Among the many negative impacts of invasive species, hybridization with indigenous species has increasingly become recognized as a major issue However, relatively few studies have characterized the phenotypic outcomes of hybridization following biological invasions Here we investigate the genetic and morphological consequences of stocking invasive tilapia species in two water bodies in central Tanzania We sampled individuals from the Mindu Reservoir on the Ruvu river system, and at Kidatu on the Great Ruaha–Rufiji river system We screened individuals at 16 microsatellite loci, and quantified morphology using geometric morphometrics and linear measurements In both the Mindu and Kidatu systems, we identified evidence of hybridization between indigenous Wami tilapia (Oreochromis urolepis) and the introduced Nile tilapia (Oreochromis niloticus) or blue-spotted tilapia (Oreochromis leucostictus) At both sites, purebred individuals could largely be separated using geometric morphometric variables, with hybrids occupying a broad morphospace among the parental species Our data demonstrate that the gene pools and phenotypic identity of the indigenous O urolepis have been severely impacted by the stocking of the invasive species Given the lack of evidence for clear commercial benefits from stocking invasive tilapia species in waters already populated by indigenous congenerics, we suggest further spread of introduced species should be undertaken with considerable caution

/pdf/losing-cichlid-fish-biodiversity-genetic-and-morphological-4lbm2g4aav.pdf

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

Genetic resources of Nile tilapia (Oreochromis niloticus Linnaeus, 1758) in its native range and aquaculture

Five introduced strains of Nile tilapia (Oreochromis niloticus) were tested for growth performance both in fresh- and brackish-water (2 salinity units) environments for 56 days The BIG NIN, GIFT, Chitralada, "Ruvu Farm" and Silver YY strains with initial mean average weight (+/- standard error) of 964 +/- 690 g, 1041 +/- 719 g, 1372 +/- 721 g, 532 +/- 698 g and 953 +/- 711 g, respectively were used Individuals were tagged and pooled in hapas (12 mx85 mx2 m each), aligned into different ponds (20 mx20 m each) Stocking density of 5 fish/m(2) and 350 g/kg crude protein diet were used Overall, the average weight gain for GIFT strain was 75%, 32%, 45% and 865% higher than BIG NIN, Chitralada, "Ruvu Farm" and Silver YY strains, respectively, across both environments All strains performed significantly better (p<005) when reared in brackish-water than their respective counterparts in freshwater, except for the BIG NIN strain The morphometric correlations for all strains in both environments ranged from moderate (050) to strong positive (092) The GIFT strain demonstrated superior growth and genotype by environment interaction was weak and not important to be prioritized in breeding programs

/pdf/growth-performance-of-five-different-strains-of-nile-tilapia-4wbrx655bg.pdf

Growth performance of five different strains of Nile tilapia (Oreochromis niloticus) introduced to Tanzania reared in fresh and brackish waters

Pacu (Piaractus mesopotamicus) is one of the most important Neotropical freshwater fish species produced by aquaculture in South America. This study is the first attempt to inquire about aquaculture stocks in Argentina regarding genetic diversity and structure. Neither genetic characterization nor pedigree records are available for pacu stocks in farms in Argentina. The presence of hybrids in both natural environment (Lower Parana River) and farms has not been evaluated yet at the southern region of pacu distribution. Genetic characterization of pacu broodstocks, corresponding to 8 farms, and wild individuals from four areas at Lower Parana River was performed. Pacu hybrids were not detected neither in wild nor in farm stocks analyzed. In general, similar levels of genetic diversity were observed between cultured and wild fish populations. Global genetic differentiation (Fst = 0.055) indicated a low level of structure and AMOVA showed that genetic variation was mostly within populations. Reduced contemporary effective population size (Ne) was observed, and probably reflects the bottleneck by founder effect in farmed fish populations. Moreover, kinship analysis showed that in fish farms, on average, 43.00% of the individuals were genetically related, whereas in wild population it was 36.40%. We recommend that broodstock management practices, such as using large Ne, single pair mating, precise records, and tagging of brood fish, should be implemented to avoid unintentional mismanagement.

Genetic diversity and structure of the commercially important native fish pacu (Piaractus mesopotamicus) from cultured and wild fish populations: relevance for broodstock management

Whole genome resequencing data enables a targeted SNP panel for conservation and aquaculture of Oreochromis cichlid fishes

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.

/pdf/limited-hybridization-between-introduced-and-critically-469xf87ex6.pdf

Limited hybridization between introduced and critically endangered indigenous tilapia fishes in Northern Tanzania

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Limited hybridization between introduced and critically endangered indigenous tilapia fishes in Northern Tanzania