Journal
AQUACULTURE
Volume 221, Issue 1-4, Pages 491-505Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/S0044-8486(03)00075-9
Keywords
microalgal concentrates; mollusc; flocculation; food value; Pavlova lutheri; T-Iso; Chaetoceros calcitrans
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Three species of microalgae commonly used as feed for bivalves, Pavlova lutheri, Isochrysis aff. galbana (clone T-Iso) and Chaetoceros calcitrans forma pumilum, were produced with standard techniques and then harvested by a flocculation procedure. This method was effective for C calcitrans and P. lutheri though a partial deterioration of cells was observed for the latter, whereas flocculation heavily damaged T-Iso cells (diffuse cellular lysis, majority of cells clumped and/or misshapen, loss in organic matter). Quality of concentrates concentrated at I degreesC was investigated by means of gross composition analysis and pheophytin a/chlorophyll a evolution over 4 weeks of storage. P lutheri concentrates did not exhibit significant changes in gross composition over the storage period, whereas the value of pheophytin a/chlorophyll a remarkably increased, from 0.05 to 0.35. In T-Iso concentrates, a dramatic decrease in protein and carbohydrate content occurred during the first week of storage. The chemical composition of concentrated C calcitrans cells did not substantially change during the first 3 weeks of storage;, after this period, the organic matter decreased significantly (- 18%). The effectiveness of trispecific (P. lutheri +T-Iso + C. calcitrans) and bispecific (P. lutheri +T-Iso; R lutheri + C calcitrans; T-Iso+C calcitrans), fresh or concentrated (I degreesC), diets were evaluated on Pacific oyster (Crassostrea gigas) with larval and juvenile feeding trials, lasting I and 4 weeks, respectively. For larvae, concentrated diets of P. lutheri+T-Iso and T-Iso+C. calcitrans stored for 7-14 days gave better growth than the equivalent fresh diets (P<0.05). In the juvenile trial, the use of the same concentrates for a longer period (4 weeks) gave significantly lower growth compared to the corresponding fresh microalgae. In this case, the longer time of storage (8-36 days) probably prejudiced the quality of the stored concentrates. This fact was confirmed by means of larval consumption assays of fresh and concentrated microalgae using fluorimetry probes. Indeed, for P lutheri delivered as fresh microalgae, larval grazing was twice that of concentrated cells. (C) 2003 Elsevier Science B.V. All rights reserved.
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