Goldfish as an Experimental Model

Abstract

Goldfish have been used as experimental animals in various biological fields due to ease of handling and breeding, which derives from physiological and developmental characteristics. This chapter introduces goldfish characteristic features , focusing on genomic background, in addition to physiological and embryo-logical characteristics. It is known that the phylogenetic relationship between goldfish and related species is ambiguous since interspecies hybrids can easily occur. Moreover, allotetraploidization (genome duplication with species hybridiza-tion) occurred in the common ancestor of goldfish and common carp, according to whole-genome sequencing analyses. This genome duplication event seems to be significant for allowing goldfish to become animals with "easy handling and breeding ," which contributes to their use as ornamental and research animals. On the other hand, the rise of zebrafish molecular developmental genetics might have caused goldfish developmental biology to fade, partially due to the complicated genomic background of goldfish. Although several physiologists and neuroscientists still prefer to use goldfish as their experimental animals, fewer developmental biologists currently choose goldfish over zebrafish as a research model. Taking into account the above goldfish characteristics and current status of research, significant points related to the use of goldfish as a model system for evolutionary developmental biology are summarized, as follows. First, unlike the random mutagenesis-derived zebrafish, domestication-derived goldfish were subject to artificial selection. Second, in comparison with some other domesticated vertebrate species, the observation of embryonic goldfish is quite easy. These two exclusive characteristics of goldfish allow us to investigate how artificial selection and the developmental process are related. This chapter introduces several significant aspects of goldfish biology. The first three sections (Sects. 2.1, 2.2, and 2.3) describe the phylogeny, biogeography, and genomic backgrounds of goldfish, raising problems and issues that have been uncovered by recent studies. The fourth section includes a brief summary of goldfish physiological characteristics and aims to explain why the goldfish has been so often utilized by researchers, especially those in the fields of physiology and neuroscience. Finally, in the last part of the chapter, the goldfish is compared to other model