Gross morphology, histology, and ultrastructure of the olfactory rosette of a critically endangered indicator species, the Delta Smelt, Hypomesus transpacificus

Abstract

The Delta Smelt (Hypomesus transpacificus) is a small, semi-anadromous fish native to the San Francisco Bay-Delta Estuary and has been declared as critically endangered. Their olfactory biology, in particular, is poorly understood and a basic description of their sensory anatomy is needed to advance our understanding of the sensory ecology of species to inform conservation efforts to manage and protect them. We provide a description of the gross morphology, histological, immunohistochemical, and ultrastructural features of the olfactory rosette in this fish and discuss some of the functional implications in relation to olfactory ability. We show that Delta Smelt have a multilamellar olfactory rosette with allometric growth. Calretinin immunohistochemistry revealed a diffuse distribution of olfactory receptor neurons within the epithelium. Ciliated, microvillous and crypt neurons were clearly identified using morphological and immunohistochemical features. The olfactory neurons were supported by robust ciliated and secretory sustentacular cells. Although the sense of smell has been overlooked in Delta Smelt, we conclude that the olfactory epithelium has many characteristics of macrosmatic fish. With this study, we provide a foundation for future research into the sensory ecology of this imperiled fish.

Ultramicroscopic organization of the exterior olfactory organ in Anguilla vulgaris in relation to its spawning migration

“…They have a superficially positioned, ovoid-shaped soma with an apical crypt bearing microvilli and cilia. Crypt cells also showed up in many other teleost species with the same uniform morphology ( Triana-Garcia et al ., 2021 ) They were also detected even in elasmobranch Rajiformes ( Ferrando et al ., 2007 ). Crypt cells are much less abundant than ciliated receptor cells or microvillous receptor cells, if they represent any fish species ( Cheung et al ., 2021 ; Al-Zahaby et al ., 2023 ).…”

“…The first ones are bipolar neurons, with an apical end with variable appearance, and number of dendritic protrusions, and a basal axon end. Therefore, they are categorized into four cell types: ciliated, microvillous, rod-tipped, and crypt cells ( Triana-Garcia et al ., 2021 ), in addition to the Kappe neuron ( Ahuja et al ., 2014 ) and the pear-shaped neurons ( Wakisaka et al ., 2017 ), but both were not represented in eels. These receptor cells have nearly similar morphologies and ultrastructures but are variously present in different fish species, from Cyclostomata (Lampreys), Elasmobranchs, and Osteichthyes to teleosts ( Zeiske et al ., 1992 ).…”

“…The olfactory supporting cells are nonsensory cells, so they are not labeled as sensory neurons ( Triana-Garcia et al ., 2021 ). They occupy most of the olfactory epithelium, comparable to neural glial cells, so they surround the different receptor cell bodies and dendrites.…”

Comparative Morphology and Morphometry of the Olfactory Organ of the Six Korean Spined Loaches, Genus Iksookimia, as a New Taxonomic Key

“…Because such chemical reception is conducted by sensory cells on the lamellae of the rosette inside the olfactory chamber, teleost species shows species-specific structure in olfactory rosette based on their habitat environment and ecology (Cox, 2008). Teleosts show considerable morphological variability regarding the shape and location of the olfactory organ, number and arrangement of the olfactory lamellae, the distribution of sensory and non-sensory epithelium in relation to the diverse environments that the fish inhabit (Hara, 1986;Zeiske et al, 1992;Kasumyan, 2004;Ghosh and Chakrabarti, 2016;Ghosh, 2019;Triana-Garcia et al, 2021). In particular, although the number of olfactory lamellae (LN) tends to increase with growth and age, it remains constant upon teleost maturity (Hara, 1994).…”