Pearl Mussel Research Articles

Discovery of a freshwater pearl mussel population from the Kushereka River, White Sea drainage, Northern European Russia

In this paper we present the results of our field survey in the Kushereka River and preliminary data concerning the size structure, age composition, and population density of the freshwater pearl mussel M. margaritifera in the studied sites.

Resilience of Juvenile Freshwater Pearl Mussels to ThermalStress.

Climate change poses a significant threat to freshwater ecosystems by causing increases of average water temperatures, and more frequent and extreme heating events. Freshwater mussels are declining globally, and the distribution of the freshwater pearl mussel (Margeritifera margeritifera) has decreased dramatically over the past century. Even though it is likely that climate change is contributing to the decline of the species, little is known about the specific mechanisms involved. Here, we test how short episodes of water temperatures above the known thermotolerance range affect the survival and growth of the early post parasitic juvenile phase of freshwater pearl mussels. We also test if previous experience with elevated water temperatures can modify survival and growth responses to subsequent high-temperatures exposure. Mortality was very low in all treatments (< 5%) and not affected by the temperature treatments, while growth rate was positively affected by temperature. Our results suggest that juvenile mussels can survive short periods of heat stress when other environmental conditions are favourable. Future studies should therefore address how heat stress affects survival in combination with other stressors, such as reduced availability of dissolved oxygen.

The impact of acidic precipitation and eutrophication on the freshwater pearl mussel Margaritifera margaritifera (L.) in Southern Norway

In Southern Norway, there are strong indications that acidic precipitation is the main reason for the extinction of 94% of all known populations (n = 47) of the vulnerable pearl mussel Margaritifera margaritifera (L). An example is the famous pearl mussel river, the River Audna, where the death of both young and old mussels took place in the period 1930 - 50. When the pH is in the range 5.0 - 5.5 or lower for prolonged periods of time, the mussel can no longer tolerate the acidity. The only three known localities remaining in this part of the country, with ageing populations of the pearl mussel, are all lowland streams that are only very little acidified. The main threat there is eutrophication.

Genome-wide association analysis reveals genetic architecture of growth and inner shell color traits in freshwater pearl mussel Hyriopsis cumingii (Lea 1852)

Triangle sail mussel (Hyriopsis cumingii, Lea 1852) is the most important freshwater pearl mussel in China. Growth traits of host mussels and inner shell color traits of donor mussels are critical determinants for pearl size and color. In this study, we performed GWAS analysis to explore the genetic architecture of growth and inner shell color traits. Using genotype by sequencing (GBS) technique, we obtained 80,562 SNPs from a total dataset of 463 mussels, based on these data, we found weak genetic relationship (−0.1–0.4) and rapid LD decay rate among the population. Moreover, GWAS analysis identified 12 growth-related significant SNPs and 29 inner shell color related significant SNPs. Five of the 12 SNPs linked to growth traits were validated to be credible SNPs in a new population. Cyclin, SNF, PMP22, CPED1, F-box and APC/C genes were found to be significantly associated with growth traits, which may influence the growth and development of H. cumingii by regulating cell mitosis, mantle epithelial tissue activity, and Ca2+ absorption and transport capacity. Notably, redness a* showed an obvious aggregation peak in chromosome 17, indicating that this region may be closely related to the inner shell color. Furthermore, three causal genes in chromosome 17, HSP78, MAS and PKS are inferred to be the key genes on color formation of purple inner shell. These results provide some new insights into the genetic basis and physiological regulation mechanism of growth and inner shell color traits in H. cumingii. However, detailed functional identification and regulation mechanism analysis merits more investigation.

Still waters and deep: Habitat characteristics, density and distribution of a lake-dwelling population of the freshwater pearl mussel Margaritifera margaritifera

The freshwater pearl mussel, Margaritifera margaritifera is widely considered to be confined to fast-flowing, near-pristine rivers, and is highly endangered throughout its Holartic range. Here we describe a large population of some 150–200,000 individuals of the freshwater pearl mussel living in an oligotrophic Irish lake.Employing underwater photographic techniques and snorkel diving, mussels were found in two separate locations in the lake. In the first location, 200 m from the shore, mussels were found at a maximum density of 43 m−2, in a largely random distribution in the sandy bed substrate of the lake, up to 9.5 m deep. In the second shoreline location, mussels were observed in dense aggregations up to 118 individuals m−2, in sandy pockets in between boulders and bedrock, in waters 1–2 m deep. In both locations, mussels were found associated with macrophytes – the charophyte Nitella sp. in the deeper location and the quillwort Isoetes lacustris in the shallower shoreline location. Juvenile mussels (>1.5 cm length) were observed lying exposed on the sediment surface in the shallow littoral location, indicating that recruitment occurs in this population, although no estimates of juvenile density were obtained.The discovery of a large population of lentic Margaritifera margaritifera has significant implications for the species’ conservation and indicates that there may be substantial lentic populations of the species elsewhere. The environmental envelope of the species is clearly much wider than thought and our discovery challenges assumptions about the fundamental feeding and reproductive biology of this endangered species.

Biologically driven isotope fractionation in ultrastructurally different shell portions of freshwater pearl mussels (Margaritifera margaritifera): Implications for stream water δ18O reconstructions

AbstractOxygen isotopes in stream water can serve as natural tracers of watershed dynamics. Freshwater pearl mussels provide δ18Owater estimates that overcome temporal and spatial limitations of instrumental records. The reliability of shell‐based δ18Owater reconstructions depends on understanding which shell layer biomineralizes closer to oxygen isotopic equilibrium with ambient water. To determine this, both the (outer) prismatic and (inner) nacreous sublayers of the outer shell layer were sampled. Over 2500 isotope values were obtained from shells collected from the Our River (Luxembourg) and from mussels cultured in tanks at constant temperature and monitored δ18Owater. Calculated δ18Owater from the prismatic portion was in excellent agreement with monitored δ18Owater, while δ18Oshell of the nacreous portion was systematically offset by +0.43‰, overestimating δ18Owater by +0.53‰. Although shell portions were formed simultaneously from the same extrapallial fluid, they underwent different fractionation mechanisms, presumably due to differences in carbonic anhydrase activity catalyzing mineralization processes.

Population status and host fishes of the freshwater pearl mussel in the eastern part of the Onega Peninsula, Northern European Russia

Four populations of freshwater pearl mussel Margaritifera margaritifera were studied at lower sections of three river basins of the eastern part of the Onega Peninsula, Northern European Russia: the Bol’shaya Syarta, the Ust’-Yaren’ga and the Lopshen’ga (including Kamenny Stream). One of the populations from the Lopshen’ga River was discovered for the first time. Here we present preliminary data on the population status of M. margaritifera, its host fishes and glochidia infestation in the studied river basins. Living juvenile mussels and fishes infested by glochidia were recorded only in two waterbodies, i.e., the Bol’shaya Syarta and Ust’-Yaren’ga rivers. The pearl mussel population from the Bol’shaya Syarta River seems to represent the most prosperous among studied ones. The average density of visible mussels was small in the lower section of the river, but the proportion of young mussels was rather high (33.1 %) and intensity of glochidia infection reached 865 glochidia per fish. The highest average density was recorded in the pearl mussel population from the Kamenny Stream, Lopshen’ga River basin. However, only one juvenile mussel and none of host fishes infested by glochidia were recorded in this watercourse that may indicate the population aging and decrease of reproduction. Morphological analyses revealed significant differences between four studied populations of M. margaritifera towards the shell convexity index (SCI) and shell elongation index (SEI). In all studied basins, salmonid fishes were also infested by other parasites, mainly flatworms and their cysts. This factor may negatively impact the salmonid host fish populations that require monitoring of the current situation. The data obtained and future studies will allow to develop a system for protecting and monitoring of populations of a rare species such as the freshwater pearl mussel M. margaritifera.

Growth and longevity of the endangered freshwater pearl mussel (Margaritifera margaritifera): Implications for conservation and management

AbstractKey life‐history data, such as growth and age, are necessary to effectively manage and conserve threatened freshwater mussel species. Traditionally growth and age studies require large yet destructive sample sizes covering all age classes. Such methods pose a risk to populations of conservation concern, and therefore, alternative methods that need only limited sample sizes are necessitated to prevent further threats to such populations. We applied retrospective shell growth at age reconstructions to 98 critically endangered freshwater pearl mussel (FPM) individuals from 34 populations across Finland and Sweden, enabling the use of extremely small sample sizes (n = 1–6 per population). We compared the performance of six different growth models with the reconstructed size‐at‐age data across FPM juvenile (&lt;20 years old) and adult life stages. The growth reconstruction model showed reasonable skill in reconstructing FPM growth patterns. The von Bertalanffy model showed to be a good general descriptor of growth for FPM, but it systematically underestimated the asymptotic size. The power law model was the most accurate in estimating juvenile growth (lowest deviances from the size‐at‐age data). FPM showed great variability in longevity (Amax = 54–254 years) and growth constant k (0.018–0.057 year−1). Our results show that reasonable estimates of growth can be attained even when sample sizes are extremely limited. The results can be further applied to gain knowledge on the population's age structure, size at maturation, and recovery potential. The methodology is applicable to other freshwater mussel species of conservation concern.

Genotype by environment interactions for growth and inner shell color disparity in Hyriopsis cumingii under different light conditions

The light plays a pivotal role in influencing the growth and body color for aquaculture animals. The freshwater pearl mussel Hyriopsis cumingii, inhabiting benthic environments naturally, is predominantly cultivated by hanging methods. This aquaculture method altersmutiple environmental factors, with light being one of the maximum variationfactor. In order to comprehend the impact of light change on the growth and inner shell color of H. cumingii, a total of 14 full-sibling families were established and cultivated separately under natural light and dim light conditions for a period of 13 months in this study. The results revealed that under natural light conditions, juvenile mussel exhibited accelerated growth rates, while dim light conditions expedited purple pigmentation in the inner shell. Genetic analysis indicated general heritability range for the entire experimental population falls between 0.07 and 0.28. heritability estimates for all traits under natural light conditions (NL) ranged from 0.33 to 0.72, indicating consistently high heritability. However, heritability estimates for all traits under dim light conditions (DL) ranged from 0.05 to 0.16. The growth and inner shell color traits showed significant G × E interactions under different light conditions. The anal angle radial rib length (AARRL) trait exhibited a significantly higher correlation with body weight (BW) compared to shell height (SH) and total shell height (TSH). Furthermore, the growth and inner shell color traits of different families were compared and evaluated under the two environmental conditions in this study. Families 1 and 6 excelled in various traits under both conditions, making them promising candidates for genetic improvement breeding. In this study, pronounced influences of light exposure on the growth of pearl mussels were identified, emphasizing the need for tailored breeding strategies for both bottom seeding and suspended cultivation methods.

Exploring the optimal integrated multi-trophic aquaculture (IMTA) patterns benefiting culture animals and natural water environment

Despite bringing various benefits, rapid developments in aquaculture have contributed to the eutrophication of natural water environments. Therefore, it is imperative to mitigate nutrient load in natural water bodies while ensuring sustainable development of aquaculture. On the basis, we proposed an integrated multi-trophic aquaculture (IMTA) system, which considered a perfect solution and constructed an optimised IMTA pattern. Silver and bighead carps and freshwater pearl mussels were used as purification organisms. Six experimental groups were established for a land-based enclosure experiment: giant freshwater prawn monoculture group (G); giant freshwater prawn and freshwater pearl mussel polyculture group (GH2); giant freshwater prawn and silver and bighead carp polyculture group (GSB); giant freshwater prawn, freshwater pearl mussel and silver and bighead carp polyculture groups (GSBH1, GSBH2 and GSBH3) in different densities of freshwater pearl mussels. Each group had four replicates. Control of cyanobacterial blooms, productivity index, outputs of total nitrogen and total phosphorus and microbial community composition were studied and compared in different culturing patterns. Results showed that the GSBH1 group had the most obvious comprehensive advantages in the above four aspects (no cyanobacterial bloom occurred; the best comprehensive productivity index of giant freshwater prawn; the abundance of beneficial microorganisms in sediments was the highest; reduced phosphorus emissions in tailwater by 60.34%; the utilisation rates of nitrogen and phosphorus increased by 10.99% and 13.05%, respectively). Even so, however, the GSBH1 group might not be the most optimal IMTA pattern in practice because the mortality rate of the mussels reached 12.33% and the weight gain was −3.66%. Additionally, the presence of freshwater pearl mussel at its lowest density in this experiment had exhibited detrimental impacts on the growth of silver and bighead carps. Therefore, the most optimal IMTA pattern needs to be determined by further research.

Transcriptome analysis of mantle and pearl sac of freshwater pearl mussel Lamellidens marginalis to identify biomineralisation-associated genes

ABSTRACT The freshwater pearl mussel, Lamellidens marginalis, is widely distributed in India and is cultured for freshwater pearl production. Understanding the biomineralisation process sheds light on the genes responsible for nacre secretion. However, information on the transcriptome of L. marginalis mantle tissue and pearl sac is lacking. This study generated transcriptome resources for L. marginalis, identifying genes involved in biomineralisation. Illumina paired-end sequencing yielded 11.13 million raw reads, assembled into 133,246 contigs and 26,373 unigenes. Of these, 21,033 unigenes exhibited homology with previously reported molluscan proteins. Genes related to biomineralisation, such as pif, perlucin, calreticulin, calmodulin, chitin synthase, chitin dehydrogenase, carbonic anhydrase, tyrosinase, shell matrix protein, dermatopontin isoform X1, chitinase 3, chitinase domain-containing protein 1, and putative chitinase-1were identified. This baseline information will help to compare the expression levels between the phenotypes of high-quality and low-quality pearls. Further investigations, incorporating large sample sizes and phenotype information, could assist in identifying type I genetic markers linked to pearl quality.

Morphometry and length-weight relationships of the freshwater pearl mussel Parreysia corrugata (Muller 1774) (Bivalvia: Unionidae) from Daya River, Odisha, India

Allometry in the freshwater mussel Parreysia corrugata was studied from east-flowing riverDaya, Bhubaneswar, India. The results indicated that shell length (SL)-shell height (SH) andshell length-shell width (SW) relationships for P. corrugata were SH = 0.876 + 0.932SL andSW = 0.625 + 0.898SL. Greater correlation was found between SL and SW than between SLand SH. The length-weight, height-weight and width-weight relationships of P. corrugata wereestablished as TW = 0.00038SL2.80, TW = 0.0006SH2.95 and TW = 0.0023SW2.97 respectively.The t-test value of b indicated an isometric growth pattern in the width-weight and theheight-weight relationships. The highest r2 value was obtained for shell length-total weightand shell height-total weight equations. Present study will be helpful in strengthening theknowledge on interrelationship between the morphometric variables of P. corrugata and alsoin comparing with the earlier studies to know the existence of spatial or temporal variabilityin the morphometry of this species. This information can also be used to better understandthe biology of P. corrugata and to improve the management of this species. Keywords:Conservation, Daya River, Length-weight relationships,Morphometry

Population Reinforcement of the Endangered Freshwater Pearl Mussel (Margaritifera margaritifera): Lessons Learned

Freshwater mussel populations are in sharp decline and are considered to be one of the most imperilled groups globally. Consequently, the number of captive breeding programmes has increased rapidly in recent years, coupled with subsequent reintroductions/population reinforcements to reverse these declines. The outcomes of mussel conservation translocations are seldom reported in the primary literature, hindering opportunities for learning and for population recovery at pace. Here, we describe the methods employed to carry out a successful conservation translocation of the freshwater pearl mussel (Margaritifera margaritifera) in a declining population in northwest England. Following a small-scale pilot release in 2017, four release sites were identified for a population reinforcement of over 1300 tagged mussels in 2021. Monitoring during 2022 showed high levels of retention of juveniles at three out of the four release sites, despite the occurrence of a significant flood event during October 2021. Subsequent releases of 1100 juveniles were carried out across the three successful sites in 2023. Ongoing and regular monitoring is essential in order to provide data on the longer-term fate of propagated juveniles in the wild. This will allow for adaptive management of release activities in this river. These data will be useful to design conservation translocation strategies for other imperilled pearl mussel populations in the UK and throughout Europe.

Identification of a new gregarine parasite associated with mass mortality events of freshwater pearl mussels (Margaritifera margaritifera) in Sweden.

Freshwater bivalves play key ecological roles in lakes and rivers, largely contributing to healthy ecosystems. The freshwater pearl mussel, Margaritifera margaritifera, is found in Europe and on the East coast of North America. Once common in oxygenated streams, M. margaritifera is rapidly declining and consequently assessed as a threatened species worldwide. Deterioration of water quality has been considered the main factor for the mass mortality events affecting this species. Yet, the role of parasitic infections has not been investigated. Here, we report the discovery of three novel protist lineages found in Swedish populations of M. margaritifera belonging to one of the terrestrial groups of gregarines (Eugregarinorida, Apicomplexa). These lineages are closely related-but clearly separated-from the tadpole parasite Nematopsis temporariae. In one lineage, which is specifically associated with mortality events of M. margaritifera, we found cysts containing single vermiform zoites in the gills and other organs of diseased individuals using microscopy and insitu hybridization. This represents the first report of a parasitic infection in M. margaritifera that may be linked to the decline of this mussel species. We propose a tentative life cycle with the distribution of different developmental stages and potential exit from the host into the environment.

The mechanism underlying increased myosin solubility in pearl mussels (Hyriopsis cumingii) by epigallocatechin gallate at low NaCl level

The poor water solubility of myosin hinders the full utilization of its functions and limits its application in the food industry. The aim of this study was to investigate the effect of epigallocatechin gallate (EGCG) on the solubility of myosin in pearl mussel (Hyriopsis cumingii) muscle at low NaCl level and the underlying action mechanism. The results showed that myosin solubility increased with the increase of EGCG concentration at 0.2 M NaCl level. The polyphenol binding equivalent and thermodynamic characterization analysis implied that EGCG was mainly bound to myosin via hydrogen bonding and van der Waals force to form an EGCG-myosin complex, and compared with 0.5 M NaCl, the binding affinity of EGCG and myosin decreased at low NaCl level. Structural analysis suggested that EGCG caused myosin endogenous fluorescence quenching, a wavelength redshift and a β-sheet content increase, exposing the aromatic amino acid residues inside myosin molecules to the surface in a polar environment. Scanning electron microscopy observation and particle size result indicated that the introduction of EGCG reduced the particle size of myosin, which was more distinct at 0.2 M NaCl level. Therefore, EGCG ordered and stabilized the myosin structure at low NaCl level by forming a complex with myosin, effectively improving the myosin solubility.

Ultrasonic treatment enhanced the binding capacity of volatile aldehydes and pearl mussel (Hyriopsis cumingii) muscle: Investigation of underlying mechanisms

This study was aim to investigate the influencing mechanism of ultrasonic treatment on the interaction between volatile aldehydes and myosin. The results showed that when the mass concentration ratio of myosin to heptanal/hexanal was 1:0.3, ultrasonic treatment could enhance the binding capacity of myosin to heptanal/hexanal, especially the binding of myosin to hexanal. The entropy and enthalpy values of their interaction were negative, indicating that the interaction was mainly driven by hydrogen bond and van der Waals force. After ultrasonic treatment, the fluorescence wavelength of myosin-heptanal/hexanal complex was redshifted, the α-helix content was increased, while its roughness values, particle size and the polydispersity index were decreased. These demonstrated that ultrasonic treatment was conducive to myosin binding to heptanal/hexanal, thereby restraining the release of volatile flavor compounds from myosin, which could provide new insights for the regulation of volatile flavor compounds.

Fish and Bivalve Therapeutants in Freshwater Mussel Captive Breeding—A First Summary of Practical Experiences in European Facilities

A significant part of freshwater mussel populations has strongly declined and many species are severely threatened nowadays. Captive breeding programs often form a central part of conservation strategies. As the life cycles of many mussel species include an obligate parasitic phase, host fish health is a crucial component of successful mussel breeding efforts. However, information about the safe application of fish therapeutants in mussel captive breeding is scarce. This article summarizes information about practical experiences in Europe. In total, eight different therapeutants were used to treat infestations of eight pathogens. Treatment success varied depending on pathogen and prevalence when treatments were initiated. Mussels did not seem to be affected by treatments, especially as long as they remained encysted. In a second step, Virkon S was applied to treat a fungal infection in tanks with brown trout (Salmo trutta) carrying encysted freshwater pearl mussel (Margaritifera margaritifera) glochidia and to disinfect juvenile mussel rearing containers. In both cases, mussels were not harmed and treated fish fully recovered. Results indicate that certain therapeutants can be used safely and successfully at different stages of breeding cycles. Nevertheless, there is still a lack of standard protocols, which would improve efficiency and the safety of treatments.

Aeromonas veronii tolC modulates its virulence and the immune response of freshwater pearl mussels, Hyriopsis cumingii

Aeromonas veronii is an opportunistic pathogen that causes diseases in aquatic animals, but its key virulence factors remain unclear. We screened the gene tolC with significantly different expression levels in the two isolates, A. veronii GL2 (higher virulence) and A. veronii FO1 (lower virulence). Therefore, we constructed mutant strain ΔtolC and analyzed its immunological properties. ΔtolC exhibited the reduced ability of biofilms formation, inhibited envelope stress response mediated by several antibiotics except cefuroxime, implying the ability to evade host immunity might be restrained. Challenge tests showed that the LD50 of ΔtolC was 10.89-fold than that of GL2. Enzymatic activities of ΔtolC group were significantly lower and peak time was delayed to 12 h, as demonstrated by qRT-PCR results. Histopathological examination displayed that the degree of tissue damage in ΔtolC group was alleviated. The results show that tolC is an important virulence factor of A. veronii, which provides references for live-attenuated vaccine.

Thermal Tolerance and Vulnerability to Climate Change of a Threatened Freshwater Mussel

Freshwater pearl mussels (FPMs, Margaritifera margaritifera, Linnaeus, 1758) are endangered and particularly vulnerable to climate change. To create effective conservation strategies, we studied their thermal tolerance and the impact of elevated water temperatures on growth and survival. Our experiments included field mesocosm studies in five FPM-streams in the Vogtland region (Germany) (2016 to 2020), as well as laboratory experiments at temperatures ranging from 1 to 26 °C. Growth of juvenile FPMs increased significantly within a temperature gradient from 12 to 21 °C. In the streams, maximum growth was 8.9 µm/d in surface water and 6.5 µm/d in the interstitial. The upper thermal tolerance for the mussels ranged from 22.1 to 22.9 °C, resulting in low survival during hot summer periods in 2018 and 2019. Warming during winter (+5 °C) did not significantly affect growth and survival, but survival during winter increased with the pre-overwintering shell length. Exceeding a shell length of about 1100 µm in December indicating gill development corelated to 50% survival. Shell length in December is primarily controlled by growth depending on water temperatures during summer. These findings define the thermal niche of juvenile FPMs (average summer temperatures of 14.5–21 °C) and have implications for water management, conservation strategies, and site selection for releasing captive-breeding mussels.

Faktor-Faktor Budidaya Kerang Mutiara di Desa Maijuring Kecamatan Aru Tengah Kabupaten Kepulauan Aru

Pearl cultivation began to develop, especially in Maluku Province. With the increasing cultivation of pearl mussels, the demand for pearl seeds is also increasing, but this is also hampered by a lack of supply of seeds from wild catches or obstacles during seed production, namely high mortality at the spawning stage and in general the growth and survival of shellfish species is greatly influenced. by important factors, namely temperature and food availability and other important factors, on this basis the author conducted research which aims to determine the factors of pearl oyster cultivation in Maijuring Village, Aru Tengah District, Aru Islands Regency. The type of research used is Qualitative Descriptive analysis. With sea water samples and 5 pearl oyster cultivators. The sampling technique used is purposive sampling which uses the criteria of people who cultivate pearl oysters. The data collection techniques used are observation, documentation and interviews. The data analysis technique used is SWOT analysis. The results of the research show that in Maijuring Village there are several factors in cultivating pearl oysters, namely water quality, feed availability, water temperature, water depth, water salinity, water pH, population density, cultivation land maintenance such as water quality which is influenced by temperature, namely 26.9, pH namely 7.76, and salinity 34.42, and depth 20-30m. from the surface.