LIFE HISTORY AND FECUNDITY OF OFSPRING FROM SELECTED SMALL SIZE
EGG BEARING FEMALE OF THAI-SS ROTIFERS Brachionus rotundiformis
Tschunugunoff.
Agus Somamihardja*, Amrit. N. Bart.
Aquaculture and Aquatic Resources Management,
Asian Institute of Technology
P.O Box 4. Klong Luang, Phatumthani 12120,
Thailand.
Agus.Somamihardja@ait.ac.th
Rotifer (Brachionus sp) is one of the most important sources of live food for marine fish and
crustacean larviculture. However, rotifers size is remain too large for the newly opened
mouth stage of some marine finfish larvae. Ultra small egg bearing females (90-120 µm)
were reported and studies have been carried out to develop smaller body size rotifers
population. Study on characteristics of small size egg bearing females present in SS strain
rotifers was conducted.
Small size egg bearing females (120±6 µm
in lorica length, and 99±7µm in lorica
width) was selected by a series of sieving
through 70 µm. Offspring size; fecundity
and life history then identified. It revealed
generally they showed shorter life span
and lower lifetime fecundity (Table 1).
In another study, average size of
population derived from mass and
individual selection was compared. Mass
selection was conducted by developing
population
through
continuously
developing rotifers which was passed
through 70 µm screen net. Individual
selection was carried out by developing a
single or a few selected small size egg
bearing female. No different in average
size was observed among initial population
with the population derived from mass and
individual selection (approx. 1 month),
(Figure 1).
TABLE 1 Life history of offspring derived
from small size egg bearing females.
Variable
Normal Size
rotifer
Small size
rotifers
Life span (days)
9.65 ± 2.23
5.11 ± 1.05
Lifetime fecundity
Pre-reproductive
periods (days)
Reproductive periods
(days)
Post reproductive
Periods (days)
Reproductive rate
(Offspring/day)
11.83 ± 4.37
1.00 ± 0.1
4.78 ± 1.79
1.03 ± 0.08
6.25 ± 1.5
2.58 ± 1.15
2.31 ± 1.16
1.50 ± 0,87
1.87 ± 0.43
2.02 ± 0.70
FIGURE 1 Histogram of rotifer size
(LL=lorica length, LW=lorica width) from
initial population, and population derived
from mass and individual selection.
200
180
160
140
120
100
80
60
40
LL
20
LW
0
Initial Population
Mass selection
Individual selection