| dc.description | Postlarval bay and sea scallops (Argopecten irradians and Placopecten magellanicus) undergo extreme morphogenesis of feeding organs and may be particularly vulnerable to nutritional deficiencies which, to date, remain largely undefined. The goals of this study were to (1) identify diets of few components to optimize scallop growth and survival, (2) identify the nutritional requirements of postlarval and juvenile scallops with special focus on polyunsaturated fatty acids (PUFA) and (3) identify differences in digestive competence over development and between scallop species. To this end, five growth trials (3-4 wks) were conducted offering scallops unialgal or binary diets consisting of one of three diatoms and one of five flagellates. Two additional trials were conducted (7-9 wks) to examine ontogenetic changes in enzymatic activity. Two binary diet combinations, Chaetoceros muelleri (CHGRA) in combination with either Pavlova spp. (CCMP strain 459; Pav 459) or Pavlova pinguis, consistently ranked among the highest diets tested, yielding postlarval growth rates as high as 28 and 59 mum day-1 for bay and sea scallops, respectively. Growth response appears related to two n-6 polyunsaturated fatty acids (PUFA): arachidonic (AA) found in CHGRA and docosapentaenoic acid (DPA) provided by Pav 459 and P. pinguis. Enrichments (relative to diet) of these individual fatty acids, as well as Sigman-6 fatty acids, were observed in tissues of both scallop species regardless of dietary treatment, suggesting a requirement for n-6 fatty acids in pectinids that has been largely overlooked. By contrast, the docosahexaenoic (DHA)-deficient diet of Tetraselmis striata/CHGRA ranked lowest for postlarval sea scallops but second highest for bay scallops, suggesting a more stringent DHA requirement in sea scallops, possibly to maintain membrane fluidity at the colder temperatures to which they are adapted. Species- and stage-specific differences in enzymatic activity were also observed with the most dramatic changes occurring before ∼1.2 mm in shell height. Mean activities of the three carbohydrases tested differed between scallop species, possibly an adaptation to the natural food supply. The nutritional requirements identified in this study should aid in the development of targeted diets to optimize scallop growth and increase the understanding of natural bivalve-seston interactions. | en_US |
