Investigating interspecific hybridisation in ornamental fishes

Manuscript abstract:

Biosecurity agencies dealing with the trade in ornamental fishes have a responsibility to accurately identify the exotic organisms crossing their borders. Molecular methods such as DNA barcoding have been proposed as tools to assist in this process. However, hybrid fishes present in the ornamental aquaculture industry represent a potential problem; standard techniques such as DNA barcoding using mitochondrial genes are known to be inappropriate and potentially misleading in situations where this interspecific hybridisation has occurred. One potential solution is with the addition of genetic data from a nuclear gene. Standardised nuclear barcoding genes have, however, received little attention. The aim of this study is to assess a selection of nuclear genes using genomic resources, and investigate whether a chosen locus can: (1) detect the presence of a hybrid using sequence heterozygosity; and (2) estimate the maternal and paternal species when combined with mtDNA. The nuclear rhodopsin gene (RHO) was chosen as a potential candidate, being relatively variable among species. An experiment using laboratory-bred control hybrids Danio spp.) indicates that sequence heterozygosity can show hybridisation, and that parentage can be elucidated from the nuclear and mitochondrial data. However, when tested upon putative hybrid fishes collected from the aquarium trade, results were mixed, suggesting further work is required before a universal technique can be proposed.