Polyploids can be defined as organisms with one or more additional chromosome sets with respect to the number most frequently found in nature for a given species. Triploids, organisms with three sets of homologous chromosomes, are found spontaneously in both wild and cultured populations and can be easily induced in many commercially relevant species of fish and shellfish. The major consequence of triploidy is gonadal sterility, which is of advantage in the aquaculture of molluscs since it can result in superior growth. In fish, the induction of triploidy is mainly used to avoid problems associated with sexual maturation such as lower growth rates, increased incidence of diseases and deterioration of the organoleptic properties. Triploidy can also be used to increase the viability of some hybrids, and is regarded as a potential method for the genetic containment of farmed shellfish and fish. This review focuses on some current issues related to the application of induced polyploidy in aquaculture, namely: 1) the artificial induction of polyploidy and the effectiveness of current triploidisation techniques, including the applicability of tetraploidy to generate auto-and allotriploids; 2) the performance capacity of triploids with respect to diploids; 3) the degree and permanence of gonadal sterility in triploids; and 4) the prospects for the potential future generalised use of triploids to avoid the genetic impact of escapees of farmed fish and shellfish on wild populations. Finally, directions for future research on triploids and their implementation are discussed.

Although the unique features of asexual reproduction and hybridization among European spined loaches (genus Cobitis) have recently attracted the attention of conservation biologists, faunists and evolutionary biologists, the research has suffered from uncertain identification of specimens and their genomes because of the extreme morphological similarity of all the species within the hybrid complex. In this article, a Europe-wide study is reported, which was performed on samples collected by several research teams. Several complementary methodologies, such as allozyme analysis, karyotyping, flow cytometry and DNA sequencing allowed us to confirm or reject the existence of all previously reported species and their hybrids as well as to uncover several new hybrid biotypes. The biogeography of all the known biotypes, that is, parental species and hybrid biotypes, has been summarized here and the taxonomic position of two undescribed putative species mentioned in previous publications has been established. New polymerase chain reaction restriction fragment length polymorphism markers for species determination have further been developed and applied, which would allow the unambiguous identification of parental species and their genomes in the known hybrid biotypes within the complex.