Effect of salicylic acid and methyl jasmonate on antioxidant systems of <Emphasis Type="Italic">Haematococcus pluvialis</Emphasis>

The influence of phytohormones, salicylic acid (SA) and methyl jasmonate (MJ) on the antioxidant systems in Haematococcus pluvialis was investigated. Both SA and MJ at 500 μM concentration reduced the growth of alga with salicylic acid, having more pronounced effect. Carotenoid and chlorophyll contents were decreased by SA and increased by MJ. Salicylic acid (100 μM) increased astaxanthin content to 6.8-fold under low light (30 μmol m⁻² s⁻¹), while MJ (10 μM) showed marginal increase in astaxanthin. Salicylic acid (500 μM) increased superoxide dismutase activity to 4.5- and 3.3-fold and ascorbate peroxidase (APX) activity to 15.5- and 7.1-fold under low and high light, respectively. Methyl jasmonate increased catalase activity (1.4-fold) under high light and APX activity (5.4-fold) under low light. Different mechanism of oxidative stress induced antioxidant production may be the plausible reason for this varied response for salicylic acid and methyl jasmonate. Higher concentrations of SA and MJ inhibited astaxanthin accumulation by different mechanisms either by scavenging the free radicals or by increasing primary carotenoids production. At lower concentrations, these phytohormones could be used for elicitation of secondary carotenoid production.     

Towards genetic improvement of commercially important microalga Haematococcus pluvialis for biotech applications

Haematococcus pluvialis is a unicellular green alga which produces a ketocarotenoid, astaxanthin which has pharmaceutical and nutraceutical applications owing to its high antioxidant activity. Biotechnological approaches such as genetic transformation methods (Agrobacterium-mediated) and cloning strategies, are essential to improve/regulate this ketocarotenoid in Haematococcus. For this studies are necessary to improve Haematococcus through biotechnological means. In this connection, a suitable cocultivation medium for Haematococcus and Agrobacterium tumefaciens was standardized and different antibiotics were screened. Among the cocultivation media viz Z₈, Bold’s Basal Medium, Tris Acetate Phosphate Z₈ with 0.5% mannitol and BBM and Z₈ with half strength LB TAP medium was found suitable for growth of both the alga Haematococcus and Agrobacterium. For the different antibiotics screened to identify the sensitivity of algae, hygromycin at more than 2 mg L⁻¹ showed lethal effect which can be used as a selectable marker gene in genetic transformation, whereas cefotaxime and augmentin showed no effect up to 2,000 mg L⁻¹. The growth of algae was higher in solid selection medium when compared to the liquid selection medium.     

Effect of sudden change in potassium concentration on <Emphasis Type="Italic">Penaeus latisulcatus</Emphasis> Kishinouye survival,osmolality and health in inland saline water cultures

The aim of the project was to determine the effects of sudden change in potassium concentration in inland saline water on the survival, osmolality and condition indices of western Australian King Prawn—Penaeus latisulcatus Kishinouye. Australia has large volumes of inland saline water that could be used for aquaculture but is often deficient in K⁺. Western king prawn is a candidate species for culture in inland saline water. Such waters require K⁺ fortification for prawn survival and growth. Trials were conducted in tanks to determine the effect of sudden change in K⁺ concentration in inland saline water samples on the survival, osmolality and condition indices of western king prawns. Prawns in tanks were acclimated to inland saline water procured from Wannamal—an inland location in Western Australia. After 3 days of acclimation, prawns were subjected to sudden increase in medium K⁺ concentration over 1 h, ranging from 80% to 100% of the marine water K⁺ concentration by adding potassium chloride. Identical inland saline water was added to the control tanks over the same time period. Survival, ingestion rate and osmoregulatory capacity (OC) were then recorded over 19 days. At the conclusion of the trial, survival ranged from 71% to 78% in the potassium-enriched tanks whereas 100% mortality was observed in the control tanks by day 11. Ingestion rate of prawns was significantly higher in the experimental tanks than in the control. Osmoregulatory capacity of potassium-enriched prawns was significantly lower post- than pre-ionic change and significantly higher at the conclusion of the trial than both pre- and post-ionic change. There was no significant difference in OC between water types at any time period. These results indicate that prawns can tolerate sudden increase in K⁺ content in inland saline water and the higher K⁺ concentration increases survival and OC, but other measures indicate the prawns were experiencing stressful conditions. Guest Editors: J. John & B. Timms Salt Lake Research: Biodiversity and Conservation—Selected Papers from the 9th Conference of the International Society for Salt Lake Research     

Operation of packed-bed immobilized cell reactor featuring active β-galactosidase inclusion body-containing recombinant <Emphasis Type="Italic">Escherichia coli</Emphasis> cells

In this study, we developed a packed-bed immobilized cell reactor containing active β-gal (β-galactosidase) inclusion body (IB)-containing Escherichia coli (E. coli) cells in alginate beads. This packed-bed reactor was operated using a substrate feed solution 0.72 ∼ 38.4 mM ONPG (o-nitrophenyl-β-D-galactoside) prepared in Z buffer supplemented with chloroform and 0.1% SDS (sodium dodecyl sulfate). The production rate of ONP (o-nitrophenol) in the reactor containing cells that were incubated with α-MG (α-methyl D-glucospyranoside) or D-fucose after induction was superior to those prepared with cells that were not incubated with α-MG or D-fucose. The ONP production rate was increased proportionally with ONPG concentration in the substrate feed up to a concentration of 38.4 mM. However, as the ONPG concentration was increased in the substrate feed solution, galactose inhibition inside the alginate beads was increased. This most likely occurred due to problems with diffusion. In addition, partial breakage of alginate beads was observed during the later periods of operation. In this study, we demonstrated that active β-gal IB-containing E. coli cells were sustained in the immobilized cell reactor during operation. Particularly, these findings demonstrate the feasibility of using active IBs in an enzymatic reaction without the need for any purification step. In addition, we showed that these IB-containing cells could be directly used in an immobilized reactor.     

Complementary limiting factors of astaxanthin synthesis during photoautotrophic induction of <Emphasis Type="Italic">Haematococcus pluvialis</Emphasis>: C/N ratio and light intensity

We investigated the effect of carbon/nitrogen (C/N) ratio on astaxanthin synthesis in Haematococcus pluvialis during photoautotrophic induction by continuous input of both CO₂–air mixture and intense light. When H. pluvialis was induced by constant irradiance induction at 200 μmol photon m⁻² s⁻¹, there was a positive correlation with astaxanthin content and C/N ratio, which was similar to the case for heterotrophic induction. Lower C/N ratios did not retard Haematococcus encystment, but did increase culture biomass, resulting in a decrease in astaxanthin production because of light limitation. However, induction using variable irradiance showed that reduction of astaxanthin production at low C/N ratios was successfully overcome by simply increasing the light intensity from 200 to 300 μmol photon m⁻² s⁻¹ to overcome the light limitation. This resulted in a greatly enhanced astaxanthin synthesis in proportion to cell density in cultures with low C/N ratios. Our results indicate that light intensity is more critical than C/N ratio in astaxanthin production by H. pluvialis during photoautotrophic induction.     

Physiological comparison of copper toxicity in the lichens <Emphasis Type="Italic">Peltigera rufescens</Emphasis> (Weis) Humb. and <Emphasis Type="Italic">Cladina arbuscula</Emphasis> subsp. <Emphasis Type="Italic">mitis</Emphasis> (Sandst.) Ruoss

Peltigera rufescens (Weis) Humb. with a prokaryotic photobiont Nostoc sp. and Cladina arbuscula subsp. mitis (Sandst.) Ruoss with a eukaryotic photobiont Trebouxia sp. were studied to determine the copper sensitivity of lichens with different algal symbionts. Samples growing on historic copper mine-spoil heaps at Ľubietová–Podlipa, Slovakia were assessed for physiological parameters, including total and intracellular uptake of copper, assimilation pigmentation, activity of photosystem II, ergosterol levels, thiobarbituric acid reactive substances and water-soluble protein content. Our results indicate that P. rufescens was more sensitive to copper exposure than C. arbuscula subsp. mitis.     

Cloning of a Novel Omega-6 Desaturase from Flax (<Emphasis Type="Italic">Linum usitatissimum</Emphasis> L.) and Its Functional Analysis in <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

The Δ12 desaturase represents a diverse gene family in plants and is responsible for conversion of oleic acid (18:1) to linoleic acid (18:2). Several members of this family are known from plants like Arabidopsis and Soybean. Using primers from conserved C- and N-terminal regions, we have cloned a novel Δ12 desaturase gene amplified from flax genomic DNA, denoted as LuFAD2-2. This intron-less gene is 1,149-base pair long encoding 382 amino acids—putative membrane-bound Δ12 desaturase protein. Sequence comparisons show that the novel sequence has 85% similarity with previously reported flax Δ12 desaturase at amino acid level and shows typical features of membrane-bound desaturase such as three conserved histidine boxes along with four membrane-spanning regions that are universally present among plant desaturases. The signature amino acid sequence ‘YNNKL’ was also found to be present at the N terminus of the protein, which is necessary and sufficient for ER localization of enzyme. Neighbor-Joining tree generated from the sequence alignment grouped LuFAD2-2 among the other FAD2 sequences from Ricinus, Hevea, Jatropha, and Vernicia. When LuFAD2-2 and LuFAD2 were expressed in Saccharomyces cerevisiae, they could convert the oleic acid to linoleic acid, with an average conversion rate of 5.25 and 8.85%, respectively. However, exogenously supplied linoleic acid was feebly converted to linolenic acid suggesting that LuFAD2-2 encodes a functional FAD2 enzyme and has substrate specificity similar to LuFAD2.     

News & Notes: Virulence of Vibrio alginolyticus Isolated from Diseased Tiger Prawn,Penaeus monodon

Outbreaks of mass mortality among cultured tiger prawns (Penaeus monodon) with white spotted syndrome (WSS) in the carapace occurred in the summer of 1994 in I-Lan, Taiwan. A swarming strain Val was isolated from hemolymph of the moribund prawns with tryptic soy agar (TSA, supplemented with 1% NaCl, Oxoid) and/or thiosulfate citrate bile salt sucrose (TCBS, Difco) agar. This strain was characterized and identified to be Vibrio alginolyticus. The strain was susceptible to antibiotics such as chloramphenicol, ciprofloxacin, doxycycline hydrochloride, nalidixic acid, oxolinic acid, and oxytetracycline while resistant to ampicillin, novobiocin, penicillin G, sulfisoxazole, and sulfonamide. The bacteria and their extracellular products (ECP) were lethal to both tiger prawns (P. monodon) and kuruma prawns (P. japonicus) with LD₅₀ values of 1.13 × 10⁵, 2.46 × 10⁵ CFU/g, and 0.23, 0.63 μg protein/g prawn body weight, respectively.     

Probiotic Potential of the Farmed Olive Flounder,Paralichthys olivaceus,Autochthonous Gut Microbiota

In recent years, considerable and growing attention has been given to the application of host-associated microorganisms as a more suitable source of probiotics in aquaculture sector. Herein, we isolated and screened the olive flounder gut microbiota for beneficial bacterial strains that might serve as potential probiotics in a low fishmeal extruded aquafeed. Among the ten identified isolates, Bacillus amyloliquefaciens SK4079 and B. subtilis SK4082 were screened out based on their heat-resistant ability as well as enzymatic and non-hemolytic activities. Although both strains were well able to utilize carboxymethyl cellulose (CMC), xylan, and soybean meal (SBM) as a single carbon source in the minimal nutrient M9 medium, B. subtilis exhibited significantly higher cellulase, xylanase, and protease activities than B. amyloliquefaciens. The two selected strains were well able to degrade the undesirable anti-nutritional component of the SBM, which would limit its utilization as protein source in aquafeed industry. Significantly higher biofilm formation capacity and notably stronger adhesive interactions with the flounder’s skin mucus were detected in B. subtilis than B. amyloliquefaciens. Immobilization of the spores from the selected strains, in a SBM complex carrier, remarkably enhances their thermal resistance at 120 °C for 5 min and different drying conditions. It was also interesting to learn that the B. subtilis spores could survive and remain viable after being sprayed onto extruded low-fish meal feed pellets for as long as 6 months. Overall, the findings of the present study could help the food/feed industries achieve their goal of developing cost-effective yet efficient products.

     

The gene for indole-3-acetyl-L-aspartic acid hydrolase from Enterobacter agglomerans : molecular cloning, nucleotide sequence, and expression in Escherichia coli

A 5.5-kb DNA fragment containing the indole-3-acetyl-aspartic acid (IAA-asp) hydrolase gene (iaaspH) was isolated from Enterobacter agglomerans strain GK12 using a hybridization probe based on the N-terminal amino acid sequence of the protein. The DNA sequence of a 2.4-kb region of this fragment was determined and revealed a 1311-nucleotide ORF large enough to encode the 45-kDa IAA-asp hydrolase. A 1.5-kb DNA fragment containing iaaspH was subcloned into the Escherichia coli expression plasmid pTTQ8 to yield plasmid pJCC2. Extracts of IPTG-induced E. coli cultures containing the pJCC2 recombinant plasmid showed IAA-asp hydrolase levels 5 to 10-fold higher than those in E. agglomerans extracts. Homology searches revealed that the IAA-asp hydrolase was similar to a variety of amidohydrolases. In addition, IAA-asp hydrolase showed 70% sequence identity to a putative thermostable carboxypeptidase of E. coli. Received: 12 March 1998 / Accepted: 30 March 1998     

Micropropagation of ornamental <Emphasis Type="Italic">Prunus</Emphasis> spp. and GF305 peach,a <Emphasis Type="Italic">Prunus</Emphasis> viral indicator

A micropropagation approach was developed for nine ornamental Prunus species, P. americana, P. cistena, P. glandulosa, P. serrulata ‘Kwanzan’, P. laurocerasus, P. sargentii, P. tomentosa, P. triloba, P. virginiana ‘Schubert’, commercially important in North America, and GF305 peach, commonly used for Prunus virus indexing. The micropropagation cycle based on proliferation of vegetative tissues includes establishment of tissue culture through introduction of shoot meristems in vitro, shoot proliferation, root induction and plant acclimatization steps and can be completed in 5 months. A meristem sterilization protocol minimized bacterial and fungal contamination. Multiple shoot formation in ornamental Prunus was obtained through the use of 1 mg l⁻¹ 6-benzyladenine. For GF305 peach, alteration in the sugar composition, fructose instead of sucrose, and addition of 1 mg l⁻¹ ferulic acid had a significant impact on the shoot proliferation rate and maintenance of long-term in vitro culture. Rooting and plant acclimatization conditions were improved using a two-step protocol with a 4-day root induction in indole-3-butiric acid (IBA)-containing media with consequent 3-week root elongation in IBA-free media. One-month incubation of rooted shoots in a vermiculite-based medium resulted in additional shoot and root growth and provided better acclimatization and plant recovery. The micropropagation approach can be used for maintenance of the clonal properties for Prunus spp. as well as a protocol to support meristem therapy against viral infection.     

Cytotoxity of the <Emphasis Type="Italic">trans</Emphasis>10,<Emphasis Type="Italic">cis</Emphasis>12 isomer of conjugated linoleic acid on rat hepatoma and its modulation by other fatty acids,tocopherol, and tocotrienol

Summary This study was performed to evaluate the isomer-specific cytotoxic effects of conjugated linoleic acid (CLA) on rat hepatoma dRLh-84 cells in vitro. A 10trans,12cis (10t,12c)-CLA showed a strong cytotoxic effect on dRLh-84 cells in culture, whereas no such effect was observed with 9cis,11trans (9c,11t)-CLA or linoleic acid. The optimum concentration for induction of cytotoxity by 10t,12c-CLA was 5 to 10 μM, but the effect was alleviated at higher concentrations. Coincubation with oleic or palmitoleic acid and 10t,12c-CLA cancelled the cytotoxic effect, but other major saturated or polyunsaturated fatty acids and eraidic acid did not interfere with 10t,12c-CLA-induced cytotoxity. The cytotoxic effect was also alleviated by α-tocopherol (α-toc) and α-tocotrienol but not by any other antioxidant regent examined. Significant cytotoxity of 10t,12c-CLA was detected after only a 15-min incubation, and the most noticeable effect was seen after 3 h. After incubation with 10t,12c-CLA at 10 μM, an additional 90 μM, an additional 90 μM of 10t,12c-CLA or 100 μM of α-toc was also able to alleviate the cytotoxity. When cells were treated with 10 μM 10t,12c-CLA for more than 48 h, treatment with additional CLA or α-toc could not prevent cell death.     

Enhancing phagocytic activity of hemocytes and disease resistance in the prawn Penaeus merguiensis by feeding Spirulina platensis

Exposing the prawn Penaeus merguiensis to the bacteria Vibrio harveyi and Escherichia coli for an hour or feeding the prawns with Spirulina (Arthrospira) platensis (0.3% w/w feed) enhanced the phagocytic activity of their hemocytes. Improvement of the phagocytic activity was primarily through the activation of the hemocytes. The activated phagocytic hemocytes had a higher capacity to engulf foreign agents, such as bacteria, and a higher rate of phagocytosis. The phagocytic enhancement effect peaked on the fourth day of feeding with Spirulina. In the in vitro study, the granular cells from prawns took 45–60 min to complete the process of degranulation. Pre-exposure to Salmonella typhimurium and Bacillus subtilis did not result in enhancement of phagocytic activity of hemocytes. Only 10% prawns fed with Spirulina died in the first 14 days when challenged by V. harveyi at a concentration of 1 × 10⁴CFUs mL^–1, while all control prawns (basal feed without Spirulina) died within 14 days.     

The effects of dietary supplementation of algae and synthetic astaxanthin on body astaxanthin, survival, growth, and low dissolved oxygen stress resistance of kuruma prawn, Marsupenaeus japonicus Bate

Natural carotenoids from astaxanthin containing alga Haematococcus pluvialis (H) and a non-astaxanthin carotenoid-containing alga Spirulina pacifica (S), and a synthetic astaxanthin Carophyll Pink (A) were supplemented in formulated diets at two concentrations, 50 (I) and 100 (II) mg kg⁻¹, resulting in seven pigmented diets HI, SI, AI, HII, SII, AII, and HS (H-50 mg kg⁻¹+S-50 mg kg⁻¹). Formulated diet without carotenoid supplementation served as a control (C). The different diets were fed to juvenile kuruma prawn Marsupenaeus japonicus for 9 weeks. Dietary carotenoid effects on survival, growth, and pigmentation were compared by the treatment individually or collectively. A low dissolved oxygen stress test was conducted 2 weeks later and prawns' survival time and oxygen consumption rate were also compared among treatments. After 9 weeks' rearing, C-fed prawn had significantly lower survival rate than the pigmented diets-fed prawns. No difference in weight gain was found among all prawns. C-fed prawn had 66.4% less flesh astaxanthin (FA) and 75.5% less shell astaxanthin (SA) than the pigmented diets-fed prawns. I-fed (AI, HI, and SI) prawns had 31.1% less FA and 29.6% less SA than II-fed (AII, HII, SII, and HS) prawns. No significant differences were found in the comparisons by other categories. The use of these three sources of carotenoids for pigmentation in crustacean was discussed along carotenoid conversion, deposition, digestibility, and absorption. When subjected to low dissolved oxygen stress, C-fed prawn had higher oxygen consumption rate (OCR) and shorter survival time (ST) than the prawns fed the pigmented diets. No differences in OCR or ST were found in the comparisons by other categories.     

Growth dynamics and the proximate biochemical composition and fatty acid profile of the heterotrophically grown diatom <Emphasis Type="Italic">Cyclotella cryptica</Emphasis>

To investigate the nutritional value of the diatom Cyclotella cryptica as an alternative feed for aquaculture, its heterotrophic growth characteristics were studied. First, the proximate biochemical composition and fatty acid profiles were studied under a controlled heterotrophic growth condition. The approximate total ash, carbohydrate, lipid, and protein content were 245 mg g⁻¹ (dry weight), 360 mg g⁻¹, 165 mg g⁻¹ and 260 mg g⁻¹, respectively. Polyunsaturated fatty acids accounted for 24.5, 31.3, 45.1 and 17.3% of the total lipids in the phospholipid, sterol, free fatty acid and triglyceride classes. Secondly, the effect of aeration and agitation rates on the specific growth rate of C. cryptica under heterotrophic conditions was studied. The maximum specific growth rate was not significantly affected (P > 0.05) by the rate of agitation within the range of 100 to 160 rpm, but it was significantly affected (P > 0.05) by the rate of aeration. Optimal growth occurred when the aeration rate was within the range of 0.44 to 1.07 v/v/min. Viability measurements throughout the growth period showed that the C. cryptica cells remained viable in spite of the varied cultivation conditions. Hydrodynamic forces are an important parameter within biological systems, and optimisation is crucial for the successful scale-up of microalgal cultivation systems. Whilst the investigation was preliminary in nature, the information gained in this study will be useful for the continual development of an alternative and cost-effective feed for bivalve spat rations.     

Evaluation of <Emphasis Type="Italic">Kluyveromyces marxianus</Emphasis> as a source of yeast autolysates

Cells of Kluyveromyces marxianus FII 510700 and Saccharomyces cerevisiae CBS 1907 were autolysed in phosphate buffer, pH 4.5, for a maximum of 10 days to compare chemical changes that occur in the carbohydrate, protein, amino acid and nucleic acid content. Approximately 2.2–3% carbohydrate, 9.5–12% protein, 0.6–1.0% DNA and 6–7% RNA were recovered in the autolysates. The main amino acids were β-alanine, phenylalanine, cysteine, methionine, glutamic acid and isoleucine. No significant differences in the yeast autolysates of K. marxianus and S. cerevisiae were observed. Consequently, K. marxianus produced from lactose-based media has potential as a source of yeast autolysates used in the food industry. Electronic Publication     

QTL for phytosterol and sinapate ester content in <Emphasis Type="Italic">Brassica napus</Emphasis> L. collocate with the two erucic acid genes

Improving oil and protein quality for food and feed purposes is an important goal in rapeseed (Brassica napus L.) breeding programs. Rapeseed contains phytosterols, used to enrich food products, and sinapate esters, which are limiting the utilization of rapeseed proteins in the feed industry. Increasing the phytosterol content of oil and lowering sinapate ester content of meal could increase the value of the oilseed rape crop. The objective of the present study was to identify quantitative trait loci (QTL) for phytosterol and sinapate ester content in a winter rapeseed population of 148 doubled haploid lines, previously found to have a large variation for these two traits. This population also segregated for the two erucic acid genes. A close negative correlation was found between erucic acid and phytosterol content (Spearman’s rank correlation, r _s = −0.80^**). For total phytosterol content, three QTL were detected, explaining 60% of the genetic variance. The two QTL with the strongest additive effects were mapped on linkage groups N8 and N13 within the confidence intervals of the two erucic acid genes. For sinapate ester content four QTL were detected, explaining 53% of the genetic variance. Again, a close negative correlation was found between erucic acid and sinapate ester content (r _s = −0.66^**) and the QTL with the strongest additive effects mapped on linkage groups N8 and N13 within the confidence intervals of the two erucic acid genes. The results suggests, that there is a pleiotropic effect of the two erucic acid genes on phytosterol and sinapate ester content; the effect of the alleles for low erucic acid content is to increase phytosterol and sinapate ester content. Possible reasons for this are discussed based on known biosynthetic pathways. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Redescription of <Emphasis Type="Italic">Bregmaceros mcclellandi</Emphasis> Thompson, 1840 (Gadiformes: Bregmacerotidae)

 This study redescribes Bregmaceros mcclellandi Thompson, 1840, based on one specimen (74.4 mm SL) from the Bay of Bengal and 66 specimens (30.0–84.7 mm SL) from Mumbai (Bombay), India, because the type specimens have apparently been lost. The present specimens are characterized by having black dorsal, pectoral, and caudal fins and show the following morphology: caudal fin slightly forked; body chromatophores present mainly at the dorsal part; no scales on cheek; vertebrae 52–55 (13–15 + 38–41); dorsal rays 52–59; anal rays 54–60; pectoral rays 18–20; caudal rays 27–31 (principal rays 14); transverse scales 14–15. In the 66 Mumbai specimens, it was confirmed that the distinctive black fin pigmentation developed sequentially with growth, with complete pigmentation first on the anterior lobe of the dorsal fin, then simultaneously on the posterior lobe of the dorsal fin, the caudal fin, and the pectoral fin, and last, on the anal fin. This species is known only from the Arabian Sea, Bay of Bengal, and Gulf of Thailand. A review of 16 nominal Bregmaceros species indicates that, besides B. mcclellandi, the distinctive dark fin pigmentation is found in B. atripinnis (Tickell), B. atlanticus Goode and Bean, B. japonicus Tanaka, and B. lanceolatus Shen. B. atripinnis is considered a junior synonym of B. mcclellandi, and the others are clearly distinct from B. mcclellandi. Comments are made on some of the characters to more fully characterize the species and for reference in future revisionary and phylogenetic studies. Received: June 17, 2002 / Revised: December 2, 2002 / Accepted: December 24, 2002     

Effect of the Nutritional Status of Semi-continuous Microalgal Cultures on the Productivity and Biochemical Composition of <Emphasis Type="Italic">Brachionus plicatilis</Emphasis>

The rotifer Brachionus plicatilis was cultured using the microalga Isochrysis aff. galbana clone T-ISO as feed. T-ISO was cultured semi-continuously with daily renewal rates of 10%, 20%, 30%, 40%, and 50% of the volume of cultures. The increase of renewal rate led to increasing nutrient and light availability in microalgal cultures, which caused differences in the biochemical composition of microalgal biomass. Growth rate, individual dry weight, organic content, and biomass productivity of rotifer cultures increased in response to higher growth rate in T-ISO cultures. Rotifer growth rate showed a strong negative correlation (R ² = 0.90) with the C/N ratio of microalgal biomass. Rotifer dry weight was also affected by nutrient availability of T-ISO cultures, increasing up to 50% from nutrient-limited to nutrient-sufficient conditions. Consequently, biomass productivity of rotifer cultures increased more than twofold with the increase of renewal rate of T-ISO cultures. Rotifer organic content underwent the same trend of total dry weight. Maximum content of polyunsaturated fatty acids was reached in rotifers fed T-ISO from the renewal rate of 40%, with percentages of docosahexaenoic acid (22:6ω-3, DHA) and eicosapentaenoic acid (20:5ω-3, EPA) of 11% and 5% of total fatty acids, respectively. Selecting the most appropriate conditions for microalgal culture can therefore enhance the nutritive quality of microalgal biomass, resulting in a better performance of filter feeders and their nutrient content, and may constitute a useful tool to improve the rearing of fish larvae and other aquaculture organisms that require live feed in some or all the stages of their life cycle.