Platichthys Stellatus Research Articles

FISH AND DECAPODS IN THE ESTUARIES OF THE OLGA BAY

Species composition in 64 catches obtained by fry seine (length 15 m, height 2.5 m, mesh size 5 mm) in the estuaries of the Olga Bay (Primorye) in the daytime in warm seasons of the 2012 and 2013 are analyzed, including 4 catches in the Olga River estuary, 43 in the Avvakumovkа estuary and 17 in the Tihaya Pristan Bight, as the common external estuary of both rivers. In total, 53 taxa of aquatic organisms belonged to 23 families were defined: 49 fish species and 4 species of decapods. The families with the highest species diversity were Cottidae — 7 species, Gobiidae — 5 species, and Hexagrammidae — 5 species. The most common species were Tribolodon spp. (occurrence 92 %), Crangon spp. (66 %), Gasterosteus nipponicus (64 %), and Megalocottus platycephalus taeniopterus (59 %). The species richness decreased in the order: Tihaya Pristan Bight (42 species) — Avvakumovka estuary (29 species) — Olga estuary (11 species). Seven mass species made about 90 % of the total catch: Tribolodon spp., Eriocheir japonica, Megalocottus platycephalus taeniopterus, Platichthys stellatus, Gasterosteus nipponicus, Oncorhynchus keta, and Hypomesus sp. Among them, M. platycephalus taeniopterus and Tribolodon spp. were the most frequent. Species domination by Simpson index decreased in the order: Olga estuary (0.434) — Tihaya Pristan Bight (0.373) — Avvakumovka estuary (0.243). The biomass distribution density was calculated using the coefficient of catchability 1.0. It was the highest in the Tihaya Pristan Bight — 10.1 g/m 2 and considerably lower in both internal estuaries: the Avvakumovka — 6.1 g/m 2 and the Olga — 4.9 g/m 2 . The mean density fluctuated in the range of 2.5–8.9 g/m 2 with the average value of 6.7 g/m 2 . Tribolodon spp., E. japonica, P. stellatus, M. platycephalus taeniopterus, and G. nipponicus prevailed in the freshwater biotopes of the internal estuaries distinguished by low salinity and strong water flow with the mean distribution density 2.5, 0.9, 0.7, 0.6, and 0.4 g/m 2 , respectively. Tribolodon spp., M. platycephalus taeniopterus, H. octogrammus, M. stelleri, L. pinnifasciata, and O. ocellatus prevailed in the marine biotopes of the external estuary distinguished by relatively warm, salty and calm water, shallow depths and thickets of Zostera marina, their mean distribution density was 10.1, 2.7, 0.7, 0.5, 0.4, and 0.4 g/m 2 , respectively.

Parallel opsin switches in multiple cone types of the starry flounder retina: tuning visual pigment composition for a demersal life style

Variable expression of visual pigment proteins (opsins) in cone photoreceptors of the vertebrate retina is a primary determinant of vision plasticity. Switches in opsin expression or variable co-expression of opsins within differentiated cones have been documented for a few rodents and fishes, but the extent of photoreceptor types affected and potential functional significance are largely unknown. Here, we show that both single and double cones in the retina of a flatfish, the starry flounder (Platichthys stellatus), undergo visual pigment changes through opsin switches or variable opsin co-expression. As the post-metamorphic juvenile (i.e., the young asymmetric flatfish with both eyes on one side of the body) grows from ~5 g to ~196 g, some single cones and one member of unequal double cones switched from a visual pigment with maximum wavelength of absorbance, λmax, at shorter wavelengths (437 nm and 527 nm) to one with longer λmax (456 nm and 545 nm, respectively) whereas other cones had intermediate visual pigments (λmax at 445 nm or 536 nm) suggesting co-expression of two opsins. The shift toward longer wavelength absorbing visual pigments was in line with maximizing sensitivity to the restricted light spectrum at greater depths and achromatic detection of overhead targets.

Identification and Characterization of Megalocytivirus Type 3 Infection with Low Mortality in Starry Flounder, Platichthys stellatus, in Korea

AbstractMVSF‐12 belonging to megalocytivirus type 3 was isolated from cultured starry flounder; Platichthys stellatus, at the moribund or subclinical stage with low mortalities in Korea. Of 20 apparently healthy fish in the farms, 17 were also confirmed in nested polymerase chain reaction to be infected by megalocytivirus. When starry flounder; rock bream, Oplegnathus fasciatus; and olive flounder, Paralichthys olivaceus, were artificially infected by MVSF‐12 or iridovirus sachun‐1 (IVS‐1, megalocytivirus type 1), starry flounder and olive flounder showed no mortality until Day 24, without any clinical signs including enlarged spleen, while rock bream showed 100% mortality by IVS‐1 infection within 11 d but no mortality by MVSF‐12. Although it was not pathogenic, MVSF‐12 in infected fish at Day 24 was viable when successfully cultured in vitro using primary rock bream embryo cells and produced a cytopathic effect (CPE) with the viral copy numbers between 1.76 × 107 and 5.23 × 107/mL of culture supernatant. In conclusion, this study demonstrates the low pathogenicity of MVSF‐12 and low susceptibility of starry flounder and olive flounder to both MVSF‐12 and IVS‐1. Indeed, MVSF‐12 at the subclinical stage could be replicated with CPE in vitro, indicating a possibility to induce pathogenic effects and mortality under adverse environment or physiologic conditions.

Fine-tuning light sensitivity in the starry flounder (Platichthys stellatus) retina: Regional variation in photoreceptor cell morphology and opsin gene expression.

Vertebrate color vision relies on the differential expression of visual pigment proteins (opsins) in cone photoreceptors of the retina. The diversity of opsins and their retinal expression patterns appear greatest for animals that experience variable light habitats, as is the case with flatfishes. Yet, opsin repertoires and expression patterns in this group of fishes are poorly described. Here, we unveil the visual opsin expression patterns of juvenile starry flounder (Platichthys stellatus) and describe the localization of cone types, their visual pigments and opsin expression. Juvenile starry flounder express eight opsins (Rh1, Sws1, Sws2A1, Sws2A2, Sws2B, Rh2A1, Rh2A2, Lws) and possess a corresponding number of photoreceptor visual pigments, with peak absorbance ranging from 369 to 557 nm. Retinal (vitamin A1) was the only chromophore detected in the retina. Intraretinal variation in opsin abundance consisted of greater expression of both RH2, and lesser expression of SWS1 and both SWS2A, opsin transcripts in the dorsal compared to the ventral retina. Overall cone density was greater in the dorsal retina which was also characterized by a larger proportion of unequal double cones compared with the ventral retina. Together, our results suggest that large opsin repertoires serve to optimize visual function under variable light environments by differential expression of opsin subsets with retinal location.

Fecundity of the Far-Eastern flatfishes Pleuronectiformes. 1. General characterization of fecundity of Pleuronectiformes in the northern part of the Pacific Ocean

Cited and archive data on fecundity of 31 flatfish species are generalized for the North Pacific. General characterization of the fecundity is presented and correlation between absolute individual fecundity of the females and their body length or age is analyzed and formalized in equation form. Spatial variability of fecundity is described for different species: pacific halibut and starry flounder have the highest absolute fecundity in the eastern Bering Sea and Okhotsk Sea, greenland halibut, yellowfin sole, alaska plaice, sakhalin flounder, longhead dab, and flathead sole - in the Okhotsk Sea, northern rock sole - in the waters at East and West Kamchatka. kamchatka flounder - in the Bering Sea, arrowtooth flounder - in the Pacific waters at North America. So, the Okhotsk Sea is the area where the absolute fecundity of majority wide-spread flatfish species can reach the maximal level. However, the maximal fecundity of longsnouted flounder is higher in the Japan Sea than in the Okhotsk Sea.

Seasonal Variability In Subtidal Fish Assemblages Inhabiting Sandy-Bottom Habitats Off Humboldt Bay, California

Abstract This study documents the seasonal fine-scale distribution, species richness, and abundance of subtidal fish species inhabiting sandy-bottom habitats in areas adjacent to Humboldt Bay, California. In total, 3 sampling areas, 2 located 5-km offshore, and 1 located 1-km offshore, were sampled quarterly for 1 y. Flatfish species (families Pleuronectidae and Bothidae) were the most common finfish sampled, although seasonal and spatial patterns varied among individual species. For instance, the abundance and size of English Sole (Parophrys vetulus) and Pacific Sanddab (Citharichthys sordidus) varied across both seasons and sampling areas, which may be attributed to their ontogenetic migration to offshore adult habitat. Species such as Starry Flounder (Platichthys stellatus) and Butter Sole (Isopsetta isolepis), did not vary seasonally, but did differ across sampling areas, likely as a function of depth. Although not the primary focus of our study, we include the abundance and diversity of invertebrates...

Effect of Beta-1-3-Glucan and Mannans on Growth and Fitness of Starry Flounder (Platichthys Stellatus): A Potential New Candidate for Aquaculture in Temperate Regions

Continuously intensifying aquaculture demands reductions in pathogen infections without increased therapeutics use. A potential solution is the use of prebiotic feed additives like β-glucan and mannan oligosaccharides (MOS). This study focusses (1) on the effect of prebiotics glucan/MOS on growth and fitness of Starry flounder and (2) on the viability of Starry flounder as an aquaculture candidate (as it is considered in South Korea). Over 56- days, juvenile Starry flounder were fed with glucan/MOS enhanced diet and a control diet. Feeding behavior, growth rate, morphological and blood physiological parameters were monitored. Fish fed glucan/MOS enriched diets exhibited significantly increased growth over the experimental period (GLM, p<0.01). Concentrations of cholesterol (P=0.043) and albumin (P=0.016) were significantly increased in the blood plasma of fish fed glucan/MOS. Whole body proximate analysis revealed significantly elevated crude protein (P=<0.001) and lipid (P=<0.005) in fish fed glucan/MOS compared to the control. Significant improvements in growth, numerous fitness factors and product quality parameters can be achieved through glucan/MOS supplementation to P. stellatus. The observed growth performance and the feed conversion ratio, especially at low water temperatures, suggest Starry flounder is indeed a promising candidate for aquaculture in temperate regions. More detailed investigation, highlighting the economic and market perspective, is needed before introduction to commercial production.

Effects of replacing fish oil with microalgae meals on growth performance, tissue proximate composition, and biochemical indices in juvenile starry fiounder, Platichthys stellatus

Effects of replacing fish oil with microalgae meals on growth performance, tissue proximate composition, and biochemical indices in juvenile starry fiounder, <i>Platichthys stellatus</i>

Comparison of the effects of dietary single and multi-probiotics on growth, non-specific immune responses and disease resistance in starry flounder, Platichthys stellatus

An 8-week feeding trial was conducted to evaluate the effects of dietary probiotics on growth performance and non-specific immune responses in starry flounder, Platichthys stellatus. Fish averaging 46.5 ± 0.65 g (mean ± SD) were fed one of the six experimental diets; one control (Cont), and five other diets were prepared by supplementing single-probiotics 1 (Bacillus subtilis; SP1, 2 × 109 CFU kg−1 diet), single-probiotics 2 (Bacillus licheniformis; SP2, 2 × 109 CFU kg−1 diet), multi-probiotics 1 (Bacillus subtilis + Bacillus licheniformis; MP1, 2 × 109 CFU kg−1 diet), multi-probiotics 2 (commercial probiotics; Bacillus subtills + Bacillus licheniformis + Paenibacillus polymyxa + Aspergillus oryzae + Saccharomyces cerevisiae; MP2, 2 × 109 CFU kg−1 diet) and oxytetracycline (OTC) at 5 g OTC kg−1 diet. At the end of 8 weeks feeding trial, weight gain (WG) and specific growth rate (SGR) of fish fed SP1, MP1 and MP2 diets were significantly higher than those of fish fed control diet (P < 0.05). Superoxide dismutase (SOD) activity of fish fed MP2 diet was significantly higher than those of fish fed OTC diet (P < 0.05). Nitro blue tetrazolium (NBT) activity and lysozyme activity of fish fed SP1, MP1 and MP2 diets were significantly higher than those of fish fed OTC diet (P < 0.05). However, there was no significant difference among fish fed SP1, SP2, MP1 and MP2 diets. During the Edwardsiella tarda challenge test, the first mortality occurred on day 2. After the 14 days challenge test, cumulative survival rate of fish fed MP1 and MP2 diets were significantly higher than those of fish fed control diet (P < 0.05). However, there was no significant difference among fish fed SP1, SP2, MP1, MP2 and OTC diets in survival rate at the termination of the challenge test. Although there was little advantage in immunological parameters with fish fed MP diets, single and multi-probiotics were equally effective statistically. These results demonstrated that single or multi-probiotics had equal beneficial effect as an antibiotic replacer in terms of growth performance, non-specific immune responses and disease resistance in starry flounder.

Evidences for involvement of growth hormone and insulin-like growth factor in ovarian development of starry flounder (Platichthys stellatus).

Although gonadotrophins are major regulators of ovarian function in teleosts and other vertebrates, accumulating evidence indicates that the growth hormone (GH)-insulin-like growth factor (IGF) axis also plays an important role in fish reproduction. As a first step to understand the physiological role of the GH-IGF system in the ovarian development of starry flounder (Platichthys stellatus), the expression profiles of GH and IGF messenger RNAs (mRNAs) and plasma GH, IGF-I, estradiol-17β (E2), and testosterone (T) levels during the ovarian development were investigated. The developmental stages of ovaries were divided into five stages (II, III, IV, V, and VI) by histological analysis. The hepatosomatic index (HSI) and gonadosomatic index (GSI) values increased and peaked at stage IV and stage V, respectively, and then declined at stage VI. Pituitary GH mRNA levels decreased sharply at stage III and raised to top level at stage VI. The hepatic IGF-I mRNA levels ascended to maximum value at stage V and then declined significantly at stage VI. However, the hepatic IGF-II mRNA levels remained stable and increased significantly at stage VI. In contrast, the ovarian IGF-I mRNA levels increased gradually and peaked at stage VI. The ovarian IGF-II mRNA levels were initially stable and increased significantly at stage V until the top level at stage VI. Consistent with the pituitary GH mRNA levels, plasma GH levels reduced sharply at stage III and remained depressed until stage V and then raised remarkably at stage VI. Plasma IGF-I level peaked at stage V and then declined to initial level. Plasma E2 level peaked at stage IV and then dramatically descended to the basal level. Plasma T level peaked at stage V and then declined significantly back to the basal level. Based on statistical analysis, significant positive correlations between hepatic IGF-I mRNA and GSI, ovarian IGF-II mRNA and hepatic IGF-II mRNA, ovarian IGF-I mRNA and ovarian IGF-II mRNA, and plasma IGF-I and plasma T were observed, respectively. These results suggest that the GH-IGF system may be involved in the ovarian development of starry flounder; GH and IGFs appear to play distinct roles in the regulation of the ovarian development in paracrine/autocrine manners. These findings extend our knowledge of the roles of the GH-IGF axis on reproduction regulation in fish.

넙치(Paralichthys olivaceus)와 강도다리(Platichthys stellatus)간 유도된 잡종 3배체의 난발생

We investigated the characteristics and rate of development of allotriploid embryos derived from a cross between female olive flounder Paralichthys olivaceus and male starry flounder Platichthys stellatus. The allotriploidy was induced by cold shocking fertilized eggs three minutes post-fertilization at 3&#xB0;C for 45 minutes. The average cellular DNA content of the allotriploid embryos was 2.06&#xB1;0.03 pg/cell, which is equal to the sum of the cellular DNA content of a diploid olive flounder (1.42 pg/cell) and a haploid starry flounder (0.66 pg/haploid cell). The first cleavage, midblastula, gastrula and Kupffer's vesicle appearance stages of the allotriploid eggs began at 1.5, 8, 13 and 26 hours after cold shocking at 18&#xB0;C, respectively. The developmental rate of allotriploid eggs was equivalent to that of diploid and triploid olive flounder eggs at 10, 14 and 18&#xB0;C. However, the hatching times of allotriploid eggs, 7 h at 10&#xB0;C, 5 h at 14&#xB0;C and 4 h at 18&#xB0;C, were earlier than those of diploid and triploid olive flounder.

Change of body height is regulated by thyroid hormone during metamorphosis in flatfishes and zebrafish

Flatfishes with more body height after metamorphosis should be better adapted to a benthic lifestyle. In this study, we quantified the changes in body height during metamorphosis in two flatfish species, Paralichthys olivaceus and Platichthys stellatus. The specific pattern of cell proliferation along the dorsal and ventral edge of the body to allow fast growth along the dorsal/ventral axis might be related to the change of body height. Thyroid hormone (T4 and T3) and its receptors showed distribution or gene expression patterns similar to those seen for the cell proliferation. 2-Mercapto-1-methylimidazole, an inhibitor of endogenous thyroid hormone synthesis, inhibited cell proliferation and decreased body height, suggesting that the change in body shape was dependent on the local concentration of thyroid hormone to induce cell proliferation. In addition, after treatment with 2-mercapto-1-methylimidazole, zebrafish larvae were also shown to develop a slimmer body shape. These findings enrich our knowledge of the role of thyroid hormone during flatfish metamorphosis, and the role of thyroid hormone during the change of body height during post-hatching development should help us to understand better the biology of metamorphosis in fishes.

Toxic effects and depuration after the dietary lead(II) exposure on the bioaccumulation and hematological parameters in starry flounder (Platichthys stellatus).

Platichthys stellatus (mean length 20±2cm, mean weight 160.15±15g) were exposed to the different levels of dietary lead(II) at the concentrations of 0, 30, 60, 120, 240mg/kg for 4 weeks. Depuration was conducted for 2 weeks after exposure. The lead exposure over 60mg Pb/kg induced the significant bioaccumulation in tissues of P. stellatus (5-30μg/g tissue), except for brain and muscle where the exposure to 240mg Pb/kg caused the bioaccumulation (2-4μg/g tissue). The hematological parameters such as red blood cell (RBC) counts, hematocrit (Ht) value and hemoglobin (Hb) concentration were substantially decreased over 60mg Pb/kg, and lasted even after the depuration period. For plasma components, calcium and magnesium levels in plasma were generally decreased over 60mg Pb/kg, and glucose level was also mainly increased over 60mg Pb/kg. Total protein was significantly decreased over 120mg Pb/kg after 4 weeks exposure. Glucose and total protein showed the restoration after the depuration period in groups of fish exposed previously to over 60 and 120mg Pb/kg, respectively. However, other parameters that changed during the exposure over 60mg Pb/kg did not recovered. For enzymatic components in plasma, glutamic oxalate transminase (GOT), glutamic pyruvate transminase (GPT) and alkaline phosphatase (ALP) were significantly increased over 120mg Pb/kg, and there was only restoration observed after the depuration for ALP over 120mg Pb/kg.

Analysis of transcriptome profiling from the brain at maturation and regression phases in starry flounder (Platichthys stellatus)

This study was to investigate the regulatory mechanisms of reproduction and endocrinology in starry flounder (Platichthys stellatus). Total RNA from the mixed sample of pituitary gland and hypothalamus of brain at the maturation and regression phases was isolated. The RNA sequencing (RNA-Seq) library was prepared and sequenced on Illumina Hiseq 2000 platform. A total of 53,567,296 and 75,630,680 short fragments were obtained from the samples of maturation and regression phases, respectively. After splicing, 30,640 unigene sequences were obtained based on the blasting results from National Center for Biotechnology Information (NCBI) database. Homogonous sequences of 24,128 unigenes (78.8%) were found and analyzed with eggNOG and KEGG (Kyoto Encyclopedia of Genes and Genomes). All 24,128 unigenes with eggNOG annotations were divided into 26 categories that are mostly associated with physiological processes, including signaling transduction, translation mechanism, etc. Based on KEGG analysis, all unigenes at the maturation phase were involved in 98 metabolic pathways, with 135 up-regulated sequences, while the unigenes at the regression phase were related to 192 metabolic pathways, with 648 up-regulated sequences. Moreover, 334 differentially expressed genes (DEGs) were up-regulated at the maturation phase, while 987 up-regulated DEGs were found at the regression phase. Total 408 unigenes were associated with the regulation of reproduction and endocrinology. The mRNA expression of some reproduction-associated DEGs including growth hormone releasing hormone (GnRH), neurokinin B (NKB), gonadotropin (GtH), follicle stimulating hormone (FSH), kisspeptin (Kiss) and prolactin-releasing peptide receptor (PrRPR) in the hypothalamus and pituitary gland at two phases was verified by qRT-PCR. Except FSH, all other 5 DEGs showed higher expression at the regression phase. This study provides valuable data for understanding the transcriptome profiles of starry flounder brain and improving the technologies of artificial breeding.

Morphological characteristics and distribution of Pleuronectidae (Pisces) eggs in the western margin of the East Sea

Seven species of Pleuronectidae (Platichthys stellatus, Kareius bicoloratus, Pseudopleuronectes herzensteini, Microstomus achne, Glyptocephalus stelleri, Hippoglossoides dubius, and Limanda punctatissima) were identified based on eggs collected from the western margin of the East Sea (east coast of Korea), using DNA barcoding. The eggs of P. herzensteini and G. stelleri were relatively widely distributed along the east coast of Korea, whereas those of P. stellatus and K. bicoloratus were narrowly distributed; in particular, the eggs of P. stellatus were restricted to areas near bays. The eggs, which share common morphological characteristics (such as a homogeneous yolk and smooth membrane) were divided into three groups according to egg size: group A (more than 1.60 mm in egg diameter, including genera Hippoglossoides and Microstomus), group B (1.00–1.60 mm, including genera Kareius, Glyptocephalus, and Platichthys), and group C (less than 1.00 mm, including genera Limanda and Pseudopleuronectes). This paper provides an overview of the morphological characteristics of the eggs of the family Pleuronectidae collected from the east coast of Korea. Our approach to the analysis of eggs, based on DNA barcoding, morphological characteristics, and geographic distributions, provides a rapid and accurate basis for identifying spawning areas and spawning periods, thus facilitating the assessment and management of fisheries stocks and resources.

Assessing the Effects of Dietary Inclusion of Hydrolyzed Soy Protein on the Growth, Nutrient Retention, Body Composition, and Serum Hormone of Juvenile Starry Flounder, Platichthys stellatus

AbstractEnzymatic hydrolysis of soy protein has the potential to be an excellent protein source in marine fish feeds. Here we assessed the effects of different inclusion levels of hydrolyzed soy protein (HSP) on growth performance, nutrient retention, body composition, and serum hormone levels in juvenile starry flounder to define HSP utilization. Five isoenergetic and isoprotein diets were formulated with 0 (control), 10, 20, 30, and 40% HSP (SP10–40) to replace 0, 25, 50, 75, and 100% soy protein concentrate (SPC), respectively. At the end of the feeding trial, fish fed diets SP20 and SP30 had significantly increased weight gain, percent weight gain, and feed efficiency (FE) compared with fish fed the control diet (P &lt; 0.05). Diets SP20 and SP30 supported significantly higher levels of protein retention, and diet SP20 significantly increased energy retention (P &lt; 0.05) in the fish offered these diets. In terms of nutritional composition of whole fish, feeding diets SP20 and SP30 increased crude protein content (P &lt; 0.05) and diets SP10, SP20, and SP30 increased ash content (P &lt; 0.05). Fish fed diets SP20 and SP30 had higher serum insulin‐like growth factor 1 (IGF‐1) level than that of the control treatment (P &lt; 0.05). When SPC was included at 40% of the diet, 20–30% HSP (43% soluble nitrogen) is recommended to replace 50–75% SPC for maximal growth performance and FE of starry flounder.

Ontogenetic changes in digestive enzyme activities and the amino acid profile of starry flounder Platichthys stellatus

Ontogenetic changes in digestive enzyme activities and the amino acid (AA) profile of starry flounder, Platichthys stellatus, were investigated and limiting amino acids were estimated compared with the essential AA profile between larvae and live food to clarify starry flounder larval nutritional requirements. Larvae were collected at the egg stage and 0, 2, 4, 7, 12, 17, 24 days after hatching (DAH) for analysis. Larvae grew from 1.91 mm at hatching to 12.13 mm at 24 DAH. Trypsin and chymotrypsin activities changed slightly by 4 DAH and then increased significantly 4 DAH. Pepsin activity increased sharply beginning 17 DAH. Lipase activity increased significantly 4 DAH and increased progressively with larval growth. Amylase activity was also detected in newly hatched larvae and increased 7 DAH followed by a gradual decrease. High free amino acid (FAA) content was detected in starry flounder eggs (110.72 mg/g dry weight). Total FAA content dropped to 43.29 mg/g in 4-DAH larvae and then decreased gradually to 13.74 mg/g in 24-DAH larvae. Most FAAs (except lysine and methionine) decreased >50% in 4-DAH larvae compared with those in eggs and then decreased to the lowest values in 24-DAH larvae. Changes in the protein amino acid (PAA) profile were much milder than those observed for FAAs. Most PAAs increased gradually during larval development, except lysine and phenylalanine. The percentages of free threonine, valine, isoleucine, and leucine decreased until the end of the trial, whereas the protein forms of these four AAs followed the opposite trend. A comparison of the essential AA composition of live food (rotifers, Artemia nauplii, and Artemia metanauplii) and larvae suggested that methionine was potentially the first limiting AA. These results may help develop starry flounder larviculture methods by solving the AA imbalance in live food. Moreover, the increased digestive enzyme activities indicate the possibility of introducing artificial compound feed.

Effect of exogenous hormones on ovulation and gonadal steroid plasma levels in starry flounder, Platichthys stellatus

The present study was designed to examine the potential for inducing ovulation in starry flounder (Platichthys stellatus) using gonadotropin-releasing hormone analog (GnRHa) and human chorionic gonadotropin (hCG) to assess whether starry flounder are differentially responsive to GnRHa and hCG. Female starry flounder were injected or implanted with different doses of hCG or GnRHa pellets to examine their ovulation-inducing potential and effects on plasma levels of testosterone (T), 17β-estradiol (E2), and 17,20β-dihydroxy-4-pregnen-3-one (17,20βP). Blood samples were collected for up to 10 or 25 days post-injection or post-implantation in two separate experiments designed to mimic the early and middle stages of spawning, respectively. Fish treated with the GnRHa pellets (100 µg) showed a significant increase in the total number of stripped eggs relative to the controls. GnRHa administration had no effect on the floating rate or fertilization rate of ovulated eggs in the both experiments, whereas hCG injection affected both of these rates. Plasma T levels were not significantly different between the exogenous hormone-treated and control fish. In contrast, the plasma E2 level was elevated in those fish treated with GnRHa, regardless of injection or implantation, and was accompanied by increased numbers of stripped eggs in both experiments. Treatment with GnRHa resulted in higher 17,20βP levels compared to the controls, and there was a positive relationship between elevated plasma 17,20βP and an increase in ovulated eggs in response to GnRHa treatment. The implantation of starry flounder with GnRHa-containing pellets was effective at inducing sustained ovulation compared to hCG treatment.

Shallow-water habitat use by Bering Sea flatfishes along the central Alaska Peninsula

Flatfishes support a number of important fisheries in Alaskan waters and represent major pathways of energy flow through the ecosystem. Despite their economic and ecological importance, little is known about the use of habitat by juvenile flatfishes in the eastern Bering Sea. This study describes the habitat characteristics of juvenile flatfishes in coastal waters along the Alaska Peninsula and within the Port Moller–Herendeen Bay system, the largest marine embayment in the southern Bering Sea. The two most abundant species, northern rock sole and yellowfin sole, differed slightly in habitat use with the latter occupying slightly muddier substrates. Both were more common along the open coastline than they were within the bay, whereas juvenile Alaska plaice were more abundant within the bay than along the coast and used shallow waters with muddy, high organic content sediments. Juvenile Pacific halibut showed the greatest shift in distribution between age classes: age-0 fish were found in deeper waters (~ 30m) along the coast, whereas older juveniles were found in the warmer, shallow waters within the bay, possibly due to increased thermal opportunities for growth in this temperature-sensitive species. Three other species, starry flounder, flathead sole, and arrowtooth flounder, were also present, but at much lower densities. In addition, the habitat use patterns of spring-spawning flatfishes (northern rock sole, Pacific halibut, and Alaska plaice) in this region appear to be strongly influenced by oceanographic processes that influence delivery of larvae to coastal habitats. Overall, use of the coastal embayment habitats appears to be less important to juvenile flatfishes in the Bering Sea than in the Gulf of Alaska.

Complete mitochondrial genome of the Pseudopleuronectes yokohamae (Pleuronectiforll: Pleuronectidae)

In this study, the complete mitochondrial genome of the Pseudopleuronectes yokohamae was sequenced. The mitochondrial genome is 17 383 bp in length, consisting of 13 protein-coding genes, 2 ribosomal RNA genes (rRNAs), 22 transfer RNA genes (tRNAs) and a control region (D-loop). The gene order and composition of P. yokohamae mitochondrial genome was similar to that of most other vertebrates. Two rRNA genes for 12S rRNA (949 bases) and 16S rRNA (1716 bases) are located between tRNA-Phe (GAA) and tRNA-Leu (TAA) and separated by the tRNA-Val. The control region of P. yokohamae, is located after tRNA-Pro and found to be 1679 bp. The overall nucleotides base composition of the heavy strand is A (27.55%), T (26.45%), G (28.75%), C (17.26%). With the exception of the NADH dehydrogenase subunit 6 (ND6) and eight tRNA genes, all other mitochondrial genes are encoded on the heavy strand. The 22 tRNA genes could be folded into a typical clover-leaf secondary structure. The phylogenetic trees consistently show that P. yokohama, Kareius bicoloratus and Platichthys stellatus from the same genus clustered into one branch. The complete mitogenome sequence information of P. yokohamae would provide useful data for further studies on population genetics and molecular systematics.