First feeding of winter
flounder (Pseudopleuronectes americanus) larvae: use of Brachionus
plicatilis acclimated at low temperature as live prey
L. Mercier, C. Audet, J. de la Noüe, B. Parent,
Ch.C. Parrish, N.W. Ross-2004
Aquaculture, 229(1-4): 361-376
Abstract:
Brachionus plicatilis
are used as live prey for rearing winter flounder larvae at first feeding.
This rotifer is grown between 20 and 25 °C (its optimal growth temperature)
and then introduced into the 10 °C water in which larvae are reared. The
rapid thermal difference between the two media is thought to reduce B.
plicatilis quality and consequently affect larval rearing efficiency. In
order to optimize larval rearing, a study was conducted to compare the
effects of two different diets on larval growth performance and nutritional
condition: (1) larvae fed B. plicatilis reared at 24 °C and (2)
larvae fed B. plicatilis reared at 24 °C but acclimated overnight at
10 °C. Comparisons were undertaken using morphometric measurements, nucleic
acid (RNA/DNA) ratios, total protein content, trypsin activity, and
triacylglycerol/sterol ratios. Fatty acid composition of larvae was also
studied with a focus on the levels and ratios of three essential fatty acids
(docosahexaenoic acid or DHA, eicosapentaenoic acid or EPA, and arachidonic
acid or AA). Unique information regarding trypsin activity and lipid
components (phospholipid, triacylglycerol, and sterol) of winter flounder
larvae is provided in this study. Trypsin activity was detected very early
in larvae and was not affected by acclimation of prey. Phospholipid,
triacylglycerol, and sterol composition showed no significant difference
between the two diets tested and was characterized by high phospholipid
content as well as low triacylglycerol and sterol contents. EPA, DHA, AA,
DHA/EPA, and DHA/AA decreased from days 12 to 26. Interestingly, DHA content
was significantly higher in larvae fed acclimated rotifers and AA content
decreased significantly in 26-day-old larvae fed acclimated B. plicatilis.
Overall results indicate that overnight acclimation of B. plicatilis
at 10 °C is not important for optimizing the rearing of winter flounder
larvae although it does influence the fatty acid composition.
(Institut des Sciences de la Mer de Rimouski,
Université du Québec à Rimouski, 310 allée des Ursulines, Rimouski,
Quebec, Canada G5L 3A1, e-mail of C. Audet: celine_audet@uqar.qc.ca)