Ingestión y digestión de siete especies de microalgas por larvas de Strombus gigas (Mesogastropoda: Strombidae) / Ingestion and digestion of seven species of microalgae by larvae of Strombus gigas (Mesogastropoda: Strombidae)

The potential nutritional value of seven microalgal diets as measured by their ingestibility and digestibility to queen conch Strombus gigas larvae was tested with 30 day old larvae reared at 28 degrees C and fed at 1000 cells x ml(-1). The algae were Tetraselmis suecica, Tetraselmis chuii Isochrysis aff. galbana, Dunaliella tertiolecta, Chlamydomonas coccoides, Chaetoceros sp. and Thalassiosira fluviatilis. Ingestion and digestion were measured by the four nutritional stages studied with epifluorescence microscopy with live larvae. Temporal and absolute indices showed that larvae fed Chaetoceros sp. and T. fluviatilis had lower ingestion and digestion levels. The other algae are recommend to feed S. gigas larvae.

Ciclo reproductor e índices de condición usados en Melongena corona (Mollusca: Gastropoda) / Reproductive cycle and index of condition used for Melongena corona (Mollusca: Gastropoda)

Melongena corona bispinosa was studied in Yucatán, México (21 degrees 16' N, 89 degrees 49' W) for a year. Males have reproductive peaks in February and December, and a post-copulation peak in June. Female peaks are in March and May, plus oviposition peaks in April and January. Males and females differ in the mean gonadosom ic index (F=13.79, p<0.05) but not in the dry tissue/shell weight (F=0.0902, p<0.05), dry tissue and total weight (F=0.2466, p<0.05) and dry tissue weight/internal shell volume (F=1.0565, p<0.05).

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.

Desarrollo embrionario de Strombus pugilis (Mesogastropoda: Strombidae) en el laboratorio / Embrionary development of Strombus pugilis (Mesogastropoda: Strombidae) in the laboratory

Stages from oviposition to veliger hatching are described for Strombus pugilis under laboratory conditions. Two egg masses from Playa Seyba, México, (20 degrees 45' N, 91 degrees 45' W) were used (three sub-samples per mass). Each sub-sample was immersed in a 11 container at 29 +/- 1 degrees C. This description is based on stages known from Strombus gigas, which include number of: fertilized eggs, morulae, gastrulae, trochophore larvae with slow movements, larvae with primordium foot, larvae with eyes, larvae with statocyst and veliger larvae. Eggs with first division appeared five hours after oviposition in the three replicates of each mass, although in greatest number in one of the egg masses. Trochophore larvae with slow movements appear after 50-54 hours and veligers hatch after 90 hours.

Distribución, abundancia, densidad y morfometría de Strombus gigas (Mesogasteropoda: Strombidae) en el Arrecife Alacranes, Yucatán, México / Distribution, abundance, density and morphometry of Strombus gigas (Mesogasteropoda: Strombidae) in Alacranes reef, Yucatán, México

A population of the conch Strombus gigas was sampled in 109 transects (100 x 10 m each) for an area of 109000 m2 (eight surveys in 1998 and six in 1999) in Yucatan, Mexico; S. gigas was the most abundant conch species (97% of individuals) and ocurred at depths of 0.5-18 m. Mean density was 0.0084 individuals/m2 (Standard deviation SD=0.0138, n=1910). Maximum density (0.015 individuals/m2) was at 0.5-2 m and minimal (0.001 individuals/m2) at 16-18 m. Shell length was 120-290 mm (mena=211.6, SD=26, n=1136). Shell lip thickness, measured only in adults, was 1-28 mm (mean=8.7, SD=7.5, n=1136).

Crecimiento y sobrevivencia de semillas del ostión Crassostrea virginica en una granja camaronícola en Yucatán, México / Growth and survival of seeds of the Crassostrea virginica oyster on a shrimp farm in Yucatán, México

A lot of 1600 seeds of American oyster Crassostrea virginica from the coastal lagoon La Redonda, Tabasco, Mexico was cultured in main drainage channel (S1), a secondary drainage channel (S2), the floodgate of a white shrimp Pennaeus vannamei pond (S3) and the marine water supply pond (S4). The seeds, with a total height and initial humid weight of 31.67 +/- 3.43 mm and 4.29 +/- 1.32 g, respectively, were cultured in suspended Nestier oyster boxes at 575 org/m2. Biological and environmental parameters were recorded after 296 days, the seeds in S4 reached height and weight values of 52.55 +/- 7.51 mm and 16.30 +/- 4.94 g, respectively. The index of physiologic condition along the experiment had a variation of 1.26% to 3.45%. In S4 the survival was 81.0%. In the other places the mortality was total after 90 days.