Effect of temperature on resting egg formation of the tropical SS-type rotifer Brachionus rotundiformis Tschugunoff

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 × 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).

Effect of salinity during resting egg formation and hatching on descendent reproduction in the rotifer Brachionus rotundiformis Tschugunoff

“…We hypothesized that resting egg formation and hatching associated with seasonal changes of salinity could affect descendent sexual reproduction. In order to test this hypothesis, culture conditions (i.e., temperature and food) were adjusted to induce active sexual reproduction of B. rotundiformis according to previous studies (Assavaaree et al, 2003;Hagiwara et al, , 1995Hirayama and Rumengan, 1993). In the presence of abundant and high quality food and an optimal temperature for rotifer population growth, the rotifers in the current study showed strong population growth compared to a natural population (<0.5 ind/mL, Snell et al, 2001).…”

“…For organisms to survive and successfully colonize this area, they must possess certain physiological tolerances (Calder and Maÿal, 1997;Dumont, 1983;Nybakken, 2001;Saraswathy and Nair, 1974). The estuarine rotifer Brachionus rotundiformis Tshugunoff is capable of tolerating salinity variation like many other euryhaline zooplanktons (Assavaaree et al, 2003). We hypothesized that resting egg formation and hatching associated with seasonal changes of salinity could affect descendent sexual reproduction.…”

Waste-grown phototrophic bacterium supports culture of the rotifer,Brachionus rotundiformis

“…However, a sudden drop in temperature from 23°C to 18°C resulted in high mortality of S‐type B. rotundiformis although they could withstand the sudden rise in temperature from 23°C to 28°C (Fielder, Purser & Battaglene ). While higher water temperatures of 30–35°C induced mixis in SS‐type B. rotundiformis , the rotifers exhibited higher growth rate and produced significantly more resting eggs at 25°C than at 30°C (Assavaaree, Hagiwara, Kogane & Arimoto ). In contrast, the larger L‐type rotifer, Brachionus plicatilis prefers cooler temperatures of 18–25°C (Hagiwara et al .…”

Nutritional value and production of three species of purple non-sulphur bacteria grown in palm oil mill effluent and their application in rotifer culture

“…Assavaaree et al . () reported that B. rotundiformis fed with microalgae at 15 g L −1 salinity exhibited reduced growth rate and higher resting egg production when water temperature was brought down from 30 °C to 25 °C. Thus, a stable water temperature sustained in an indoor hatchery appears necessary to maintain a higher rotifer density.…”