Growth and health status of cultured edible oyster, Crassostrea madrasensis (Preston) in the Panadura estuary, Sri Lanka

Abstract

To intensify the production of edible oyster in Sri Lanka in the future it is essential to analyse the status of the present culture practices. The present study was carried out to investigate the growth and health of cultured edible oyster, Crassostrea madrasensis in relation to the prevailing water quality parameters and external fouling in a small-scale, commercial farm located in the Panadura estuary, Sri Lanka. The mean growth rate in shell length and shell width varied between 0.06 ± 0.01 mm and 2.19 ± 0.09 mm and between 0.02 ± 0.02 and 2.11 ± 0.39 mm per week, respectively. There were positive significant relationships between the growth rate in shell width and salinity, as well as the conductivity of culture water (p < 0.05). Mean total dissolved solids in culture water had a positive significant relationship to the growth rate of oysters in shell length (p < 0.05). External fouling organisms that grew on the outer shell surface caused significant reduction in growth rate as well as the weight gain of cultured C. madrasensis (p < 0.05).

Histological sections of the gills, mantle, digestive gland and digestive tract of oysters exhibited structures similar to plasmodia of a haplosporidian parasite, which reached the stage of rupturing during the period of low salinity. C. madrasensis could tolerate the low salinity, ranging from 0 gL1 to 6.0 gL-1 with 83.0 ± 2.47 % survival; the highest mortality recorded during the period with low salinity in culture water was 15.00 ± 2.50 %.