Effect of lipid emulsion and kelp meal supplementation on the maturation and productive performance of the geoduck clam, Panopea globosa

Abstract

Adult Panopea globosa clams were conditioned in the laboratory during 8weeks (mid Oct–Dec) under a decreasing temperature regime (22–18°C) and using a semi-open recirculating system to investigate the effect of kelp meal (powdered Macrocystis pyrifera) or fish oil supplementation to live microalgal diets (w/w basis) on the live body weight (BW), flesh weight (FW), body water content (BWC), gonad weight, gonadosomatic (GI) and condition indices (CI) of experimental organisms. Three dietary treatments were used, and consisted of 100% of the flagellate Isochrysis sp. clone T-ISO (treatment I), 70% T-ISO+30% kelp meal (IK), and 70% T-ISO+30% cod liver oil (IO). Ingestion rates (IR) were also assessed during the first month of the experiment in clams from treatment I. The IR exhibited by adult P. globosa remained relatively constant during the evaluation period (0.027–0.035%BWd−1). In contrast, significant time- and diet-dependent effects were observed in the live weight of conditioned organisms, those from treatment I showing the maximum values (1369 to 1533g) after 7weeks, followed by IO and IK. Lowest BWC (39.0 to 42.1%) coincided with the timing of maximum live weight and female gonad weight. Female and male gonad weights increased 2-fold and 1.4-fold respectively within the first month. Gonads from the IK treatment tended to be lighter than those from diets I or IO. Significant time, diet, and time×diet effects were observed on the flesh weight of the organisms, with higher values on the 8th week for organisms from treatment I. Neither CI nor GI was significantly affected by the test factors. Viable oocytes were detected only after 6weeks of conditioning. Overall, the ration demanded by adults of P. globosa is relatively low, and adults can be successfully matured in the laboratory within a period of 6 to 8weeks with Isochrysis sp. clone T-ISO as the sole diet, and an effective accumulated temperature of ca. 230degree-days.