Care and Use of Siamese Fighting Fish (Betta Splendens) for Research

Abstract

Betta splendens, also called Siamese fighting fish or ‘betta,’ are a popular species in the fishkeeping hobby. Native to Southeast Asia, betta have been selectively bred for their fighting ability for hundreds of years, which has resulted in the species’ characteristic male aggression. More recently, betta have been bred for a number of ornamental traits such as coloration, fin morphology, and body size. Betta have unique characteristics and an evolutionary history that make them a useful model for studies in the fields of behavior, endocrinology, neurobiology, genetics, development, and evolution. However, standard laboratory procedures for raising and keeping these fish are not well established, which has limited their use. Here, we briefly review the past and present use of betta in research, with a focus on their utility in behavioral, neurobiological, and evolutionary studies. We then describe effective husbandry practices for maintaining betta as a research colony.

Genetic manipulation of betta fish

“…Animals were maintained according to our standard procedures (Lichak et al, 2022). All animal protocols were approved by the Columbia University Institutional Animal Care and Use Committee.…”

“…The night prior to injections, we set up mating pairs according to published protocols (Lichak et al, 2022). We added each mating pair to a 5 L acrylic tank filled to a height of 10 cm with system water.…”

“…This enables the microinjection of zygotes in a similar manner to methods for genetic manipulation of zebrafish and medaka. Nevertheless, the asynchronous egg fertilization resulting from a protracted mating process that can last many hours, coupled with a short interval between fertilization and cell division, as well as a thick chorion, constitute significant challenges for genetic manipulation (Valentin et al, 2015;Lichak et al, 2022). Although a few studies have successfully utilized these tools, their reported success rates have been low, and none have reported germline transmission (Wang et al, 2021(Wang et al, , 2022Yue et al, 2022).…”

“…Native to Southeast Asia, betta have experienced a long history of domestication and selective breeding beginning at least 400 years ago (Kwon et al, 2022). Due to their morphological and phenotypic diversity, relatively compact genome size (~440 Mb), their ease of growth in the laboratory, and their amenability to behavioral and neurobiological experimentation, betta have become an increasingly popular organism for scientific study (Lichak et al, 2022). The recent publication of high-quality reference genomes of both domesticated and wild betta has allowed for in-depth genetic and genomic analyses of sex determination, phenotypic traits such as pigmentation, fin shape and aggression, and of the evolutionary relationships between Betta species (Fan et al, 2018;Prost et al, 2020;Wang et al, 2021Wang et al, , 2022Kwon et al, 2022;Yue et al, 2022;Zhang et al, 2022).…”

“…Establishing genetic tools in betta will advance their use as a powerful experimental system to study developmental processes and behavioral traits. Genetic manipulation of betta is facilitated by their reproductive biology: Betta fertilize externally and produce clutches of ∼250 eggs, each with a relatively large diameter of 1 mm (Valentin et al, 2015; Lichak et al, 2022). This enables the microinjection of zygotes in a similar manner to methods for genetic manipulation of zebrafish and medaka.…”