Comparative Endocrinology and Integrative Biology Group, Centre for Marine Sciences, University of Algarve, Campus of Gambelas, Building 7, 8005-139 Faro, Portugal.
J Exp Biol. 2024 Feb 1;227(3). doi: 10.1242/jeb.246448. Epub 2024 Feb 7.
The olfactory epithelium of fish is - of necessity - in intimate contact with the surrounding water. In euryhaline fish, movement from seawater to freshwater (and vice versa) exposes the epithelium to massive changes in salinity and ionic concentrations. How does the olfactory system function in the face of such changes? The current study compared olfactory sensitivity in seawater- (35‰) and brackish water-adapted seabass (5‰) using extracellular multi-unit recording from the olfactory nerve. Seawater-adapted bass had higher olfactory sensitivity to amino acid odorants when delivered in seawater than in freshwater. Conversely, brackish water-adapted bass had largely similar sensitivities to the same odorants when delivered in seawater or freshwater, although sensitivity was still slightly higher in seawater. The olfactory system of seawater-adapted bass was sensitive to decreases in external [Ca2+], whereas brackish water-adapted bass responded to increases in [Ca2+]; both seawater- and brackish water-adapted bass responded to increases in external [Na+] but the sensitivity was markedly higher in brackish water-adapted bass. In seawater-adapted bass, olfactory sensitivity to l-alanine depended on external Ca2+ ions, but not Na+; brackish water-adapted bass did respond to l-alanine in the absence of Ca2+, albeit with lower sensitivity, whereas sensitivity was unaffected by removal of Na+ ions. A possible adaptation of the olfactory epithelium was the higher number of mucous cells in brackish water-adapted bass. The olfactory system of seabass is able to adapt to low salinities, but this is not immediate; further studies are needed to identify the processes involved.
鱼类的嗅上皮组织必然与周围的水密切接触。在广盐性鱼类中，从海水到淡水（反之亦然）的移动会使上皮组织暴露在盐度和离子浓度的巨大变化下。在面对这些变化时，嗅觉系统是如何发挥作用的？本研究通过嗅神经的细胞外多单位记录，比较了适应海水（35‰）和半咸水（5‰）的海鲈的嗅觉敏感性。适应海水的鲈鱼在海水中对氨基酸气味的嗅觉敏感性高于在淡水中。相反，适应半咸水的鲈鱼在海水中和淡水中对相同气味的敏感性基本相似，尽管在海水中的敏感性仍然略高。适应海水的鲈鱼的嗅觉系统对外部[Ca2+]的降低敏感，而适应半咸水的鲈鱼则对[Ca2+]的增加敏感；适应海水和半咸水的鲈鱼都对外部[Na+]的增加有反应，但在适应半咸水的鲈鱼中，敏感性明显更高。在适应海水的鲈鱼中，对 l-丙氨酸的嗅觉敏感性取决于外部 Ca2+离子，但不取决于 Na+；适应半咸水的鲈鱼在没有 Ca2+的情况下也能对 l-丙氨酸做出反应，尽管敏感性较低，但去除 Na+离子对敏感性没有影响。嗅上皮组织的一种可能适应是适应半咸水的鲈鱼中有更多的黏液细胞。海鲈的嗅觉系统能够适应低盐度，但这不是立即发生的；需要进一步的研究来确定涉及的过程。
