Ocorrência de ostras perlíferas no Marajó, rio Pará

Abstract

Ostras perlíferas foram encontradas em águas que circundam a parte sul da ilha do Marajó, próxima à confluência dos rios Tocantins e Pará. As conchas das ostras possuem uma camada espessa de conchiolina, que lhes confere qualidades de madrepérola. Um lote de 12 pérolas naturais apresentou as seguintes características: cores variadas do branco rosa ao cinza escuro; tamanhos de 3 a 11 mm; formas esféricas a subesféricas, cilíndricas (algumas cinturadas) a barrocas. Sob irradiação UV de onda longa, duas amostras apresentaram cor azul forte e uma cor azul média. Respectivamente cores azuis mais fracas são obtidas por UV de onda curta. A parte interna da concha da ostra apresenta cor azul fraca, tanto sob irradiação UV de onda longa quanto de onda curta. A superfície externa das pérolas é lisa com brilho nacarado característico, sendo que algumas apresentam um tom metálico dourado. Essa é, provavelmente, a primeira região brasileira mais importante com ocorrência de pérolas naturais atuais, abrindo perspectivas para a produção de pérolas cultivadas em água doce.<br>The occurrence of perliferous freshwater oysters in the southern region of Marajó Island, at the mouth of Amazon River, is reported. The oyster's shell presents a thick layer of conchioline. A set of 12 freshwater pearls present white to dark gray colors with nacarous luster, some with golden metallic hue; sizes from 3 to 11 mm and spheric to cylindrical (with belts) to barroc forms. At long wave UV light, two samples present strong and one presents medium blue color. Paler blue colors are shown at short wave UV light. The inner side of the shell presents pale blue colors at both, long and short wave UV light. This occurrence represents, probably, the first important region in Brazil with natural pearls, opening a perspective for freshwater pearl cultivation

Feeding ecology of immature Lithodoras dorsalis (Valenciennes, 1840) (Siluriformes: Doradidae) in a tidal environment, estuary of the rio Amazonas

“…Considering the low taxonomic variety of items ingested, L. dorsalis exhibited a behariour tending to specialist, eating principally fruits and seeds from the riparian forest, varying the species consumed probably according to availability. Futhermore, the presence of sediments in the stomach of Lithodoras dorsalis specimens indicates that the species also forages on the bottom, where it obtains the bivalves (mussels and oysters) consumed (Beasley, 2001;Hohn & Costa, 2002). This type of foraging behavior has also been recorded in other doradid species (e.g., Hahn et al, 1997;Lowe-McConnell, 1999).…”

Shape, Microstructure, and Chemical Composition of Pearls from the Freshwater Clam Diplodon chilensis Native to South America

“…Pearl production in this species is not a rare phenomenon since many species of the superfamily Unionoidea Rafinesque, 1820, are potential producers of pearls [ 40 ]. However, in South America, only a few species have been described with this capability [ 23 , 41 , 42 ].…”

“…Our results suggest that the shell size does not seem to influence the ability to produce pearls because several individuals from Lake Villarrica in the 4.0 to 5.0 cm size class produced pearls, while twice or three times as many individuals from Lake Caburgua between 5.0 and 7.0 cm did not, except for the 65.6 mm specimen. According to Hohn and Costa [ 42 ], acidic waters prevent the proper formation of pearls in bivalves, but this would not be the case since the waters of lakes Caburgua and Villarrica have very similar pH [ 52 ], although some variation has been reported in this water body [ 53 ]. Rahman et al [ 54 ] detected seven species of pearl-producing bivalves in waters off the coast of Bangladesh with a pH of 8.1 to 8.3.…”

“…Decussata (Linnaeus, 1758), they generally do not exceed 6 mm [ 55 , 56 ]. In the production of cultured pearls, a typical 9-mm round non-beaded pearl takes about 4 years to form [ 42 ].…”

“…However, not all species that have pearls of different colors exhibit these bands [ 72 , 76 ]. On the other hand, there are also other factors involved in the color of pearls, including geographics, genetics, type of mollusk (species), harvest season, water characteristics, depth, quality, and quantity of food (plankton), and the thickness of the pearl [ 24 , 42 , 75 , 77 , 78 , 79 , 80 , 81 ].…”