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Perna perna (Linnaeus, 1758) is the main marine bivalve mussel yielded commercially in Brazil. In spite of this, scientific data is very scarce regarding its productivity in tropical shallow waters. The Condition Index (CI) is used worldwide in mariculture to assess animal health, harvest time, and yield. In this study, the authors used CI results from nine different methods to assess the season effect on the mussel CI and also to evaluate the potential yield of three southern Brazilian bays. The results from nine CI methods were used for the comparison of the seasonality and yield of mussels reared in three marine bays. Sampling was carried out monthly within two 4-month periods, from December 2008 to August 2009. The results show a trend for seasonal effects on the CI results. The winter months showed the highest and the lowest values. Between bays, higher CI values were detected in animals reared at Sepetiba Bay, followed by Guanabara Bay and Ilha Grande Bay. We suggest that the CI (that considers the ratio between bivalve soft tissue wet weight and total length) should be used by fishermen, since this formula was able to detect differences between sites and is more easily applied.

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). The ultrastructural study of plasmodial instars showed that this parasite belongs in the order Balanosporida (Joly and Comps, 1979). Recently, histological examinations demonstrated a pathogenic agent pertain­ ing to this group of protozoans on Ruditapes decussatus from the area of the Algarve (Portugal). The sporulated instars were studied by means of light and electron microscopy. The first signs of the haplosporidian infection are plasmodial forms (p) (Fig. 2), mostly located in the digestive epithelia, whereas intense sporulation occurs in the interstitial connective tissue underlying the digestive gland and the gills (s: spores) (Fig. 1). The spore (Fig. 5) has an operculum (op), is slightly ovoid and averages 5 to 6 fJ.m length and 4 to 6 fJ.m width. It is delimited by a thick wall consisting oftwo principallayers which result from the stacking of several dense and lucent strata. The wall is extended by a flattened lid whose free edges are finely bristling with filamentous matter (mC) (Fig. 4). Typieal organelles of haplosporidian spores are present: spherules (sp), haplo­ sporosomes (h), mitochondria (m) (Figs. 3, 5). The characteristics of these spores permit one to link the parasite with the order Balanosporida (Sprague, 1979). Nevertheless, absence of or­ namentation and filaments stemming from the spore wall, a character which is considered as a taxonomie criterion for the genus (Ormières, 1980; Perkins and Van Banning, 1981) lead us to classify this haplosporidian in the genus Minchinia under the appellation Minchinia tapetis.

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