Host Mussels Research Articles

Greft İmplantasyonunda İnci Kesesi Oluşumunun Dört Midye Türünde (Unionidae) Karşılaştırılması

Bu çalışmada, inci kesesi oluşumu için en uygun manto bölümü ve en iyi konakçı midye türü tespit edilmeye çalışılmıştır. Araştırma için dört farklı midye türünden oluşan (Unio terminalis, Potamida littoralis, Leguminaia wheatleyi ve Anodonta pseudodopsis) toplam 400 adet midye kullanılmıştır. Midyelerin ortalama dorso-ventral uzunlukları sırasıyla; 7,89±0,25; 7,28±0,38; 10,68±0,27 ve 11,14±0,34 cm‘dir. Manto dokusunun pallial kenarından 3×3 mm büyüklüğünde elde edilen manto doku dilimleri, greft olarak kullanılmıştır. Biri manto boşluğu diğeri manto dokusu üzerinde açılan kesitler olmak üzere, greft implantasyonu için iki farklı manto bölümü tercih edilmiştir. Üç aylık inci kültürü sonunda, manto boşluğu bölümü en iyi greft implant bölgesi olarak belirlenmiştir. U. terminalis, yaşama oranı ve inci kesesi oluşumu bakımından en başarılı tür olarak tespit edilmiştir. P. littoralis‘in ikinci başarılı tür olduğu, L. wheatleyi‘nin ise türler arasında en düşük sonuç veren tür olduğu belirlenmiştir. Bu araştırma, inci üretiminde önemli görülen sedef kalınlığı ve kalitesi konusunda, uzun süreli inci üretim çalışmaları için bir rehber niteliği taşımaktadır.

The Effect of Two Selected Strains of Mussels as Donor or Host on the Color of Cultivated Pearls

Color is an important indicator in evaluating the quality of pearls. Despite the well-developed technology of pearl production, evidence for what determines pearl color is largely absent. In the present study, a 2 × 2 complete double-row implantation experiment was conducted using the purple and white strains of mussels of Hyriopsis cumingii in three different aquaculture environments. The effect of purple and white strains of mussels on seedless pearl color was analyzed using a mixed linear model. The results showed that the effect of the donor mussel, which provides the mantle tissues, on seedless pearl color was significant (P < 0.001), whereas neither the strain of the host mussel nor the aquaculture environment had a significant influence on pearl color. The estimated values for the effect of the donor mussel on pearl color parameters CIE L*, a*, and b* were –9.35, 2.49, and 3.33, respectively. This study provides direct evidence that the color of a seedless pearl is mainly determined by the donor mussel, and both the host mussel and the aquaculture environment have a negligible role in the determination of pearl color.

Influence of Himasthla elongata (Trematoda: Echinostomatidae) metacercariae on heart rate in blue mussels (Mytilus edulis)

Whether metacercariae of the digenean Himasthla elongata (Himasthlidae) are harmful to their secondary intermediate hosts, the blue mussel, Mytilus edulis, is a disputable question. To shed light on this issue, we performed field monitoring of the heart rate (HR) in mussels infected with H. elongata over a period of 1.5 years. We observed a significant rise in HR in infected mussels, but only 1 year after infection and at temperatures of 15–17 °C. HR variance also grew sharply in infected mussels within the same temperature range. We also detected a decreased ability of infected mussels to compensate for the rise in the environment temperature. Finally, growth rate in the infected mussels was slower compared to the control group. We provide evidence for measurable pathogenic effects caused by H. elongata metacercariae in their secondary intermediate mussel hosts.

Comparative transcriptomic analysis illuminates the host-symbiont interactions in the deep-sea mussel Bathymodiolus platifrons

Bathymodiolus platifrons adapted the chemosynthetic ecosystems, both cold seeps and hydrothermal vents, by harbouring gill symbionts. To survive these extreme and volatile ecological niches, the host mussel must be able to strictly regulate the symbionts in response to the environmental fluctuations. However, despite the research efforts, the molecular mechanisms governing host-symbiont interaction in deep-sea mussels are still largely unknown. Here, using the model deep-sea mussel Bathymodiolus plantiforns, we profiled the transcriptomic dynamic of the mussel gill during the loss and re-contact with symbionts with RNA-seq technology. The analysis of DEGs between untreated and symbiont loss samples revealed that metabolic and cellular organizational changes in the gill were associated with increased ribosomal activities, ubiquitin-proteasome systems, and autophagy. Meanwhile, the DE immune genes suggest that the host recognizes and interacts with endosymbionts through the pattern recognizing receptors, especially the Toll-like receptors. In addition, the DEGs between symbionts treated and environmental bacteria treated samples shed light on the mechanism of symbiont recognition. The symbionts treatment not only partially reversed the transcriptomic changes caused by symbiont-loss, but also suppressed host immune system which might facilitate the symbionts’ entrance and survival in the host bacteriocytes. All together, these results suggest that the host-symbiont system in B. platifrons is tightly regulated but also with plasticity to fit environmental fluctuations.

Rhodeus amarus(Bloch, 1782): a new potential threat forMargaritifera auricularia(Spengler, 1793) (Unionoida, Margaritiferidae)

AbstractRhodeus amarus is a cyprinid fish that spawns in the mantle cavity of freshwater mussels, resulting in a fitness cost to the host mussel. Rhodeus amarus is expanding its geographic range in...

Ecological correlates and phylogenetic signal of host use in North American unionid mussels

Mussels in the order Unionoida comprise ∼75% of the world’s freshwater bivalve species and are free-living apart from a brief larval stage that parasitizes fish. We investigated the relationships among species of North American unionid mussels and their known host fishes from a macroevolutionary perspective to test whether and how ecological and evolutionary factors correlate with patterns of host use. A subset of 69 mussel species was chosen based on data availability regarding their fish host repertoires, phylogenetic relationships, and ecology. Despite the brevity of their parasitic life stages, the mussels conformed to the right-skewed distribution of host specificity typical of parasitic taxa, in which most species are specialists and a few are generalists. Phylogenetic least squares regression models identified affinity for low-gradient and riffle habitats, and colonization of post-glacial watersheds as the best predictors for the number of fish host species per mussel. However, the second-best model identified citation number as a predictor of the number of hosts, implying that many mussel–host interactions still remain to be identified. A Multiple Regression Mantel test was performed to identify factors associated with the proportion of hosts shared between pairs of mussel species. Range overlap, citations, genetic distance, and similarity in host infection strategy were significantly correlated with the proportion of hosts shared, yet total variation as explained by the best model was low (R2 = 0.14). There was evidence of a topological association between mussels and their hosts (P = 0.001) and a significant phylogenetic signal of host specificity (λ = 0.81, P = 0.003), indicating closely related mussels that overlap in range are more likely to be competing for hosts. Our results provide an initial macroevolutionary framework for studying the evolution of host infection strategies in these mussels but also highlights gaps still remaining in our fundamental ecological knowledge of this endangered clade.

Greater macroinvertebrate diversity and freshwater mussel density in meander margins of an Amazon river

AbstractMeanders are complex aquatic environments exhibiting different flow and sediment characteristics that influence macroinvertebrate distribution. Differences in macroinvertebrate composition, freshwater mussel density (mainly Castalia ambigua Lamarck, 1819) and habitat variables were investigated, using uni‐ and multivariate analyses, in two zones, the margin and thalweg, of the meanders of a 7‐km stretch of a morphologically unaltered tropical alluvial lowland river. Clear differences were found between meander zones, with greater taxonomic and functional diversity of macroinvertebrates and greater freshwater mussel densities in the meander margin. A total of 12 families of macroinvertebrates were exclusive to the meander margin, and macroinvertebrate indicators of zones were Philopotamidae and Leptoceridae (meander margin) and Chironomidae and Elmidae (meander thalweg). In the meander margin, there were no differences in macroinvertebrate abundance, and taxonomic and functional group diversity among areas with low, medium and high mussel density. Macroinvertebrate abundance did not vary between zones, but in both, abundance was associated with lower pH and higher electrical conductivity. Low shear velocity, which stabilises the river bed, high organic matter content and percentage silt in the meander margin were associated with higher taxonomic and functional macroinvertebrate diversity, as well as the presence of freshwater mussels. Natural unaltered meanders are spatially heterogeneous in both habitat and biodiversity and, similar to restored meanders, support greater macroinvertebrate taxonomic and functional diversity, as well as maintain freshwater mussel beds, mainly by stabilising the river bed. The meander margin may also be important for attracting mussel host fish that feed on macroinvertebrates and aid mussel dispersal. Thus, the meander margins, and other similar riparian habitats with low shear velocity, for example, side channels and pools, have potentially high conservation value and should be afforded due protection.

Light and Scanning Electron Microscopic Studies of Unionicola tetrafurcatus (Acari: Unionicolidae) Infecting Four Freshwater Bivalve Species and Histopathological Effect On Its Hosts.

Water mites of the genus Unionicola are the most common symbionts of freshwater bivalves. During the current investigation, a total of 120 live freshwater mussels representing 5 species, Corbicula fluminea (Veneroida), Coelatura aegyptiaca (Unionoidea), Mutela rostrata, and Chambardia rubens (Mutelidae), were collected from 2 localities in Tura (Helwan Governorate) and El Kanater (Qaluobiya Governorate), Egypt. Only 3 of the 4 bivalve species listed are considered freshwater bivalves (members of Unionoidea). Corbicula fluminea belong to the family Cyrenidae within Veneroida. Collected mussels were dissected and examined for the presence of unionicolid mites. It was found that 30.83% (37/120) were infected with a single mite species, Unionicola tetrafurcatus (Unionicolidae). The highest prevalence was observed during the summer with 83.33% (25/30) whereas the least was observed in autumn, i.e., 33.33% (10/30). Mites were recovered from the gills, gonads, and visceral mass of mussel hosts. Gills of host mussels were the primary site of oviposition for Unionicola mites. Smaller bivalves in size had significantly greater numbers of mites than did larger ones in size. Numbers of mites per host species was variable and the highest prevalence level of 83.33% (25/30) was recorded in Cor. fluminea while the lowest one of 16.66% (5/30) was found in Ch. rubens. Morphological and morphometric characterizations of mites revealed some differences between the present species and other related Unionicola. Histopathological responses of host mussels to the eggs, larvae, and cuticular remnants of U. tetrafurcatus were also studied. Therefore, the present study demonstrated that freshwater bivalves have a new host and locality records for infection with U. tetrafurcatus. Future studies are recommended to include advanced molecular characteristics for these mites.

Oviposition behavior and host records for the parasitic midge Trichochilus lacteipennis (Johannsen) (Chironomidae: Orthocladiinae)

Adult female Trichochilus lacteipennis were observed to extrude long strings of eggs (up to 15 cm) in flight over a lake in Maine, USA. Once extruded females dropped to the water surface and released the strings. Larvae of T. lacteipennis are parasitic on Elliptio complanata at this site and probably additional unionid mussel species elsewhere. Based on our dissections of parasitized mussels and previous reports, it appears T. lacteipennis spend all or nearly all of their larval life within their mussel host, with first instars initially free-living inside the mantle. At some point larvae enter the marsupium and complete larval development on a diet of mussel eggs and/or glochidia before pupating within the marsupium.

Trophic relationship between the invasive parasitic copepod Mytilicola orientalis and its native blue mussel (Mytilus edulis) host

Invasive parasites can spill over to new hosts in invaded ecosystems with often unpredictable trophic relationships in the newly arising parasite-host interactions. In European seas, the intestinal copepod Mytilicola orientalis was co-introduced with Pacific oysters (Magallana gigas) and spilled over to native blue mussels (Mytilus edulis), with negative impacts on the condition of infected mussels. However, whether the parasite feeds on host tissue and/or stomach contents is yet unknown. To answer this question, we performed a stable isotope analysis in which we included mussel host tissue and the primary food sources of the mussels, microphytobenthos (MPB) and particulate organic matter (POM). The copepods were slightly enriched in δ15N (mean Δ15N ± s.d.; 1·22 ± 0·58‰) and δ13C (Δ13C 0·25 ± 0·32‰) with respect to their host. Stable isotope mixing models using a range of trophic fractionation factors indicated that host tissue was the main food resource with consistent additional contributions of MPB and POM. These results suggest that the trophic relationship of the invasive copepod with its mussel host is parasitic as well as commensalistic. Stable isotope studies such as this one may be a useful tool to unravel trophic relationships in new parasite-host associations in the course of invasions.

Embryonic development characteristics and host mussel utilization of flat bitterling Acheilognathus rhombeus (Cyprinidae) during winter in Korea

This study aimed to investigate the embryonic development characteristics and host mussel utilization of Acheilognathus rhombeus to determine its adaptations or host utilization for improving survival during winter in the wild; the study was conducted from August 2014 to May 2015. Spawning of A. rhombeus occurred between mid-September and early November, peaking between late September and early October of 2014 when the water temperature was 19–21°C. The embryos of A. rhombeus were first found in early October of 2014 and remained inside the host mussel for 7 months. Development retardation and diapause in embryonic stages (stages C and D) occurred before eye pigmentation and continued until late March of 2015. Subsequently, the embryos resumed development (stage E) when the water temperature increased to about 10 °C. The positions during the development of A. rhombeus embryos in the mussels were mainly present in the farthest suprabranchial cavity and not in the water tube. The embryos were frequently found in the two inner demibranches of the four gills of the mussels regardless of their sex. We assume that embryonic diapause and use of suprabranchial cavity and inner demibranches of the gills of the mussels by A. rhombeus might be the optimal adaptation to maintain high embryonic survival in low water temperature during winter and to avoid interspecific competition.

The role of local adaptation in shaping fish‐mussel coevolution

AbstractThe survival of affiliate (dependent) species in a changing environment is determined by the interactions between the affiliate species and their available hosts. However, the patterns of spatial and temporal changes in host compatibility are often unknown despite host shifts having direct impact on the persistence of local populations. Bivalves of the order Unionida (freshwater mussels) are a functionally important but declining group of affiliate species, which are dependent on freshwater fish to host their parasitic larvae. The role of local adaptations and host fish resistance in shaping freshwater mussel host relationships remains poorly understood.We used an invasive East Asian unionid bivalve,Sinanodonta woodiana, and its potential host fishes to study the mechanisms shaping fish‐mussel coevolution using a combination of laboratory cross‐exposure methods and field‐collected data. We tested whether generalist host use ofS. woodianais pertinent to native host species, with special attention to bitterling fishes (Cyprinidae: Acheilognathinae) that are characterised by a mutual association with freshwater mussels. We also tested whether the pattern of the parasite–host association varies temporally (between areas of ancient and recent sympatry) and spatially (at a sub‐basin level in its native range).Results revealed the ability ofS. woodianato widely exploit non‐bitterling host fishes at a global scale. In contrast, the ability ofS. woodianato exploit closely associated bitterling fishes was low in its native range (with ancient sympatry). In areas of recent sympatry (non‐nativeS. woodianarange in Europe),S. woodianaglochidia were demonstrated to readily parasitise local, evolutionarily naive bitterling species at high density.The results of a population‐level experiment with three native populations ofS. woodianaand rose bitterling,Rhodeus ocellatus, from various sub‐basins of the River Yangtze confirmed that mussel populations vary in their compatibility with particular host populations. However, there was no evidence of population‐specific adaptive coevolution.This study provides the first evidence for a role of fish counter‐adaptations against freshwater mussel glochidia, and documents the importance of population‐level variation in shaping compatibility between glochidia and their host fishes. This outcome can inform predictions on the impact of biotic homogenisation on endangered affiliate species in general and freshwater mussels in particular.

Local adaptation studies and conservation: Parasite–host interactions between the endangered freshwater mussel Unio crassus and its host fish

Abstract Parasite–host interactions can involve strong reciprocal selection pressure, and may lead to locally adapted specializations. The highly threatened unionoid mussels are temporary parasites on fish, but local adaptation has not yet been investigated for many species. Patterns of local adaptation of one of Europe's most threatened unionoids, the thick‐shelled river mussel (Unio crassus) were investigated. Eurasian minnows (Phoxinus phoxinus) from two rivers (separate drainage areas) were cross‐infested in the laboratory with sympatric and allopatric mussel larvae, while bullheads (Cottus gobio), inhabiting only one of the rivers, were infested with sympatric or allopatric mussel larvae. Larval encystment, juvenile mussel excystment and survival were measured. For one river, but not the other, juvenile excystment from P. phoxinus was highest when infested with sympatric mussels. The opposite pattern was found for C. gobio in this river, where juvenile excystment and post‐parasitic juvenile survival from allopatric C. gobio were highest. The results thus cannot confirm local adaptation of U. crassus to P. phoxinus in the study rivers, as excystment was not consistently higher in all sympatric mussel–host combinations, whereas there were potential maladaptive signs of U. crassus in relation to C. gobio. There was no loss of encysted larvae 3 days after infestation until juvenile excystment. Most juveniles were excysted between 17 and 29 days after infestation, and the numbers of excysted juveniles increased with fish size. The results have implications for parasite–host ecology and conservation management with regard to unionoid propagation and re‐introduction. This includes the need to (1) test suitability and adaptation patterns between U. crassus and multiple host fish species, (2) evaluate the suitability of certain unionoids and host fish strains after more than 3 days, and (3) determine whether large fish produce more juvenile mussels than smaller fish.

Geographic variation in host fish use and larval metamorphosis for the endangered dwarf wedgemussel

Abstract Host fishes play a crucial role in survival and dispersal of freshwater mussels (Unionoida), particularly rare unionids at conservation risk. Intraspecific variation in host use is not well understood for many mussels, including the endangered dwarf wedgemussel (Alasmidonta heterodon) in the USA. Host suitability of 33 fish species for dwarf wedgemussel glochidia (larvae) from the Delaware and Connecticut river basins was tested in laboratory experiments over 9 years. Relative suitability of three different populations of a single host fish, the tessellated darter (Etheostoma olmstedi), from locations in the Connecticut, Delaware, and Susquehanna river basins, was also tested. Connecticut River basin A. heterodon metamorphosed into juvenile mussels on tessellated darter, slimy sculpin (Cottus cognatus), and Atlantic salmon (Salmo salar) parr. Delaware River basin mussels metamorphosed using these three species, as well as brown trout (Salmo trutta), banded killifish (Fundulus diaphanus), mottled sculpin (Cottus bairdii), striped bass (Morone saxatilis), and shield darter (Percina peltata). Atlantic salmon, striped bass, and sculpins were highly effective hosts, frequently generating 5+ juveniles per fish (JPF) and metamorphosis success (MS; proportion of attaching larvae that successfully metamorphose) ≥ 0.4, and producing juveniles in repeated trials. In experiments on tessellated darters, mean JPF and MS values decreased as isolation between the mussel source (Connecticut River) and each fish source increased; mean JPF = 10.45, 6.85, 4.14, and mean MS = 0.50, 0.41, and 0.34 in Connecticut, Delaware, and Susquehanna river darters, respectively. Host suitability of individual darters was highly variable (JPF = 2–11; MS = 0.20–1.0). The results show that mussel–host fish compatibility in A. heterodon differs among Atlantic coastal rivers, and suggest that hosts including anadromous Atlantic salmon and striped bass may help sustain A. heterodon in parts of its range. Continued examination of host use variation, migratory host roles, and mussel–fish interactions in the wild is critical in conservation of A. heterodon and other vulnerable mussel species.

Avoidance of host resistance in the oviposition-site preferences of rose bitterling

A contemporary outcome of dynamic host–parasite coevolution can be driven by the adaptation of a parasite to exploit its hosts at the population and species levels (parasite specialisation) or by local host adaptations leading to greater host resistance to sympatric parasite populations (host resistance). We tested the predominance of these two scenarios using cross-infection experiments with two geographically distant populations of the rose bitterling, Rhodeus ocellatus, a fish brood parasite of freshwater mussels, and four populations of their mussel hosts (two Anodonta woodiana and two Unio douglasiae populations) with varying degrees of geographic sympatry and local coexistence. Our data support predictions for host resistance at the species level but no effect of local coexistence between specific populations. Rhodeus ocellatus showed a preference for allopatric host populations, irrespective of host species. Host mussel response, in terms of ejection of R. ocellatus eggs, was stronger in the more widespread and abundant host species (A. woodiana) and this response tended to be higher in sympatric populations. These outcomes provide support for the importance of host resistance in bitterling oviposition-site decisions, demonstrating that host choice by R. ocellatus is adaptive by minimizing egg ejections. These findings imply that R. ocellatus, and potentially other bitterling species, may benefit from exploiting novel hosts, which may not possess appropriate adaptive responses to parasitism.

Genomic Evidence that Methanotrophic Endosymbionts Likely Provide Deep-Sea Bathymodiolus Mussels with a Sterol Intermediate in Cholesterol Biosynthesis.

Sterols are key cyclic triterpenoid lipid components of eukaryotic cellular membranes, which are synthesized through complex multi-enzyme pathways. Similar to most animals, Bathymodiolus mussels, which inhabit deep-sea chemosynthetic ecosystems and harbor methanotrophic and/or thiotrophic bacterial endosymbionts, possess cholesterol as their main sterol. Based on the stable carbon isotope analyses, it has been suggested that host Bathymodiolus mussels synthesize cholesterol using a sterol intermediate derived from the methanotrophic endosymbionts. To test this hypothesis, we sequenced the genome of the methanotrophic endosymbiont in Bathymodiolus platifrons. The genome sequence data demonstrated that the endosymbiont potentially generates up to 4,4-dimethyl-cholesta-8,14,24-trienol, a sterol intermediate in cholesterol biosynthesis, from methane. In addition, transcripts for a subset of the enzymes of the biosynthetic pathway to cholesterol downstream from a sterol intermediate derived from methanotroph endosymbionts were detected in our transcriptome data for B. platifrons. These findings suggest that this mussel can de novo synthesize cholesterol from methane in cooperation with the symbionts. By in situ hybridization analyses, we showed that genes associated with cholesterol biosynthesis from both host and endosymbionts were expressed exclusively in the gill epithelial bacteriocytes containing endosymbionts. Thus, cholesterol production is probably localized within these specialized cells of the gill. Considering that the host mussel cannot de novo synthesize cholesterol and depends largely on endosymbionts for nutrition, the capacity of endosymbionts to synthesize sterols may be important in establishing symbiont–host relationships in these chemosynthetic mussels.

Does the symbiotic scale-worm feed on the host mussel in deep-sea vent fields?

The scale-worm Branchipolynoe pettiboneae is frequently found in the mantle cavity of Bathymodiolus mussels living in hydrothermal vents and seeps around Japan. To investigate its feeding habits and symbiotic relationship with the host mussels, we determined the stable nitrogen isotopic composition of glutamic acid and phenylalanine for representative scale-worms including a symbiotic juvenile and a symbiotic adult, both with their host mussels, and a free-living adult, collected from hydrothermal vents of the Hatoma Knoll (~1532 m in depth) in the Okinawa Trough, Japan. The isotopic data suggested the feeding habits that Bathymodiolus platifrons is a major source of amino acids for symbiotic adult scale-worm but not for free-living adult and symbiotic juvenile scale-worms.

Freshwater nucleated pearl quality is influenced by host mussel growth traits in Hyriopsis cumingii

Freshwater nucleated pearl quality is influenced by host mussel growth traits in <i>Hyriopsis cumingii</i>

Distribution of unionid freshwater mussels and host fishes in Texas. A study of broad-scale spatial patterns across basins and a strong climate gradient

Unionid freshwater mussels are a threatened fauna, and understanding their distribution is essential to aid and promote conservation efforts. Therefore, we (1) compared patterns of species richness and endemism of Texas mussel and fish species, as mussels depend on fish for their reproduction and dispersal; (2) examined how distribution and community composition of mussels and fishes varies across river basins; and (3) how much variation in mussel community composition could be explained by the distribution of potential host fish, river basin (as a spatial component), ecoregion (as proxy for large-scale environmental differences), and flow variability. Mussel and fish community compositions in rivers differed significantly between river basins with an east-to-west gradient of decreasing species richness following the transition from sub-humid to arid climate. River basin explained 25% of the variation in mussel community composition, and potential host fish presence explained 20%. The total variation explained by both variables was 34%, as part of the variation in host fish presence (11.5%) was spatially structured by differences in river basins. Flow variability explained an additional 14% of the variation in mussel community composition, and ecoregion an additional 9% compared with river basin alone. Locations of significantly higher mussel species richness and/or endemism were present in rivers from all regions of Texas. These locations should be protected, especially as human population continues to expand and urbanize in these regions. A better understanding of mussel–host fish relationships and the impact of flow variation on the distribution of mussels will be needed to inform conservation efforts.

A delayed effect of the aquatic parasite Margaritifera laevis on the growth of the salmonid host fish Oncorhynchus masou masou

Parasitic species often have detrimental effects on host growth and survival. The larvae of the genus Margaritifera (Bivalvia), called glochidia, are specialist parasites of salmonid fishes. Previous studies have reported negligible influences of the parasite on their salmonid hosts at natural infection levels. However, those studies focused mainly on their instantaneous effects (i.e., during the parasitic period). Given the time lag between physiological and somatic responses to pathogen infections, the effect of glochidial infection may become clearer during the post-parasitic period. Here, we examined whether the effect of glochidial infections of Margaritifera laevis on its salmonid host Oncorhynchus masou masou would emerge during the post-parasitic period. We performed a controlled aquarium experiment and monitored fish growth at two time intervals (i.e., parasitic and post-parasitic periods) to test this hypothesis. Consistent with previous observations, the effects of glochidial infection were unclear in the middle of the experiment (day 50; parasitic period). However, even with a natural glochidial load (48 glochidia per fish), we found a significant reduction in growth rates of infected fish in the extended period of the experiment (day 70; post-parasitic period). Our results suggest that examining only instantaneous effects may provide misleading conclusions about mussel–host relationships.