Search

In order to investigate the live food value of microalgae for efficacious rearing of larvae and spats of bivalve, we studied growth rates of four microalgal species (Isochrysis galbana, Pavlova lutheri, Chaetoceros simplex, Tetraselmis tetrathele) cultured in different environmental conditions. These include changes in temperatures (20, 25, 30 and 35℃), salinities (20, 25, 30 and 33 psu) and light intensities (60, 100 and 140 μmol m -2 s -1 ). The growth rate of I. galbana was faster at 25℃ than that of 20℃. At 25℃ the highest growth rate of I. galbana was observed at 33 psu (0.413) and the lowest at 20 psu (0.368) in 10 days of culture (P < 0.05). The growth rate of I. galbana was lower at 25 psu (0.383) than that of 30 psu and higher than that of 20 psu (P < 0.05). Similar temperature and salinity-dependent changes were also found in P. lutheri and T. tetrathele. C. simplex showed faster growth rate at 30℃ than that of 25℃. The highest growth rate of C. simplex was observed at 33 psu (0.428) and the lowest at 20 psu (0.389) in 10 days of culture (P < 0.05). Upon exposure to the light with different intensities, all four microalgal species showed a significantly faster growth rate at 140 μmol m -2 s -1 than at 100 μmol m -2 s -1 (P < 0.05).

This study aimed to evaluate the effect of nutrient depletion during the cultivation of the microalgae Tetraselmis tetrathele, and to verify the algal growth and productivity in different culture media (Guillard f/2 and Conway). The experiment was conducted in nine-liter containers, with working volume of eight liters, salinity 35 ± 2‰, temperature 28 ± 1°C, with constant light and aeration, around 200 μE cm -2 s -1 and 3 L air min. -1 . Results showed that microalgae development caused nutrient depletion, since we observed an inversely proportional relationship between nitrate concentration and algal biomass during the cultivation. Regarding the culture media, a higher algal productivity was observed in the cultivation developed in Conway medium (p < 0.05), obtaining at the end of the cultivation, biomass of 3.38 ± 0.02 g L -1 . In the Guillard medium, only 2.47 ± 0.05 g L -1 was obtained. The cultivation in Conway medium presented better results concerning microalgae growth, with a more pronounced exponential phase. This was due to the higher nitrate availability, which was reduced more rapidly in the culture medium Guillard f/2.

This study examined the morphology and hatchability of Brachionus plicatilis resting eggs as a function of the aging of maternal fertilized mictic females. One-hundred twenty fertilized B. plicatilis (Australian strain) were individually cultured and monitored daily until death. All cultures were maintained at 25°C, 11 ppt, and fed the micro-algae Tetraselmis tetrathele. Resting eggs produced by the females were investigated using two parameters: egg morphology, and hatching rate. Under these culture conditions, females normally produce 1-6 (mean ± SD = 2.7 ± 1.2) resting eggs during their lifetime. However, the number of resting eggs with abnormal morphology increased as a function of maternal age. Among resting eggs with normal morphology (n = 225), 82.2% were produced during the first and second spawning, and had hatching rates of more than 60%, while the hatching rates were below 30% in resting eggs with a spawning order of >2. Thus, the quality of B. plicatilis resting eggs was negatively correlated with maternal age., Hydrobiologia, 662(1), pp.107-111; 2011

The authors are grateful to Rogelio Gacutan, Prof. Zosima Vicencio, Dr. Veronica Alava, Dr. Doris Bagarinao and to the anonymous reviewers for the helpful comments on the manuscript. This work was supported by the MNR/BFAR/SEAFDEC/PCARR Graduate Study Grant.

Rotifer resting eggs can potentially be preserved in a manner similar to Artemia cysts and used as live feed in larval rearing. The potential for producing resting eggs from the most desirable rotifer stocks, the L-type (Japanese stock) and the S-type (Hawaiian stock), at different tempera-tures was investigated. Rotifers from these stocks were reared in 1000l tanks and fed Tetraselmis tetrathele. Salinities were controlled at optimum levels for resting egg production (8 ppt and 32 ppt for L- and S-type, respectively). At culture temperatures ranging from 23.1 to 30.6°C, the L-type rotifers produced more resting eggs at the lowest temperature (23.1°C) and the S-type pro-duced more at a higher temperature (28.2 and 30.6°C). The relationship of resting egg produc-tion to temperature is expressed by a logistic curve. The highest total number of resting eggs was 17.8 million in 8 days at 23°C for L-type rotifers and 101.5 million in 10 days at 28°C for S-type rotifers. The maximum number of resting eggs produced was 3, 400 and 14, 000 per 10, 000 L-type and S-type rotifers respectively. The maximum number of resting eggs produced per 1×108 cells of T. tetrathele was 2, 270 and 11, 100 for the L- and S-types respectively.

A minute alga Tetraselmis tetrathele is one of the food organisms which have been intoroduced into Japan recently. T. tetrathele was well evaluated already as a substitute for Chlorella because of the high food value for a rotifer Brachionus plicatilis and its eurythermal characteristic beside the tolerance to high temperature. But, the dietary value of the rotifer cultured with T. tetrathele remains unknown. Tje doetary value of rotifers cultured with T. Tetrathele (TR) or both T. tetrathele and Chlorella sp. (TCR) was compared with those cultured with Chlorella (CR) by feeding these various rotifers to larval red seabream for 17 days. The rotifers enriched by Chlorella (12-24 hours) after culturing with T. tetrathele (TR-C) was also given to the larvae. The survival rate and the total length of fish fed TR was better than those receiving CR (75.6 and 83.5% vs. 65.1 and 75.6% in survival rate, 7.5 and 8.1 mm vs. 6.5 and 6.9 mm in average T. L.), although there were no significant dif-ferences in body weight. Furthermore, the survival rate and the growth of fish fed TCR or TR-C were superior to the former, i. e., 68.0-80.1% and 8.7-8.8mm in TCR, 74.4-81.1% and 8.5-9.1mm in TR-C. There were no differences in proximate composition of the rotifers with various feeds and treatment. The difference in survival rate and growth among the larvae with different feeds might be due to the difference in the conten of ω3 HUFA. Thepercentage of ω3 HUFA in the lipids of TR, TCR, TR-C, and CR were 12.4%, 20.9%, 20.4-25.4%, and 23.9%, respectively. The amount of ω3 HUFA in the rotifers cultured with T. tetrathele was not enough, but might be the minimum (0.3% in rotifer). The influence of 18:3ω3 included in the rotifer at high per-centage (22.4%) should be studied in future works.

The marine rotifer Brachionus plicatilis typicus (Clone 8105A, Univ. of Tokyo) was cultured in 500 ml beakers to form resting eggs. Tetraselmis tetrathele was used as a culture food. Just after formation, resting eggs were exposed to various temperature (5–25 °C) and light regimes (24L: OD and OL : 24D). When eggs were exposed to light just after formation, the eggs hatched sporadically over a month. No hatching was observed for six months when eggs were preserved under dark conditions regardless of the temperature. These eggs hatched simultaneously after being exposed to light and eggs preserved at 5 °C showed twice as high hatching rate (40%) as that of eggs preserved at 15–25 °C (24%). Clones from resting eggs that were kept under different temperature and light regimes were reared individually to the third generation. Incubation at 25 °C with lighting produced the highest (5.4% and 5.2 %) rate of mictic females during their 2nd and 3rd generations, respectively. The lowest rates (0 and 1.5%) were found when the eggs were kept at 5 °C in total darkness for six months. A lower rate of amictic female production was found in clones with higher rates of mixis.