Effect of sedentary biofoulers on the growth and survival of cultured oysters (Crassostrea tulipa) towards its mass culture in the Densu Delta, Ghana

Abstract

Biofouling has been reported to be both harmful and innocuous on the growth and survival of cultured bivalves. If harmful, it could increase the operational cost substantially in an attempt to mitigate it. The study investigated the effect of sedentary biofoulers on the growth and survival of Crassostrea tulipa cultured on coconut shell and oyster shell cultches in the Densu Delta, Ghana, from December 2017 to July 2018. Physico-chemical parameters were monitored. Environmental temperature (26.4 ± 0.07 °C–29.5 ± 0.50 °C) and pH (7.2 ± 0.01–8.8 ± 0.01) were found to be within optimum levels for oyster propagation. The low levels of salinity (0.2 ± 0.01 ‰) and DO (0.6 ± 0.01 mg/l) and high turbidity (31.4 ± 2.91 NTU) could explain the observed high mortality of cultured oysters in July 2018. The observed fouling organisms were Fistubalanus pallidus (barnacle), Brachidontes sp. (mussel), Ficopomatus sp. (tube worm), Chaetomorpha antennina (green alga), and sea anemone. Oysters cultured on the undersurface of biofouled oyster shell cultches exhibited significantly faster growth than their cleaned counterparts but comparable on the upper surfaces of the cultches. The growth of cultured oysters on biofouled coconut shell cultches exhibits faster but insignificant growth than the oysters on cleaned cultches. There was no significant difference between the survival of oysters cultured on biofouled and cleaned coconut shell and oyster shell cultches. Marketable size oysters (≥ 6 cm shell height) are attainable in 7 to 8 months for both treatments. It was concluded that biofouling had no deleterious effect on the growth and survival of oysters. Besides, given the preferred shucked oysters in the Ghanaian market, it is inessential to incur further cost to control biofoulers.