Finding new diatoms for
intensive rearing of the pacific oyster (Crassostrea gigas): energy
budget as a selective tool
L.
Barillé, J. Haure, E. Pales-Espinosa, M. Morançais-2002
Aquaculture, 217(1-4) : 501-514
Abstract:
Intensive shellfish rearing in the polders of
Bourgneuf Bay on the French Atlantic coast (46–47°N, 1–2°W) relies on
the diatom Skeletonema costatum (Grev.) Cleve produced in
nutrient-rich saline ground water. An episodic reduction in biomass
production caused by an unidentified protozoon stressed the need to find new
microalgal species as substitutes for S. costatum and diversify the
microalgae used by the bivalve industry. Three species met the requirements
for year-round availability in Bourgneuf Bay coastal waters and growth
potential in saline ground water: Nitzschia acicularis (Kützing), Nitzschia
closterium (Ehrenberg) Wm Smith and Nitzschia gandersheimiensis
Krasske=Nitzschia tubicola Grunow. These microalgae were tested as
food sources for adult Pacific oysters (Crassostrea gigas) by
comparing short-term bivalve physiological responses with those obtained
with S. costatum as reference. Suspended particulate matter
concentrations in experimental diets ranged from 9.3 to 18.6 mg l-1
and particulate organic matter concentrations from 3.3 to 5.7 mg l-1.
Significant differences were observed, with clearance rates ranging from 4.0
l h-1 g-1 for N. acicularis to 7.3 l h-1
g-1 for N. gandersheimiensis. The filtration rate for
organic matter was significantly higher for N. gandersheimiensis than
the other species, but this algae was also significantly more rejected in
pseudofaeces. No differences were found among the four mean faeces
production rates. Net energy balance differed significantly among the four
microalgae tested, ranging from 282 J h-1 g-1 for S.
costatum to 27 J h-1 g-1 for N. closterium.
However, no differences were found between S. costatum, N.
acicularis and N. gandersheimiensis. These results suggest that N.
acicularis and N. gandersheimiensis could be tested on a larger
scale involving the production of microalgae in 50-m3 outdoor
tanks in association with Pacific oyster growth experiments.
(Laboratoire
de Biologie Marine, Faculté des Sciences, ISOMER, 2 rue de la Houssinière,
B.P. 92208, 44322, Nantes Cedex 3, France, e-mail : barille@isomer.univ-nantes.fr)