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Fatty acid desaturases catalyze the formation of a C=C double bond from a C–C single bond in fatty acids, leading to diversification of the fatty acid pool. In this study, we identified the fatty acid desaturase genes in the monogonont marine rotifer Brachionus koreanus, measured the messenger RNA (mRNA) expression, and quantified fatty acid composition under feeding with the alga Tetraselmis suecica. Eight fatty acid desaturase genes were identified and classified by phylogenetic analysis. Fatty acid desaturases in the rotifer B. koreanus were categorized into two Δ4 desaturases, five Δ5/6 desaturases, and one Δ9 desaturase. mRNA expression of B. koreanus under the alga T. suecica-fed condition clearly indicated that transcriptional levels of desaturase genes were increased compared to the non-T. suecica-fed group. Also, the distribution of fatty acids of B. koreanus fed T. suecica was more balanced compared to that of T. suecica. These results provide a better understanding of the role of fatty acid desaturases in B. koreanus fed the alga T. suecica.

Two common live feeds, the Brachionus plicatilis species complex SS-type and L-type were used to assess whether there were any differences in protein hydrolysis and digestive trypsin activity in first feeding Japanese flounder. There were no significant differences in hydrolysis activity at 2, 3 and 7 days after hatching (DAH). At 5 DAH, hydrolysis activity was significantly higher in larvae fed SS-type (p

The low temperature adaptation ability of five selected strains of the Brachionus plicatilis species complex, i.e., three native strains [ Japanese (NH1L), Australian, German] and two hybrid strains [♀NH1L and ♂Australian (N × A) and ♀NH1L and ♂German (N × G),was investigated in terms of life history traits, reproductive characteristics, and mobility under different thermal conditions (12 and 25 °C). The life history traits of these five strains included a longer lifespan, reproduction period and generation times at 12 °C than at 25 °C, combined with reduced lifetime egg and offspring production. At 12 °C, the intrinsic rate of natural increase was higher in NH1L and N × A strains. Reproductive characteristics determined at 12 °C by batch culture showed active population growth for NH1L and N × G strains, while no resting egg production was observed in all of the strains tested. The ratio of swimming rotifers at 12 °C was monitored every hour for 6 h (short term) and every day for 10 days (long term). In the short-term study there was a 81% ratio of swimming rotifers of the NH1L strain, while other strains exhibited low swimming ratios (75% swimming ratio from the initial day of the study. These results suggest that outcrossing of rotifer strains is useful to obtain live food resources for the larviculture of cold water fish., Fisheries Science, 83(1), pp.65-72; 2017

In seedling production of seawater fish, providing appropriate nutrition is a necessity for successful production of quality larvae and juveniles. Mass-produced live prey organisms, such as the rotifer Brachionus plicatilis species complex and brine shrimp Artemia spp., alone do not provide sufficient nutrition to the larvae and juveniles of seawater animals. This inadequacy has led to various problems related to fish quality and health, including increased incidence of morphological and behavioral abnormalities and mass mortalities. It is, therefore, important to identify the factors associated with these problems to improve seedling production techniques. This review collates the efforts made during the past two decades in larval nutrition–focusing on advances made in the use of certain nutrients, such as docosahexaenoic acid, vitamin A derivatives, and taurine that are important for the mass production of seawater fish larvae and juveniles–with an aim to improve the quality and health of fish.

Insulin/insulin-like growth factor (IGF)-like signaling plays important roles in the aging processes of various animals. However, little is known about this signaling in rotifers, which have been used as a model animal in aging studies. Here we report that the aqueous extracts of the rotifer Brachionus plicatilis show activity similar to that of insulin/IGFs. Rotifers were cultured under four different feeding regimens (fed, starved for about ten days, or re-fed for 30 and 120 min after starvation), and then their aqueous extracts were added to culture media of rat L6 myoblasts. Treatment with these extracts increased the phosphorylation levels of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) and two Akt substrates of approximately 48 and 60 kDa, and these phosphorylations were diminished when cells were preincubated with specific inhibitors of their upstream kinases (MAPK/ERK kinase and phosphoinositide 3-kinase, respectively). Furthermore, the extracts from fed rotifers provoked higher phosphorylation levels of MAPK/ERK and Akt substrates than the extract from starved rotifers, suggesting that the production of substance(s) with insulin/IGF-like activity is stimulated upon feeding in the rotifer.

There is a need to develop low-cost methods for larviculture that emphasize disease prevention. We evaluated stagnant water larviculture in flounder Paralichthys olivaceus using rotifer amictic eggs treated with glutaraldehyde. Growth and survival of the larvae were similar to in larvae reared by standard running water larviculture with daily feeding of rotifers (control). In the experimental group, the n-3 highly unsaturated fatty acid content of rotifers in the rearing water was higher than in the enriched rotifers fed to the control group. We also observed a similar pattern for the fatty acid composition of flounder larvae. The viable bacterial counts associated with rotifers in stagnant water were lower than those associated with enriched rotifers, and there were fewer bacterial genera. However, the viable bacterial count was the same or higher in the experimental rearing water compared with that in the control group. The α-Proteobacteria and Cytophaga–Flavobacterium–Bacteroidetes group dominated the bacterial community structure after larval hatching. To our knowledge, this is the first time that stagnant water larviculture, using only disinfected amictic eggs, has been successfully demonstrated on a mass production scale. This method appears to offer benefits including improved nutrition, more favorable bacterial communities, and lower cost.

Gamma-aminobutyric acid (GABA) at 50 μg/ml and porcine growth hormone (GH) at 0.025 IU/ml were tested to see whether these chemicals would reduce the stress experienced by euryhaline rotifers Brachionus plicatilis species complex (L-, S- and SS-morphotypes) during low temperature (4–12°C) storage. Rotifers cultured at 25°C were transferred to 4–12°C for 10–30 days and transferred back to 25°C for recovery. GABA or GH were added to the rotifers at three different time points: 6 h before transfer from 25°C to low temperature (6h−), on day 7 after preservation at low temperature (7d+) and on the first day of recovery. For L-type rotifers, the GH treatment before the transfer to 4°C for 30 days was effective for better survival, while the GABA treatment was most effective for the S-type preserved at 10°C for 14 days. For the SS-type, the chemical treatments were not effective when the rotifers were preserved at 12°C for 14 days. After low temperature preservation, GABA treatments with the S- and SS-type rotifers just after their transfer to 25°C induced a relatively faster recovery of the rotifer population.

Calorie restriction (CR) in the rotifer Brachionus plicatilis extends its lifespan, as it enhances the expression of antioxidant enzymes such as manganese superoxide dismutase (Mn SOD) and catalase. Here we show that CR also increased the mRNA levels of these antioxidant enzymes upon exposure to oxidative stress. Rotifers cultured under CR showed a higher survival rate than those fed ad libitum (AL) upon exposure to 0.05–0.2 μM juglone, an oxidative stress inducer. The relative mRNA levels of Mn SOD and catalase before exposure to juglone were slightly higher in the CR rotifers than in their AL counterparts, although these differences were not statistically significant. AL rotifers showed no apparent upregulation of the mRNA levels of these antioxidant enzymes upon exposure to 0.025 and 0.05 μM juglone. In contrast, the CR rotifers increased the mRNA levels of Mn SOD and catalase by up to 5.4-fold and 4.2-fold, respectively, resulting in significant differences between their levels in AL and CR rotifers under oxidative stress conditions. Furthermore, the protein level of catalase was clearly higher in CR than in AL rotifers 6 h after exposure to oxidative stress. These results suggest that the upregulation of Mn SOD and catalase genes is involved in CR-induced resistance to oxidative stress in the rotifer.

金沢大学大学院自然科学研究科 信頼性システム工学, A continuous culture of rotifer was conducted to investigate the effect of combination feeding of both a high density of Nannochloropsis oculata (N) and condensed freshwater Chlorella (FC) on the fatty acid composition of L-type rotifer Brachionus plicatilis in a continuous culture system. The algal feeding of the rotifers was carried out in three successive steps: N-feeding → N+FC-feeding → FC-feeding. The culture was conducted at 24°C and 25-27 psu in a 2000 mL bottle with 50% of water exchanged daily. The combination N+FC-feeding was effective in increasing rotifer density. The rotifers fed on N+FC (N+FC-R) had more non-polar lipids than polar ones, similar to those on N (N-R), opposite to the rotifers fed on FC (FC-R). N+FC-R contained higher levels of 16:2, 18:2n-6 (linoleic acid [LA]) and 20:2n-6, but lower levels of 18:1, 20:4n-6 (arachidonic acid), 20:5n-3 (eicosapentaenoic acid [EPA]) and 22:5n-3 (docosapentaenoic acid [DPA]) compared with N-R. Whereas N+FC-R contained higher levels of 16:1n-7, EPA and DPA, but lower levels of 16:2 and LA compared with FC-R. N+FC-R had more DPA in polar lipids than in non-polar ones. The Σn-6/Σn-3 ratio in N+FC-R was 0.9-1.0, significantly different from those in N-R (0.4) and FC-R (6.6-8.4). Therefore, it is inferred that the fatty acid profile of the N+FC-R cultured in a continuous culture system was affected by both N and FC. Also, the combination N+FC-feeding may be effective in manipulating the Σn-6/Σn-3 ratio in continuously cultured rotifers. © 2008 Japanese Society of Fisheries Science.

In the present study, Schizochytrium limacinum OUC88, a thraustochytrid with high content of docosahexaenoic acid (DHA, 22∶6 n−3), was used as feed for rotifer Brachionus plicatilis and Artemia franciscana. The rotifer and Artemia were harvested at 3, 6, 9, 12, 18, and 24-h intervals, analyzed for fatty acid composition, and compared with the control which fed on yeast only. The highest DHA content resulted from an enrichment period of 12 h for both fed organisms, reached 13.4 and 10.9% of the total fatty acids (TFAs) in rotifers and Artemia nauplii, respectively, and the DHA level reduced sharply if enrichment time was longer than 12 h. The pseudoalbinism rate of turbot Scophthalmus maximus juveniles fed enriched rotifers and Artemia nauplii reduced greatly (40% lower than in control group). Thus, enrichment of rotifers and Artemia nauplii by DHA-rich Schizochytrium limacinum OUC88 may provide a practical strategy for feeding fish juveniles in aquaculture.

The dynamics of vitamin A (VA) compounds in live food during enrichment were examined under different light conditions. Rotifers Brachionus plicatilis and Artemia nauplii (Artemia) were enriched with or without 10 mg VA palmitate (VAp) in 1 L of culture medium for 24 h under either bright (2000 lx), or dark (

A growth hormone (GH)-like substance was extracted from the rotifer Brachionus plicatilis and subsequently purified by gel filtration and ion exchange chromatography. The GH-like substance had a molecular weight of approximately 28 kDa and had cross-reactivity with salmon GH antibody. In vivo bioassay showed a higher intrinsic rate of increase and net reproduction rate of B. plicatilis treated with the GH-like substance.

We amplified three kinds of cDNA fragments encoding stress proteins from the rotifer Brachionus plicatilis by polymerase chain reaction in order to investigate the molecular mechanisms underlying mediation of its lifespan. The stress proteins were heat shock protein 70 (HSP70), glucose regulated protein 94 (GRP94) and ubiquitin-conjugating enzyme, which have been suggested to extend the lifespans of fruitfly and yeast. The isolated clones consisted of 579, 776 and 257 bp in the above order, respectively, and their deduced amino acid sequences showed 81, 59 and 48% identities, respectively, with corresponding sequences from the nematode Caenorhabditis elegans. As rotifers in the stationary phase can extend their lifespan we subsequently performed northern blot analysis on rotifers both in the exponential and stationary phases. The mRNA levels of HSP70 and GRP94 in the exponential growth phase were 2.5 and 1.6 times higher, respectively, than those in the stationary phase, whereas those of ubiquitin-conjugating enzyme did not differ between rotifers in the two phases. These results suggest that stress proteins are not directly responsible for the extension of rotifer lifespan, but another factor(s) is possibly involved. Our results, however, demonstrated that these genes are useful as molecular markers for monitoring the population growth of rotifer.

The ability of newly hatched larvae of Japanese Spanish mackerel Scomberomorus niphonius to resist starvation was studied in rearing experiments. Because Japanese Spanish mackerel larvae exhibit almost complete piscivory from the first feeding stage and begin to cannibalize under lack of piscine prey, they were isolated from one another during the experiments. Newly hatched larvae commenced feeding on fish prey (red sea bream Pagrus major larvae) on day 6 (after hatching) and completed yolk sac absorption by day 9 at 18.5°C. All the starved larvae had died by day 10. More than 90% of fish fed red sea bream larvae survived until day 10, whereas all fish fed rotifer (Brachionus plicatilis) had died by the same day, indicating that rotifer is useless as a prey for the survival of Japanese Spanish mackerel larvae at the first feeding stage. A clear point-of-no-return (PNR), 0–1 day of recoverable starvation, was found at the post-first feeding stage. Delayed feeding experiments demonstrated that the percentage survival on day 10 was 100% for larvae fed from day 5, 91.6% from day 6, 16.7% from day 7, 8.3% from day 8, and 0% for those fed from day 9. Fish first fed from day 7 or 8 showed significantly retarded growth during the following adequately fed period compared with fish fed from the first feeding (day 6). These results show that Japanese Spanish mackerel larvae are highly vulnerable to fasting and that the larvae’s first feeding success might be critical for growth and survival in the period that follows.