Search

Female fishes allocate a certain quantity of lipids for egg production once mature. In aquaculture, such physiological changes often result in the deterioration of flesh quality. In the study reported here, we aimed to characterize the seasonal changes in the lipid contents in aquaculture-produced female Pacific bluefin tuna (PBT) Thunnus orientalis, which is one of the most commercially important species for aquaculture worldwide. We analyzed the seasonal changes in the lipid content and weight of tissues and organs responsible for lipid allocation towards egg production, including the muscles, liver, mesenteric fat (perigonadal fat), and ovaries. During the spawning season, the total lipid content of the muscles and liver of the mature females decreased, whereas that of the ovaries increased; similarly, the weight of perigonadal fat decreased. We hypothesized that muscle, liver, and perigonadal fats contribute significantly to the accumulation of lipids during the maturation of female PBT. This is the first study to report an association between a reduction in muscle lipid content and sexual maturation in aquaculture-produced female PBT. These findings provide important insights regarding efficient aquaculture operations for this economically important fish. In addition, this study is the first to provide data on the association between the lipid dynamics of female PBT and sexual maturation in aquaculture, further enhancing our understanding of the energy allocation strategy during maturation of female bluefin tuna. [ABSTRACT FROM AUTHOR]

Hatchery-produced Pacific bluefin tuna (PBT) Thunnus orientalis juveniles experienced mass mortality after being transferred to sea cages in a cove on Kakeromajima Island, Kagoshima, Japan, in July 2022. Manca and juveniles of cymothoid isopods were highly prevalent in the branchial cavity of the few surviving PBT juveniles. We identified two species of cymothoid parasites based on their mitochondrial DNA sequences. Most parasites had cytochrome c oxidase subunit 1 (COI) and 16S rDNA sequences similar to those of Norileca indica, while some were identified as Ceratothoa carinata. Adult cymothoids were found in the bigeye scad Selar crumenophthalmus in the same area and were also morphologically and molecularly identified as N. indica. Therefore, it is likely that the mancae and juveniles of the cymothoids accidentally infested the PBT juveniles after they were released from adult parasites in wild natural hosts, such as S. crumenophthalmus, living around the PBT farming cages. This is the first record of N. indica in Japan and the northernmost record of this species. To our knowledge, this is the first report of mass mortality in PBT juveniles caused by parasitic isopods. Our study is the first step in developing measures to avoid the damage caused by the parasites. [ABSTRACT FROM AUTHOR]

Triploidization influences various biological characteristics of fish, which is associated with reductions in the number of multiple cell types in different tissues/organs. Our behavioral analyses revealed that triploid Pacific bluefin tuna (Thunnus orientalis) larvae exhibit lower sensitivity to light compared to diploids. Furthermore, histological analyses revealed a reduction in the number of ganglion cells and an increase in their size in the retinas of triploid T. orientalis larvae. Our findings provide the first evidence indicating that triploidization reduces sensory perception during the larval stage of fish. [ABSTRACT FROM AUTHOR]

Abstract Pacific bluefin tuna (PBT), Thunnus orientalis, is one of the most important species for aquaculture worldwide. For the conservation of this species and sustainable development of the tuna farming industry, production based on closed‐cycle aquaculture should be promoted. In this study, to develop an efficient method for transporting PBT eggs, we simulated egg transportation to optimize stocking density and shipping duration, which are the two variables critical to the transportation procedure of PBT. Based on the findings of this study, we concluded that PBT eggs should be transported at a density of 1 × 104 eggs/L within 12 h in the field. Furthermore, we showed that collisions between eggs during transportation negatively affected the normal hatching rates of eggs, and polyethylene glycol (PEG) treatment (at 1000 μg/mL for 12 h) could reduce such damage. Our results suggest that PEG treatment is a practical approach that contributes to the stable transportation of PBT eggs, particularly in cases where the effects of physical shock damage is considerably increased.

Pacific bluefin tuna (PBT), Thunnus orientalis, is one of the most important species for aquaculture worldwide. For the conservation of this species and sustainable development of the tuna farming industry, production based on closed‐cycle aquaculture should be promoted. In this study, to develop an efficient method for transporting PBT eggs, we simulated egg transportation to optimize stocking density and shipping duration, which are the two variables critical to the transportation procedure of PBT. Based on the findings of this study, we concluded that PBT eggs should be transported at a density of 1 × 104 eggs/L within 12 h in the field. Furthermore, we showed that collisions between eggs during transportation negatively affected the normal hatching rates of eggs, and polyethylene glycol (PEG) treatment (at 1000 μg/mL for 12 h) could reduce such damage. Our results suggest that PEG treatment is a practical approach that contributes to the stable transportation of PBT eggs, particularly in cases where the effects of physical shock damage is considerably increased. [ABSTRACT FROM AUTHOR]

Keywords: Dead end; Pacific bluefin tuna; Primordial germ cell; Sterile; Thunnus orientalis EN Dead end Pacific bluefin tuna Primordial germ cell Sterile Thunnus orientalis 3872 3876 5 06/14/22 20220701 NES 220701 The I dead-end i ( I dnd i ) gene was first identified in zebrafish, I Danio rerio i , as a germ plasm component encoding an RNA-binding protein (Weidinger et al., 2003). To examine germ cell deficiency in addition to observations by GFP labeling, we conducted whole-mount immunostaining using anti-germ cell marker Vasa antibodies, as described previously (Hayashida, Higuchi, Hashimoto, et al., 2021), and histological analysis. In fact, inhibiting I dnd i expression causes faulty migration and ablation of zebrafish PGCs, resulting in germ cell deficiency (Weidinger et al., 2003). The zebrafish Dnd protein binds to 3' untranslated regions (3'UTR) of germline RNAs, such as I nanos i mRNAs, thereby protecting them against microRNA-mediated degradation, so they can contribute to the migration and survival of primordial germ cells (PGCs) (Kedde et al., 2007; Weidinger et al., 2003). [Extracted from the article]

Pacific bluefin tuna (PBT), Thunnus orientalis , is one of the most important species for aquaculture in Japan. Recently, the reduction in muscle fat content associated with sexual maturation in farmed PBT has become a serious problem. To develop technologies for inducing sterility, detailed and reliable data on gonadal development in PBT are needed. Here, we demonstrated the process of gonadal sex differentiation, and of early ovarian and testicular development during the immature stages in PBT. Gonadal sex differentiation was first characterized by the formation of the ovarian cavity in female and of the efferent ducts in male 57 days post hatching (dph). The gonads then differentiated into ovaries or testes according to the genotypic sex until 83 dph. During this period, primordial germ cells, oogonia, and type-A spermatogonia were solitarily distributed in the gonads, and the number of germ cells did not differ between sexes. After gonadal sex differentiation, gonads of PBTs developed in a sexually dimorphic manner: proliferation and differentiation of germ cells occurred earlier in the ovaries than in the testes. The oogonia in ovaries formed cysts at 185 dph, but the type-A spermatogonia were solitarily distributed in testes at this stage, and cysts of type-A spermatogonia were first observed at 247 dph. Moreover, the oogonia entered meiosis and differentiated into chromatin-nucleolus stage oocytes until 247 dph, and subsequently into peri-nucleolus stage oocytes until 285 dph, whereas the type-A spermatogonia differentiated into type-B spermatogonia, spermatocytes, spermatids, and spermatozoa from 446 dph onwards. We believe the results of this study provide the necessary basis for future studies on sterile PBT production. • To develop technologies for producing sterile fish, detailed and reliable data on gonadal development are needed. • We demonstrated the morphological changes and timing of gonadal sex differentiation in Pacific bluefin tuna (PBT). • We also showed the developmental process of the ovary and testis during the immature stages of PBT. • This study will provide the necessary basis for future studies on sterile PBT production. [ABSTRACT FROM AUTHOR]

Abstract Pacific bluefin tuna (Thunnus orientalis) is one of the commercially important species in Korea as well as other countries of the North Pacific. Korean offshore large purse seine fisheries targeting small pelagic fishes such as chub mackerel have caught T. orientalis temporarily in the east of Jeju Island. The catch of T. orientalis in March through June occupied approximately 60% of the total. The monthly catch around Jeju Island from 2004 to 2013 showed a negative correlation (r = − 0.755, p

Recently, based on the histological studies it is suggested that Pacific bluefin tuna (PBF) spawns in the Kuroshio–Oyashio transition, off the Pacific coast of northeastern Japan, in addition to the previously identified two spawning areas of the northwestern Pacific around the Nansei Islands and the Sea of Japan. Distributional surveys for PBF larvae have not been conducted in the Kuroshio–Oyashio transition, and thus, we conducted PBF larval surveys at twenty stations in this area in early August 2018 to obtain evidence for the spawning of PBF. Twelve PBF larvae (3.9–7.2 mm in body length) were collected at six stations where sea surface temperature ranged from 27.2 to 28.2°C. Otolith microstructure analysis indicated that age of these larvae ranged from 4 to 11 days after hatching and the larvae hatched in late July. Growth of the collected larvae was comparable to those in the other two spawning grounds. Therefore, PBF spawns, hatches, and at least survives to the postflexion stage, 11 days after hatching in the Kuroshio–Oyashio transition. This fact potentially has a large impact on recruitment processes of PBF if they survive to recruitment in this third spawning ground. [ABSTRACT FROM AUTHOR]

Abstract Nucleotide sequences of four distinct calmodulin genes (designated as CaM-A to -D) of the Pacific bluefin tuna (Thunnus orientalis) were compared. Nucleotide sequence divergence between the coding regions of four genes ranged from 16.0 to 21.6%, and locus-specific eight primer pairs targeting introns were designed. These primer pairs amplified expected size of fragments in five congeneric tuna species, and utility of these primer pairs was investigated using distant fish species.

The consumption of fish and shellfish worldwide is steadily increasing, and tuna is a particularly valuable fish species. However, infection caused by Kudoa spp. is causing problems in many fish including the Pacific bluefin tuna (Thunnus orientalis), and there is much controversy about the association of these infections with foodborne disease. In this study, using haematological and histological analyses of the blood and internal organs (liver, spleen, kidney, heart, stomach, intestine, gill, and muscle) of Pacific bluefin tuna cultured in South Korea, infection with Myxosporea was first identified, and molecular biological analysis was conducted. In this study, Kudoa hexapunctata was finally identified. The Pacific bluefin tunas analysed in this study did not show any gross pathology lesions, such as visible cysts and/or myoliquefaction, of infection with this species. The histological analytical results can provide guidelines for the identification of K. hexapunctata. In the case of K. hexapunctata-induced infection, unlike other countries, such as Japan, there have been no reports in South Korea, and this study is the first to detect K. hexapunctata infection in Pacific bluefin tuna cultured in South Korea. The correlation between K. hexapunctata and food poisoning is not yet clear, however, it is thought that continuous observation of its infection is necessary.

This study aims to clarify some aspects of the growth of Atlantic bluefin tuna, Thunnus thynnus (L.), (ABFT) mainly regarding parameters of the growth equation and of relative growth, in this case length-weight relationships. There is a great volume of literature on these matters and there is a danger that the resulting confusion may give rise to mistaken decisions. In spite of the publication of 55 articles on absolute growth (FL > 50 cm), which contain a total of 43 growth equations, no consensus has yet been reached within the ABFT assessment group (AG) of the SCRS on parameters such as Lmax and L∞. The results of the present study indicate that the L∞ = 314.9 cm of the growth equation used for the western stock by the AG from 2010 (Lt = 314.9 [1 - e-0.089 (t+ 1.13)]), which was discarded in 2016, lies within the confidence limits of the maximum Ls presented in this study (Lmax= 321.4 ± 8.7 cm), confirming that this equation fit the biology of the ABFT growth. With regard to the length-weight relationships, 38 articles (FL > 50 cm) have been consulted containing a total of 71 equations, but in spite of this the models adopted by the AG in 2014 underestimate the weight of spawners (>2 m) in high fattening phase by up to 23%. The coincidence of the length-weight model for the ABFT western stock, discarded by the AG in 2014, with that of Pacific bluefin tuna, Thunnus orientalis (T & S), (PBFT) indicates that both species must have the same growth, something that is not surprising since both were the same species until 2003. Other coincidences, such as the trend of condition factor K in adults and the growth in the first months of life, could ratify it. In the Pacific Ocean, where far fewer growth studies have been made on PBFT than on ABFT in the Atlantic and Mediterranean, the management of growth models for the purposes of stock assessment in the International Scientific Committee (ISC) makes more sense than that carried out by the SCRS on this matter. [ABSTRACT FROM AUTHOR]

Pacific bluefin tuna ( Thunnus orientalis ) has two spawning grounds, and each is used at different times: May–June in the Nansei Islands of western North Pacific Ocean and July–August in the Sea of Japan. Although previous studies developed body-length based methods to differentiate between individuals originating in each spawning ground, these methods are only applicable to the young-of-the-year (YOY). In this study, we evaluate a simple technique for discerning the natal grounds of Pacific bluefin tuna greater than one year in age by observing the first annulus on the vertebrae of fish caught around Japan. We found a significant linear relationship between fork length and vertebral radius, and determined that the first annulus forms in boreal winter. Both the back-calculated fork length at the time of first annulus formation and the measured fork length of YOY in February and March had a bimodal frequency distribution, and the peaks of the two frequency distributions had similar means. The larger fork length individuals appear to have originated near the Nansei Islands, whereas the smaller fork length individuals appear to have originated in the Sea of Japan. This is because PBF hatched around the Nansei Islands will have longer growth time for the YOY to develop the first annulus at longer distance from the vertebrae center. Similarly, we observed bimodal distributions for the vertebral first annulus radius of mature Pacific bluefin tuna (>120 cm) in both spawning grounds. Our technique offers improved sample treatment efficiency and lower costs. In addition, this method may help reveal the contribution rate of each spawning ground. [ABSTRACT FROM AUTHOR]

The spawning fraction (SF) is an important reproductive trait used to assess the reproductive potential of indeterminate spawning fishes. To estimate the SF more accurately, the durations of spawning markers in ovaries need to be determined. The SF of the Pacific bluefin tuna Thunnus orientalis (PBF) in the Sea of Japan (SOJ) is higher than the SFs in its other main spawning grounds. The present study aimed to revisit the SF of the PBF in the SOJ by focusing on diurnal changes in spawning markers and estimating the duration of spawning markers in PBF ovaries. According to diurnal changes in the postovulatory follicle (POF) degeneration process and final maturation process of oocytes, POFs were observed in ovaries up to 38.5 h after ovulation. The revisited total SF throughout the spawning season was 0.34–0.43 in Area 1 and 0.50–0.64 in Area 2; these values are smaller than the SF previously estimated in the SOJ. The estimated SF of the PBF in the present study was equal to or slightly higher than that in the water between the Nansei Islands, Japan, and the northeast of the Philippines and higher than that in the Kuroshio-Oyashio transition area. • Postovulatory follicles were retained up to 38.5 h after ovulation. • The spawning fraction, estimated by Day 0 spawners, may have been overestimated. • The revisited total spawning fraction throughout the Sea of Japan was 0.43. • The estimated spawning fraction depended on the fishing area and fishing date. [ABSTRACT FROM AUTHOR]

Three experiments were conducted to investigate the growth, survival, and standardized cohort biomass of Pacific bluefin tuna, Thunnus orientalis, larvae fed nutritionally enhanced prey during the first week of feeding using two commonly used, commercially available enrichment media, AlgaMac Enrich and Marine Glos. T. orientalis larvae exhibited exponential growth in standard length and dry weight. The daily specific growth rates in length and weight are the first reported for T. orientalis larvae and the averages ranged from 3.8 to 4.1% and 27.5%, respectively, for larvae in the AlgaMac treatment and from 4.1 to 6.1% and 31.5%, respectively, in the Marine Glos treatment. Average daily growth rates in length ranged from 0.16 to 0.23 mm/d for larvae in the AlgaMac treatment and from 0.17 to 0.27 mm/d for those in the Marine Glos treatment. Daily growth rates in length were similar to those reported for other tuna larvae reared in the laboratory but slower than most published estimates for larval tunas in situ at similar water temperatures. Mean prey number per gut was positively associated with mean prey level in the tank. Both enrichment media appear to be good sources of nutritional improvement of planktonic prey for T. orientalis larvae. [ABSTRACT FROM AUTHOR]

The present study used otolith analysis-based body size back-calculation to: (1) evaluate the hypothesis of growth-dependent survival in young Pacific bluefin tuna (PBF; Thunnus orientalis) from the north-western Pacific Ocean; (2) identify critical developmental stages for survival; and (3) compare interannual differences in early growth. To this end, we compared the daily growth trajectories of a large number of larvae (standard length (SL) <15 mm), juveniles (15 ≤ SL ≤ 150 mm), and young-of-year (YOY; SL >150 mm) collected between 2011 and 2015. Otolith radius and SL were highly correlated and yielded a single relationship applicable for the five year-classes. Body size back-calculation showed that only larvae with fast, steady growth successfully transitioned to the juvenile stage. The ontogenetic analysis of daily growth rates revealed interannual differences only in larvae, and not in the larval stage of juveniles and YOY. Neither sudden decreases nor increases in growth rates were observed during the larval stage of any of the stages, suggesting that the observed variability in larval body size may be the result of individual differences in growth rates rather than of drastic, one-time events. Overall, the results of the present study indicate that growth-dependent survival of larvae may be the most critical for PBF recruitment. [ABSTRACT FROM AUTHOR]

Success of swim bladder inflation ( SBI) is crucial for early survival of Pacific bluefin tuna ( PBF) larvae, because it reduces larval sinking death by enhancing buoyancy. In Experiment 1, we examined the effect of photoperiod on SBI and survival in PBF larvae by comparing photoperiods of 9L: 15D (9L), 14L: 10D (14L: natural photoperiod), 19L: 5D (19L) and 24L: 0D (24L) during 2-10 days post hatch (dph). In Experiment 2, the combined effects of photoperiod (24L and 14L) and nighttime aeration rate (enhanced night-time aeration: ENA of 1300 mL min−1 as a countermeasure for sinking death and 130 mL min−1) on the survival and SBI were also examined during 2-10 dph. Moreover, in Experiment 3 the effect of photoperiod on vertical distribution of larvae in night-time was examined on 3-5 dph. Photoperiod of 24L in Experiment 1 significantly inhibited SBI compared with 14L and 19L; nevertheless, it significantly improved survival compared with other photoperiods with a dark period. On the other hand, the shortened light period (9L) showed significantly reduced SBI and also survival. In Experiment 2, the countermeasure for sinking death of ENA under 24L did not further improve the survival; rather it tended to reduce the survival. In Experiment 3, larvae distributed less in the bottom layer in 24L than in 14L, suggesting the reducing effect of 24L on sinking death. The results indicate that 24L without ENA is suitable for survival which is the most serious problem in PBF larviculture. [ABSTRACT FROM AUTHOR]

Environment-recruitment relationships can be difficult to delineate with parametric statistical models and can be prone to misidentification. We use non-parametric time-series modeling which makes no assumptions about functional relationships between variables, to reveal environmental influences on early life stages of bluefin tuna and demonstrate improvement in prediction of subsequent recruitment. The influence of sea surface temperature, which has been previously associated with larval growth and survival, was consistently detected in recruitment time series of bluefin tuna stocks that spawn in the Mediterranean Sea, the North Pacific, and the Southern Ocean. Short time series for the Gulf of Mexico stock may have precluded a clear determination of environmental influences on recruitment fluctuations. Because the non-parametric approach does not require specification of equations to represent system dynamics, predictive models can likely be developed that appropriately reflect the complexity of the ecological system under investigation. This flexibility can potentially overcome methodological challenges of specifying structural relationships between environmental conditions and fish recruitment. Consequently, there is potential for non-parametric time series modeling to supplement traditional stock recruitment models for fisheries management. [ABSTRACT FROM AUTHOR]

A variety of tunas of the genus Thunnus are consumed daily in Japan as sliced raw fish (sashimi and sushi). The consumption of fresh sliced raw fish, i.e., unfrozen or uncooked, can sometimes cause food poisoning that is manifested by transient diarrhea and vomiting for a single day. One of the causes of this type of food poisoning has been identified as live Kudoa septempunctata (Myxosporea: Multivalvulida) in the olive flounder ( Paralichthys olivaceus). Furthermore, raw slices of fresh tunas are highly suspected to be a possible causative fish of similar food poisoning in Japan. In the present study, we conducted a survey of kudoid infections in tunas (the yellowfin tuna Thunnus albacares, the Pacific bluefin tuna Thunnus orientalis, and the longtail tuna Thunnus tonggol) fished in the western Pacific Ocean off Japan and several East Asian countries and characterized morphologically and genetically the kudoid myxospores in pseudocysts or cysts dispersed in the trunk muscles. Pseudocysts of solely Kudoa hexapunctata were identified in the Pacific bluefin tuna (four isolates), whereas in the yellowfin tuna (21 isolates) pseudocysts of Kudoa neothunni and K. hexapunctata were detected at a ratio of 15:6, respectively, in addition to cyst-forming Kudoa thunni in five yellowfin tunas. In the trunk muscles of six longtail tunas examined, pseudocysts of K. neothunni (all six fish) and K. hexapunctata (two fish) were densely dispersed. The myxospores of K. neothunni found in these longtail tunas had seven shell valves and polar capsules (SV/PC) instead of the more common six SV/PC arranged symmetrically. Nucleotide sequences of the 18S and 28S ribosomal RNA gene (rDNA), some with the internal transcribed spacer regions as well, of K. hexapunctata and K. neothunni from the three Thunnus spp., including the seven-SV/PC morphotype, were very similar to previously characterized nucleotide sequences of each species, whereas the 18S and 28S rDNA of four isolates of K. thunni from yellowfin tunas showed a range of nucleotide variations of 99.0-99.9% identity over 1752-1763-bp long partial 18S rDNA and 97.4-99.9% identity over 797-802-bp long partial 28S rDNA. Therefore, this rather high variation of the rDNA nucleotide sequences of K. thunni proved to be contrary to the few variations of K. neothunni and K. hexapunctata rDNA nucleotide sequences. The present study provides a new host record of the longtail tuna for K. neothunni and K. hexapunctata and reveals a high prevalence of the seven-SV/PC myxospore morphotype of K. neothunni in this tuna host. [ABSTRACT FROM AUTHOR]

Nucleotide sequences of four distinct calmodulin genes (designated as CaM-A to -D) of the Pacific bluefin tuna ( Thunnus orientalis) were compared. Nucleotide sequence divergence between the coding regions of four genes ranged from 16.0 to 21.6%, and locus-specific eight primer pairs targeting introns were designed. These primer pairs amplified expected size of fragments in five congeneric tuna species, and utility of these primer pairs was investigated using distant fish species. [ABSTRACT FROM AUTHOR]

Pacific bluefin tuna (Thunnus orientalis) is a highly valued seafood consumed globally. The red color of tuna meat is considered a crucial indicator of its freshness and value, influencing consumer purchasing decisions. Therefore, the present study aimed to investigate the effect of lactic acid bacteria (LAB) isolated from traditional Korean fermented seafood (jeotgal) on preventing the discoloration of tuna meat during storage. Thirty-six strains of LAB (M1–M36) were isolated and examined for superior antioxidant and metmyoglobin conversion activities. Two strains, M1 (Lactococcus lactics) and M8 (Leuconostoc citreum), were selected. Subsequently, the tuna meat was treated with the cell-free supernatant (CFS) of the selected LAB strains and stored at 4 °C. Treatment with CFS maintained a significantly high level of redness (a*) in the tuna meat for up to 48 h; furthermore, this tendency was consistent with the relative quantification of myoglobin derivatives. The oxymyoglobin content in CFS-treated tuna meat remained above 60% for up to 60 h. Conversely, the metmyoglobin content in the untreated group reached over 60% only after 48 h, resulting in complete discoloration. Conclusively, this study demonstrated that LAB-CFS can prevent tuna meat discoloration during refrigerated storage, indicating its potential for maintaining the quality and color of tuna meat. • LAB isolated from jeotgal prevented discoloration of tuna meat. • Two strains showed superior antioxidant activity and metmyoglobin conversion. • LAB cell-free supernatant treatment to maintain redness and to prevent discoloration. [ABSTRACT FROM AUTHOR]

Farming of Pacific bluefin tuna (PBT), Thunnus orientalis , is a rapidly growing industry in Japan. Aporocotylid blood flukes of the genus Cardicola comprising C. orientalis, C . opisthorchis and C . forsteri are parasites of economic importance for PBT farming. Recently, terebellid polychaetes have been identified as the intermediate hosts for all these parasites. We collected infected polychaetes, Terebella sp., the intermediate host of C . opisthorchis , from ropes and floats attached to tuna cages in Tsushima, Nagasaki Prefecture, Japan. Also, Neoamphitrite vigintipes (formerly as Amphitrite sp. sensu Shirakashi et al., 2016), the intermediate host of C . forsteri , were collected from culture cages in Kushimoto, Wakayama Prefecture, Japan. The terebellid intermediate hosts harbored the sporocysts and cercariae in their body cavity. Developmental stages of these blood flukes were molecularly identified using species specific PCR primers. In this paper, we describe the cercaria and sporocyst stages of C . opisthorchis and C . forsteri and compare their morphological characteristics among three Cardicola blood flukes infecting PBT. We also discuss phylogenetic relations of the six genera of the terebellid intermediate hosts ( Artacama , Lanassa , Longicarpus , Terebella , Nicolea and Neoamphitrite ) of blood flukes infecting marine fishes, based on their morphological characters. [ABSTRACT FROM AUTHOR]

Elucidating fishing effects on fish population dynamics is a critical step toward sustainable fisheries management. Despite previous studies that have suggested age or size truncation in exploited fish populations, other aspects of fishing effects on population demography, e.g., via altering life histories and density, have received less attention. Here, we investigated the fishing effects altering adult demography via shifting reproductive trade-offs in the iconic, overexploited, Pacific bluefin tuna Thunnus orientalis. We found that, contrary to our expectation, mean lengths of catch increased over time in longline fisheries. On the other hand, mean catch lengths for purse seine fisheries did not show such increasing trends. We hypothesized that the size-dependent energetic cost of the spawning migration and elevated fishing mortality on the spawning grounds potentially drive size-dependent skipped spawning for adult tuna, mediating the observed changes in the catch lengths. Using eco-genetic individual-based modeling, we demonstrated that fishing-induced evolution of skipped spawning and size truncation interacted to shape the observed temporal changes in mean catch lengths for tuna. Skipped spawning of the small adults led to increased mean catch lengths for the longline fisheries, while truncation of small adults by the purse seines could offset such a pattern. Our results highlight the eco-evolutionary dynamics of fishing effects on population demography and caution against using demographic traits as a basis for fisheries management of the Pacific bluefin tuna as well as other migratory species. [ABSTRACT FROM AUTHOR]

Background: Pacific bluefin tuna (Thunnus orientalis) spawning adults, juveniles and larvae are all reported to occur in areas between Philippine Sea and Japan Sea. However, no DNA evidence has been generated to support this. Context and purpose of the study: In this study, Pacific bluefin tuna caught North of Polilio Island in the Philippine Pacific Seaboard, was identified through DNA barcoding using mitochondrial DNA D-loop region and cytochrome oxidase 1 gene. Findings: The results show clustering of Philippine-caught bluefin tuna D-loop and CO1 sequences with published reference sequences for T. orientalis and supported by pairwise distances <0.034. Conclusion: This study provides the first DNA evidence on the occurrence of T. orientalis in Philippine waters. [ABSTRACT FROM AUTHOR]

Fish blood flukes (Aporocotylidae) are important pathogens of farmed finfish around the world. Among them, Cardicola spp. infecting farmed tuna are considered to be serious threats to tuna farming and have received tremendous attention. We conducted periodical samplings at a tuna farming site in Japan between January and May, 2015 to determine the life cycle of Cardicola spp. We collected over 4700 terebellid polychaetes from ropes, floats and frames of tuna culture cages and found nearly 400 infected worms. Sporocysts and cercariae found in Nicolea gracilibranchis were genetically identified as Cardicola orientalis by 28S and ITS2 ribosomal DNA sequences. This was the first discovery of the intermediate host for this parasite species. Infection prevalence and the abundance of N. gracilibranchis significantly varied between sampling points and the highest number of infected terebellids were collected from ropes. We also demonstrated morphologically and molecularly that asexual stages found in a single Amphitrite sp. (Terebellidae) and adult worms isolated from farmed juvenile tuna were Cardicola forsteri . This is the first report of C. forsteri in Pacific bluefin tuna (PBT) Thunnus orientalis in Japan. Our results demonstrated that all three species of Cardicola orientalis , C. forsteri and Cardicola opisthorchis exist in Japanese farmed PBTs and that they all use terebellid polychaetes as the intermediate hosts. [ABSTRACT FROM AUTHOR]

Bluefin tunas are one of the most important fishery resources worldwide. Because of high market values, bluefin tuna farming has been rapidly growing during recent years. At present, the most common form of the tuna farming is based on the stocking of wild-caught fish. Therefore, concerns have been raised about the negative impact of the tuna farming on wild stocks. Recently, the Pacific bluefin tuna (PBT), Thunnus orientalis , has succeeded in completing the reproduction cycle under aquaculture conditions, but production bottlenecks remain to be solved because of very little biological information on bluefin tunas. Functional genomics approaches promise to rapidly increase our knowledge on biological processes in the bluefin tuna. Here, we describe the development of the first 44K PBT oligonucleotide microarray (oligo-array), based on whole-genome shotgun (WGS) sequencing and large-scale expressed sequence tags (ESTs) data. In addition, we also introduce an initial 44K PBT oligo-array experiment using in vitro grown peripheral blood leukocytes (PBLs) stimulated with immunostimulants such as lipopolysaccharide (LPS: a cell wall component of Gram-negative bacteria) or polyinosinic:polycytidylic acid (poly I:C: a synthetic mimic of viral infection). This pilot 44K PBT oligo-array analysis successfully addressed distinct immune processes between LPS- and poly I:C- stimulated PBLs. Thus, we expect that this oligo-array will provide an excellent opportunity to analyze global gene expression profiles for a better understanding of diseases and stress, as well as for reproduction, development and influence of nutrition on tuna aquaculture production. [ABSTRACT FROM AUTHOR]

Juvenile Pacific bluefin tuna (PBT, Thunnus orientalis) are known to migrate from western Pacific spawning grounds to their eastern Pacific nursery and feeding grounds in the California Current Large Marine Ecosystem (CCLME), but the timing, durations, and fraction of the population that makes these migrations need to be better understood for improved management. To complement recent work focused on stable isotope and radiotracer approaches ("tracer toolbox"; Madigan et al., 2014) we explored the suitability of combining longitudinal analyses of otolith microstructure and trace elemental composition in age ~1-2 PBT (n = 24, 66-76 cm curved fork length) for inferring the arrival of individuals in the CCLME. Element:Ca ratios in transverse otolith sections (9-12 rows, triplicate ablations from primordium to edge, ø50 µm) were quantified for eight elements: Li, Mg, Mn, Co, Cu, Zn, Sr, and Ba, which was followed by microstructure analysis to provide age estimates corresponding to each ablation spot. Age estimates from otoliths ranged from328 to 498 d post-hatch. The combined elemental signatures of four elements (Ba, Mg, Co, Cu) showed a significant increase at the otolith edge in approximately half of the individuals (30-60 d before catch). Given the different oceanographic properties of oligotrophic open Pacific vs. high nutrient, upwelling CCLME waters, this signal is consistent with the entry of the fish into the CCLME, which was estimated to occur primarily in July after a transoceanic migration of _~1.5-2.0 months. Our approach comprises a useful addition to the available tracer toolbox and can provide additional and complementary understanding of trans-Pacific migration patterns in PBT. [ABSTRACT FROM AUTHOR]

This study examined the influence of swimbladder inflation ( SBI) failure on mortality (Experiment 1), lordotic deformity (Experiment 2) and growth (Experiment 1, 2) in Pacific bluefin tuna, Thunnus orientalis, postflexion larvae and juveniles by producing larvae lacking inflated swimbladders. Experiment 1 was conducted for postflexion larvae to juveniles (from 18 to 30 days-post-hatch; dph). Mortality was not significantly different between the fish with ( WIS) and without ( WOIS) inflated swimbladders. Standard length ( SL) and body weight ( BW) were significantly smaller in WOIS than WIS. Moreover, the SBI was found in WOIS after postflexion stage. In Experiment 2, two examination trials were conducted on SBI, vertebral deformity and growth for juvenile stage. Lordotic deformities were found neither in the WOIS nor in the WIS. Although SL and BW were significantly smaller in WOIS than WIS at 22 dph, after 37 dph no significant differences were found between them. The results of Experiment 1 and 2 indicate that SBI failure causes growth retardation until juveniles of 30 dph; however, it does not cause growth retardation in juveniles after 37 dph and mortality of postflexion larvae and juveniles. Moreover, SBI failure did not cause lordotic deformity in PBT differently from many other fish. [ABSTRACT FROM AUTHOR]

This study investigated the optimal timing of day to promote initial swimbladder inflation ( ISI) for improved Pacific bluefin tuna ( PBT), Thunnus orientalis, larval survival. Larval swimbladder inflation frequency was compared based on three experiments using different time schemes of surface film removal ( SFR) from 3 to 9 days post hatch (dph). SFR was conducted from 05:00 to 19:00 hours (light period: S.5-19), 19:00 to 05:00 hours (dark period: S.19-5), 08:00 to 19:00 hours (S.8-19) and the entire day (S.24) in Experiment 1; from 08:00 to 19:00 hours (S.8-19-E2), 08:00 to 13:00 hours (S.8-13), 13:00 to 19:00 hours (S.13-19) in Experiment 2; and from 13:00 to 16:00 hours (S.13-16), 16:00 to 19:00 hours (S.16-19), 18:00-19:00 hours (S.18-19) in Experiment 3. The swimbladder inflation frequency at the experiment termination (9 dph) was significantly higher ( P < 0.001) in S.24 (91.1 ± 5.7%), S.5-19 (92.2 ± 5.1%) and S.8-19 (93.3 ± 3.4%) than in S.19-5 (11.1 ± 5.1%) in Experiment 1, and remarkably higher in S.8-19-E2 (81.7%) and S.13-19 (88.3%) than in S.8-13 (0.0%) in Experiment 2, and significantly higher ( P < 0.001) in S.16-19 (84.4 ± 5.1%) and S.18-19 (70.0 ± 12.0%) than in S.13-16 (7.8 ± 3.9%) in Experiment 3. These results suggest that the optimal timing to promote larval ISI by SFR is a few hours before the end of light period (16:00-19:00 hours) from 3 to 9 dph. [ABSTRACT FROM AUTHOR]

Tuna are known for exceptional swimming speeds, which are possible because of their thunniform lift-based propulsion, large muscle mass and rigid fusiform body. A rigid body should restrict maneuverability with regard to turn radius and turn rate. To test if turning maneuvers by the Pacific bluefin tuna (Thunnus orientalis) are constrained by rigidity, captive animals were videorecorded overhead as the animals routinely swam around a large circular tank or during feeding bouts. Turning performance was classified into three different types: (1) glide turns, where the tuna uses the caudal fin as a rudder; (2) powered turns, where the animal uses continuous near symmetrical strokes of the caudal fin through the turn; and (3) ratchet turns, where the overall global turn is completed by a series of small local turns by asymmetrical stokes of the caudal fin. Individual points of the rostrum, peduncle and tip of the caudal fin were tracked and analyzed. Frame-by-frame analysis showed that the ratchet turn had the fastest turn rate for all points with a maximum of 302 deg s-1. During the ratchet turn, the rostrum exhibited a minimum global 0.38 body length turn radius. The local turn radii were only 18.6% of the global ratchet turn. The minimum turn radii ranged from 0.4 to 1.7 body lengths. Compared with the performance of other swimmers, the increased flexion of the peduncle and tail and the mechanics of turning behaviors used by tuna overcomes any constraints to turning performance from the rigidity of the anterior body morphology., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2023. Published by The Company of Biologists Ltd.)

Juvenile Pacific bluefin tuna ( Thunnus orientalis; PBT) often experience high mortality during ship transportation. This study investigated whether the addition of colours or patterns to the walls of tanks affected survival rate. In the first experiment, three colours and lattice patterns were tested: dark blue single-colour, red single-colour, and red-blue lattice pattern. Fish in all tanks exhibited abnormal behaviours when sunlight entered the tanks between 0800 and 1000 hours, but mortality only increased in the single-coloured tanks as a result of collision with the tank walls. In the second experiment, four colours and patterns were tested: dark blue single-colour, red-blue lattice pattern, red-blue lattice pattern with shade sheet and red-green lattice pattern with shade sheet. Again, we visually observed that fish in all treatment groups exhibited abnormal behaviour when sunlight entered the tanks, but there were no collision deaths in the lattice-patterned tanks and survival in this group was significantly higher than in the single-coloured tanks. Thus, the use of a high-contrast colour pattern can prevent mass death of juvenile PBT during ship transportation. [ABSTRACT FROM AUTHOR]

We present a numerical approach that, in conjunction with a fully set up Dynamic Energy Budget (DEB) model, aims at consistently approximating the feeding history of cultivated fish from the commonly measured aquaculture data (body length, body mass, or the condition factor). We demonstrate the usefulness of the approach by performing validation of a DEB-based model for Pacific bluefin tuna ( Thunnus orientalis ) on an independent dataset and exploring the implied bioenergetics of this species in captivity. In the context of validation, the results indicate that the model successfully accounts for more than 75% of the variance in actual fish feed. At the 5% significance level, predictions do not underestimate nor overestimate observations and there is no bias. The overall model accuracy of 87.6% is satisfactory. In the context of tuna bioenergetics, we offer an explanation as to why the first reproduction in the examined case occurred only after the fish reached seven years of age, whereas it takes five years in the wild and sometimes as little as three years in captivity. Finally, we calculate energy conversion efficiencies and the supply stress throughout the entire lifetime to theoretically underpin the relatively low contribution of growth to aerobic metabolism implied by respirometry and high feed conversion ratio observed in bluefin tuna aquaculture. [ABSTRACT FROM AUTHOR]

The genetic population structure of the Pacific bluefin tuna (PBF) Thunnus orientalis and the yellowfin tuna (YFT) T. albacares in the North Pacific Ocean was investigated. The polymorphism of microsatellite (SSR) loci and sequences of mitochondrial DNA control region (mtCR) were analyzed for 71 samples of PBF from Japan and Mexico and 45 samples of YFT from Japan and Panama. In the SSR analyses, both single-locus (−0.010 to 0.008 in PBF and −0.023 to 0.020 in YFT) and global multilocus (0.003 in PBF and −0.002 in YFT) F values among the geographic populations were low and not significant in these species. In the mtCR analyses, neither the neighbor-joining tree nor the minimum spanning network showed genetic differentiation among the geographic populations in each species. The pairwise F values among the geographic populations of them (−0.005 in PBF and −0.020 to −0.014 in YFT) were low and not significant. Our SSR and mtCR data suggested that genetic differentiations were not evident among the eastern and western populations in the North Pacific Ocean either in PBF or in YFT. Mismatch distributions, demographic parameters, and neutrality tests suggested that sudden population expansion of PBF and YFT in the North Pacific Ocean occurred 628,000-731,000 and 450,000-525,000 years ago, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Since Kudoa septempunctata in olive flounder (Paralichthys olivaceus) was indicated to cause food poisoning in humans, other Kudoa species are suspected to have pathogenic potential. Recently, a myxosporean possibly associated with food poisoning in humans consuming raw Pacific bluefin tuna, Thunnus orientalis, was identified as Kudoa neothunni. This is a known causative myxosporean of post-harvest myoliquefaction in yellowfin tuna Thunnus albacares. Regardless of the significant differences in the 28S rDNA sequence and the pathological character (with/without myoliquefaction) between the two T. orientalis and T. albacares isolates, they were considered intraspecific variants of K. neothunni. However, the light and low-vacuum electron microscopic observations in the present study revealed that there were two morphotypes; pointed- and round-type spores, which were significantly differentiated by the ratio of suture width to spore width. Furthermore, the two morphotypes were genetically distinguishable by the 28S rDNA sequence analysis. This morphological and molecular evidence validates that the two Kudoa types are separate species, and thus the pointed- and round-types are referred to as K. neothunni and Kudoa hexapunctata n. sp., respectively. K. neothunni was detected solely from T. albacares, whereas K. hexapunctata n. sp. was found not only from T. orientalis but also from T. albacares. [Copyright &y& Elsevier]

Large pelagic predators play important roles in oceanic ecosystems, and may migrate vast distances to utilize resources in different marine ecoregions. Understanding movement patterns of migratory marine animals is critical for effective management, but often challenging, due to the cryptic habitat of pelagic migrators and the difficulty of assessing past movements. Chemical tracers can partially circumvent these challenges by reconstructing recent migration patterns. Pacific bluefin tuna ( Thunnus orientalis; PBFT) inhabit the western and eastern Pacific Ocean, and are in steep decline due to overfishing. Understanding age-specific eastward transpacific migration patterns can improve management practices, but these migratory dynamics remain largely unquantified. Here, we combine a Fukushima-derived radiotracer (134Cs) with bulk tissue and amino acid stable isotope analyses of PBFT to distinguish recent migrants from residents of the eastern Pacific Ocean. The proportion of recent migrants to residents decreased in older year classes, though the proportion of older PBFT that recently migrated across the Pacific was greater than previous estimates. This novel toolbox of biogeochemical tracers can be applied to any species that crosses the North Pacific Ocean. [ABSTRACT FROM AUTHOR]

This study investigated the influence of initial swimbladder inflation ( ISI) failure on survival of Pacific bluefin tuna ( PBT), Thunnus orientalis, larvae to prevent mass mortality due to sinking death. In Experiment 1, swimbladder inflation frequency and survival within an ISI promoted ( PS) group, for which surface film of rearing water was removed, and a group without ISI promotion ( NPS) were compared in 20 and 30 kL tanks. The PS group demonstrated significantly higher swimbladder inflation frequency and increased survival than the NPS group within 20 kL tanks at 9 days post hatching (dph). Similar tendencies were observed within 30 kL tanks. In Experiment 2, larval distribution and swimbladder inflation frequency in the night-time were examined through larval sampling within the upper and middle layers of the water column and tank bottom within 1.6 and 30 kL tanks at 5 dph. Larvae at tank bottom had higher distributional density and significantly lower swimbladder inflation frequency than those distributed in the upper and middle layers within 1.6 kL tanks. Similar tendencies were observed within 30 kL tanks. Results of this study suggest the improvement of larval survival due to prevention of sinking death through ISI promotion in mass-scale PBT larviculture. [ABSTRACT FROM AUTHOR]

Abstract: We found aporocotylid larval stages (sporocysts and cercariae) from five individuals of terebellid polychaete Terebella sp., which were collected from seabed substrate and ropes and floats attached to tuna cages in a tuna farm on the coast of Tsushima Island, Nagasaki, Japan. Nucleotide sequences of the regions of internal transcribed spacer 2 ribosomal DNA and 28S ribosomal DNA from these larval stages were 100% identical to those of Cardicola opisthorchis registered in GenBank. C. opisthorchis is a pathogen causing blood fluke infection of Pacific bluefin tuna Thunnus orientalis, which is considered to have a significant impact on the Japanese Pacific bluefin tuna aquaculture industry. This is the first description of the intermediate host of C. opisthorchis. This indicates that the life cycle of C. opisthorchis is completed within tuna farms in this area. [Copyright &y& Elsevier]

In the aquaculture of Pacific bluefin tuna (PBT, Thunnus orientalis), low survival rates during the larval stage remain a significant issue for the stable supply of seedlings reared from eggs. Egg quality is an important factor affecting seedling production success. If egg quality can be evaluated before hatching, the efficiency of seedling production will be improved by selectively cultivating the seedlings with a high survival rate. In our previous study, we developed a system using a convolutional neural network to evaluate PBT egg quality by estimating the normal hatching rate. The system used an image containing one PBT egg as the input. To further improve the efficiency of the egg quality estimation system, we updated the system that estimates the egg quality of a bulk sample (approximately 30 eggs). Our results indicated that the proposed system can estimate the normal hatching rate of the bulk sample with higher accuracy than the visual inspections of three field experts and visualize the normal hatching rate of each egg in the bulk sample. The proposed system will serve as a foundation for assessing the quality of PBT eggs and increasing the efficiency of seedling production. • System developed for estimating normal hatching rate for bulk PBT egg samples. • System leverages deep learning to estimate normal hatching rates from bulk images. • Estimated normal hatching rate of each egg in a bulk sample is visualized. • Estimation of proposed system is more accurate than experts' visual inspections. [ABSTRACT FROM AUTHOR]

A feeding experiment was conducted to evaluate the efficacy of, and determine the requirements for dietary AsA ( l-ascorbic acid) using its popular derivative l-ascorbyl-2-monophosphate-Mg (APM) for juvenile Pacific bluefin tuna (PBT). The five test diets (with APM-0, -400, -800, -1200 and -1600) were prepared by adding 0, 400, 800, 1200 and 1600 mg of APM kg diet, respectively. These diets, together with chopped sand lance (the control diet), were administered, in duplicate to 0.27 g PBT at 25 days after hatching (300 juveniles per 15 m tank). The PBT were fed to apparent satiety 6 times a day for 2 weeks. While final body weight, feed conversion and survival showed no differences among diets APM 400-1600, PBT fed APM-0 indicated lower growth performance together with anorexia, dark pigmentation and ataxia from 5 days and reached 80 % mortality at 12 days after the start of the feeding trial. In addition, liver and brain ascorbic acid (AsA) concentrations increased with increasing dietary APM levels, the values were similar in PBT fed diets with APM-1200 and APM-1600, and liver and brain concentrations of AsA were significantly higher in these fish than in the PBT fed the other diets ( P < 0.05). The PBT responded to increasing dietary APM, and the fish fed APM-1200 had the highest weight gain, protein and lipid content. The data indicate that PBT can utilize APM as an AsA source and suggest that dietary supplementation with APM-1200 (454 mg AsA kg diet) would result in satisfactory growth. [ABSTRACT FROM AUTHOR]

Initial swimbladder inflation ( ISI) of Pacific bluefin tuna ( PBT), Thunnus orientalis, larvae was studied to increase the survival of cultured larvae. Experiment 1 was conducted to explore promotion and inhibition of ISI under different water surface conditions; including the use of surface skimmer to remove autogenous surface substances ( SS), covering the water surface with liquid-paraffin-layer ( LP) and oil film ( OF), and a control (non-treatment, NT). Significantly higher inflation frequency was observed in SS (62.2%) than NT (11.9%), LP (2.7%) and OF (3.9%). This indicates that ISI in PBT larvae can be promoted by removal of surface substances on rearing water which inhibit larval air gulping. Experiment 2 aimed to elucidate proper day of larval age to start skimming for promoting ISI with four different periods of oil film removal: from 3 to 8 ( SF3D), 4 to 8 ( SF4D), 5 to 8 ( SF5D), 6 to 8 ( SF6D) days-post-hatch (dph). Significant improvement in ISI frequency was observed in SF3D (80.2%) but the frequency was very poor in SF4D, SF5D, and SF6D (17.8-7.5%). This implies the need of oil film removal without missing a narrow window, 1 day of 3 dph, to promote ISI in practical PBT larviculture. [ABSTRACT FROM AUTHOR]

Abstract: Although full-cycle aquaculture of Pacific bluefin tuna, Thunnus orientalis, has been established by Kinki University, Japan, most juvenile die after transfer to net cages offshore due to the stress associated with fluctuations in environmental conditions. We examined the effect of environmental conditions on mortality of juvenile using a generalized liner model (GLM). Juveniles were reared for more than 300days in a net cage and number of dead fish was examined over time and in relation to water temperature, salinity, moon phase, and water transparency. Mortalities soon after transferring the fish from the indoor rearing tank to the net cage occurred independently of environmental factors and were considered to be due to the handling stress and lack of acclimation. In subsequent periods, fluctuations in water temperature were the most critical factor affecting juvenile survival. Our results showed that optimal water temperatures for juvenile bluefin tuna aquaculture are considered to range between 15 and 25°C. Salinity and lunar irradiance (half moon to full moon) fluctuations had less marked effects on juvenile survival. Juveniles in net cages cannot move to avoid those unfavorable environmental fluctuations and this inability to locate areas of optimal temperature may complicate their body temperature maintenance because the capacity for endothermy in juveniles is undeveloped. We propose that sites selected for culturing juvenile Pacific bluefin tuna have water temperatures ranging from 15 to 25°C with constant temperatures that avoid large fluctuations. [Copyright &y& Elsevier]

High levels of larval mortality are a significant barrier to the artificial mass production of Pacific bluefin tuna (Thunnus orientalis). Mortality may occur when larvae sink and come into contact with the bottom of the rearing tank during the first 10 days after hatching. We evaluated the effect of flow control by aeration on the survival of T. orientalis larvae. These larvae were held in 500-L tanks in which the aeration rate was varied during the night. Larval survival increased with air supply. We documented the cross-sectional flow pattern and gravitational sinking velocities of larvae to assess the correlation between survival and circulation patterns in the tank. The sinking velocity of T. orientalis larvae at night increased with larval body density, which varied with swimbladder volume. Larvae with uninflated swimbladders sank significantly faster than larvae with inflated swimbladders. Both water circulation speed and survival increased at higher aeration rates. Our results suggest that aeration rates >900 ml min–1 may increase larval survival by counteracting sinking. [ABSTRACT FROM PUBLISHER]

Abstract: A new aporocotylid blood fluke is described, based on specimens from the ventricle of the Pacific bluefin tuna, Thunnus orientalis (Temminck et Schlegel), cultured in Wakayama and Nagasaki Prefectures, Japan. The new species is morphologically similar to the members of the genus Cardicola Short, 1953, but shows distinct differences in the body form, location of the testis and the orientation of the ootype. The body of the new species is long and slender, whereas other Cardicola species are small and generally lanceolate. The testis is mostly located posterior to the caeca and anterior to the ovary, occupying 31–45% of body length, in contrast to the known Cardicola species, whose testis is typically intercaecal. The ootype is oriented anteriorly, while in most congeners, it is directed posteriorly or horizontally. Phylogenetic analyses of this aporocotylid, together with Cardicola orientalis Ogawa, Tanaka, Sugihara et Takami, 2010 from the same host, were conducted based on DNA sequences of the ITS2 rDNA and the 28S region of ribosomal RNA. The analyses revealed that the new blood fluke belongs to the genus Cardicola despite the marked morphological differences. Thus, this aporocotylid is named Cardicola opisthorchis n. sp. and the generic diagnosis is emended in this paper. In addition, 100% identity among the ITS2 sequences from the present species, Cardicola sp. from T. orientalis in Mexico and Cardicola sp. from the northern bluefin tuna, Thunnus thynnus (Linnaeus) in Spain suggests that C. opisthorchis n. sp. has a broad geographical distribution and that it infects both the Pacific and northern bluefin tuna. [Copyright &y& Elsevier]

Abstract: We reviewed research on the broodstock management and larviculture of the Pacific northern bluefin tuna (PBT) Thunnus orientalis in Japan. Japan has been at the forefront of PBT research since 1970 due to the participation by federal and prefectural governments and universities in a national project aimed to optimize productivity of the sea around Japan. In 1979, scientists at Kinki University succeeded in the first spontaneous spawning in captivity by the broodstock of 5year-old PBT. Successful spawning was also performed in 1980 and 1982, but no spawning then occurred until 1993, when Maruha Nichiro Holdings, Inc. (MNH) and Nippon Formula Feed Manufacturing Company, Ltd. (NFFMC) became involved in tuna farming and succeeded in the spawning of four-year-old broodstock. Since then, successful spawning of PBT in captivity has been reported from several sites as well as spawning in Kinki Univ. since 1994. With the successful spawning of PBT, the Fisheries Research Agency (FRA; formerly, Japan Sea Farming Association) of Kinki University, in conjunction with MNH, NFFMC, and Takuyo Ltd., has actively carried out research on and development of tuna larviculture technology. Thus, knowledge about broodstock management and larviculture has accumulated in Japan, but technical problems with larviculture still remain to be solved. There are 9 sites of successful spawning in net pens in Japan so far. At 4 of these sites in regions around Amami Island, yearly spawning has stably occurred. We have been accumulating data about the period of maturation, environmental key factors triggering the spawning, the age of onset of spawning, and the pattern of spawning through measurement of the ambient environment, gonad morphometry, endocrinology, mitochondrial DNA analysis, and daily careful observation of broodstock. Research on PBT larviculture at Kinki University, FRA, MNH, NFFMC, and Takuyo have succeeded in producing tens of thousands of hatchery-raised juveniles. As a result, Kinki University succeeded in establishing the full life cycle of PBT in captivity, and also achieved its aquaculture life cycle. However, solutions are needed for the remaining technological issues of PBT larviculture, including sinking syndrome, where larvae die on the bottom of the tank during the early phase of larviculture, the search for appropriate food (species, size, and nutrition) around the transition stage from larva to juvenile, cannibalism and collision against walls in the juvenile, and malformation and viral diseases in the young stage. [Copyright &y& Elsevier]

Abstract: Kudoa prunusi n. sp. (Myxozoa; Multivalvulida) is described from the brain of Pacific bluefin tuna Thunnus orientalis cultured in Japan. Numerous white cysts, up to 0.5mm in size, were found on and in the brain. Spores having typically five spore valves and five polar capsules resembled a five-petal cherry blossom in apical view and were conical shape with a round bottom in side view. Average spore size was 9.63 (8.5–10.3)μm in width and 7.50 (6.7–8.6)μm in length. The spore dimensions of K. prunusi overlapped with those of Kudoa yasunagai ex Sillago ciliata having five to six spore valves, but they were clearly distinct in spore shape, 18S rDNA and 28S rDNA sequences (0.3% and 1.7% differences, respectively). Phylogenetic analysis of 18S rDNA revealed that K. prunusi grouped with the brain-infecting multivalvulid species, K. yasunagai, K. chaetodoni, K. lethrini and K. neurophila, rather than five-valved Kudoa spp. Combined with morphological, molecular and biological differences, K. prunusi was proven to be a new species. [ABSTRACT FROM AUTHOR]

The article discusses a study which investigated the natal origin of Pacific bluefin tuna Thunnus orientalis inferred from otolith oxygen isotope composition. The study demonstrated that otolith oxygen isotope values varied from -2.5 to -2.2% between the otolith core for age-0 tuna caught in the Japan Sea, while those caught in the Pacific Ocean varied between -2.8 and-2.2%. It was also observed that the temporal difference in experienced water temperatures produces an earlier increase of otolith oxygen isotope values for tuna caught in the Japan Sea than in the Pacific Ocean.

During the parasitological survey of cultured juvenile Pacific bluefin tuna (PBT) Thunnus orientalis in 2007 and 2008, two myxosporeans and one microsporidian were found. Morphological and molecular analysis showed that the heart-infecting and brain-infecting myxosporeans are identified as Kudoa shiomitsui and K. yasunagai, respectively. This is a new host record for both species. High prevalence of infection (77-100%) with K. shiomitsui was observed in October to December (1-2 months post-transfer to sea cages), whereas only a few fish were infected with K. yasunagai. A microsporidian observed as white 'cysts' in the trunk muscle of PBT had a resemblance to Microsporidium seriolae, the causative parasite of beko disease in yellowtail. Phylogenetic analysis showed that the microsporidian from PBT is closely related to but distinct from several other muscle-infecting species such as M. seriolae, Microsporidium sp. RSB, and Microsporidium sp. SH. Additionally, the spore dimension (2.7 × 1.5 μm on average) was remarkably smaller than the others. These results suggest that the present microsporidian is an undescribed species and designated Microsporidium sp. PBT. Prevalence and intensity of infection with Microsporidium sp. PBT reached a maximum of 100% and 20 cysts/fish, respectively. Although pathogenic effects of the two Kudoa species on fish health remain unknown, the microsporidian could be of concern to PBT aquaculture due to unsightly cysts in the musculature, reducing the market value of the fish. [ABSTRACT FROM AUTHOR]

Abstract: Schooling behavior traits during the process of retinomotor response from scotopic to photopic vision were examined in cultivated juvenile Pacific bluefin tuna (PBT) at 3 different ages. After a sudden change in illumination from darkness to 300lx, retinal adaptations changed from scotopic to photopic vision. Retinomotor and schooling indices showed strong agreement, with juvenile PBTs forming polarized schools upon complete retinal adaptation to photopic vision. The behavioral and retinal adaptation to sudden illumination took 20, 15, and 10min after illumination in PBT 25, 40, and 55days after hatching (dah). At 40dah, PBT took a longer time to adapt than fish aged 55dah and showed the highest swimming speed, including momentary bursts of swimming immediately after illumination. This suggested that these fish were swimming at high speed under poor visibility conditions. In contrast, PBT at 55dah showed a gradual increase in swimming speed that correlated with their retinal adaptation. Therefore, behavioral and retinal adaptation traits changed during growth, suggesting that the high mortality in PBT around 40dah, due to collisions with the tank and net walls at dawn, may be because these adapt more slowly than fish at 55dah and were swimming at a relatively high speed under conditions of poor visibility. [Copyright &y& Elsevier]