Editorial: Application of fishes as biological models in genetic studies

During the 1930s and 40s, the findings of great proponents of genetics and evolution such as Mendel, Darwin, Wallace, Fisher, Haldane, Wright, Dobzhansky, Mayr, and others were brought together to form the neo-Darwinian synthesis (Mayr, 2004). In addition, in the 40s genetics started its molecular revolution, which, driven by sequencing technology, gave rise to the late 70's genomics era. It took approximately 100 years to formulate the theoretical foundations of genetics to understand how information is transmitted to the next generations. Now, less than 45 years after the beginning of the genomic era, it is possible to identify complete genomes in less than a week, as evidenced during the COVID-19 pandemic (Virological.org, 2020 1 ).The comparative use of in vivo models, such as mice, rats, zebrafish, and fruit flies, have been fundamental for the advance of medicine and biological research. Among animals, fishes are between the most relevant groups in genetic studies, due to their diversity and plasticity. Although fish studies played a role in applying and corroborating to Mendel's findings in the first decades of the 19th century, these studies contributed little to the development of classical genetics. However, fish studies have been of great importance for the development of modern molecular genetics and other "omics" sciences.Due to this increase in genomic knowledge, several fish species have become an important biological model around the world. For example, zebrafish are already being used as avatars of human patients in personalized medicine as part of clinical trials in search of better treatments (Usai et al., 2020). Other examples are the studies for usage of tilapia islets to treat diabetes (Wright et al., 2014) and tilapia skin for healing of burn lesions (Costa et al., 2019;Dias et al., 2020). Also, fish can be used for the study of genes and genomes, epigenetics, and genetic expression, as it is presented by the studies of this research topic. The acknowledgement of the importance of fishes in scientific research would certainly not be possible without studies like these. Together they provided a glimpse of the Application of Fishes as Biological Models in Genetic Studies around the globe.The broad diversity of the studies submitted in this topic, represent and highlight the multifaceted character of applications of fishes in genetic studies today, as exposed in the sub-topics cited below.Austrolebias genus, a group of annual killifish, has been proposed by García et al., as an excellent model for evolutionary genomic processes due to its large genome size -probably associated to transposable elements -besides high chromosome instability, occurrence of natural hybridization between sister species, and burst speciation events.Another suggestion of fish as an animal model is Astyanax altiparanae, as reviewed by Yasui et al. This specie, popularly known as yellowtrail tetra, can be an alternative for studies directed to neotropical fishes. The A. altiparanae has been considered the most advanced fish regarding fish biotechnology within the Neotropical region. It has already described artificial fertilization, germ cell transplantation, chromosome set manipulation, and other technologies with applications in aquaculture and conservation of genetic resources. Also, Beck et al. suggests that threespine stickleback (Gasterosteus aculeatus) can be a model for human diseases related to mitochondrial DNA. In this study, it was provided the first complete coding region analysis of the two mitotypes of G. aculeatus, which mitogenomic divergence can be exceeded to other mammal models, including humans. Still, Dohi and Matsui reinforce in a brief research report, that small fish can be used to prospect studies of human aging since genes involved in human pathways and diseases are shared among other fish species, such as zebrafish, medaka, and the turquoise killifish (Nothobranchius furzeri).Genetic and molecular studies are also being performed for fish species to clarify evolutionary aspects of the species. Additionally, it was found that genetic diversity was significantly higher in migratory rather than in landlocked populations, presenting higher differentiation among lakes than estuaries.Using cytogenetic studies in Gymnotus carapo, Machado et al. subsidized the hypothesis that is not a single widespread species, but a group of cryptic species. Chromosome painting has shown more complex rearrangements, a high number of repetitive DNA sites, and extensive karyotype reorganization in comparison to previous studies by classical cytogenetics.In-depth knowledge of the fish genome can bring new alternatives to overcome old barriers. Merlano et al. presented the production of a recombinant cystatin-B (rCYST-B) from red piranha Pigcentrus nattereri to control bacterial growth in aquaculture. This protein showed bacteriostatic action, inhibiting Escherichia coli and Bacillus subtilis growth, suggesting a potential biotechnological use.For Nile tilapia, two studies in this topic brought new clarifications in the production and aquaculture of this specie using a molecular approach. Martins et al. evaluated the expression of genes responsible for appetite regulation, metabolic and physiological changes, and osmoregulation in tilapia exposed to different salinity concentrations. It was found that the gene modulation generated by the salinity increase may have contributed to a decrease in weight gain and growth rate, as an increase in oxidative damage in blood cells. Also in Nile tilapia, Chen et al. demonstrate that individuals with higher growth have significantly higher total protein, total triglyceride, total cholesterol, and high-and low-density lipoproteins, but significantly lower glucose, when compared with individuals in the lower growth group. Transcriptomics has also been evaluated, showing more than one thousand genes differentially expressed between the higher and lower growth