Morphological and morphometric aspects of Crassostrea rhizophorae (Guilding, 1828) oocytes in three stages of the gonadal cycle / Aspectos Morfológicos y Morfométricos de Oocitos de Crassostrea rhizophorae (Guilding, 1828) en Tres Fases del Ciclo Gonadal

Crassostrea rhizophorae (Guilding, 1828) es una de las especies de ostras tropicales cultivadas en la costa brasilera, que presenta alto valor comercial, no existiendo información sobre las características gonadales, durante las fases reproductivas de esta especie. El objetivo de este trabajo fue analizar la morfología de los ovocitos y de los folículos gonadales de Crassostrea rhizophorae, en tres fases del ciclo gonadal. Analizando los cortes histológicos de las gónadas y considerando los ovocitos que presentaban núcleo y nucléolo evidentes, fueron determinadas tres fases del ciclo gonadal: gametogénesis inicial, crecimiento y maduración. En la fase de gametogénesis inicial, el diámetro de los folículos y de los ovocitos era de 180,29 (+ - 41,91) e 18,66 (+ - 6,85) µm, respectivamente; también identificamos gran cantidad de tejido conjuntivo interfolicular y un número mayor de ovocitos previtelogénicos. En la fase de crecimiento, el diámetro de los folículos y de los ovocitos era de 218,02 (+ - 43,19) y 25,92 (+ - 9,94) µm, respectivamente. Este fase fue caracterizada por una pequeña cantidad de tejido conjuntivo interfolicular y predominio de ovocitos vitelogénicos. En la fase de maduración, el diámetro de los folículos y de los ovocitos era de 298,16 ( + - 99,24) y 35,27 (+ - 6,2) µm, respectivamente, existiendo gran número de ovocitos maduros. De esta manera, concluimos que durante la implantación del cultivo, Crassostrea rhizophorae tolera la influencia de los factores intrínsecos y extrínsecos y no presenta alteraciones significativas en su actividad reproductiva.

Crassostrea rhizophorae (Guilding, 1828) is one of the tropical species of oysters cultivated on the Brazilian shore. Despite its high commercial value, there is no information on the gonadal characteristics during the reproductive stages of this species. The objective of this work was to analyze the morphology and morphometry of Crassostrea rhizophorae oocytes and follicles in three stages of the gonadal cycle. Were analized histological sections of gonads considering that the oocytes presented visible nuclei and nucleoli, it was observed three gonadal cycle stages: early gametogenesis, growth and maturation. In the early gametogenesis stage, follicles and oocytes presented diameters of 180.29 (± 41.91) and 18.66 (± 6.85) µm, respectively, and presence of large amount of connective tissue and previtellogenic oocyte. In the growth stage, follicles and oocytes presented diameters of 218.02 (± 43.19) and 25.92 (± 9.94) µm, respectively, this stage was characterized by a small amount of interfollicular connective tissue with vitellogenic oocyte predominate. In the maturation stage, follicles and oocytes presented diameters of 298.16 (± 99.24) and 35.27 (± 6.2) µm, respectively, and presence of large number of mature oocytes. We concluded that during culture Crassostrea rhizophorae tolerates the influence of intrinsic and extrinsic factors and does not undergo significant changes in reproductive activity.

Parasitas em ostras de cultivo (Crassostrea rhizophorae e Crassostrea gigas) da Ponta do Sambaqui, Florianópolis / Parasites in cultured oysters (Crassostrea rhizophorae and Crassostrea gigas)from Ponta do Sàmbaqui, Florianópolis

Estudou-se a presença de parasitas e realizaram-se exames macroscópicos e histológicos em ostras (Crassostrea rhizophorae e Crassostrea gigas) cultivadas. Entre agosto de 2002 a maio de 2003, 30 indivíduos adultos de cada espécie foram coletados sazonalmente, totalizando 240 ostras. Os animais, provenientes de desova em laboratório, foram mantidos em lanternas de cultivo, em sistema suspenso tipo espinheI, com densidade de 40 ostras/andar. A cada coleta era registrada a mortalidade das ostras, a temperatura e a salinidade da água. A temperatura variou de 19 a 28,5°C e a salinidade, 31 a 350/00. A mortalidade foi de 48,3 para C. gigas e 70,8 para C. rhizophorae. A infestação pelo poliqueta Polydora websteri em C. gigas foi 100 durante todo o período e em C. rhizophorae, 100 em fevereiro e maio. O mal do pé foi observado em novembro (3,3) e maio (23,3) em C. gigas e maio (6,6) em C. rhizophorae. As maiores prevalências do protozoário Nematopsis sp. foram de 70 e 60 em C. gigas e C. rhizophorae, respectivamente. O protozoário Trichodina sp. ocorreu em 1,6 de C. rhizophorae, e larvas do cestóide Tylocephalum sp. foram observadas em 2,5 de C. gigas. Nenhum dos parasitas encontrados foi associado à mortalidade das ostras.

Disponibilidad de juveniles por captación natural de la ostra Pteria colymbus (Bivalvia: Pteriidae) en el Golfo de Cariaco, Venezuela / Availabilty of juveniles from natural sources of the Pteria colymbus oyster (Bivalvia: Mytilidae), in the Gulf of Cariaco, Venezuela

We examined the spat availability the oyster Pteria colymbus at 6-8 and 19-21 m depths for 15 months (March 1993-June 1994) in Turpialito, Golfo de Cariaco, Venezuela. Spats were trapped using artificial collectors (plastic filaments in bags, 30 x 60 mm), suspended from a long line. Each collector was replaced by a replica monthly to analyse abundance, shell dimension and mass of P. colymbus. Intraweekly, the temperature, salinity, oxygen and food availability (Chlorophyll a, total seston, organic and inorganic seston) were determinated. There is juvenile recruitment all year, suggesting continuous reproduction. Spat counts were higher at 6-8 m (generally 50-230 juveniles per collector) with peaks in August and December 1993 (April and June 93 at 19-21 m). The length-weigh mass relation was higher at 19-21 m, suggesting greater food availability because of lower organism density (including P. colymbus) and a greater water flux. Phytoplanktonic abundance and temperature were correlated (r2=0.38) with juvenile abundanc; this relationship and the association of juvenile abundance with higher temperature and Chlorophyll a levels, suggest that spat abundance was higher at the beginning of the water stratification period, when phytoplankton biomass is high.

Producción somática de dos especies de Crassostrea virginica e Ischadium recurvum (Bivalvia) en Mecoacán, Tabasco, México / Somatic production of two species: Crassostrea virginica and Ischadium recurvum Bivalvia in Mecoacán, Tabasco, México

The Mexican oyster fishery, 90% supported by the coastal lagoons of the Gulf of Mexico, has decreased drastically in the last six years as a result of anthropogenic pollution and improper management. The mussel Ischadium recurvum has proliferated and competes with oysters for space and probably food. Crassostrea virginica and Ischadium recurvum were studied to evaluate somatic production with biometry and physiological condition indices (PCI's) during an annual cycle. A random sample of 200 organisms was taken montly for each species. Condition indices wet flesh weigth: wet shell weight ratio (WFW/WSW), dry flesh weight: wet flesh weight ratio (DFW/WFW), dry flesh wet: dry shell weight ratio (DFW/DSW), and ash free dry weight: tissue dry weight (AFDW/TDW) were calculated. In order to stablish physiological condition and temporal variability, these indices were compared between species and months. The somatic production of mussels was higher than in oysters. This enhancement in production could be explained by: 1) Mussel uses less energy for shell production, 2) a constant recruitment of mussel almost year-round, and 3) the mesohalin lagoon was more favourable to the mussel.