Limited hybridization between introduced and Critically Endangered indigenous tilapia fishes in northern Tanzania

Abstract

Hybridization between introduced and indigenous species can lead to loss of unique genetic resources and precipitate extinction. In Tanzania, the Nile tilapia ( Oreochromis niloticus ) and blue-spotted tilapia ( Oreochromis leucostictus ) have been widely introduced to non-native habitats for aquaculture and development of capture fisheries. Here, we aimed to quantify interspecific hybridization between these introduced species and the indigenous species Oreochromis esculentus , Oreochromis jipe and Oreochromis korogwe . In the Pangani basin, several hybrids were observed ( O. niloticus × O. jipe , O. leucostictus × O. jipe , O. niloticus × O. korogwe ), although hybrids were relatively uncommon within samples relative to purebreds. Hybrids between the native O. jipe × O. korogwe were also observed. In the Lake Victoria basin, no evidence of hybrids was found. Analysis of body shape using geometric morphometrics suggested that although purebreds could be discriminated from one another, hybrids could not be readily identified on body and head shape alone. These results provide the first evidence of hybridization between the introduced species and the Critically Endangered O. jipe in Tanzania. Given uncertainty regarding benefits of introduced species over large-bodied indigenous species in aquaculture and capture fisheries, we suggest that future introductions of hybridization-prone species should be carefully evaluated. Electronic supplementary material The online version of this article (10.1007/s10750-018-3572-5) contains supplementary material, which is available to authorized users.

Population Structure and Genetic Diversity of Nile Tilapia (Oreochromis niloticus) Strains Cultured in Tanzania

“…The Kingolwira aquaculture center obtained their broodstock from Lake Victoria. Native species to Lake Victoria are O. esculentus and O. variabilis while O. leucostictus and O. niloticus were introduced in the lake in 1950s (Bradbeer et al, 2018 (Shechonge et al, 2019). As such species available at Karanga station are O. pangani, O. niloticus, O. jipe and probably hybrids of three species.…”

Losing cichlid fish biodiversity: genetic and morphological homogenization of tilapia following colonization by introduced species

“…Samples from the reference species O. niloticus and O. leucostictus were collected from seine nets from Kerenge on the Pangani river, and thus allopatric to the indigenous O. urolepis (Table 1 ). The two species could be separated in the field on the basis of body shape and colour patterning, and at this site no hybridization between O. niloticus and O. leucostictus has been observed (Bradbeer et al 2018 ). Reference (pure) samples of O. urolepis were collected from artisanal fishers at Lugongwe near Utete on the lower Rufiji river (Table 1 ).…”

“…Tanzania is a hotspot for natural diversity of the genus Oreochromis . Here, Nile tilapia is native only to the Lake Tanganyika catchment (Trewavas 1983 ), but has been widely distributed across the country for aquaculture and fishery enhancement (Genner et al 2013 ; Bradbeer et al 2018 ; Shechonge et al 2018 ). It was initially introduced into Lake Victoria in the 1950s (Goudswaard et al 2002 ), where it is now the dominant species in the tilapia fishery with estimated landings of 36,000 tonnes per annum in 2011 (Mkumbo and Marshall 2015 ).…”

Preface: advances in cichlid research III: behavior, ecology, and evolutionary biology

“…In this issue, Shechonge et al (2019) report unexpectedly broad distributions of the invasive Nile tilapia (Oreochromis niloticus) and blue-spotted tilapia (Oreochromis leucostictus) in Tanzania and clarify the distributions of native species. To quantify the extent of hybridization among invasive and indigenous oreochromines, Bradbeer et al (2019) studied Oreochromis communities in the Lake Victoria and Pangani catchments of northern Tanzania using microsatellites and geometric morphometrics. They found that hybrids were relatively rare at their study sites, compared to purebreds, implying that assortative mating dominates in these habitats.…”