Interaction between handling cost and growth of the bivalve-feeder Halla okudai under rearing conditions, in relation to prey species

Abstract

In order to evaluate the interaction between handling cost and growth of the bivalve-feeder Halla okudai (Polychaeta: Lysaretidae), the observation of foraging behavior and measurement of energy budget were conducted in laboratory feeding experiments by offering three different bivalves: the short-neck clam Ruditapes philippinarum, the blue mussel Mytilus galloprovinciallis, and the Pacific oyster Crassostrea gigas. The total handling time was 1.6-2.7 times longer in the oyster-group (25.6 ±9.3 h) than in the clam and mussel-groups, while the total searching and feeding time hardly varied with prey species. No significant difference in the amount of ingestion (4.5-5.3 kcal/polychaete per 15 days) was shown among the three prey groups. However, the growth increment was 1.5-2.1 times higher in the clam-group (1.85±0.65kcal/polychaete per 15 days) than in the other two prey groups. In contrast, the scope for active rate of respiration and jelly-like material secreted during handling was higher in the oyster-group (0.66±0.14 and 0.24±0.07 kcal/polychaete per 15 days, respectively) and mussel-group (0.62±0.07 and 0.16±0.05kcal/ polychaete per 15 days) than in the clam-group (0.48±0.09 and 0.06±0.01 kcal/polychaete per 15 days), although there were no significant differences in the standard rate of respiration, excretion, feces and jelly-like material secreted during feeding among the three groups. These results indicate that growth of H. okudai increases with a decreasing handling cost, when feeding on the optimal prey species.