Juvenile Japanese Flounder Paralichthys Olivaceus Research Articles

Validation of otolith daily ring deposition and hatch date estimations in larval and juvenile Japanese flounder Paralichthys olivaceus

The early life history traits of Japanese flounder Paralichthys olivaceus, a commercially important species, have been well studied; however, daily ring formation in otoliths (lapilli and sagittae) of this species has not been investigated in detail. We examined the daily periodicity of ring deposition in otoliths using hatchery-reared Japanese flounder larvae and juveniles. In both lapilli and sagittae, a check corresponding to the radius at hatching (ca. 6 µm) was discernible throughout the pelagic larval and settled juvenile periods. The otolith rings were faint in the preflexion larval period and distinct in the flexion larval and later periods. Regression analyses for the number of rings by age in days showed that ring deposition occurred daily in lapilli but not in sagittae. Double marking of juveniles with alizarin complexone confirmed the daily ring periodicity in lapilli. However, the first faint ring was observed in the innermost areas in lapilli at 3–16 d post-hatching, and the faint rings were often unrecognisable, even under a scanning electron microscope, which interfered with daily age estimation. To estimate the number of days corresponding to the obscure zone with unrecognisable rings in lapilli, we developed the estimation method using logarithmic functions derived from the relationship between the radius (restricted to <20 µm) of lapilli and the ring counts for individual data. The error for the estimated days was − 0.05 ± 2.13 (n = 26, mean ± SD), indicating that this method is useful for hatch date estimation. Thus, the present study provides a novel method for analysis of otolith daily increments with unclear narrow rings in the innermost part of the otoliths.

Porous microplastics enhance polychlorinated biphenyls-induced thyroid disruption in juvenile Japanese flounder (Paralichthys olivaceus)

Microplastics and polychlorinated biphenyls are ubiquitous in the marine environments. To illuminate their combined biological impacts, juvenile Japanese flounder (Paralichthys olivaceus) were exposed to 500 ng/L PCBs alone or 500 ng/L PCBs plus 2, 20, and 200 μg/L 10-μm porous MPs for 21 days. Compared to PCBs alone, co-exposure to PCBs and 20, 200 μg/L MPs reduced fish body length and body weight, and the concurrence of MPs aggravated PCBs-induced thyroid-disrupting effects, including significantly decreased L-thyroxine and L-triiodothyronine levels, more severe damage to the thyroid tissue and gill morphology, and disturbance on the expression of hypothalamus-pituitary-thyroid axis genes. The PCBs concentrations in the seawater were decreased dramatically with the increase of MPs concentrations, confirming that MPs absorbed PCBs from the seawater. Our results demonstrated that MPs enhanced the thyroid disruption of PCBs, suggesting that the risk of MPs and thyroid-disrupting chemicals on marine organisms should be paid more attention.

Annual variation in the prey utilization of juvenile Japanese flounder in southwestern Hiuchi-Nada, Seto Inland Sea, Japan

Past studies indicated that newly settled juvenile Japanese flounder Paralichthys olivaceus depend on mysids as their main prey source, but little is known about the prey of juveniles in nursery grounds with a low density of mysids. This study aimed to reveal the annual variation in the main prey items of juvenile Japanese flounder in relation to their growth in southwestern Hiuchi-Nada, the Seto Inland Sea, Japan. Juvenile flounder consumed chiefly larval anchovy in 1995 and 1999, while small crangonid shrimp Crangon uritai were the main prey items in 1998, 2003, and 2004. The growth rates of juvenile flounder ranged from 0.82–1.33 mm d−1 during the five years of this study. Mysids were almost absent and small crangonid shrimp were abundant in the study area. Our results indicate that juvenile Japanese flounder prefer larval anchovy, but small crangonid shrimp function as the alternative prey when larval anchovy and mysids are not available in the study area.

Discrimination of nursery locations of juvenile Japanese flounder Paralichthys olivaceus on the Pacific coast of northern Japan based on carbon and nitrogen stable isotope ratios

To test whether stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) can be used to understand the ecological connectivity of Japanese flounder Paralichthys olivaceus, we evaluated the isotopic signatures of juvenile P. olivaceus from the Pacific coast of northern Japan (i.e., from Aomori to Ibaraki Prefectures). We measured δ13C and δ15N in muscle and collagen extracted from vertebrae and found that isotope ratios were strongly correlated in both. The discrimination models we developed for muscle and collagen proved useful in distinguishing among juvenile P. olivaceus collected from the five prefectures (Aomori, Iwate, Miyagi, Fukushima, and Ibaraki). Juveniles collected in Aomori in particular showed significantly lower values of δ13C and δ15N than those from the other prefectures, which likely reflects the greater influence of the Tsugaru Warm Current in that region. Because collagen in the vertebral centrum can be used to reconstruct annual isotopic records, our results may also assist in developing migration tracking procedures for adult P. olivaceus along the Pacific coast of northern Japan.

Skin darkening with increasing densities in juvenile Japanese flounder Paralichthys olivaceus

Skin darkening with increasing densities in juvenile Japanese flounder Paralichthys olivaceus

Comparison of UV-B tolerance between wild-type and albino Japanese flounder Paralichthys olivaceus juveniles

Comparison of UV-B tolerance between wild-type and albino Japanese flounder Paralichthys olivaceus juveniles

Evaluation of different Pyropia yezoensis extracts as feed additives for growth and immunity of Japanese flounder Paralichthys olivaceus

We evaluated the effects of diets incorporating the red algae Pyropia yezoensis, prepared by several different extraction methods, on the growth of juvenile Japanese flounder Paralichthys olivaceus. We assessed growth performance, as well as the levels of amino acids, fatty acids, insulin-like growth factor I (IGF-I) and interleukins (ILs). Four experimental diets were developed based on different methods of processing P. yezoensis. A commercial feed, laver powder (P), high-pressure heat extraction of laver (HPHE) and acid hydrolysis extraction of laver were used as the experimental diets. Three experimental replicates were established for each diet (40 fish/group, body weight 123.7 ± 1.1 g), and the fish were fed for 6 weeks. We found no significant differences in weight gain, specific growth rate or feeding efficiency among the groups (P > 0.05); however, the fish fed HPHE had the greatest growth performance. Fish fed the laver extracts exhibited the highest protein efficiency ratio compared with the control and P groups. The experimental groups fed P. yezoensis extracts had significantly higher levels of IGF-I (P < 0.05) than those of the control group. High levels of IL-2 were found in the P and HPHE groups, IL-12 in the HPHE group, and IL-6 in all experimental groups. Therefore, these results suggest that a P. yezoensis extract improved the growth performance and immunity of Japanese flounder. In particular, the high-pressure heating process was a useful extraction method for preparing a P. yezoensis extract, which had beneficial effects as a dietary supplement in Japanese flounder.

Effect of sampling procedures on skin darkening in juvenile Japanese flounder Paralichthys olivaceus

Effect of sampling procedures on skin darkening in juvenile Japanese flounder Paralichthys olivaceus

Impact of the great tsunami in 2011 on the quality of nursery grounds for juvenile Japanese flounder Paralichthys olivaceus in Sendai Bay, Japan

AbstractThe impact of the great tsunami, which was generated by the Great East Japan Earthquake on 11 March 2011, on the quality of a nursery ground for juvenile Japanese flounder Paralichthys olivaceus with a sandy bottom of &lt;15 m in depth in Sendai Bay, Japan, was evaluated. Growth rates of juveniles, as an index of the quality of the nursery ground, were compared between before and after the tsunami. Recent growth rates (RGR; mm day−1) between 1 and 6 days before collection in 2011–2013, which were estimated from the width of otolith increments, ranged from 0.84 to 2.37 mm day−1 for juveniles of 24.8–146 mm in total length (TL). These figures are comparable to the maximum RGR for juvenile Japanese flounder in the literature. A linear model for RGR selected TL and bottom temperature but rejected biomass of the mysid Orientomysis mitsukurii, the main prey item, as explanatory variables, indicating that the growth rates of juveniles after the tsunami were not controlled by food density, i.e., optimal food condition occurred in the nursery. A linear model for observed growth rate (mm day−1), which was calculated from the temporal changes in the juvenile size frequency distribution, suggested the growth rate did not change between before and after the tsunami. Additional information on prey abundance and sediment size distribution also support this conclusion. Therefore, we conclude that the quality of the nursery ground for juvenile Japanese flounder in the study site has not been damaged by the great tsunami.

A simulation model for estimating optimum stocking density of cultured juvenile flounder Paralichthys olivaceus in relation to prey productivity

The determination of the optimum stocking density of hatchery-reared juveniles in relation to the carrying capacity of the nursery ground is important to the success of any stock enhancement programs. In order to estimate the surplus productivity of nursery grounds available to support hatchery-reared fish, a population growth model for juvenile Japanese flounder Paralichthys olivaceus was developed by extending an ecophysiology-based model on growth of juvenile fishes. Parameters of the model were adjusted using field-collected data from Ohno Bay in northeastern Japan. This model predicted the optimum stocking density, namely the maximum number of hatchery-reared juvenile Japanese flounder released into the bay without decreasing the growth of conspecific wild juveniles owing to food limitation. The optimum stocking density for juveniles of 89mm total length was estimated to be 2000 individuals per 250,000m2 in Ohno Bay in 1989. Under the model, the most important factors affecting the optimum stocking density of Japanese flounder were the abundance of mysids and wild juveniles at the time of release. The effect of abundance of a competing flatfish species on growth of wild Japanese flounder was less important.

Inter-annual variation in the surplus prey production for stocking of Japanese flounder Paralichthys olivaceus

Stocking hatchery fish into the wild should only be implemented at a level that can be sustained within the available food-based carrying capacity to avoid food resource competition with wild conspecifics. We constructed a simulation model to assess the growth of wild conspecifics under different magnitudes of hatchery fish releases, including no releases and actual release levels, and under different wild fish abundancies. Stocking of juvenile Japanese flounder Paralichthys olivaceus (approximately 70–110mm TL) in Fukushima from 2003 to 2005 was analyzed. We monitored post-release changes in abundance of both cultured and wild juveniles and their prey (mysids). Our survey and modelled simulations revealed that the surplus prey production was sufficient to support the consumption of stocked and wild Japanese flounder (up to 150,000 individuals per site in 2003 and 2004), during which wild juveniles achieved nearly maximum growth rates. However, in 2005, during which a dominant year class of wild Japanese flounder occurred, the body size of wild juveniles was 49% smaller than the predicted size based on the maximum growth rates. This suggests that the food-based carrying capacity was reached in that year. Thus, it is important to evaluate the existing prey and wild juveniles levels and adjust the release accordingly every year.

Comparative Effects of Dietary Supplementation Levels of Eucheuma denticulatum and Sargassum fulvellum in Diet of Juvenile Japanese Flounder Paralichthys olivaceus

Comparative Effects of Dietary Supplementation Levels of Eucheuma denticulatum and Sargassum fulvellum in Diet of Juvenile Japanese Flounder Paralichthys olivaceus

Mortality of juvenile Japanese flounder Paralichthys olivaceus caused by scavenging amphipods and ostracods in trap experiments

Trap experiments were conducted using wild and artificially reared juvenile Japanese flounder in various conditions as baits in a flounder nursery habitat of Mano Bay. All of the live wild flounder placed in the traps with sand survived in good health. However, most of the live wild flounder in the traps without sand and live-reared flounder in the traps with and without sand, as well as injured and dead-reared flounder, were consumed and stripped to skeletons overnight. A large number of the lysianassoid Orchomene sp. and Orchomene naikaiensis, and the cypridinid Vargula hilgendorfii, which are typical scavengers, accumulated in the traps with consumed flounder; however, few amphipods and ostracods occurred in traps without consumed flounder. Thus, once flounder are detected and reached by a swarm of these crustaceans, flounder may be preyed on, irrespective of the condition of the fish. This finding is supported by aquarium observations that amphipods and ostracods were able to kill and consume live flounder. Burial in sand will potentially prevent the crustaceans from detecting wild flounder by interfering with the odor from the fish. The results of our study raise the possibility that scavenging crustaceans are able to predate hatchery-reared flounder released in the sea.

Prey availability and daily growth rate of juvenile Japanese flounder Paralichthys olivaceus at a sandy beach in the central Seto Inland Sea, Japan

The aim of this study was to characterize a nursery ground (Ohama Beach, Hiuchi-nada) for the Japanese flounder Paralichthys olivaceus in the central Seto Inland Sea having insufficient availability of mysids, Nipponomysis ornata and Iiella oshimai. We examined daily growth rates of wild juveniles; this measure can be used as an index of quality of a nursery. Juveniles consumed not only mysids, but also Crangon uritai and fishes. Mysid availability was lower at the study beach than in the nursery in the Sea of Japan; however, mean growth rates (MGRs) from May to June varied from 0.75 to 1.84 mm day−1 and equaled that in the nursery with sufficient availability of mysids in the Sea of Japan. Prey availability was high from May to June and decreased after July. Additionally, water temperatures after late July were higher than the optimal temperature. Multiple regression analysis suggested that the low availability of prey and high water temperatures reduced the MGR after July. The results indicate that the optimal season for releasing hatchery-reared juveniles is from May to June, a period characterized by high availability of prey.

Disruption of the Thyroid System by the Thyroid-Disrupting Compound Aroclor 1254 in Juvenile Japanese Flounder (Paralichthys olivaceus)

Polychlorinated biphenyls (PCBs) are a group of persistent organochlorine compounds that have the potential to disrupt the homeostasis of thyroid hormones (THs) in fish, particularly juveniles. In this study, thyroid histology, plasma TH levels, and iodothyronine deiodinase (IDs, including ID1, ID2, and ID3) gene expression patterns were examined in juvenile Japanese flounder (Paralichthys olivaceus) following 25- and 50- day waterborne exposure to environmentally relevant concentrations of a commercial PCB mixture, Aroclor 1254 (10, 100, and 1000 ng/L) with two-thirds of the test solutions renewed daily. The results showed that exposure to Aroclor 1254 for 50 d increased follicular cell height, colloid depletion, and hyperplasia. In particular, hypothyroidism, which was induced by the administration of 1000 ng/L Aroclor 1254, significantly decreased plasma TT4, TT3, and FT3 levels. Profiles of the changes in mRNA expression levels of IDs were observed in the liver and kidney after 25 and 50 d PCB exposure, which might be associated with a reduction in plasma THs levels. The expression level of ID2 mRNA in the liver exhibited a dose-dependent increase, indicating that this ID isotype might serve as sensitive and stable indicator for thyroid-disrupting chemical (TDC) exposure. Overall, our study confirmed that environmentally relevant concentrations of Aroclor 1254 cause significant thyroid disruption, with juvenile Japanese flounder being suitable candidates for use in TDC studies.

Interactive effects of vitamin C and E supplementation on growth performance, fatty acid composition and reduction of oxidative stress in juvenile Japanese flounder Paralichthys olivaceus fed dietary oxidized fish oil

Abstract A study was conducted to determine the interactive effects of vitamin C (VC) and E (VE) supplementation on growth, fatty acid composition and oxidative status of Japanese flounder juveniles. Fish (initial average body weight of 1.1 ± 0.1 g) in triplicate were fed five test diets for 60 days. Control diet contained fresh fish oil (FFO, 8.9 meq/kg) with 100 mg α-tocopherol (α-Toc) equivalents/kg of VE and 500 mg ascorbic acid (AsA) equivalents/kg of VC (FFO100E/500C). The other four diets contained oxidized fish oil (OFO, 167.8 meq/kg) with varying levels of VE (mg/kg) and VC (mg/kg) (OFO100E/500C, OFO200E/500C, OFO100E/1000C and OFO200E/1000C). Fish fed FFO100E/500C and OFO100E/500C had no differences in body weight gain (BWG). However, fish fed OFO200E/1000C diet had a significantly lower BWG than FFO100E/500C. Fish fed OFO200E/500C and OFO100E/1000C showed no differences in thiobarbituric acid-reactive substance values compared with FFO100E/500C. Increasing the levels of VC and VE supplementation increased liver AsA and α-Toc contents, respectively. Liver α-Toc content was significantly increased with incremental dietary VC levels, indicating a sparing effect of VC on liver α-Toc content of fish. Increasing the levels of dietary VC and VE supplementations decreased concentrations of 20:5n-3, 22:5n-3 and 22:6n-3 in fish liver. Fish fed OFO100E/500C and OFO200E/1000C diets showed higher oxidative stress condition than those fed FFO100E/500C. In conclusion, dietary VC and VE supplementation could maintain normal growth and health condition of juvenile Japanese flounder fed OFO. However, high doses of both vitamin supplements induced fish lipid peroxidation under oxidative stress condition.

Optimum Supplementations and Interactive Effects of Methionine and Tryptophan on Growth and Health Status of Juvenile Japanese Flounder Paralichthys olivaceus

Optimum Supplementations and Interactive Effects of Methionine and Tryptophan on Growth and Health Status of Juvenile Japanese Flounder Paralichthys olivaceus

Interactive effects of dietary arginine and histidine on the performances of Japanese flounder Paralichthys olivaceus juveniles

A 60-day feeding trial was carried out to investigate the interactive effects of arginine and histidine on the performances of Japanese flounder juveniles. Fish were fed experimental diets containing six different rations of arginine (Arg) and histidine (His), 2 levels of Arg such as 1.74 (AL) and 2.75g/100g diet (AH), combined with 3 levels of His such as 1.01(HL), 1.50 (HM) and 1.88g/100g diet (HL), respectively. The results indicated that the growth performances (final body weight, body weight gain and special growth rate) were highest in fish fed AH–HM combined group. Those parameters were significantly higher than other groups except AH–HL group. On the other hand, the interactions of arginine and histidine were found on the growth parameters. In addition, the significantly better nutrient utilizations (feed conversion ratio, protein efficiency ratio and protein retention) were also observed in higher Arg supplemented groups. There were no significant effects on the hematocrit, hemoglobin, glucose, total cholesterol, total bilirubin and mucus bactericidal activity of experimental fish among treatments. Japanese flounder fed the diet containing low dietary arginine together with low dietary histidine showed higher oxidative stress and lower lysozyme activities. The dietary arginine and histidine levels significantly affected the concentrations of fish muscle free amino acids. It would be concluded that dietary Arg and His functioned interactively, and the flounders fed the diet containing 2.70g arginine with 1.56g histidine/100g diet showed the better growth performance and physiological status than other groups.

Formation process of staining-type hypermelanosis in Japanese flounder juveniles revealed by examination of chromatophores and scales

Staining-type hypermelanosis, defined as blind-side melanosis occurring after completion of metamorphosis, reduces commercial value in hatchery-produced flatfishes. Detailed characterization was performed on the stained area of juvenile Japanese flounder Paralichthys olivaceus to physiologically understand this phenomenon. From 80 to 120 days after hatching, juveniles were reared in sandy and sandless tanks. By classifying the staining degree into 7 levels, about 2 times higher occurrence of middle-level staining was reconfirmed in sandless tank (about 80 %) than in sandy tank (about 40 %). In the stained area, we found 3 types of chromatophores (melanophore, xanthophore, and iridophore) and ctenoid scales, which would be typically observed on the normal ocular side. Detailed examination on the melanophores revealed further similarity between the stained area and the normal ocular side, in terms of the distribution at 2 layers (shallower and deeper than scale), and the densities in both layers (about 1000 cells/mm2 above scale and 200 cells/mm2 beneath scale). These results strongly suggest that the staining is a status change in the body surface conditions from the blind side to that on the ocular side, and not a simple darkening caused by disordered proliferation of melanophores on the blind side.

Bottom feeding and net chasing improve foraging behavior in hatchery-reared Japanese flounder Paralichthys olivaceus juveniles for stocking

We examined the effect of bottom feeding and net chasing as means to improve the maladaptive off-bottom swimming of hatchery-reared Japanese flounder Paralichthys olivaceus juveniles for stock enhancement. Three treatments were tested: (1) a bottom feeding treatment in which fish were fed near the bottom; (2) a net chasing treatment in which fish were chased by a hand net two to four times a day, and (3) a surface feeding treatment in which fish were fed from the surface (control treatment). Foraging behavior at the surface with surface feeding was analyzed 1 day before initiating these treatments and 2 weeks thereafter. A comparison of the pre- and post-treatments revealed that off-bottom swimming was less in the bottom feeding treatment and net chasing treatments. A comparison of off-bottom swimming in the bottom feeding treatment between the pre- and post treatments revealed that bottom fed fish showed less off-bottom swimming than surface fed fish. These findings suggest that fish behavior can be manipulated during the rearing period and that such manipulations can be used to improve the behavior of fish for release.