The presence of a conspecific induces risk‐taking behaviour and enlargement of somata size of dopaminergic neurons in the brain of male medaka fish

Abstract

Boldness and risk‐taking behaviours in animals are important traits to obtain advantages such as habitation, food resources, reproductive success and social dominance. Risk‐taking behaviour is influenced by physiological and environmental conditions; however, whether individual fish become bolder by the presence of conspecifics remains unknown. In this study, a light–dark preference test was conducted using medaka fish (Oryzias latipes) with or without a neighbouring conspecific. It was found that individual medaka male fish preferred a light environment and avoided a dark environment, whereas the display of a neighbouring conspecific enhanced the time the male spent in the dark environment (i.e., this condition encouraged risk‐taking). The blood glucose level increased in fish confined to the dark condition but did not increase in light‐preferring fish and risk‐taking fish. Large somata expressing tyrosine hydroxylase, which is the rate‐limiting enzyme in dopamine synthesis, were detected in the telencephalic and diencephalic brain regions in risk‐taking medaka, whereas large somata were detected in the diencephalic region in medaka confined to the dark condition. These findings indicated that medaka is a good fish model to explore the central roles of dopaminergic neurons in the telencephalon and the diencephalon, which regulate risk‐taking behaviour.

The Use of Sand Substrate Modulates Dominance Behaviour and Brain Gene Expression in a Flatfish Species

“…The imbalance of this gene has been associated with several neurodevelopmental disorders in mammals, such as Parkinson’s and epilepsy [ 43 ], showing the importance of the equilibrium of the expression of this gene in some specific parts of the brain. In addition, the activity and modification of dopaminergic neurons have been associated with behavioural patterns in several fish species such as medaka ( Oryzias latipes) [ 44 ], midshipman ( Porichthys notatus ) [ 45 ] and a cichlid fish ( Astatotilapia burtoni ) [ 26 ]. This gene has been linked to behaviour, such as locomotor activity, at the early stages after hatching [ 46 ].…”

Development of Open-Field Behaviour in the Medaka, Oryzias latipes

“…The medaka, Oryzias latipes , is a teleost species increasingly used in various research fields, including genetic [ 18 , 19 ], biomedical sciences [ 20 ], and neurosciences [ 21 , 22 , 23 ]. A few studies have exploited the use of larval or juvenile medaka [ 24 ], however, to date, the behavioural characterization of medaka during ontogeny has not been conducted.…”

Together is bolder

“…In this issue, Airi Otsuka and colleagues (Otsuka et al . ) exposed medaka fish ( Oryzias latipes ) to a choice between an illuminated or a dark chamber. The fish preferentially chose the illuminated chamber when they were on their own.…”

“…Otsuka et al . () suggest that the presence of a conspefic makes medaka fish bolder as indicated by the lack of physiological stress responses.…”