Histopathological survey of parasites harboured by the clam Tawera elliptica (Lamarck, 1818) from Chiloé Archipelago, southeastern Pacific.

Tawera elliptica (commonly known as "Almeja Juliana", is a venerid clam that inhabits sandy bottoms and is distributed from Valparaíso on the Pacific coast up to the Mar del Plata area along the Atlantic coast. Harvests of this clam have declined substantially over the last decade. Therefore, an analysis of common parasites and pathological conditions of this clam was undertaken along with histopathology. Monthly samples were prepared for routine histology for examination under light and electron microscopy. T. elliptica has a sex ratio of 1:1 and the relationship between the shell length and the wet tissue weight is not significantly different between females and males. The maximum values for de condition index and meat yield were found during the austral winter. The following parasites (and their overall prevalence) were detected: intracellular microcolonies of bacteria in digestive gland (22.9%), intestinal epithelium (9.3%) and gills (3.17%), an unidentified cyst in gills (59,3%), a Steinhausia-like intraoocytic microsporidian (5.2%), Gregarine spores (41.3%), ciliated protozoa (16.7%), two metazoa, a Paravortex like flatworm (4.3%), and a digenean trematode (8%). The monthly mean intensity of the most relevant parasites was between 2.3 and 35.6 for digestive gland intracellular microcolonies of bacteria (IMC), 0-5.1 for intestinal epithelium IMC, 0-2 for branchial IMC and 0 - 48 for intraoocytic microsporidium. The prevalence and the infection intensity were low-to very low, and no World Organisation for Animal Health OIE listed parasite was detected. It is concluded that this is a healthy clam, and no disease risks for the cultivation are visualized at present. However, IMC at high prevalence and intensities of infection could be potentially impactful, and the intraoocytic microsporidian could jeopardize reproduction if present in high intensities of infection.

Full Mitochondrial Genomes Reveal Species Differences between the Venerid Clams Ruditapes philippinarum and R. variegatus.

In natural sea areas along the coast of China, venerid clams Ruditapes philippinarum and R. variegatus exhibit similar adult shell forms and are especially difficult to distinguish as spat and juveniles. This study used comparative mitochondrial genome analysis to reveal differences between these species. The results showed that: (1) the mitochondrial genomes of R. philippinarum and R. variegatus share a large number of similar gene clusters arranged in consistent order, yet they also display noncommon genes, with both gene rearrangements and random losses found; (2) the 13 protein-coding genes in R. philippinarum as well as two-fold and four-fold degenerate sites in R. variegatus have an evident AT bias; (3) the Ka/Ks ratio of the mitochondrial ATP8 gene was significantly higher in R. philippinarum than in R. variegatus, and an analysis of selection pressure revealed that the mitochondrial NADH dehydrogenase subunit 2 gene and NADH dehydrogenase subunit 6 gene of R. variegatus were under great selective pressure during its evolution; and finally, (4) the two species clustered into one branch on a phylogenetic tree, further affirming their phylogenetic closeness. Based on these results, we speculate that the species differences between R. variegatus and R. philippinarum are largely attributable to adaptive evolution to the environment. The present findings provide a reference for the development of germplasm identification.

The first complete mitochondrial genome of Antigona lamellaris (Schumacher, 1817) (Veneroida: Veneridae).

Venus clams (Veneridae) including Antigona lamellaris are commercially important fishery resources by their dominance in local benthic communities. However, despite their great diversity, the phylogenetic and taxonomic relationships in venus clams remain poorly understood. In this study, we report the first complete mitochondrial genome of A. lamellaris. The mitogenome has 17,532 base pairs (67.9% A + T content) and is made up of a total of 37 genes (13 protein-coding, 22 transfer RNAs and 2 ribosomal RNAs), plus a putative control region. This study will provide useful molecular resources for clarifying taxonomic and phylogenetic confusion in venus clams.

The Ashtamudi Lake short-neck clam: re-assigned to the genus Marcia H. Adams & A. Adams, 1857 (Bivalvia, Veneridae).

The economically valuable bivalve mollusc, known as the short-neck clam, is the major fishery resource of the brackishwater Ashtamudi Lake in Kerala, India. This fishery carries a Marine Stewardship Council certification for sustainability wherein it and all hitherto published reports identify the short-neck clam or yellow-foot clam as Paphiamalabarica (Dillwyn, 1817). It is noted that this name does not conform with current nomenclature and is now correctly referred to Protapesgallus (Gmelin, 1791). Furthermore, it is shown that the identification is also incorrect. Comparative shell morphology of venerid clams of the subfamily Tapetinae from the south Indian coast demonstrates that the short-neck clam in Ashtamudi Lake is Marciarecens (Holten, 1802). Small numbers of M.opima (Gmelin, 1791) were found in Ashtamudi Lake but appear not to be part of, or contribute significantly to, the fishery. The venerid clams Protapesgallus and P.ziczac (Linnaeus, 1758) are not found in Ashtamudi Lake but are inhabitants of the shallow coastal waters of south India. Descriptions of the four confused species M.recens, M.opima, P.gallus, and P.ziczac are given. On the basis of this study, the species involved in Marine Stewardship Council (MSC) certification may be better considered at the generic level of Marcia or at the species level as Marciarecens, the most dominant species in the Ashtamudi Lake clam fishery zone.

Positive selection adaptation of two-domain arginine kinase (AK) from cold seep Vesicomyidae clams.

Arginine kinase (AK) is an important member of Phosphagen kinases which engage in energy metabolism process, and AKs from cold seep clams may develop an effective mechanism to adapt a special habitat (e.g. low temperature). Three Vesicomyidae clams and seven Veneridae clams (belong to the same Order Veneroida) were chosen to analyze the evolution of two-domain AKs. In the present study, ten two-domain AKs were identified and Neighbor-joining tree showed that AKs were divided into two groups. Branch-site model indicated that two-domain AKs were subjected to strong positive selection (ω2a = 17.5058). 16 positively selective sites were detected and five of them showed posterior probabilities of 0.95 or more. Comparative analysis found that domain 2 might be suffered from more evolutionary selection pressure than domain 1, as most positively sites were located at domain 2. Residue Pro (positively selective site) (587P in ApAK) in domain 2 from all Vesicomyidae AKs might participate in change of the synergism and in the function of its cold-adapted characteristics. In conclusion, our studies provide evidence of positive Darwinian selection in the two-domain AKs family of Vesicomyidae clams, and may contribute to a better understanding of its adaptation mechanisms to cold seep habitats.

The complete mitochondrial genome of Cyclina sinensis (Veneroida:Veneridae).

Cyclina sinensis belongs to the family Veneroida, Veneridae, a marine mollusks having high economic value. It is distributed in the coastal waters of Southeast Asia. In recent years, the recourses of C. sinensis have been severely depleted due to overfishing and pollution. Genetic divergency has also been reported. It is necessary to protect this bivalve from the hazards. In this study, the complete mitochondrial genome of C. sinensis has been determined. The total number of nucleic acids were 21 799 bp. The genome contains 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes and a non-coding control region. The phylogenetic analysis was conducted with 11 related species and confirmed the classification status.

Genetic Distances of Three White Clam (Meretrix lusoria) Populations Investigated by PCR Analysis.

The twenty-one individuals of Meretrix lusoria were secured from Gunsan, Shinan and Yeonggwang on the coast of the Yellow Sea and the southern sea in the Korean Peninsula, respectively. Amplification of a single COI fragment (720 bp) was imagined, and no apparent size differences were observed in amplified fragments between Meretrix lusoria and M. petechialis individuals. The size of the DNA fragments also varied excitedly, from 200 to 1,600 bp. The oligonucleotides primer BION-08 produced the least loci (a total of 17), with an average of 2.43 in the Gunsan population, in comparison to the other primers used. Remarkably, the primer BION-13 detected 42 shared loci by the three populations, major and/or minor fragments of sizes 200 bp and 400 bp, respectively, which were identical in all samples. The dendrogram gained by the seven oligonucleotides primers highlight three genetic clusters: cluster 1 (GUNSAN 01 ~ GUNSAN 07), cluster 2 (SHINAN 08 ~ SHINAN 14) and cluster 3 (YEONGGWANG 15 ~ YEONGGWANG 21). The longest genetic distance among the twenty-one Meretrix lusoria individuals that displayed significant molecular differences was between individuals GUNSAN no. 01 and SHINAN no. 14 (genetic distance = 0.574). Comparatively, individuals of SHINAN population were fairly closely related to that of YEONGGWANG population. In this study, PCR analysis has discovered significant genetic distances between two white clam population pairs (P<0.05).

Population dynamics of Megapitaria squalida (Bivalvia: Veneridae) at Magdalena Bay, Baja California Sur, Mexico

The population dynamics of an intertidal population of Megapitaria squalida was studied from September 2002 to February 2003 in Bahia Magdalena, Mexico. To obtain information about the artisanal and recreational fishery of M. squalida, local fishermen at different parts of the bay were interviewed. Clam densities were determined at one unexploited and two exploited sites along perpendicular transects from the shore line. Average clam density was 2.01+/-1.41 ind/m2, densities did not differ significantly between the three sampling sites. The length-total mass relation was Mtot = 0.0001*SL3.1644 (r2 = 0.9804, n = 92) and the length-tissue mass relation was Mtis = 0.0002*SL2.7144 (r2 = 0.945, n = 92). Von Bertalanffy-growth parameters were determined using marked individuals. Strong interindividual and also seasonal differences in growth were observed. Average annual values were: K = 0.655, L[infinity] = 83 mm. Since M. squalida can reach a shell length of more than 135 mm in deeper waters, it is necessary to consider intertidal and subtidal populations separately. Average total mortality (Z) was 1.61 y(-1). No fishing mortality was calculated because total mortality Z at the unexploited control site was higher than Z at the exploited sites. It appears that M. squalida migrates into deeper water with increasing shell length, as average shell length increased at lower tidal levels and marked specimens showed a clear migration towards deeper waters. As yet no overexploitation could be found in the study area.

Se estudió la dinámica poblacional de la almeja Megapitaria squalida de setiembre 2002 a febrero 2003 en Bahía Magdalena, México. La densidad se determinó en un sitio no explotado y dos sitios explotados utilizando transectos perpendiculares desde la línea costera. También se entrevistó a pescadores locales de diferentes partes de la bahía para obtener información acerca de la pesquería artesanal y recreacional de M. Squalida. La densidad promedio estimada fue de 2.01±1.41 ind/m2, sin diferencias significativas entre sitios. La relación de masa y longitud total fue de Mtot = 0.0001*SL3.1644 (r2 = 0.9804, n = 92) y la relación de masa y longitud de tejido fue de Mtis = 0.0002*SL2.7144 (r2 = 0.945, n = 92). Los parámetros de crecimiento Von Bertalanffy se determinaron utilizando marcadores individuales. Hay grandes diferencias en crecimiento tanto interindividuales como estacionales. Los valores anuales promedio fueron: K = 0.655, L[infinito] = 83 mm. Debido a que la longitud de la concha puede superar los 135 mm en aguas profundas, es necesario considerar las poblaciones intermareal e inframareal de manera separada. La mortalidad promedio total (Z) fue de 1.61 y-1. No se calculó la mortalidad de pesca porque la mortalidad total (Z) del sitio no explotado fue mayor que la de sitios explotados. Aparentemente M. squalida migra hacia aguas más profundas al crecer. No se encontró evidencia de que estas poblaciones estén sobreexplotadas. Palabras clave: Megapitaria squalida, Veneridae, dinámica poblacional, intermareal, Bahía Magdalena, México.Se estudió la dinámica poblacional de la almeja Megapitaria squalida de setiembre 2002 a febrero 2003 en Bahía Magdalena, México. La densidad se determinó en un sitio no explotado y dos sitios explotados utilizando transectos perpendiculares desde la línea costera. También se entrevistó a pescadores locales de diferentes partes de la bahía para obtener información acerca de la pesquería artesanal y recreacional de M. Squalida...

Veneridae (Mollusca, Bivalvia) da costa norte do Estado de São Paulo, Brasil / Veneridae (Mollusca, Bivalvia) from the north coast of São Paulo State, Brazil

Coletas intensivas da fauna bentônica marinha da costa norte do Estado de São Paulo, realizadas pelos programas de pesquisa "Fauna de Praia/UNICAMP" de agosto de 1995 a julho de 1997 e "Biota/FAPESP" de março de 2001 a dezembro de 2002 recolheram 2769 exemplares pertencentes a dezesseis espécies, doze gêneros e sete subfamílias. A caracterização de cada espécie foi ampliada com redescrição e ilustrações detalhadas, baseadas nos caracteres da concha. Tabelas comparativas dessas características e uma chave dicotômica de identificação das subfamílias são apresentadas neste estudo.

This study concerns the Veneridae bivalves sampled during the research programs "Fauna de Praia/UNICAMP" and "Biota/FAPESP" carried out between August 1995 and July 1997 and between March 2001 and December 2002 respectivelly, in the north coast of São Paulo State, Brazil. A total of 2769 individuals belonging to sixteen species, twelve genera and seven subfamilies were recorded and the characterization of each species improved with detailed redescription and illustrations based on the shell characters. Comparative tables and a identification dichotomic key for subfamilies focused in this study are provided.