Nutritional value of fresh
and concentrated algal diets for larval and juvenile Pacific oysters (Crassostrea
gigas)
E.
Ponis, R. Robert, G. Parisi-2003
Aquaculture, 221(1-4): 491-505
Abstract:
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 1 °C 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; P. lutheri+C.
calcitrans; T-Iso+C. calcitrans), fresh or concentrated (1 °C),
diets were evaluated on Pacific oyster (Crassostrea gigas) with
larval and juvenile feeding trials, lasting 1 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.
(Dipartimento di Scienze Zootecniche, Università di
Firenze, Via delle Cascine 5, 50144, Florence, Italy, e-mail of R. Robert: rrobert@ifremer.fr)