Anatomy and histology of the olfactory organ of the javelin goby Synechogobius hasta (Gobiiformes, Gobiidae)

Abstract

The olfactory organ of Synechogobius hasta was investigated with a focus on its environmental adaptation, using stereo microscopy and light microscopy. This research revealed the following anatomical and histological characteristics: (i) tubular anterior nostril, (ii) one longitudinal lamella, (iii) two accessory nasal sacs, (iv) lymphatic cells in the lower part of the sensory epithelium, (v) four to five villi of olfactory receptor neurons, (vi) abundant blood capillaries beneath the sensory epithelium, and (vii) rod-shaped erythrocytes. These findings hint that the olfactory organ of S. hasta has anatomical and histological adaptations to intertidal pools that undergo periodic hypoxia and increased temperature under stagnant water conditions due to the tidal cycle.

Keywords: Synechogobius; Anatomy; Erythrocyte; Histology olfactory organ; Nasal sac; Nostril; Tidal pool.

Fig. 1

The photograph of Synechogobius hasta (A) and its intertidal habitat (B, N35°01’53” E126°08’59”). The bar indicates 10 cm

Fig. 2

Schematic diagram of the lateral and front view of the head of Synechogobius hasta and the external (left photograph) and internal (right) structure of its olfactory organ. The blue arrow indicates water flowing. AN, anterior nostril; ENS, ethmoidal nasal sac; L, lamellae; LNS, lacrimal nasal sac; OC, olfactory chamber; PN, posterior nostril

Fig. 3

Histological characteristics of the olfactory epithelium of Synechogobius hasta, stained with hematoxylin and eosin (A, C, D), Masson’s trichrome (B). (A, B), the olfactory epithelium composed of sensory and non-sensory regions; (C) the sensory epithelium showing olfactory receptor neurons, supporting cells, basal cells, and lymphatic cells, and numerous blood capillaries and fibroblast cells in the connective tissue; (D) the non-sensory epithelium showing stratified epithelial cells, mucous cells, lymphatic cells, and unidentified cells. BC, basal cell; CT, connective tissue; FBC, fibroblast cell; L, lamella; LC, lymphatic cell; MC, mucous cell; NSE, non-sensory epithelium; OC, olfactory chamber; ORN, olfactory receptor neuron; SE, sensory epithelium; SEC, stratified epithelial cell; SC, supporting cells; unidentified cells, UC; yellow asterisk, blood capillary. The bars indicate 200 μm in A and B, 50 μm in C and D, respectively

Fig. 4

Scanning electron micrographs showing the olfactory lamella (A) and the surface of the sensory epithelium (B and C) of Synechogobius hasta. Bars indicate 500 μm in A, 5 μm in B, 500 nm in C. Arrow, olfactory receptor neuron’s dendrite; Arrowhead, olfactory receptor neuron; L, lamella