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A total of 30 specimens of A. tuberculosa were collected during April, May, June and October 2000 from two traditional clam-fishing areas, Bahia Magdalena and Bahia Almejas. Specimens were collected from the mud, between the roots of mangroves Avicennia germinans, Laguncularia racemosa and Rhizophora mangle. In the field, specimens were fixed in 10% formalin, and the shell dimensions and meat weight were recorded in the laboratory. To carry out the histological study specimens of the visceral mass were embedded in paraffin. The gut middle portion was located and frontal-dorsal 7µm-thick sections were obtained, including the stomach and intestine. Sections were stained with hematoxylin-eosin and mounted in syn­thetic resin. Histological sections were observed under a phase contrast microscope, and gut and intestine contents were identified to genus or species using taxonomic keys. The number of phytoplankton cells was determined, and the result was expressed as a percentage. The Anadara tuberculosa specimens collected exhibited an average size of 58 mm and an average meat weight of 15 g (with no shell). Stomach content analysis counted 1,002 items, 917 of which corresponded to diatoms (91.5%), the most abundant being Paralia sulcata (46.3%), Thalassiosira spp. (42.9%), Thalasionema nitzchioides (2.7%), and Diploneis sp. (1.2%). The silicoflagellate Dictyocha sp. (1.6%) appeared in low quantity. Additionally, another 85 non-diatom structures were found (8.5%), including bivalve eggs (1.8%), sponge spicules (0.4%) and unidentified materials (6.3%). Oocytes of this same species were found in the gut content, even in males. According to our findings we conclude that, for this bivalve and probably for other marine mollusks, histological sections represent a new alternative for studying the gut and intestine content, which allow the accurate identification of ingested diatoms. This method identified a wide spectrum of microalgae filtered by the bivalves. To better understand the food habits of these organisms it is important to make diverse histological cuts in various sections of the gut and intestine.

Palabras clave: Chaetognaths; Anadara tuberculosa; microalgas; contenido intestinal

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