains, and underscore the importance of genetic baseline studies to guide conservation planning for wild populations.
Highlights
The Nile tilapia (Oreochromis niloticus) is one of the most widely introduced fish species outside its native range
This study was conducted in order to: (1) Characterize the genetic background of Nile tilapia O. niloticus being farmed in Ghana using sequence variation at the mitochondrial displacement loop (D-loop) and COI regions and amplification of fragment size variation at ten nuclear microsatellite loci, and (2) assess the genetic effects of aquaculture on wild populations using selected farms operating on the Volta Lake in Ghana
This study was conducted in order to characterize the genetic background of Nile tilapia O. niloticus strains being farmed in Ghana, and to assess the genetic effects of aquaculture on wild populations using selected farms operating on the Volta Lake in Ghana
Summary
The Nile tilapia (Oreochromis niloticus) is one of the most widely introduced fish species outside its native range. From Africa and the Middle East, the Nile tilapia has been introduced to most tropical and sub-tropical regions, primarily for aquaculture purposes [1,2]. Many genetically improved tilapia strains have been developed for aquaculture production, including the Genetically Improved Farmed Tilapia (GIFT), Genetically Enhanced Tilapia-Excellent (GET-EXCEL), Brackishwater Enhanced Saline Tilapia (BEST), Genetically Male Tilapia (GMT), Chitralada, YY-male, Cold-tolerant tilapia (COLD), and Florida red strains [3]. The Genetically Improved Farmed Tilapia (GIFT) strain of O. niloticus was founded using parental stocks from eight countries, including four African countries (Egypt, Ghana, Kenya, and Senegal), and developed by 15 generations of selective breeding [4]. Due to the risk of contamination of locally adapted native genetic stocks, the WorldFish The subsequent distribution of the GIFT strain for commercial farming in Asia revolutionized tilapia aquaculture in Asia and contributed to increased global tilapia production [4,5,6,7,8].
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