Japanese Aquaculture Research Articles

Distribution and geochemical speciation of metals in the sediments of marine aquaculture areas in Japan.

Metal contamination is a crucial environmental issue because of its persistence and toxicity, which can have deleterious effects on aquatic ecosystems. Coastal sediments serve as reservoirs for metals. Aquaculture is an important human activity in coastal areas; however, the actual status of metal distribution in these areas has not been well characterized. We investigated the distribution and geochemical speciation of metals in the sediments of the Japanese aquaculture areas of Shidugawa and Furue Bays. Total metals were generally in the order Zn > Cu > Ni > Cd > Pb and occurred at high levels at the sites in the inner parts and near the fish cages in the sampling areas. Pearson's correlations and principal component analysis results suggested that the metals in these aquaculture areas might originate from several sources, such as fish feces, fish feeds, corrosion of antifouling material residues, and local anthropogenic activities, including fertilizers and manures. Furthermore, metals were mainly in silts and fine sediments, associated with residual speciation, followed by organic fractions, oxides, and high fractions of exchangeable Cd. These results provide important insights into the accumulation of metals in sediments for better managing marine aquaculture in Japan.

Ⅱ–1. To develop the future of Japanese aquaculture

Ⅱ–1. To develop the future of Japanese aquaculture

Whole-genome analysis of red sea bream iridovirus spread in 2021 in Japan provided epidemiological and viral traits insight.

Red sea bream iridovirus (RSIV) is the pathogen that causes red sea bream iridoviral disease. It causes a huge loss to the Japanese aquaculture industry. In 2021, outbreaks of red sea bream iridovirus occurred in South Japan. This study analysed nine whole-genome sequences of RSIV isolated in Oita and Ehime Prefectures in 2021 using a short-read next-generation sequencer. Nine isolates had highly uniform sequences, and there was no variant depending on locations or host species. Phylogenetic analyses with other reported megalocytivirus isolates showed that RSIV isolated in 2021 was genetically different from RSIV previously isolated in Oita and Ehime Prefectures in 2017-2019. These results suggest that RSIV isolated in Oita and Ehime Prefectures in 2021 might spread from a common ancestor different from the recent one. Additionally, it was found that RSIV isolated in 2021 had sequence mutations on protein-coding sequences that may be involved in viral pathogenicity and infectivity.

Resident leukocyte populations and inflammatory response in the abdominal adipose tissue of the red seabream Pagrus major

Adipose tissue is not only an energy depot but also an important endocrine and immunological tissues in mammals. However, the study of functions of fish adipose tissue, other than lipid storage, is considerably limited. In the present study, we investigated resident leukocyte populations in the visceral adipose tissue (VAT) of the red sea bream, Pagrus major, an important species of Japanese aquaculture with a well-developed VAT. We found that the tissue contains a significant number of leukocytes; it is mainly composed of eosinophilic granulocytes, macrophages, unclassified large cells, and a smaller number of lymphocytes. The VAT cellular composition is similar to that of peritoneal cells, but not of the peripheral blood leukocytes. Gene expression analysis also confirmed that all examined genes, including CD4, CD8α, membrane and secretory IgM heavy chains, macrophage-colony stimulating factor receptors (type 1 and 2), macrophage mannose receptor, MHC class II, and Toll-like receptors 2, 3, 5, and 9, were expressed in the VAT. Intraperitoneal injection of formalin-killed Vibrio anguillarum markedly upregulated the mRNA expression of IL-1β, IL-8, and IL-6 in the VAT within six hours. In addition, in vitro bacterial stimulation upregulated these cytokines. These results indicate that the VAT of P. major is an immune-competent organ that evokes an inflammatory response against intraperitoneally introduced bacteria.

Bioeconomic modeling of oyster farming in Miyagi Prefecture, Japan

AbstractRational management is required for the profitability of the Japanese aquaculture industry and to promote investment in the industry. Although bioeconomic modeling could facilitate rational aquaculture management, it has not been applied in Japanese marine aquaculture. In the present study, we developed a bioeconomic model for oyster farming in Miyagi prefecture, Japan, and determined the optimal harvest schedules under labor constraints. Low, moderate, and high temperature scenarios were simulated to investigate the effects of changes in seawater temperature on farm productivity. Early initiation of harvest, particularly from late October or early November, achieved the maximum profit under the environmental and economic conditions in the present study. The moderate temperature scenario (current temperature conditions) had a high total profit (962,890 JPY) when harvest was initiated on October 29. The high temperature scenario had lower profits than the profits under current conditions, indicating that climate change could have adverse effects on oyster farming profitability in Miyagi prefecture.

Assessment of Metal Levels in Sediments and Oyster (Crassostrea gigas) Tissues from Shidugawa Bay, a Closed Japanese Aquaculture Environment

Metals are used as alternatives of antifouling paints in aquaculture and toxic to cultured fish and shellfish. To assess antifouling paints, metal levels in sediment and in oyster (Crassostrea gigas) collected from a Japanese aquaculture were investigated. Elevated metal concentrations in sediment were found in the part of the aquaculture with high density of fish nets, and significantly positive correlations among the metals in sediments indicated that source(s) of these metals were common. The levels of metals were slightly higher in oyster tissues collected near bottom than near surface of seawater of the aquaculture. The levels of Cr, Ni, and As in dry oyster tissues from the aquaculture were higher than those from most Japanese coastal areas, while Cu, Zn, and Pb in dry basis were lower than those from other areas. Estimated daily intake (EDI) for men and women followed the order of Zn > Cu > As>Cd > Cr > Ni > Pb. Non-carcinogenic health hazard (HQ) and hazard index values (total HQ) of Cd, Cr, Ni, Cu, Zn, As, Cd, and Pb were lower than 1, indicating that women and men would experience no risks of studied metals if they ingested the oysters collected from Shidugawa Bay, but target cancer risk (TR) of As suggested that oyster may pose potential health risk for adult men and women via oyster consumption. Thus, continuous monitoring of trace elements in sediments and seafoods influenced by antifouling paints should be recommended.

Impact of Climate Extremes on Suitability Dynamics for Japanese Scallop Aquaculture in Shandong, China and Funka Bay, Japan

The assessment of extreme weather events on suitable sites for aquaculture could help in establishing sustainable coastal environmental resource management. Japanese scallop culture is an economically important marine farming activity in the coastal communities of Shandong, China and Funka Bay, Japan. In this study, we improved the suitable aquaculture site-selection model (SASSM) by using Geostationary Ocean Color Imager (GOCI) data instead of Moderate Resolution Imaging Spectroradiometer (MODIS) data, as a complementary source for higher temporal and spatial resolution data that are useful for monitoring fine-scale coastal and oceanic processes. We also applied the newly developed SASSM to the Japanese scallop production site along the Shandong coast. Finally, we analyzed the correlations between environmental factors (chlorophyll a concentration, sea surface temperature (SST), and total suspended sediment), meteorological factors (precipitation, temperature, and wind), and climatic events (winter East Asian monsoon (EAM) and El Niño/La Niña Southern Oscillation), and the impacts of climate events on suitable zones for scallop aquaculture. The new SASSM maps show that GOCI products have the potential for oceanographic investigations in Shandong, China and Funka Bay, Japan. Our results highlighted higher aquaculture site suitability for scallop in Funka Bay than in Shandong coast. During the winter with a strong EAM (2011), the suitable area for Japanese scallop aquaculture increased. Conversely, in the winter during a strong El Niño (2016), we found fewer areas that were highly suitable for scallop aquaculture in Funka Bay. SST was extremely low in Funka Bay during spring and summer 2017, which caused fewer highly suitable areas (scores of 7 and 8) for scallop aquaculture relative to other years. These findings suggest that extreme climatic events significantly impact the availability of suitable sites for marine farming and thus, should be considered in the development and design of coastal aquaculture sites.

Prevention of hypermelanosis by rearing Japanese flounder Paralichthys olivaceus in net-lined tanks

In artificially reared flatfish, especially the Japanese flounder Paralichthys olivaceus, pigmented skin (hypermelanosis) frequently appears on the fish’s blind side after normal metamorphosis. As no practical prevention method has yet been proposed, we examined the effectiveness of a loose net placed inside the rearing tank that covers the bottom and walls like a pouch. When juveniles (standard length [SL] 6 cm) were transferred to the net-lined tank (mesh size 4 mm) before the first appearance of hypermelanosis, the pigmented area after 2 months covered about 0.5% of the blind side; this is about 1/40th of the area covered by pigment in fish reared in an ordinary tank (20%). Although the initial appearance of pigmentation in the axilla area (the area covered by the pectoral fin) was not suppressed, utilization of a larger mesh size (12 mm) decreased the expansion of pigmentation in this area. Juveniles reared in the net-lined tank were about 5–15% smaller (SL) than those reared in the ordinary tank, but their body depth:SL ratio was closer to that of wild-caught juveniles. From the results of this study, we propose that net-lined rearing tanks with larger-sized mesh are a practical method of preventing hypermelanosis in Japanese flounder aquaculture systems.

Occurrence of sul and tet(M) genes in bacterial community in Japanese marine aquaculture environment throughout the year: Profile comparison with Taiwanese and Finnish aquaculture waters

The use of antibiotics in aquaculture causes selection pressure for antibiotic-resistant bacteria (ARB). Antibiotic resistance genes (ARGs) may persist in ARB and the environment for long time even after stopping drug administration. Here we show monthly differences in the occurrences of genes conferring resistance to sulfonamides (i.e. sul1, sul2, sul3), and tetracyclines (tet(M)) in Japanese aquaculture seawater accompanied by records of drug administration. sul2 was found to persist throughout the year, whereas the occurrences of sul1, sul3, and tet(M) changed month-to-month. sul3 and tet(M) were detected in natural bacterial assemblages in May and July, but not in colony-forming bacteria, thus suggesting that the sul3 was harbored by the non-culturable fraction of the bacterial community. Comparison of results from Taiwanese, Japanese, and Finnish aquaculture waters reveals that the profile of sul genes and tet(M) in Taiwan resembles that in Japan, but is distinct from that in Finland. To our knowledge, this work represents the first report to use the same method to compare the dynamics of sul genes and tet(M) in aquaculture seawater in different countries.

The absorption-enhancing effect of citric acid on oral oxytetracycline treatment against Nocardia seriolae infection in yellowtail, Seriola quinqueradiata

Nocardia seriolae infection is one of the most serious bacterial diseases in Seriola species in Japanese aquaculture. In this study, the absorption-enhancing effect of citric acid on oral oxytetracycline (OTC) treatment against nocardiosis was evaluated with experimentally infected juvenile yellowtail, Seriola quinqueradiata, followed by serum, kidney and spleen OTC level analysis. When 50 mg/kg body weight (BW) of OTC was administered orally in combination with 1250 mg/kg BW of citric acid, the serum OTC level increased 3-fold at 6 h post single-dose administration, while no effect was observed when the dose of citric acid was set at 50 mg/kg BW. OTC levels in the kidney and spleen were increased 2-fold when 50 mg/kg BW of OTC and 1250 mg/kg BW of citric acid were administered for 5 consecutive days. This coadministration improved the clinical efficacy of oral OTC treatment against nocardiosis by significantly reducing the mortality rate compared to that of the group that received OTC alone and the untreated control group. These results suggest that coadministration of 1250 mg/kg BW of citric acid enhanced OTC absorption and therefore improved the clinical efficacy of oral OTC treatment against nocardiosis.

The combination effect of N-acetyl-d-glucosamine on oral oxytetracycline treatment against Nocardia seriolae infection in the yellowtail Seriola quinqueradiata

Nocardia seriolae infection is one of the most serious bacterial diseases in Seriola species in Japanese aquaculture. In this study, the combination effect of N-acetyl-d-glucosamine (NAG) with oral oxytetracycline (OTC) treatment was evaluated with the experimental infection of artificially bred juvenile yellowtail Seriola quinqueradiata. Prior to the evaluation, the efficacy of OTC treatment against nocardiosis was assessed. The oral administration of OTC at a dose of 50mg/kg body weight (BW) for 4 consecutive days did not show sufficient efficacy compared with that of the untreated control group, while the intraperitoneal administration of OTC, which caused no absorption loss in the gastrointestinal tract at a single dose of 50mg/kg BW successfully suppressed mortality (P<0.05). When OTC was orally administered with the same amount of NAG at a single dose of 50mg/kg BW, the serum OTC concentrations significantly increased at 1h and 6h post-administration (P<0.05); peak concentrations increased by 41%. In two trials evaluating the treatment of nocardiosis, the addition of NAG improved the efficacy of 5-consecutive-day oral OTC treatment by significantly reducing mortality compared with that of the untreated control group (P<0.05). These results suggest that NAG can enhance the absorption of oral OTC and therefore improve the efficacy of nocardiosis treatment.

ビブリオ病

Vibriosis is the general term for diseases caused by bacteria belonging to the genus Vibrio. “Red-pest” of eels caused by Vibrio anguillarum is the first description of fish vibriosis, and 14 Vibrio species have been known as the etiological agent of aquatic organisms. Vibrios are basically halophilic and distributed widely in ocean, and the disease occurs mainly in marine cultured fish and shellfish worldwide, except for some infections in freshwater cultured salmonids and ayu. The disease also has posed severe problems in hatchery-produced larvae and juveniles. In this review, we briefly outline vibriosis particularly important for Japanese aquaculture.

Genetic diversity of oxytetracycline-resistant bacteria and tet(M) genes in two major coastal areas of South Korea.

This study aimed to analyse the prevalence and genetic diversity of the tet(M) resistance gene as well as the species composition of oxytetracycline-resistant bacteria in coastal areas of South Korea. Both culturable and non-culturable bacterial communities were sampled in 2010 and 2011 within two coastal areas (Wando and Geoje). tet(M) and 16S rRNA gene sequences were obtained by PCR and sequencing and were used for phylogenetic analyses. Quantitative PCR (qPCR) was performed to determine the prevalence of tet(M) in sampled areas. Phylogenetic analyses revealed high heterogeneity of tet(M) sequences between Wando and Geoje areas. Sequences found in Wando were highly similar to each other and were similar to sequences found in Japanese aquaculture sites. A larger diversity of tet(M) sequences was obtained from natural assemblage in Geoje. qPCR showed a high prevalence of tet(M) in Wando's aquaculture sites (up to 10-2gene copies per 16S rRNA copy) and for industrial sites in Geoje (up to 10-3gene copies per 16S rRNA copy). 16 rRNA-based identification showed that Vibrio sp. and Photobacterium sp. were the most representative species in Wando, whereas in Geoje a broader range of species was found, with several isolates identified as pathogenic Acinetobacter, Aeromonas and Klebsiella. Altogether, these results showed a high prevalence of tet(M) in both sites, and different origins of contamination were identified. Because several pathogenic strains of oxytetracycline-resistant bacteria were reported for the first time, these results strongly warrant further analyses and actions to prevent contamination events by antibiotics in South Korea.

Isolation and characterization of tandem repeat sequences in the growth hormone gene of the red seabream, Pagrus major (Temminck &amp; Schlegel, 1843)

Growth hormone (GH) is one of the main regulators of postnatal somatic growth and stimulates anabolic processes such as cell division, skeletal growth and protein synthesis (Goodman, 1993). Several studies have reported the GH gene as a candidate for enhancing production traits such as growth (Tambasco et al., 2003), disease resistance, egg production (Kuhnlein et al., 1997), fat content (Knorr et al., 1997) and milk production (Hoj et al., 1993; Dybus, 2002) in livestock. Polymorphisms of the GH gene are also known to be associated with some level of growth performance in several aquacultured fish species such as Atlantic salmon Salmo salar (Gross and Nilsson, 1999), Japanese flounder Paralichthys olivaceus (Kang et al., 2002) and gilthead seabream Sparus aurata (Almuly et al., 2005). Red seabream, Pagrus major is an important sparid fish species in the Japanese aquaculture industry (Murata, 2005). Several hatcheries successfully developed strains showing useful economic traits such as growth (Murata et al., 1996; Taniguchi, 2011). Some strains are known to possess useful economic traits other than fast growth (Sawayama and Takagi, 2014), and efficient methods are needed to select for growth in these strains. Therefore, understanding the genetic architecture of the GH gene of red seabream (pmaGH) and polymorphisms of tandem repeats located in pmaGH is important for future breeding programs of this fish species. In this study, we isolated the GH gene from red seabream (including introns and 566 bp of the 50-flanking region) and characterized the variability in pmaGH based on polymorphisms in the satellite DNA using a wild population of this species. The genomic structure of pmaGH was also compared with some fish GH genes.

The Consideration of the Substratum of the Japanese Aquaculture Industry

The Consideration of the Substratum of the Japanese Aquaculture Industry

Tunic morphology and viral surveillance in diseased Korean ascidians: soft tunic syndrome in the edible ascidian, Halocynthia roretzi (Drasche), in aquaculture

'Soft tunic syndrome' causes mass mortality in the edible ascidian Halocynthia roretzi in Korean and Japanese aquaculture. In histopathological comparison, there were no specific differences between diseased specimens from Korea and Japan, indicating that soft tunic syndrome occurring in Korea and Japan is the same disease. No bacterial or protozoan cells were microscopically detected in either healthy or diseased tunics suggesting they are not the direct causes of soft tunic syndrome. Attempts were made to isolate virus from affected ascidians taking into account temperature conditions in which soft tunic syndrome is most prevalent in the field. However, no viruses were isolated from diseased or non-diseased specimens using chinook salmon embryo (CHSE-214), flounder fin (FFN) or epithelioma papillosum cyprini (EPC) cell lines.

Aquaculture and Florfenicol Resistance inSalmonella entericaTyphimurium DT104

To the Editor: In June 2006, the World Health Organization (WHO), the Food and Agriculture Organization of the United Nations (FAO), and the World Organisation for Animal Health (OIE) convened an Expert Consultation to consider the risks to human health represented by the use of antimicrobial drugs in aquaculture. This would, therefore, appear to be an opportune time to reexamine some of the arguments that have been presented with respect to the assessment of these risks. In their contributions to the debate regarding the risks associated with the use of antimicrobial agents in aquaculture, Angulo (1), Angulo and Griffin (2), Ribot et al. (3), and, more recently, Cabello (4) have argued that the available molecular evidence suggests that the flo gene that encodes chloramphenicol and florfenicol resistance in Salmonella enterica serovar Typhimurium DT104 (DT104) originally emerged in Japanese aquaculture and may have transferred horizontally from this host to DT104. This argument also appears in the report of the WHO/FAO/OIE consultation (ftp://ftp.fao.org/ag/agn/food/aquaculture_rep_13_16june2006.pdf). These authors (1–4) have based their argument on the assertions that florfenicol was first used in Japan and that flo gene–mediated resistance to this agent was first identified in bacteria isolated from Japanese fish farms. In attempting to identify the date of the emergence of florfenicol resistance in Japanese aquaculture, Angulo and Griffin (2) state that florfenicol had been used in this country since the early 1980s. However, Schering Plough, the manufacturer of florfenicol, reports first marketing this agent for aquacultural use in Japan in 1990 (D. Schofield, pers. comm.), and this date for the introduction of florfenicol is also provided by Kim et al. (5). It should, however, be noted that the flo gene encodes resistance to both florfenicol and chloramphenicol and, therefore, flo-containing bacteria could be selected for by the use of either agent. As a consequence, arguments about the chronology of the first use of florfenicol may have limited relevance. Florfenicol resistance in Japanese aquaculture (5) was first reported in strains of Pasteurella piscicida (now renamed Vibrio damsela). The sequence of the gene that encoded florfenicol resistance in these strains (6) was demonstrated to have a 97% nucleotide sequence similarity to that found in strains of DT104 resistant to ampicillin, chloramphenicol, streptomycin, sulfonamide, and tetracycline (ACSSuT DT104) (7). The available data (5,8) allow a reasonably accurate estimate of the date when these florfenicol-resistant strains first emerged in Japanese aquaculture. The strains of florfenicol-resistant P. piscicida were first isolated in Japan in 1992 (5). However, a previous study (8) had demonstrated 100% susceptibility to florfenicol of P. piscicida strains isolated from 1989 through 1991. Because this study examined 175 P. piscicida strains isolated from fish farms distributed over a wide geographic area in Japan, the data it generated provide strong support for the conclusions that flo-mediated florfenicol resistance in P. piscicida first emerged in Japanese aquaculture in 1992 (5). However, the presence of the floR gene has been demonstrated in a strain of ACSSuT DT104 isolated in the United States in 1985 (3). Thus, the floR gene was present in DT104 strains isolated in the United States at least 7 years before the first bacteria containing this gene (6) were isolated from an aquaculture setting in Japan (5). There are, however, data indicating that the flo gene was present in terrestrial bacteria associated with humans long before it was detected in multidrug -resistant DT104. A gene with a 95%–97% nucleotide identity with the flo gene of DT104 was detected in the Inc C plasmid R55 (9). This plasmid was originally identified in a chloramphenicol-resistant strain of Klebsiella pneumoniae isolated from a person in Paris in 1969 (10). The earliest report of the isolation of a bacterium whose florfenicol resistance was encoded by a flo gene (6) and the earliest accession date for a flo gene sequence in GenBank (www.ncbi.nlm.nih.gov/Genbank) both related to P. damsela isolated from Japanese aquaculture. Publication and accession dates do not, however, constitute evidence of the date of the first isolation of a bacterium containing this gene. Analysis of the available chronological and molecular data presented here indicates that a variant of the floR gene in DT104 (9) was present in a terrestrial bacterium isolated in 1969 (10), 23 years before the first isolation, in 1992, of a bacterium associated with aquaculture that contained this gene (5). It further demonstrates that this gene was present in strains of DT104 isolated in 1985. Thus, these data provide no support for the arguments (1–4) that implicate aquacultural use of florfenicol or the subsequent occurrence of florfenicol-resistant P. damsela in the emergence of the flo gene in DT104.

The Development of Tiger Puffer Aquaculture in China and Export to Japan

The purpose of this study is to examine puffer (tiger puffer, ocellated puffer) aquaculture and its exports from China and the imports and handling in Japan. This should help explain the details of puffer distribution and examine the spatial structure of fishery product distribution. Producers in China began the aquaculture business of puffers in 1994. In 2000, about 1000 tons of Chinese puffers were exported to Japan. The aquaculture businesses are located in north China areas such as the Yellow Sea and Sea of Bohai. Chinese fish breeders began their business of puffer aquaculture to earn large profits since puffers are sold at high prices. Chinese puffer aquaculture has achieved mass production and low density by different methods from Japanese aquaculture, for example, the use of breeding rooms to pass the cold winters and the utilization of ponds where shrimp were previously cultured. It is necessary to take countermeasures to reduce the oversupply in the market owing to the expansion of production. Since consuming puffers is currently prohibited in China, free transactions of the sale and consumption of puffers are expected in the future as well as the establishment of domestic markets. Today, low-cost puffers aquacultured in China are acknowledged as a new factor in puffer distribution. The areas that import puffers have been expanding overseas, and the users and consumers of puffers include all types of people. The target size of puffers varies depending on the size individual consumers prefer for cooking. This type of demand for selling and consuming puffers has become a major factor regulating the distribution structure, the actions of its elements and the interrelations of such elements. Cultured fish transactions, the introduction of puffers to the food culture, and the intermediations of cultured fish transactions by marketing wholesalers are also recognized.

Technical Innovations in Eel Culture Systems

Anguillid eels are high-value aquaculture species. Eel aquaculture techniques were developed in Japan and subsequently transferred to Taiwan and South Korea. When glass eel and elver supplies became a constraint in Japan, Taiwan used this opportunity to establish its own eel aquaculture industry. Later on, China and Malaysia also started to develop eel aquaculture. In Europe, many countries also adopted the Japanese eel aquaculture techniques, although Italy and France already had a long history of very extensive eel aquaculture. Driving forces for the development of eel culture techniques have been the need to overcome temperature limitations, enhance productivity, and comply with increasingly stringent environmental regulations while reducing production costs. Culture techniques have evolved from primitive methods to the highly sophisticated intensive systems. In this article, the current major growout culture systems are grouped into three categories: the outdoor culture system, the greenhouse culture system, and the intensive recirculating culture system. Innovations in Taiwan that apply Danish intensive recirculating culture technology are described separately. The eel aquaculture industry is facing constraints, such as unstable glass eel and elver supplies, lack of knowledge on larval rearing, disease occurrences, inconsistent product quality, limited markets, and a lack of culture techniques for other eel species. The challenge is to overcome these constraints in a sustainable manner with the technical, environmental, and economic considerations.

Nutrition and growth kinetics in nitrogen- or phosphorus-limited cultures of the ‘novel red tide’ dinoflagellate Heterocapsa circularisquama (Dinophyceae)

Heterocapsa circularisquama is a dinoflagellate that has only recently been recorded as producing red tides; it causes severe damage to Japanese shellfish aquaculture by killing bivalves. In order to elucidate the mechanism of red tide outbreaks, the nutrition and growth kinetics of H. circularisquama were examined in nitrogen (N)– or phosphorus (P)–limited semicontinuous culture. Inorganic N compounds, such as nitrate, nitrite, and ammonium, were found to be good nitrogen sources for the growth, whereas organic nitrogen (urea and uric acid) was not utilized. Heterocapsa circuiarisquama could successfully use a wide variety of inorganic and organic phosphorus compounds of different molecular structures as the sole P source. Under N-limited steady-state conditions, the dilution rate (= growth rate) as a function of cell nitrogen quota followed the Droop equation. Under P-limited steady state culture too, the dilution rate as a function of cell P quota followed the Droop equation. Kinetic parameters Dm, (the maximum dilution rate) and Kq (minimum cell quota) were 0.9 d−1 and 1.1 pmol N cell−1 for N-limited cultures and 1.1 d−1 and 89.4 fmol P cell−1 for P-limited cultures. The nutrient availability and kinetic parameters of H. circularisquama are compared with other red-tide organisms and the ecological implications of these characteristics are discussed.