The P. similis (Fig. 1) that we explored was collected using a
45 μm mesh plankton net from an estuary in Ishigaki Island, Okinawa,
Japan on July 2004. The water temperature and salinity during the collection
were 27 °C and 2 ppt, respectively
A clonal culture of P. similis
was subsequently acclimatized to higher salinity under laboratory
conditions, fed Nannochloropsis oculata.
The total length, body length,
and body width of P. similis ranged from 50 to 150 μm (mean ± SD;
109 ± 15 μm), 40 to 110 μm (mean ± SD; 83 ± 11 μm), and 10 to
50 μm (mean ± SD; 40 ± 6 μm), respectively.
Its body length is 38%
smaller than the lorica length of B. rotundiformis (which ranged from
70 to 170 μm), and its body width is 60% narrower than the lorica
width of B. rotundiformis which ranged from 50 to 150 μm
Temperature and salinity are two important factors that influence
the population growth of rotifers.
The life history parameters of
P. similis under a wide range of temperature and salinity measures
were undertaken.
Temperature showed a strong influence on the
population growth of P. similis under the batch culture method
The maximum density (1400 ind ml−1
) was
obtained at 30 to 35 °C. This indicates its usefulness in feeding subtropical
and tropical fish species.
Results also showed that P. similis is a
euryhaline species because it can propagate in a wide range of salinity
(2–25 ppt), although it can reproduce faster at 2 ppt
This salinity corresponds to the salinity to where P. similis was
sampled. However
found P. similis in hypersaline
water (48–98 ppt). The capability of P. similis to tolerate a wide
range of salinity is similar to that of the euryhaline rotifer Brachionus
plicatilis sp. complex, which is reported to thrive from 1 to 60 ppt
Seven-band grouper Epinephelus septemfasciatus