Effect of temperature on resting egg formation of the tropical
SS-type rotifer Brachionus rotundiformis Tschugunoff
M.
Assavaaree, A. Hagiwara, T. Kogane, M. ARIMOTO-2003
Fisheries
Science, 69(3):
520-528
Abstract:
Tropical
minute rotifer strains (SS-type) induce mixis at 30-35°C but sexual
reproduction and resting egg formation do not proceed well due to rapid
environmental change. The present study examined the effect of temperature
regulation on rotifer Brachionus rotundiformis (Langkawi strain,
SS-type) resting egg formation in small (500 mL in culture volume)- and
large-scale (500 L in culture volume) experiments. Rotifers were
cultured at 30°C in 15-17 p.p.t. seawater with an initial density of 1 individual
(ind.)/mL. After 4 days, when cultures were in exponential growth stage
with active mixis induction, the culture temperature of the experimental
rotifers was changed to 25°C. Control rotifers were cultured at 30°C
throughout the experiment. Fresh or frozen Nannochloropsis oculata
and condensed freshwater Chlorella vulgaris were used as the rotifer
diets in the small- and large-scale experiments, respectively. Significantly
higher resting egg production was observed with the experimental rotifers
(30
25°C) versus the control rotifers. In the large-scale trial, experimental
rotifers produced 2.6
x 106
resting eggs during a 9-day experiment, which was 1.6-fold more than the
control rotifers. Moreover, the efficiency of resting egg formation was
found to increase by a factor of 1.8. The present study indicates that
decreasing culture temperature from 30 to 25°C after active mixis increased
resting egg formation in B. rotundiformis (SS-type).
(Graduate School of Marine Science and Engineering,
Nagasaki University, Nagasaki, Nasagaki 852-8131, Japan, Tel:
81-95-847-1111.
Fax: 81-95-844-3516. Email of A. Hagiwara:
hagiwara@net.nagasaki-u.ac.jp)