Data from: Parasites and a host's sense of smell: reduced chemosensory performance of fathead minnows (Pimephales promelas) infected with a monogenean parasite

1. Parasites residing within the central nervous system of their hosts have the potential to reduce various components of host performance, but such effects are rarely evaluated.

2. We assessed the olfactory acuity of fathead minnows (Pimephales promelas) infected experimentally with the monogenean Dactylogyrus olfactorius, the adults of which live within the host's olfactory chambers.

3. Olfactory acuity was compared between infected and uninfected hosts by assessing electro-olfactography (EOG) neural responses to chemical stimuli that indicate the presence of food (L-alanine) or the presence of conspecifics (taurocholic acid). We also compared differences in gross morphology of the olfactory epithelium in infected and uninfected minnows.

4. Differences in EOG responses between infected and uninfected minnows to both cue types were non-significant at 30 d post-exposure. By days 60 and 90, coincident with a two times increase in parasite intensity in the olfactory chambers, the EOG responses of infected minnows were 70-90% lower than controls. When infected fish were treated with a parasiticide (Prazipro), olfactory acuity returned to control levels by day 7 post-treatment.

5. The observed reduction in olfactory acuity is best explained by the reduced density of cilia covering the olfactory chambers of infected fish, or by the concomitant increase in the density of mucous cells that cover the olfactory chambers. These morphological changes are likely due to the direct effects of attachment and feeding by individual worms or by indirect effects associated with host responses. Our results show that infection of a commonly occurring monogenean in fathead minnows reduces olfactory acuity. Parasite-induced interference with olfactory performance may reduce a fish's ability to detect, or respond to, chemical cues originating from food, predators, competitors, or mates.

1. 寄生于宿主中枢神经系统（central nervous system）内的寄生虫，可对宿主多项机能表现产生负面影响，但此类效应尚未得到广泛评估。
2. 我们对实验感染单殖吸虫（monogenean）Dactylogyrus olfactorius的黑头呆鱼（Pimephales promelas）的嗅觉敏锐度进行了评估，该寄生虫的成虫寄生于宿主的嗅腔（olfactory chambers）内。
3. 我们通过检测感染与未感染宿主对两类化学刺激的嗅觉电图（electro-olfactography, EOG）神经反应，对比二者的嗅觉敏锐度：两类刺激分别为指示食物存在的L-丙氨酸（L-alanine），以及指示同类存在的牛磺胆酸（taurocholic acid）。此外，我们还对比了感染与未感染黑头呆鱼的嗅上皮（olfactory epithelium）大体形态差异。
4. 暴露后30天，感染与未感染黑头呆鱼对两类化学信号的EOG反应差异无统计学意义。至暴露后60天与90天时，宿主嗅腔内的寄生虫载量较初始提升一倍，此时感染个体的EOG反应较对照组降低70%~90%。对感染个体使用驱虫剂（Prazipro）处理后，其嗅觉敏锐度于处理后第7天恢复至对照组水平。
5. 本研究观测到的嗅觉敏锐度下降，最合理的解释为：感染宿主嗅腔表面覆盖的纤毛密度降低，或是伴随出现的嗅腔表面黏液细胞密度升高。此类形态学变化可能源于单殖吸虫个体附着与摄食带来的直接影响，或是宿主免疫应答介导的间接效应。本研究结果表明，黑头呆鱼感染常见单殖吸虫后，其嗅觉敏锐度会出现下降。寄生虫对嗅觉功能的干扰，可能会削弱鱼类探测食物、天敌、竞争者或配偶释放的化学信号并作出响应的能力。