The intraoral tactile reception and its interaction with the gustatory system in fish

Abstract

The oral cavity in mammals and humans is a zone where tactile senses are considered to be basic and fre� quently evoked [1]. However, the intraoral tactile reception in fish has been poorly investigated. It is sug� gested that the food texture is a complex combination of mechanical characteristics, including hardness, plasticity, and firmness of the object. Its viscosity and fluidity, roughness of the surface, etc., along with taste properties, can be decisive for fish when swallowing or rejecting food objects [2, 3]. Data that can confirm this suggestion are scanty, and most of them are qualitative and demonstrate a selective consumption of food items with low hardness by fish [4–9]. The depen� dence of consumption on the texture properties of food items has been poorly studied, and the character of this dependence when both tactile and gustatory receptors in the oral cavity of fish are stimulated simultaneously is unknown. However, precisely this multisensory assessment of the food completes com� plex feeding behavior and regulates the feeding in fish and other animals. The interaction of tactile and gus� tatory systems occurs at any level from the periphery to brain centers [10], and the information provided by these sensory systems is mutually complimentary [11]. The aim of this study was to estimate the effect of the texture of the food object on its attractiveness for fish and the possibility of its modification by adding of taste substances. For the first time it has been demon� strated that the increase in the mechanical hardness of food results in the decrease of its consumption by fish. This dependence is more expressed when food items consumed by fish have a strong taste. The results testify to the participation of both tactile and gustatory intraoral contact sensory systems in the regulation of food consumption in fish. The role of each sensory system is determined by mechanic and chemosensory (gustatory) characteristics of the food object. The experiments were conducted in 13 individuals of carp with lengths of 12.4 cm and body weight of 21.3 g. We placed the fish, one by one, in aquaria (10 L) and then introduced experimental pellets of 4 mm in length and 1.35 mm in diameter to fish. The pellets were cut out from agar gel of 1, 2, 3, 4 and 5% concen� trations. All pellets had red colour by the adding of dye Ponceau 4R (5 µM) to the gel. In the trials the control p <