Heterogeneous exposure to parasites may contribute to host species differentiation. Hosts often harbour multiple parasite species which may interact and thus modify each other’s effects on host fitness. Antagonistic or synergistic interactions between parasites may be detectable as niche segregation within hosts. Consequently, the within-host distribution of different parasite taxa may constitute an important axis of infection variation among host populations and species. We investigated the microhabitat distributions and species interactions of gill parasites (four genera) infecting 14 sympatric cichlid species in Lake Victoria, Tanzania. We found that the two most abundant ectoparasite genera (the monogenean Cichlidogyrus spp. and the copepod Lamproglena monodi) were non-randomly distributed across the host gills and their spatial distribution differed between host species. This may indicate microhabitat selection by the parasites and cryptic differences in the host–parasite interaction among host species. Relationships among ectoparasite genera were synergistic: the abundances of Cichlidogyrus spp. and the copepods L. monodi and Ergasilus lamellifer tended to be positively correlated. In contrast, relationships among morphospecies of Cichlidogyrus were antagonistic: the abundances of morphospecies were negatively correlated. Together with niche overlap, this suggests competition among morphospecies of Cichlidogyrus. We also assessed the reproductive activity of the copepod species (the proportion of individuals carrying egg clutches), as it may be affected by the presence of other parasites and provide another indicator of the species specificity of the host–parasite relationship. Copepod reproductive activity did not differ between host species and was not associated with the presence or abundance of other parasites, suggesting that these are generalist parasites, thriving in all cichlid species examined from Lake Victoria.

寄生虫的异质暴露可能有助于宿主物种分化。宿主通常拥有多种寄生虫物种，它们可能会相互作用，从而改变彼此对宿主健康的影响。寄生虫之间的拮抗或协同相互作用可以作为宿主内的生态位隔离被检测到。因此，不同寄生虫类群的宿主内分布可能构成宿主种群和物种之间感染变异的重要轴。我们调查了感染坦桑尼亚维多利亚湖 14 种同域慈鲷物种的鳃寄生虫（四个属）的微生境分布和物种相互作用。我们发现两个最丰富的外寄生虫属（单系Cichlidogyrus spp. 和桡足类Lamproglena monodi) 非随机分布在寄主鳃中，它们的空间分布在寄主物种之间有所不同。这可能表明寄生虫对微生境的选择以及宿主物种之间宿主-寄生虫相互作用的隐秘差异。外寄生虫属之间的关系是协同的：Cichlidogyrus spp的丰度。桡足类L. monodi和Ergasilus lamellifer趋于正相关。相比之下，Cichlidogyrus形态种之间的关系是拮抗的：形态种的丰度呈负相关。连同生态位重叠，这表明慈鲷形态种之间的竞争. 我们还评估了桡足类物种的繁殖活动（携带卵子的个体比例），因为它可能受到其他寄生虫存在的影响，并提供了宿主-寄生虫关系物种特异性的另一个指标。桡足类繁殖活动在宿主物种之间没有差异，并且与其他寄生虫的存在或丰度无关，这表明这些是通才寄生虫，在维多利亚湖检查的所有慈鲷物种中繁衍生息。