Housing, Husbandry and Welfare of a "Classic" Fish Model, the Paradise Fish (Macropodus opercularis)

Simple Summary Paradise fish (Macropodus opercularis) has been a favored subject of behavioral research during the last decades of the 20th century. Lately, however, with a massively expanding genetic toolkit and a well annotated, fully sequenced genome, zebrafish (Danio rerio) became a central model of recent behavioral research. But, as the zebrafish behavioral repertoire is less complex than that of the paradise fish, the focus on zebrafish is a compromise. With the advent of novel methodologies, we think it is time to bring back paradise fish and develop it into a modern model of behavioral and evolutionary developmental biology (evo-devo) studies. The first step is to define the housing and husbandry conditions that can make a paradise fish a relevant and trustworthy model. Here, we define the relevant welfare parameters for keeping a healthy population of paradise fish and provide a detailed description of our recent experience in raising and successfully breeding this species under laboratory conditions. Thanks to its small size, external fertilization and fecundity, over the past four decades, zebrafish (Danio rerio) has become the dominant fish model species in biological and biomedical research. Multiple lines of evidence, however, suggest that the reliance on only a handful of genetic model organisms is problematic, as their unique evolutionary histories makes them less than ideal to study biological questions unrelated to their historically contingent adaptations. Therefore, a need has emerged to develop novel model species, better suited for studying particular problems. The paradise fish (Macropodus opercularis) has a much more complex behavioral repertoire than zebrafish and has been a favored model animal in ethological research during the last decades of the previous century. We believe that with currently available, easily adaptable genetic toolkits, this species could be easily developed into a popular model of behavioral genetics. Despite its earlier popularity, however, the description of a detailed housing and husbandry protocol for this species is still missing from scientific literature. We present here a detailed description of how to raise and breed paradise fish successfully under laboratory conditions, and also discuss some of the challenges we faced while creating a stable breeding population for this species in our facility.