Pen shells are economically important and most are threatened by overexploitation and habitat degradation. Cultivation represents an alternative for preserving the resource and increasing the production. Atrina maura was cultivated in a suspension system which was followed by a bottom phase. Samples of pen shells and tissues were collected monthly to measure absolute growth, shell height increase, and an adductor muscle index. After the trials, adults shell height was 195 ± 10 mm, total weight was 223 ± 28 g, and mean shell height increase was 0.81 cm/mo. Protective devices were vital to avoid predation by crabs and fish; survival was 90% in the suspension phase and 70% in the bottom phase. Variations in the muscle index were apparently related to reproduction, suggesting activity (partial spawning)
28°C). Gametogenic activity seemed to be strongly regulated by water temperature. The average growth rate of oocyte cohorts was calculated (0.41 ± 0.10 µm day_1), with the most rapid growth (0.67 µm day_1) from September through October. The condition index was higher in summer, but other peaks occurred in winter, producing accumulation of nutrients from increased phytoplankton biomass. The female:male ratio was 1:1.3; no hermaphrodites were detected. A reproductive classification is proposed. These results can help regulate exploitation and establish off-limit periods for this clam in the Gulf of California.]]>
The genetic variability of two consecutive generations of a new strain of Crassostrea gigas, intended to be established in the Gulf of California, was evaluated at six microsatellite loci. A total of 66 alleles and 146 genotypes in the broodstock sample and 68 alleles and 168 genotypes in the F1 sample were detected. The mean observed heterozigosity was 0,65 for the broodstock and 0,67 for F1, with no significant differences between them. All loci showed a deficit of heterozygotes with the exception of ucdCg10 in the F1, but no evidence of cumulate inbreeding was found. Five loci demonstrated differences in allelic and genotypic frequencies. The monitoring of the genetic variability in hatchery-produced organisms is not a current routine task in the quality control process of most hatcheries. Microsatellite analysis is a good tool for monitoring the heterozygosity fluctuations along the productive life of cultured strains.
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