Francisco Ruano

Histological study of a cellular reaction in Ruditapes decussatus infected by a protozoan

An infection caused by a Perkinsus -like parasite has been observed in Ruditapes decussatus from Portugal (Comps and Chagot, 1987). Following a pathological study carried out on clams affected by mortalities in the Algarve area, this parasite was found again, inducing a reaction process in the host. Histological examination reveals the parasite in the connective tissue of different organs. The adjoining tissues, particularly the epithelia, are not affected.

An infection of Ruditapes decussatus (Bivalvia) by Rickettsia

The authors report the presence of a Rickettsia in Ruditapes decussatus from natural populations of the Algarve (Portugal). Light microscopic shows infections of varying importance in gill tissues. Some enclose small procaryotic colonies (cp) scattered in all lamellae; in others, the colonies are scarce and hypertrophic (100 mu m). These different pictures suggest an amplification process. Digestive diverticulae may also be infected, but to a lesser extent. The ultrastructural features of this intravacuolar (mvd: densified vacuolar membrane) procaryote (P) and its multiplication by scission without a complex developmental cycle allows its classification in the order Rickettsiales.

RESTRICTION ENZYME DIGESTION CHROMOSOME BANDING ON TWO COMMERCIALLY IMPORTANT VENERID BIVALVE SPECIES: RUDITAPES DECUSSATUS AND CERASTODERMA EDULE

Abstract Reliable banding techniques are a major necessity for the genetic research in marine bivalves. Restriction enzyme banding (HaeIII) was performed, in this study, on chromosomes of two commercially important species of veneroid bivalves: the clam Ruditapes decussatus (Adams and Reeve) and the cockle Cerastoderma edule. Identification of the nineteen individual chromosome pairs was obtained for both species. The cytogenetic studies made in marine molluscs have recently experienced a very fast development caused by the introduction of new molecular techniques mainly fluorescence in situ hybridization (FISH). Recently it has been shown in mammalian chromosomes that restriction enzyme banding is compatible with FISH, allowing simultaneous banding, and consequent accurate identification of the localization of the probes and unambiguously identification of the chromosome(s) carrier(s). As far as we know this is the first RE-banding obtained in karyotypes of veneroid species. The application of restriction enzyme chromosome banding in veneroids are diverse and this study can constitute a fundamental step for future gene mapping on this commercially important group of bivalves and could offer a new approach to specific problems in veneroid taxonomy and genetics.

Ultrastructural study of sporulated instars of a haplosporidian parasitizing the clam Ruditapes decussatus

In 1951, Vilela pointed out the presence of a haplosporidian parasitizing Ruditapes decussatus from Portuguese waters and created the species Haplosporidium tapetis. Later, a haplosporidian was found in the same species originating from the pound of Thau (France).

Perkinsosis in the clams Ruditapes decussatus and R. philippinarum in the Northeastern Atlantic and Mediterranean Sea: A review

Perkinsosis is a disease of gastropod and bivalve molluscs caused by protozoan parasites of the Perkinsus genus. These parasites have been responsible for mass mortalities worldwide, with a significant impact in both fisheries and aquaculture, and resulting in severe economic losses. This review focuses mainly on current knowledge of diagnostic methods and on the distribution of Perkinsus spp. in the Northeastern Atlantic and Mediterranean Sea, which infect the grooved carpet shell clam Ruditapes decussatus and the Japanese carpet shell clam Ruditapes philippinarum. The association between perkinsosis and high mortality rates of R. decussatus and R. philippinarum in southern European countries such as Portugal and Italy is discussed as is the role of environmental factors in those mortality outbreaks. The putative introduction of Perkinsus olseni into the Northeastern Atlantic and Mediterranean Sea is also discussed, as are management strategies that could be used to mitigate the impact of perkinsosis in production of R. decussatus and R. philippinarum.

Infestation of the cupped oysters Crassostrea angulata , C. gigas and their first-generation hybrids by the copepod Myicola ostreae : differences in susceptibility and host response

SUMMARY We studied the prevalence and intensity of the parasitic copepod Myicola ostreae in 2 closely related oysters Crassostrea angulata and C. gigas and their F1 hybrids. The effects on host and host reaction were also analysed to better understand host-parasite relationships between copepods and bivalve molluscs. Full reciprocal crosses were carried out between C. angulata and C. gigas and the progenies were reared in the wild in Ria Formosa Lagoon (Portugal), allowing natural infestation by M. ostreae. Prevalence and intensity were significantly higher in C. angulata than in C. gigas. The parasite level of F1 hybrids was similar to C. angulata and significantly higher than in C. gigas. The results of our study support a hypothesis of dominantly inherited susceptibility to M. ostreae infestation. Moreover, copepods were observed on the gill surface of C. gigas engulfed by a capsule-like structure. Histological analyses revealed that the copepods were surrounded by a massive agglomerate of haemocyte-like cells encircled by a thin layer of fibroblast-like cells. This encapsulation response was not observed in C. angulata or in F1 hybrids. These results suggest that the differential susceptibility to M. ostreae between C. angulata and C. gigas may be ascribed to host defence factors.

Occurrence and characterization of pearls from oysters of the genus Crassostrea

The occurrence of pearls in the ‘true’ oysters, the Ostreioidea, is poorly documented despite being the most produced mollusc species in the world. Oysters of the Crassostrea genus were collected in two different sites in southern Portugal where both Crassostrea angulata and C. gigas are present, namely in: (1) the Ria Formosa lagoon where pearls were not observed (N = 446); and (2) the Guadiana estuary where pearls were found in 12 out of the 798 oysters analysed. The pearls were located mainly at the edge of the right mantle lobe in the inhalant chamber and their maximum length ranged from 0.9 to 5.5 mm. Almost all the pearls had a white-cream colouration with the exception of two pearls that had a black-brown colour. X-ray diffraction analysis of one pearl showed that it was entirely calcitic with no traces of either aragonite or vaterite. The pearls observed were therefore non-nacreous pearls. Scanning electron microscopy (SEM) revealed a diversity of microstructures including prismatic, foliae-like sheets and blocky textures, i.e. highly reminiscent of the host oyster shell microstructures. Parasites (e.g. parasitic copepods, Haplosporidium-like plasmodia) and signs of diseases (e.g. foot disease) were observed in some of the oysters analysed, but they were not associated with the occurrence of pearls. The present work is one of the few studies on the occurrence of natural pearls in ‘true’ oysters and to our knowledge the first description of their microstructure by SEM.

Detection of Marteilia refringens infecting the European flat oyster Ostrea edulis and the dwarf oyster Ostrea stentina in southern Portugal and Spain.

In the present study, Marteilia sp. was detected by histological examination and in situ hybridisation in Ostrea edulis and Ostrea stentina collected in southern Iberian Peninsula. Marteilia refringens DNA was detected by PCR in O. edulis (collected in southern Portugal) and O. stentina (collected in southern Spain and Portugal). Sequencing analysis revealed the presence of M. refringens type O in O. edulis, and type O and M in O. stentina. This is the first confirmed detection of M. refringens in Portugal and the first report on the occurrence of M. refringens infecting O. stentina in Europe.