The persistence of most coastal marine species depends on larvae finding suitable adult habitat at the end of an offshore dispersive stage that can last weeks or months. We tested the effects that ocean acidification from elevated levels of atmospheric carbon dioxide (CO2) could have on the ability of larvae to detect olfactory cues from adult habitats. Larval clownfish reared in control seawater (pH 8.15) discriminated between a range of cues that could help them locate reef habitat and suitable settlement sites. This discriminatory ability was disrupted when larvae were reared in conditions simulating CO2-induced ocean acidification. Larvae became strongly attracted to olfactory stimuli they normally avoided when reared at levels of ocean pH that could occur ca. 2100 (pH 7.8) and they no longer responded to any olfactory cues when reared at pH levels (pH 7.6) that might be attained later next century on a business-as-usual carbon-dioxide emissions trajectory. If acidification continues unabated, the impairment of sensory ability will reduce population sustainability of many marine species, with potentially profound consequences for marine diversity.climate change ͉ larval sensory mechanisms ͉ population connectivity ͉ population replenishment O cean acidification caused by the uptake of additional carbon dioxide (CO 2 ) at the ocean surface is now recognized as a serious threat to marine ecosystems (1-4). At least 30% of the anthropogenic CO 2 released into the atmosphere in the past 200 years has been absorbed by the oceans, causing ocean pH to decline at a rate Ϸ100 times faster than at any time in the past 650,000 years (1, 4). Global ocean pH is estimated to have dropped by 0.1 units since preindustrial times and is projected to fall another 0.3-0.4 units by 2100 because of existing and future CO 2 emissions (1, 5-6). Considerable research effort has focused on predicting the impact that reduced carbonate-ion saturation states that accompany ocean acidification will have on calcifying marine organisms, particularly corals and other invertebrates that precipitate aragonite skeletons (2-3, 6). However, the effects that ocean acidification will have on other marine organisms, including fishes, remain almost completely unknown, especially for conditions of atmospheric carbon dioxide and seawater pH that could occur in the near future (4, 7-9).The persistence of most coastal marine species depends on the ability of larvae to locate suitable settlement habitat at the end of a pelagic stage that can last weeks or months. Accumulating evidence for reef fishes suggests that both reef sounds (10) and olfactory cues (11-13) are used by larvae to locate reefs. The olfactory organs of many reef fishes are well-developed by the end of the larval phase (14-15), and it has recently been shown that larvae of some species can discriminate the smell of water from their natal reef compared with water from other reefs (13), which provides a mechanism to explain high levels of selfrecruitment in some reef fish populations (16)(...

The fish gustatory system provides the final sensory evaluation in the feeding process. Unlike other vertebrates, the gustatory system in fish may be divided into two distinct subsystems, oral and extraoral, both of them mediating behavioural responses to food items brought in contact with the fish. The abundance of taste buds is another peculiarity of the fish gustatory system. For many years, morphological and electrophysiological techniques dominated the studies of the fish gustatory system, and systematic investigations of fish taste preferences have only been performed during the last 10 years. In the present review, basic principles in the taste preferences of fish are formulated. Categories or types of taste substances are defined in accordance with their effects on fish feeding behaviour and further mediation by the oral or extraoral taste systems (incitants, suppressants, stimulants, deterrents, enhancers and indifferent substances). Information on taste preferences to different types of substances including classical taste substances, free amino acids, betaine, nucleotides, nucleosides, amines, sugars and other hydrocarbons, organic acids, alcohols and aldehydes, and their mixtures, is summarised. The threshold concentrations for taste substances are discussed, and the relationship between fish taste preferences with fish systematic position and fish ecology is evaluated. Fish taste preferences are highly species‐specific, and the differences among fish species are apparent when comparing the width and composition of spectra for both the stimulants and the deterrents. What is evident is that there is a strong similarity in the taste preferences between geographically isolated fish populations of the same species, and that taste preferences are similar in males and females, although at the individual level, it may vary dramatically among conspecifics. What is noteworthy is that taste responses are more stable and invariable for highly palatable substances than for substances with a low level of palatability. Taste preferences as a function of pH is analysed. There is a good correspondence between development of the gustatory system in fish ontogeny and its ability to discriminate taste properties of food items. There is also a correspondence between oral and extraoral taste preferences for a given species; however, there is no correlation between smell and taste preferences. Taste preferences in fish show low plasticity (in relation to the diet), appear to be determined genetically and seem to be patroclinous. Fish feeding motivation and various environmental factors like water temperature and pollutants such as heavy metals and low pH water may shift fish taste preferences. Comparisons between bioassay and electrophysiological data show that palatability is not synonymous with excitability in the gustatory system. The chemical nature of stimulants and deterrents in various hydrobionts is outlined. The significance of basic knowledge in fish taste preferences for aquaculture and fisheries is emp...

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We observed the surface of the anterior part of the nasal septum of living subjects using an endoscope. In approximately 13% of 1842 patients without pathology of the septum, the vomeronasal pit was clearly observed on each side of the septum, and in 26% it was observed only on one side. The remaining observations indicated either the presence of putative pits or no visible evidence of a pit. However, repetitive observations on 764 subjects depicted changes over time, from nothing visible to well-defined pits and vice versa. Based on 130 subjects observed at least four times, we estimate that approximately 73% of the population exhibits at least one clearly defined pit on some days. By computer tomography, the vomeronasal cavities were located at the base of the most anterior part of the nasal septum. Histological studies indicated that the vomeronasal cavities consisted of a pit generally connected to a duct extending in a posterior direction under the nasal mucosa. Many glands were present around the duct, which contained mucus. There was no sign of the pumping elements found in other mammalian species. Most cells in the vomeronasal epithelium expressed keratin, a protein not expressed by olfactory neurons. Vomeronasal epithelial cells were not stained by an antibody against the olfactory marker protein, a protein expressed in vomeronasal receptor neurons of other mammals. Moreover, an antibody against protein S100, expressed in Schwann cells, failed to reveal the existence of vomeronasal nerve bundles that would indicate a neural connection with the brain. Positive staining was obtained with the same antibodies on specimens of human olfactory epithelium. The lack of neurons and vomeronasal nerve bundles, together with the results of other studies, suggests that the vomeronasal epithelium, unlike in other mammals, is not a sensory organ in adult humans.

Monopolar DC-recordings were made simultaneously from two positions on the olfactory bulb of chars (Salmo alpinus L.) and graylings (Thymallus thymallu L.) using bile acids and amino acids as olfactory stimulants. The bile acids induced responses with characteristic spatial differences from those of the amino acids. The distribution of responses to bile acids indicated a neuronal activity in the medial part of the bulb. In contrast, amino acids elicit responses in the lateral part of the bulb. Taurine conjugated bile acids were up to 1 000 times more potent as olfactory stimuli than methionine. The results suggest that olfactory receptors are of two types, one responding to bile acids, the other to amino acids. 3 -alpha-hydroxysteroids are released from the fish into the water in quantities that suffice for detection by their olfactory system. The odorant potency of the bile acids, their evolutionary history and variability, together with their renowned adherent properties made them interesting candidates for specific signals in the acquatic environment.