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

Abstract

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.

The paradise fish, an advanced animal model for behavioral genetics and evolutionary developmental biology

“…Given the large number of interesting questions to be tackled, well-established breeding protocols (Rácz et al, 2021) and a highquality reference genome (Fodor et al, 2023), the paradise fish is well on track to become a new, complementary genetic model organism (Matthews & Vosshall, 2020).…”

“…Decades of ethological observations have already created a vast literature about paradise fish behavior, defining the paradise fish ethogram under diverse conditions (Csányi, 1993;Miklósi et al, 1995Miklósi et al, , 1997Rácz et al, 2021). Recent methodological advances, such as the adoption of novel, open-source methods for automated video analysis and pose estimation, such as DeepLabCut, DeepPoseKit or PoseR, will enable high-throughput data analysis, introducing new quantification standards into ethology (Graving et al, 2019;Luxem et al, 2023;Mullen et al, 2023;Nath et al, 2019).…”

“…Adult fish are sexually dimorphic both in their appearance and behavior. Males sport long dorsal, caudal and anal fins, and a bright coloration with vibrant blue and red stripes, while females have rounder bellies and are significantly paler (Rácz et al, 2021). Territorial males also show a higher level of aggression towards conspecifics than females, especially towards other males (Davis et al, 1974).…”

“…Previous work has already described the ethogram of the species, defining several characteristic elements of its complex behavioral repertoir regarding either social or non-social contexts (Csányi, 1993;Csányi et al, 1985aCsányi et al, , 1985bRácz et al, 2021). For example, during aggressive male-male encounters usually a combination of the following behavioral elements can be observed: head-tail display (Figure 3a), head-head display (Figure 3b), parallel swimming, flaring of the gill covers (opercula).…”

“…And indeed, further rigorous experiments supported this observation, demonstrating that the paradise fish is an inherently curious species, with a complex behavioral repertoire. Some elements of this repertoire are directly related to its special physiology and adaptations to its environment, while others derive from the complex social networks these fish can develop in their natural habitats (Csányi, 1993; Rácz et al, 2021; Tate et al, 2017).…”