Growth and habitat of spotted halibut Verasper variegatus in the shallow coastal nursery area, Shimabara Peninsula in Ariake Bay, Japan

ABSTRACT:   To determine the growth performances and habitat characteristics of spotted halibut Verasper variegatus , successive samplings were conducted in the south-eastern coastal area of Shimabara Peninsula in Ariake Bay. The push-net samplings were performed at Kamaga beach from May 2003 to April 2004 to determine the horizontal distribution of larvae and juveniles, while the gill net samplings were done in the coastal waters of Tatsuishi beach from July 2003 to July 2004 to collect the larger juveniles and adults. A total of 478 individuals from metamorphosing larvae to 2-year-old fish (15.2–447.0 mm total length [TL]) were sampled. In particular, the 2003-year class fish were successively collected from May 2003 to June 2004 (15.2–350.0 mm TL; n  = 418) and the mean total length in March, June, September, December 2003 and May 2004 was 22.4, 82.5, 172.5, 203.9 and 296.4 mm, respectively. The present study found that metamorphosing larvae migrated into the estuarine tidal flats during March 2003; newly settled juveniles inhabited the shallow intertidal areas; and juveniles had a remarkably high growth in shallow coastal areas. It is suggested that young fish around 300 mm TL migrated from the nursery grounds in Ariake Bay to deeper waters around Tachibana Bay during May–June 2004.     

Occurrence and distribution during the post-settlement stage of two Choerodon species in shallow waters around Ishigaki Island, southern Japan

The recruitment patterns of black-spot tuskfish Choerodon schoenleinii were compared with those of orange-dotted tuskfish (OT) C. ancholago. Individuals at the settlement and juvenile stages were collected using a push net in the intertidal zone and a seine net in seagrass beds. Relative values of standard length to total length (TL) for the two Choerodon species indicated an inflection point at approximately 10?C20?mm TL, suggesting that both species complete metamorphosis at a similar size. However, their temporal and spatial occurrence patterns were distinct. Newly settled individuals (postflexion stage) of black-spot tuskfish were collected mainly within foliage of Sargassum plants of the intertidal zone around March?CApril, while those of OT occurred in both the intertidal zone and seagrass beds mainly in May and June. In seagrass beds, the abundances of both species increased from May or June; however, the TL of black-spot tuskfish was bigger than that of OT. Therefore, black-spot tuskfish progressively migrate to seagrass beds after settling and completing metamorphosis in the intertidal zone, indicating that they utilize two different habitats as nursery grounds. Early spawning and migration from the intertidal zone by this species contributed to the occurrence of relatively large individuals in seagrass beds.     

Genetic population evaluation of two closely related flatfish species, the rare barfin flounder and spotted halibut, along the Japanese coast

ABSTRACT:   Barfin flounder and spotted halibut have been selected as target species for stock enhancement in Japan. Understanding the genetic condition of the wild stock is a principal requirement in any stock enhancement program. The genetic variability of barfin flounder and spotted halibut, and the population structure of spotted halibut were evaluated using microsatellite DNA markers (msDNA) and the control region of the mitocondrial DNA (mtDNA). Barfin flounder and spotted halibut showed high genetic variability at the msDNA level. Barfin flounder A was 16.7 and H _e was 0.860; spotted halibut A _n ranged from 7.7 to 10.2 and H _e ranged from 0.710 to 0.774. At the mtDNA level, high haplotype ( h  = 0.922) and low nucleotide (π = 0.002) diversities were observed for barfin flounder; however, low haplotype and nucleotide diversities ( h  = 0.603–0.620 and π = 0.001–0.002), and very low haplotype and nucleotide diversities ( h  = 0.193 and π = 0.0003) were observed for spotted halibut in the north and south locations, respectively. Slight genetic differentiation among spotted halibut sampling locations was observed from the msDNA. MtDNA analyses showed genetic differentiation between north and south locations, but not within them. The designation of north-specific and south-specific management units in the future stock enhancement activities of spotted halibut is recommended.     

Habitat utilization,feeding, and growth of wild spotted halibut <Emphasis Type="Italic">Verasper variegatus</Emphasis> in a shallow brackish lagoon: Matsukawa-ura,northeastern Japan

Habitat utilization, feeding, and growth of a rare pleuronectid flatfish, spotted halibut Verasper variegatus, were examined in a brackish lagoon in northeastern Japan: Matsukawa-ura. The distribution and date–length data of spotted halibut collected mainly from beam-trawl samplings during 1983–2008 indicated that age-0 juveniles [n = 25, 6.0–18.0 cm total length (TL)] and older spotted halibut (n = 71, 13.8–43.0 cm TL) inhabited almost the entire northern part of Matsukawa-ura. Comparative distribution surveys of spotted halibut, stone flounder, and marbled flounder during 1985–1989 revealed similar distribution patterns of these flatfishes; the highest densities were found around the central part of Matsukawa-ura, although significantly lower abundance was detected for spotted halibut. Linear growth equations of age-0 juveniles demonstrated that spotted halibut were able to achieve high growth after June, probably because abundant prey (e.g., mysids and gammarids) and suitable physical conditions (warmer water temperature and lower salinity) were present. The main prey items shifted from various crustaceans including mysids, caridean shrimps, and anomurans to brachyura Hemigrapsus spp. (≥20 cm TL). Our study shows that spotted halibut use the shallow brackish lagoon as an important nursery for juveniles, and also as a feeding ground for young and adults.     

Ontogenetic habitat shift of age-0 Japanese flounder <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis> on the Pacific coast of northeastern Japan: differences in timing of the shift among areas and potential effects on recruitment success

Ontogenetic habitat shift and feeding habits in the shallow (< 15 m) and deep (30–80 m) habitats of age-0 Japanese flounder Paralichthys olivaceus in Sendai Bay, the Pacific coast of northeastern Japan, were examined to understand the mechanisms that potentially enable area-specific high recruitment success. The flounder was able to use the shallow nursery habitat for about 1 year, until the next summer of their settlement (June–August) when they had reached 250 mm total length (TL). In addition, age-0 flounder between 150 and 250 mm TL used both shallow and deep habitats from winter to the next summer of their settlement, where species, size, and availability of potential food and susceptibility to predators are considerably different. These area-specific characteristics in Sendai Bay are clearly different from other areas around Japan that have been described in the literature: shorter residence in the shallow habitat and smaller size at emigration to the deep habitat. The characteristics in Sendai Bay seem to be enabled by prolonged good feeding conditions in the shallow habitat, which result from an abundant food supply and relatively lower temperature that does not exceed the uppermost temperature (25 °C) for maximum growth of the age-0 flounder. We consider that the prolonged better feeding conditions in the shallow habitat in the study area for ca. 1 year after settlement contribute to higher recruitment success.     

Comparison of factors affecting recruitment variability of walleye pollock Theragra chalcogramma in the Pacific Ocean and the Sea of Japan off northern Japan

The Japanese Pacific stock (JPS) and the northern Japan Sea stock (JSS) of walleye pollock Theragra chalcogramma are mainly distributed in the Pacific Ocean and the Sea of Japan off northern Japan, respectively. This paper summarizes and compares the factors affecting the recruitment variability of these two stocks. Spawning season is from December to March for both stocks. JPS recruitment has a positive relationship with the water temperature in January and February, whereas that of JSS has a negative relationship with the water temperature in January, February, and April. One possible reason for this is that pollock larvae have an optimum growth temperature of approximately 5 °C in the field. Drift of early life stages also appears to be an important influence on the recruitment of both stocks. Because the current generated by the northwest wind carries eggs of JPS into the main larval nursery ground, JPS recruitment is enhanced in years when the northwest wind is predominant in February. On the other hand, early life stages of JSS are transported into the nursery ground by the Tsushima Warm Current. However, this current also carries early life stages into the Sea of Okhotsk and offshore, resulting in poor JSS recruitment in years when this current is strong in March. In contrast to JPS, the recruitment of which is significantly impacted by cannibalism, young pollock have not been found in the stomachs of adult JSS. Warm temperatures in the Sea of Japan seem to induce the separation of young and adult pollock, and the shape of the stock–recruitment relationship also suggests that cannibalism is not important for JSS. Based on this knowledge, and on the hatch date distributions of larvae and juveniles, we propose mechanisms that can explain the recruitment fluctuations for JPS and JSS pollock.     

条斑星鲽和圆斑星鲽线粒体12S rRNA与16S rRNA基因序列及其系统分析

采用PCR产物直接测序法分别测定了条斑星鲽和圆斑星鲽线粒体基因组序列,并对12SrRNA和16S rRNA基因核苷酸全序列进行分析,条斑星鲽和圆斑星鲽线粒体12S rRNA的核苷酸序列长度分别为948 bp和949 bp,16S rRNA均为1716 bp。试验结果表明,由12S rRNA和16S rRNA基因所构建的两个系统树的结构基本一致,21种鱼主要分为3个大的分支:鲤形目、鲶形目聚为1支,鲑形目独立聚为1支,鲈形目和鲽形目聚为1大支。鲆鲽类与鲈形目的鲹科、鲷科鱼类聚类在一支,且与鲹科的日本竹荚鱼、大西洋竹荚鱼构成姊妹群,支持鲆、鲽类是从鲈形目分化出来的观点,而同属于鲽形目的鳎科鱼类塞内加尔鳎在12S rRNA树中成为一个独立的分支,在16S rRNA树中聚到鲈形目和鲽形目的分支中,并且与鲈形目关系更近些,鳎类是1个特殊类群,其分类地位有待进一步探讨。线粒体基因组序列已提交到GenBank中,序列号为:DQ403797和EF025506。     

Distribution of marine birnavirus in cultured marine fish species from Kagawa Prefecture, Japan

To determine the distribution of marine birnavirus (MABV) in cultured populations of different marine fish species, 1291 pooled tissue samples from 2672 fish belonging to 22 species and one hybrid were collected from Kagawa Prefecture, Japan, during 1999-2001. Using cell-culture MABV was isolated from three species: yellowtail, Seriola quinqueradiata Temminck & Schlegel (positive number/sample number, 10/419), amberjack, S. dumerili (Risso) (4/72), and Japanese flounder, Paralichthys olivaceus (Temminck & Schlegel) (41/481). Using PCR on MABV-negative samples, the MABV genome was detected in the same three species [yellowtail (9/409), amberjack (4/68) and Japanese flounder (93/440)] and two additional species, spotted halibut, Verasper variegatus (Temminck & Schlegel) (5/11), and goldstriped amberjack, S. lalandi Valenciennes (1/5). These MABV-positive species can be taxonomically divided into two groups: the genus Seriola and flatfish. In Japanese flounder, MABV was detected during all seasons, and the infection rate was correlated with water temperature. Aquaculture sites with MABV-positive fish were evenly distributed over the surveyed area, suggesting that MABV is widely distributed at aquaculture sites in Kagawa Prefecture. The nucleotide sequence at the variable region, the VP2/NS junction, revealed that the 39th base mutation occurs host-specifically for flatfish. Flatfish are suspected to be the main reservoir of MABV and might be responsible for establishing the infection cycle in aquaculture environments.     

Proteolytic digestive enzyme response in Japanese flounder larvae <Emphasis Type="Italic">Paralichthys olivaceus</Emphasis> fed two types of rotifers <Emphasis Type="Italic">Brachionus plicatilis</Emphasis> species complex

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?<?0.05) at 50 kDa in 1.5- and 3-h incubation whereas L-type treatment had not completely hydrolyzed the proteins after 3 h at the same molecular weight. Larvae fed SS-type had significantly higher (p?<?0.05) trypsin activity at 3, 5, 6, 7 DAH. Contribution of live prey to trypsin fraction in larvae showed significantly higher (p?<?0.05) fraction for SS-type at 5 DAH (2.18?±?0.44%) and 6 DAH (2.04?±?0.29%) and the effect of exogenous trypsin from live prey was relatively low when compared to the total trypsin activity in larvae. This study discusses the differences in ability to digest proteins in Japanese flounder when fed different rotifer morphotypes and highlights the adaptability of this species to alternative rotifer morphotypes during its early developmental stages.     

Morphological and habitat characteristics of settling and newly settled Roughscale Sole Clidoderma asperrimum collected in the coastal waters of northeastern Japan

This report first describes the morphological and habitat characteristics of larval and juvenile Roughscale Sole Clidoderma asperrimum. Five metamorphosing larvae (22.1–31.7 mm standard length, SL) and 12 juveniles (23.7–46.4 mm SL) were collected from two locations in coastal waters of northeastern Japan, Shizugawa Bay (rocky habitats, 6–12 m depth) and Iwaki (sandy habitats, 10–50 m depth), respectively, using a hand net while SCUBA diving and a small trawl net during May–August in 2008 and 2010. Underwater observation in Shizugawa Bay revealed that metamorphosing larvae and juveniles that had settled on rocks or stones showed transparent and variegated body coloration, which is cryptic to a rocky habitat. Juveniles in Iwaki showed monotonic coloration. The settlement would occur during metamorphosis because the same larva observed on a stone subsequently swam with a left-lateralized body posture. The larval morphology was characterized by a dense covering of fine spines on the whole body surface. Spines on the ocular side developed steadily, gradually forming bony tubercles with growth, whereas those on the blind side regressed with development and finally disappeared in metamorphosed juveniles. Our results indicate that Roughscale Sole can settle and adapt to rocky and sandy habitats in coastal waters with wide depth range.     

Distribution and drift pathways of Greenland halibut (Reinhardtius hippoglossoides) during early life stages in the eastern Bering Sea and Aleutian Islands

We describe the spatial distribution and dispersal pathways of Greenland halibut (Reinhardtius hippoglossoides) early life stages based on historical field data from the eastern Bering Sea and adjacent water along the eastern Aleutian Islands. Our results indicate that Greenland halibut from preflexion larvae to newly settled juveniles have a long pelagic duration and are subject to extended drift pathways. Hatching may occur in deep water, below 530 m, and larvae rise in the water column as they grow. Flexion/postflexion larvae are mostly found around the Pribilof Islands over the middle shelf (50–100‐m isobaths) in July, and settling occurs during late summer on the middle shelf near St. Matthew Island. However, given that age‐1 individuals were primarily found on the outer shelf, it appears that Greenland halibut actively move to deeper water with age (or size). The mechanisms of slope–shelf connectivity in preflexion larvae may be related to the Bering Slope Current in the vicinity of both Bering and Pribilof Canyons. This study shows that Greenland halibut early life stages have extensive horizontal ontogenetic migrations in the Bering Sea, and utilize a range of geographic areas over the basin and slope along the Aleutian Islands and in the eastern Bering Sea. Based on these results, it is hypothesized that settlement success and recruitment of Greenland halibut may be influenced by variability in currents and flows of the Bering Sea slope and shelf during their transport.     

Late arrival of Anguilla japonica glass eels at the Sagami River estuary in two recent consecutive year classes: ecology and socio-economic impacts

To determine the actual status of the recruiting glass eel stock of Anguilla japonica, we conducted a continuous monthly monitoring program for 2?years between November 2009 and October 2011 at the Sagami River estuary, Japan. A total of 114 and 372 A. japonica glass eels were observed in the 2009?C2010 and 2010?C2011 seasons, respectively. Recruitment patterns were the same in both years, starting in early winter (December in 2009 and November in 2010), increasing slightly until March, decreasing in April, but attaining the largest peak in June, after which no glass eels were observed during August?COctober. The Japanese eel has been known to spawn mainly in the summer, and glass eels recruit to their freshwater growth habitats during the winter to early spring. Our results clearly demonstrate an unexpected late arrival of glass eels in the early summer for two recent consecutive year classes. The summer recruitment found in our study indicates the unusual phenology of the Japanese eel, which may be a possible response to recent climate change.     

Artificial gynogenesis and assessment of homozygosity in meiotic gynogens of spotted halibut (<Emphasis Type="Italic">Verasper variegatus</Emphasis>)

In the present study, methodology of gynogenetic induction in spotted halibut were developed and optimized; the sex ratio of putative meiotic gynogenetic diploids was determined using AFLP-based molecular sexing technique; the homozygosity of gynogenetic population was assessed as opposed to cultivated population. The results showed that high percentage of meiotic gynogenetic diploids were generated when the eggs fertilized with irradiated heterologous sea perch frozen sperm (30–50 mJ cm⁻²) were cold shocked in sea water of −1°C for 40–75 min at 5 min after fertilization. About 15,200 diploid gynogenetic larvae were achieved and they exhibited normal morphology similar to diploid control. The gynogenetic diploids were 100% female, which first confirmed the female homogamete (XX/XY) sex determination in spotted halibut. The genetic analysis showed that the average H _O was, respectively, 0.404 and 0.724 in gynogenetic population and cultivated population, indicating an increase of homozygosity in gynogenetic population.     

Comparison of the color vision and spectral sensitivity of three flatfish species of different ecotypes,and application to selective fishing methods

In this study, we determined the color vision and spectral sensitivity of pointhead flounder, slime flounder, and red halibut by recording electrophysiological S-potentials from isolated retinas; this basic data was collected to aid the selection of appropriate colors and effective wavelengths for selective fishing gear for sustainable fisheries. Four kinds of L-response and one C-response were recorded in the pointhead flounder and red halibut. Two kinds of L-response were recorded in the slime flounder. The occurrence of a C-response indicates the possession of color vision. The C-responses show that the pointhead flounder has superior distinction from blue to yellow, and red halibut has superior distinction from blue and green to red. The most frequently recorded L-responses indicate high spectral sensitivity at 544 nm in pointhead flounder and 518 nm in slime flounder and red halibut. All recorded L- and C-responses indicate sensitivity to ultraviolet wavelengths.     

Transport and survival of Japanese sardine (Sardinops melanostictus) eggs and larvae via particle‐tracking experiments

Particle‐tracking experiments were performed to infer the distribution of larvae of the Japanese sardine (Sardinops melanostictus) and to detect effects of transport environment on sardine recruitment, using the output of a high‐resolution ocean general circulation model and observed data of sardine spawning grounds during 1978–2004. By the 60th day following spawning, approximately 50% of the larvae had been transported to the Kuroshio Extension (KE). Whereas the spawning period and grounds changed markedly in relation to the stock level, the proportion of larvae transported to the KE remained relatively constant and no significant correlations were found between sardine recruitment and the transport proportion. Instead, the recruitment was found to be correlated with physical parameters including the mixed layer depth and the sea surface temperature along several major transport trajectories of sardine larvae. The correlations were most significant for the trajectories in the region 0.5° south to 1° north of the Kuroshio axis (defined as the location of velocity maxima at each longitude) and for larvae spawned in February and March during the high stock period (1978–94), and for larvae spawned in March and April during the low stock period (1995–2004).     

Horizontal movement and emigration of juvenile spotted halibut <Emphasis Type="Italic">Verasper variegatus</Emphasis> released in a shallow brackish lagoon: Matsukawa-ura,northeastern Japan,revealed by acoustic telemetry

To elucidate the post-release movement and emigration of juvenile spotted halibut Verasper variegatus, ten hatchery-reared age-0 individuals (10 months old, 17.0–19.7 cm total length) surgically implanted with acoustic transmitters were released near the center of Matsukawa-ura, a shallow brackish lagoon, on 25 November 2009 (water temperature 13.8 °C). They were monitored by ten acoustic receivers for 5 months. Of ten individuals, eight left the release site during December–March. Three of these emigrated to the outer ocean on 17 and 29 January and 30 March 2010, respectively. Juveniles probably started wintering migration in December and January when water temperatures decreased considerably in the lagoon (mean 9.5 and 6.0 °C, respectively). They stopped their migration in the coldest month, February (mean 5.7 °C), and restarted it in March when water temperatures frequently exceeded a plausible threshold for movement (≥6 °C). Statistical analyses revealed that the fish started migration significantly more frequently at nighttime. The migration track of an individual recorded from 11 to 30 March showed gradual nocturnal movements and a slow migration speed (estimated maximum speed 2.2 m/min). Our results revealed that water temperature primarily governed the seasonal timing of nocturnal migratory movements of juvenile spotted halibut.     

Ocean transport paths for the early life history stages of offshore-spawning flatfishes: a case study in the Gulf of Alaska

Offshore‐ and deepwater‐spawning flatfish species face the problem of transport of their planktonic stages to shallow juvenile nursery grounds that are often far shoreward in bays or estuaries. We compare life history attributes of four offshore‐spawning flatfish species in the Gulf of Alaska: Pacific halibut (Hippoglossus stenolepis), arrowtooth flounder (Atheresthes stomias), rex sole (Glyptocephalus zachirus) and Dover sole (Microstomus pacificus) to examine how their larvae get from a spawning location at the edge or beyond the continental shelf to specific inshore nursery zones. We utilize historical records of survey catches of different life stages to characterize the stage‐specific changes in distribution of spawning, planktonic stages and juvenile nursery areas. We infer transport mechanisms based on the shifts in distribution of the life stages and in comparison with local physical oceanography. This comparison provides insight into the different mechanisms marine species may use to solve the common ‘problem’ of planktonic drift and juvenile settlement.     

圆斑星鲽sox9基因的克隆与表达

本研究筛选到圆斑星鲽(Verasper variegatus)的性别相关基因sox9,并通过RACE技术获得了全长序列,基因全长为3287 bp,包括1431 bp的ORF,编码477个氨基酸,368 bp的5¢ UTR和1488 bp的3¢ UTR。在3¢ UTR中有多聚腺苷酸尾和加尾信号AATAAA。通过荧光定量PCR测定了sox9基因在圆斑星鲽成鱼不同组织中的表达水平,发现sox9基因在圆斑星鲽的脑、眼、鳃、心、肝、胆、肠、精巢、卵巢、肾和肌肉等各个组织中都有不同程度的表达。在鳃、脑和精巢组织中检测到较高水平的sox9转录,其中精巢中的转录水平显著高于其他组织,sox9基因在性腺中的表达显示出性别两相性差异。其在精巢中的表达水平要显著高于卵巢,说明sox9基因与雄性性腺发育相关。通过测定sox9基因在圆斑星鲽幼鱼不同发育时期(20、30、40、50、60、70和80日龄)的表达水平,发现其在20~50日龄表达量逐渐下降,在60日龄时表达量上升,推测表达量上升可能与幼鱼性腺分化相关。     

Antigenic differences of the scuticociliate Miamiensis avidus from Japan

In Japan and Korea, outbreaks of scuticociliatosis have frequently occurred in Japanese flounder, Paralichthys olivaceus . Morphological observations and small subunit rRNA gene sequences have shown that the causative agent of scuticociliatosis in the flounder is Miamiensis avidus (syn. Philasterides dicentrarchi ). In this study, we elucidated the antigenic differences between six Japanese M. avidus isolates as an initial step toward developing an effective vaccine against the disease. Four Japanese flounder isolates (IyoI, Nakajima, JF05To and Mie0301 isolates), one spotted knifejaw, Oplegnathus punctatus, isolate (SK05Kyo), and one ridged-eye flounder, Pleuronichthys cornutus , isolate (RF05To) were subjected to serological analysis. Antisera against IyoI, SK05Kyo, Nakajima and Mie0301 isolates were raised in rabbits and used for immobilization assays and Western blotting. Immobilization assays showed that the six isolates could be divided into three groups, tentatively designated serotype I for IyoI, JF05To, RF05To, SK05Kyo, serotype II for Nakajima and serotype III for Mie0301. Western blotting results supported these three serotypes, with marked similarities in the banding profiles of IyoI, JF05To, RF05To and SK05Kyo isolates, which were distinct from the Nakajima and Mie0301 isolates. Three isolates, IyoI, Nakajima and Mie0301 that were selected as representatives of each serotype, were highly pathogenic to Japanese flounder by experimental infection. Based on these findings, we propose that there are at least three M. avidus serotypes in Japan.     

Channel Catfish,Ictalurus punctatus,Immunity to Saprolegnia sp.

ABSTRACT

The Japanese flounder, Paralichthys olivaceus, is one of the most common finfish cultured in Japan and Korea. Despite the relatively high production of fingerlings, some problems remain, mainly related to the larval feeding and cost of maintaining microalgae and rotifers. In order to determine the effects of different diets on the Japanese flounder larval growth and survival, a series of experiments was carried out related to the size and nutritional value of different live feeds. The larvae culture conditions were at 10 or 20 larvae/L in 50 to 2,000 L tanks, with aeration and with or without “green water,” and a temperature range of 18.5 to 22.5°C. The live foods used were microalgae (Chlorella ellipsoidea and Nannochloris oculata), baker's yeast, experimental n-yeasts, oyster trochophore larvae, three strains of rotifer Brachionus plicatilis (L-type, S-type and U-type) and Artemia nauplii. Variations were detected in size, dry weight, and chemical composition of the three strains of rotifers used. The maximum number of rotifers ingested by flounder larvae increased steadily from 7 individuals, at first feeding (3.13 mm), to 42 individuals at 5.25 mm of total length (6 days after first feeding). There was a relationship between larval total length and size of the rotifers ingested. The effect of rotifer size on larval growth and survival appeared to be limited to the first two days of feeding. Of the diets tested in the growth and survival of larval flounder during 14 days after hatching, rotifers fed on C. ellipsoidea and raised in green-water gave the best results. Rotifers cultured on enriched N. oculata and n-yeasts did not support larval growth and caused higher mortalities. The n-yeasts used as rotifer enrichment appeared to satisfy, partially, the nutritional requirement of 7-day-old flounder larvae, as did n-yeast squid wintering oil the requirements of 14-day-old larvae. From 7-9-days after hatching and throughout the second 14-day period, rotifers and Artemia cultured on N. oculata improved the survival of flounder compared with those fed on rotifers cultured on C. ellipsoidea. Moreover, the larval growth did not vary significantly between both microalgae-rotifer feedings. No clear relation was found between total protein, lipid, amino acids and fatty acids of live feeds with the growth and survival of flounder larvae, although the total lipid was higher in C. ellipsoidea than in N. oculata. The Artemia nauplii San Francisco strain appeared to be more suitable for the growth and survival of flounder larvae, than the Utah strain. The nutritional value of Artemia nauplii (Utah strain) for flounder larvae remained unchanged despite the use of either microalgae as nauplii enrichment.