Introducing the Amphibious Mudskipper Goby as a Unique Model to Evaluate Neuro/Endocrine Regulation of Behaviors Mediated by Buccal Sensation and Corticosteroids

Abstract

Some fish have acquired the ability to breathe air, but these fish can no longer flush their gills effectively when out of water. Hence, they have developed characteristic means for defense against external stressors, including thirst (osmolarity/ions) and toxicity. Amphibious fish, extant air-breathing fish emerged from water, may serve as models to examine physiological responses to these stressors. Some of these fish, including mudskipper gobies such as Periophthalmodon schlosseri, Boleophthalmus boddarti and our Periophthalmus modestus, display distinct adaptational behaviors to these factors compared with fully aquatic fish. In this review, we introduce the mudskipper goby as a unique model to study the behaviors and the neuro/endocrine mechanisms of behavioral responses to the stressors. Our studies have shown that a local sensation of thirst in the buccal cavity—this being induced by dipsogenic hormones—motivates these fish to move to water through a forebrain response. The corticosteroid system, which is responsive to various stressors, also stimulates migration, possibly via the receptors in the brain. We suggest that such fish are an important model to deepen insights into the stress-related neuro/endocrine-behavioral effects.

Behavioural osmoregulation during land invasion in fish: Prandial drinking and wetting of the dry skin

“…Behaviour of each mudskipper in an estuary (35° 60’ N, 139° 55’ E) at low tide was recorded with a video camera (HC-VX985M, Panasonic, Japan) from May to June (e.g., rolling behaviour in S1 Movie [ 13 ]). No permits of the field site access were required because the site is not a sanctuary.…”

“…Their hunting can be observed clearly as a bending of the body followed by biting in the mud [ 12 ]. Migration of mudskippers to a tide pool is frequently observed after eating (see S1 Movie in our previous report [ 13 ]). This implies that buccal sensation of food or drying motivates mudskippers to move to water for drinking.…”

“…Another potential osmoregulatory behaviour is observed on tidal flats: rolling over onto the dorsal surface and subsequent returning to their normal position. This is defined as ‘rolling behaviour’ [ 13 ] and has been suggested to moisten the dorsal skin, which is not keratinized [ 15 ]. However, it is unclear if this behaviour arises from cutaneous drying or other stimuli, such as systemic/blood parameters for osmoregulation.…”