Functional morphology and performance of New Zealand geoduck clam (Panopea zelandica) larvae reared in a flow-through system

Abstract

Understanding the parameters required for a reliable hatchery seed production of the endemic geoduck clam Panopea zelandica (Quoy and Gaimard, 1835) is crucial if New Zealand is to develop a geoduck aquaculture industry. To provide the foundation for routine geoduck larval rearing practices, this study reports on physiological, morphological, and behavioral characteristics throughout the larval developmental process. P. zelandica larvae were reared at 17°C and 35ppt, and fed continuously with Tisochrysis lutea and Chaetoceros calcitrans in a flow-through system. The initial veliger stocking densities ranged from 50 to 200larvaemL−1, while residual algal levels were maintained at 20,000 to 80,000cellsmL−1 in three rearing batches. Larval behavior and morphology were described through observation using video recordings, photomicrographs and scanning electron microscopy. The larval development took 16–19days from first D-veliger and metamorphosis occurred across a wide size range (300–375μm shell length). The increase in shell length was linear over time and correlated with the deposition of striae in the prodissoconch II. The ingestion rate followed a power function with time and was closely correlated with the development of the alimentary system, including mouth, esophagus, stomach, style sac, intestine, and digestive gland. Rearing with an initial stocking density of 100larvaemL−1 and residual algal background of 20,000cellsmL−1 resulted in about 76% survival and 15μmd−1 growth rate. The results of the preliminary production trials inform rearing practices and provide biological descriptions that appear to be effective as a baseline protocol for the successful commercial production of P. zelandica larvae. Statement of relevanceThis is the first detailed study of larval development within hatchery conditions for the New Zealand endemic geoduck clam (Panopea zelandica). We identified timing of larval developmental stages, including metamorphosis and growth and feeding parameters that are relevant for successful rearing practices of this species for commercial production.