Feeding behaviour and metabolic efficiency contribute to growth heterosis in Pacific oysters [Crassostrea gigas (Thunberg)]

Physiological measurements were made on Pacific oysters from controlled cro sses between inbred lines. Hybrid individuals were expected to perform bett er than inbred oysters, for a variety of traits related to feeding behaviou r. The oysters were offered a diet simulating natural suspended particulate matter. By quantifying the organic and inorganic fractions of food, faeces and pseudofaeces, various aspects of feeding were elucidated. The results agreed with expectation; on average, hybrid oysters had higher rates and ef ficiencies of feeding and growth than inbreds. In one experiment there were significant differences between hybrids and inbreds for seventeen out of t wenty cases; in another experiment hybrids performed better than inbreds fo r eight out of sixteen cases. In both experiments, we find significant diff erences between the reciprocal hybrids, though heterosis for growth is evid ent for all hybrids. Our experiments therefore confirmed heterosis for grow th and hybrid superiority for physiological traits, independent of ration l evel; emphasised the complexity of these relationships amongst genotypes; a nd demonstrated the segregation of physiological traits in the F-2 generati on. (C) 1999 Elsevier Science B.V. All rights reserved.