Condition index, meat yield and biochemical composition of Crassostrea brasiliana and Crassostrea gigas grown in Cabo Frio, Brazil

Abstract

Samples of tray-grown Crassostrea gigas from imported seed and of the closely related Crassostrea brasiliana from a local natural population in tropical waters of Brazil were examined monthly during a 4-year period. Parameters of condition, including the condition index, wet meat yield and gross biochemical composition, were determined and seasonal and annual differences assessed. It was concluded that C. gigas harvested in their first year of growth compared favourably in quality with the native species. Condition varied seasonally and in both species highest values were during the summer when coastal waters were influenced by the upwelling of relatively nutrientrich water. Median condition indices were 79.4 for the native oyster and 72.3 for C. gigas. The lower median value for C. gigas was related to the predominance of larger animals in samples; there being a significant relationship between animal size and condition index ( P<0.001). C. gigas which grew to 100 g live weight in 1 year yielded about 11 g wet meat whereas the largest C. brasiliana at 42 g live weight yielded 5.3 g wet meat. Glycogen values as a percentage of dry meat weight peaked at 16% in October in the native species and 12.5% in December in C. gigas. The potential for the culture of C. gigas in the tropical region of Brazil is discussed.