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《African Journal of Marine Science》2013,35(3):567-575
Culture of pearl oysters is rapidly increasing worldwide, including the western Indian Ocean. The oyster Pinctada margaritifera L., which produces the most highly valued black pearls, occurs in East Africa, a nd as been exploited there for the shell for many decades. The growth patterns of P. margaritifera from a natural population in the sheltered back-reef, and fro oysters translocated to a tidal current-swept site, both sites within Gazi Bay, Kenya, are described. The growth rate in the natural population ranged from 31.3mm year?1 (60–65mm size-class) to 7.6mm year?1 (105–110mm size-class). The von Bertalanffy growth coefficient (K), calculated with a fixed L∞ of 127.2mm, was 0.30 for the natural population and 0.38 for the translocated oysters. The mean growth rate during the north-east monsoon season was approximately double that for during the south-east monsoon season. The dailyrate of nacre deposition ranged from 1.3μm to 5.9μm (mean 3.45μm); it declined with the size of oysters and was marginally higher at the high-energy current site. At that rate, it would take approximately two years to produce a marketable cultured half pearl with a 2.5mm layer of nacre. The results of the study are relevant to the understanding of the influence of the environment on growth, and are applicable to the optimisation of growth rate of pearl oysters in the inshore region along the east coast of Africa. 相似文献
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《African Journal of Marine Science》2013,35(1):51-60
The sagittal otoliths of Lophius upsicephalus, although extremely variable in shape, were found to be the only structures suitable for age estimation. The annuli are multi-ringed zones separated by "wider than normal" opaque zones. They are difficult to interpret, especially those of fish older than nine years. Periodicity of annulus formation could not be determined by standard methods. By inference, annulus formation could be related to feeding habits and reproductive seasonality. The growth in length (sexes combined) is best described by Length-at-age = 733,7 (1 – e?0,1054 (t + 1,879))mm. There is a significant difference in growth by mass between the sexes. The respective equations describing growth by mass (in g) for males and females are: Weight-at-age = 8616 (1 – e?0,1054 (t + 1,879))2,805 and Weight-at-age = 9499 (1 – e?0,1054 (t + 1,879))2,890. 相似文献
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