Growth of postlarval sea
scallops, Placopecten magellanicus, on microalgal diets, with
emphasis on the nutritional role of lipids and fatty acids
L.M. Milke, V. Monica Bricelj, Ch.C. Parrish-2004
Aquaculture, 234(1-4): 293-317
Abstract:
Culture of the sea scallop, Placopecten
magellanicus, is constrained by a reliable supply of high-quality
postlarvae, yet little is known about the diets and essential nutrients
required to maximize growth and survival during these vulnerable stages.
Therefore, post-settlement sea scallops were exposed to binary microalgal
diets consisting of a flagellate: Pavlova lutheri, Pavlova sp.
(Pav, CCMP 459) or Tetraselmis striata (Plat-P) and a diatom: Chaetoceros
muelleri, Thalassiosira weissflogii or Fragilaria familica
for 28–30 days. The combination Pav 459/C. muelleri provided a
superior diet for sea scallop postlarvae, yielding a growth rate of up to 28
µm day-1. However, when these algae were offered singly, a 32%
(Pav 459) and 64% (C. muelleri) decrease in growth rates was
observed, indicating that both species made a significant contribution to
the success of the mixed diet. The two species are characterized by unique
signatures of n-6 polyunsaturated fatty acids (PUFAs): C. muelleri
has high levels of arachidonic acid (AA), and Pav 459 (in contrast to P.
lutheri) has high levels of n-6 docosapentaenoic acid (DPA). DPA
was selectively incorporated into tissues of scallops fed all binary diets
except the one rich in DPA (Pav 459/C. muelleri). These results,
coupled with a marked increase in n-6/n-3 ratios between the
diet and tissues, provide evidence that n-6 PUFAs may play an
important and previously underestimated role in scallop nutrition. The diet
of T. striata and C. muelleri, which yielded the lowest growth
rate (8.1 µm day-1) contained dietary docosahexaenoic acid (DHA;
22:6n-3) concentrations 4.5–7× lower than any other binary
treatment. Low DHA levels may thus explain the poor performance of this
diet. Tissue protein and triacylglycerol concentrations reflected diet
performance, with higher values generally associated with more successful
diets. This work suggests that DHA, as well as the n-6 PUFAs AA and
DPA, may be essential for optimizing growth of sea scallop postlarvae.