Differential expression of olfactory genes in Atlantic salmon (Salmo salar) during the parr–smolt transformation

Abstract

The anadromous salmon life cycle includes two migratory events, downstream smolt migration and adult homing migration, during which they must navigate with high precision. During homing migration, olfactory cues are used for navigation in coastal and freshwater areas, and studies have suggested that the parr–smolt transformation has a sensitive period for imprinting. Accordingly, we hypothesized that there would be significant changes in gene expression in the olfactory epithelium specifically related to smoltification and sampled olfactory rosettes from hatchery‐reared upper growth modal juvenile Atlantic salmon at 3‐week intervals from January to June, using lower growth modal nonsmolting siblings as controls. A suite of olfactory receptors and receptor‐specific proteins involved in functional aspects of olfaction and peripheral odor memorization was analyzed by qPCR. Gene expression in juveniles was compared with mature adult salmon of the same genetic strain caught in the river Gudenaa. All mRNAs displayed significant variation over time in both modal groups. Furthermore, five receptor genes (olfc13.1, olfc15.1, sorb, ora2, and asor1) and four olfactory‐specific genes (soig, ependymin, gst, and omp2) were differentially regulated between modal groups, suggesting altered olfactory function during smoltification. Several genes were differentially regulated in mature salmon compared with juveniles, suggesting that homing and odor recollection involve a different set of genes than during imprinting. Thyroid hormone receptors thrα and thrβ mRNAs were elevated during smolting, suggesting increased sensitivity to thyroid hormones. Treatment of presmolts with triiodothyronine in vivo and ex vivo had, however, only subtle effects on the investigated olfactory targets, questioning the hypothesis that thyroid hormones directly regulate gene expression in the olfactory epithelium.

Neural pathways of olfactory kin imprinting and kin recognition in zebrafish

“…Based on RT-qPCR or microarrays, the expression of olfactory receptor genes did not differ in imprinted and non-imprinted fish (Gerlach et al 2019). Thus, we concluded that perhaps different from salmons (Dittman et al 2015;Madsen et al 2019), imprinting does not change the frequency or composition of olfactory receptors in the nasal epithelium, but other mechanisms must be responsible. Therefore, we will have a look at the peripheral level of olfactory perception.…”

Environmental enrichment in fish aquaculture: A review of fundamental and practical aspects

“…For example, increased ventilation rate, decreased foraging and swimming activity, increased dashing and dorsal fin erection 176 or even morphological changes 179 are within the effects of exposing fish to chemical cues. These effects should not be taken lightly as many of the most farmed fish species have been characterised in terms of chemical sensing, such as salmonids, 180,181 tilapias, 182‐184 carps, 185 European seabass, 186 gilthead seabream 187 or Senegalese sole 188 …”

“…177,178 For example, increased ventilation rate, decreased foraging and swimming activity, increased dashing and dorsal fin erection 176 or even morphological changes 179 are within the effects of exposing fish to chemical cues. These effects should not be taken lightly as many of the most farmed fish species have been characterised in terms of chemical sensing, such as salmonids, 180,181 tilapias, [182][183][184] carps, 185 European seabass, 186 gilthead seabream 187 or Senegalese sole. 188 In this context, manipulation of odours or other chemical stimulations, whether in the form of olfactory stimuli that are specific or non-specific to an animal's natural habitat, or pheromonal in nature, have been proposed as potential EE for both land animals and captive fish.…”

The Effects of Rearing Environment on Organization of the Olfactory System and Brain of Juvenile Sockeye Salmon, Oncorhynchus nerka

“…Th e lif espa n of vert ebrat e OS Ns is o nly mo nths ( Mac kay-S im and Kitt el 1991 ), as OSNs are exposed and vulnerable to the surrounding enviro nment ( Moul to n 1974 ). In salmo nids, olfacto ry recepto r gene exp ressio n is sensi tive t o c hanges in deve lopm ental an d environm ental cues ( Johnston e et al 2011 ;Bett et al 2018 ;Madsen et al 2019 ). Patterns of OS N plastici ty may, therefo re, be p art ia l ly influence d by olfacto ry experience ( Wilso n et al 2004 ).…”