King, N., Howell, H., Tomlinson, A., Bidwell, D., Fairchild, E.
Abstract:
The addition of microalgae to larval rearing systems ("green water"
treatment), has been shown to enhance the growth and survival of
certain marine fish species. Along with the presence or absence of
microalgae, diet type effects larval growth, and several studies have
demonstrated that cultured live food organisms (e.g. rotifers and brine
shrimp) are nutritionally inferior to wild zooplankton as a first food
for marine finfish larvae.
In a 2 X 2 factorial design experiment that lasted for 5 weeks from
first feeding, we examined the effects of green water, clear water,
wild zooplankton and cultured rotifers (Brachionus plicatilis) on the
growth of winter flounder (Pleuronectes americanus) larvae. The
experiment was initiated by stocking 200 larvae into each of eight 20
liter, round plastic aquaria. A clear starvation treatment served as the
control. Treatments were static with 50% water changes every third
day. Algae (Isochrysis galbana (Tahitian strain)) were added to green
water treatments every third day at a density of 200,000 cells/ml.
Cultured rotifers (Brachionus plicatilis) were fed at an average daily
rate of 2,600/liter. Wild zooplankton, consisting mostly of copepod
nauplii ranging in size from 48 - 200 microns, were fed at a daily rate
of 2100/liter. Water temperature ranged from 8 to 15 C with a daily
average of 10 C, and salinity was maintained at 30 - 32 ppt. A random
sample of 10 larvae from each treatment were measured to the nearest
mm (SL) each week. Data were analyzed using 2x2 factorial analyses.
In each week of the experiment, fish in green water treatments,
regardless of food type, were significantly longer (P<0.05) than those
in clear water treatments. There were no differences (P>0.05) in
larval lengths between food types within either green or clear water.
Specific growth rates (length increases per week) were 15.4, 14.2,
10.4, and 8.4% for green water/wild zooplankton, green
water/rotifers, clear water/rotifers, and clear water/wild zooplankton,
respectively.
Results of this study indicate that green water enhances the growth of
winter flounder larvae, and that there is little, if any, difference
between wild zooplankton and rotifers as a first feeding diet.
(UNH Coastal Marine Laboratory, PO Box 474, Newcastle, NH
03854, USA)