Zebrafish (Danio rerio) and medaka fish (Oryzias latipes) are popular vertebrate models for various biology fields. Medaka fish have recently attracted attention in the field of social neuroscience due to some of their unique advantages. First, medaka fish females have an extremely short ovarian cycle (24 h), which allows one to obtain a large number of female individuals of a similar physiological status according to their synchronized reproductive rhythms, facilitating quantitative analysis of female behaviors that are strongly influenced by the ovarian cycle; other experimental models such as mice and zebrafish have a longer ovarian cycle and/or unpredictable ovarian maturation. Second, medaka fish possess the visual ability to recognize conspecifics and make appropriate behavioral choices based on their social relationship. Third, the medaka fish are an established model in the field of molecular genetics (as are zebrafish) and state-of-the-art molecular-genetic methods are available. Here we describe several experimental procedures for behavioral paradigms to quantify medaka social behaviors, which are primarily mediated by visual cues.

Abstract The first mating (sexual) experience leads to the maturation of male mating behavior across species (insects, fish, rodents). Here, we investigated whether the first mating experience leads to maturation of male mating behavior in medaka using repeated mating tests. In “naïve” (sexually inexperienced) males after the first mating experience, the latency to mate with the same female partner was significantly decreased, whereas when the partner was swapped, the latency to mate was not affected. These findings suggest that repeated matings (3 times) enhanced male mating activity for the familiarized female, but not for an unfamiliarized female. In “experienced” (> 7 matings) males, repeated matings (3 times) with the same partner did not influence the latency to mate, suggesting that multiple matings (> 7 times) abolish the mate preference of naïve males. Furthermore, we identified 10 highly and differentially expressed genes after the mating experience in the brains of the post-naïve males, and revealed 3 genes that are required for a functional cascade of the thyroid hormone system. These findings together suggest that the first mating experience abolishes the preference to mate with a familiarized female via neural maturation triggered by thyroid hormone activation in the medaka brain.

Mating experience shapes male mating behavior across species, from insects, fish, and birds, to rodents. Here, we investigated the effect of multiple mating experiences on male mating behavior in "naïve" (defined as sexually inexperienced) male medaka fish. The latency to mate with the same female partner significantly decreased after the second encounter, whereas when the partner was changed, the latency to mate was not decreased. These findings suggest that mating experiences enhanced the mating activity of naïve males for the familiar female, but not for an unfamiliar female. In contrast, the mating experiences of "experienced" (defined as those having mated > 7 times) males with the same partner did not influence their latency to mate. Furthermore, we identified 10 highly and differentially expressed genes in the brains of the naïve males after the mating experience and revealed 3 genes that are required for a functional cascade of the thyroid hormone system. Together, these findings suggest that the mating experience of naïve male medaka fish influences their mating behaviors, with neural changes triggered by thyroid hormone activation in the brain.