Genetic Diversity in Commercial Danio rerio and Its Implications for Ecotoxicology

The zebrafish ( Danio rerio ) is a widely used aquatic model organism. However, fish from confined groups may experience inbreeding and loss of heterozygosity, which could affect biological responses and research outcomes. Therefore, we aimed to investigate the genetic differences among zebrafish populations from different commercial suppliers and assess their influence on responses to copper exposure. Seven groups of 3-month-old zebrafish were obtained from the major commercial breeders in the Arequipa region, Peru, and coded as zfRS, zfRN, zfHN, zfHV, zfHS, zfDN, and zfCN. Morphometric and morphological analyses were performed on a subsample, while genetic assessments focused on the mitochondrial cytochrome oxidase I (COI) gene, examining phylogeny, haplotypes, and polymorphisms. Additionally, mortality, sublethal effects, and liver histology were evaluated in response to four copper concentrations (ranging from 0.125 to 1.0 mg/L). No evident morphometric or morphological distinctions were observed between groups. On the contrary, COI gene assessment classified the seven groups into two main genetic clades, with the zfRS group being genetically distinct from the others. Two primary origins (Asian and North American) were identified, and moderate haplotype diversity (0.43 ± 0.06) and low nucleotide diversity (0.00137 ± 0.00) were observed. The zfHS and zfRN groups exhibited the highest intra-group variability. Significant differences in lethal and sublethal responses to copper exposure were found, along with distinct forms of histological damage (e.g., steatosis, hemorrhages, fibrosis, and nuclear damage). Notably, the most genetically diverse groups (zfHS and zfRN) exhibited the highest resistance to copper-induced stress. Relying exclusively on fish from commercial breeders with uncontrolled confined populations for ecotoxicology research may lead to biased conclusions, as these factors affect the consistency and reliability of biological responses in laboratory testing. Therefore, the use of fish from potentially long-standing confined groups in research must be avoided.