Japanese Jack Mackerel Trachurus Japonicus Research Articles

Hatch date and early growth of juvenile Japanese jack mackerel Trachurus japonicus caught in the Uwa Sea.

Development and growth rate variations during early life are important for understanding the mechanisms of recruitment dynamics. We examined the larval growth rate and age at the onset of metamorphosis (dm ) of juvenile Japanese jack mackerel recruited to a population in the Uwa Sea, Japan. Otolith microstructure analyses revealed that the hatch date of juveniles ranged from February to April in 2011-2015, and that their dm were 25.5-30.5 d and mean growth rates at the larval (GL ) were 0.30-0.34 mm d-1 . Among these, dm showed significant negative correlations with juvenile abundance. Moreover, the hatch date did not coincide with the spawning period of this species in the Uwa Sea, and the hatch date and mean growth rate at the larval stage were comparable to those of Japanese jack mackerel juveniles sampled in the East China Sea (ECS). These findings suggest that most juvenile Japanese jack mackerel originated in other waters, including the ECS, and that larval stage duration influence their recruitment abundance in the Uwa Sea. This article is protected by copyright. All rights reserved.

Redescription of Bomolochus decapteri Yamaguti, 1936 (Copepoda, Cyclopoida, Bomolochidae) recovered from three species of Carangidae (Pisces, Perciformes) in Japan, with the first description of the male of the species

Abstract Bomolochus decapteri Yamaguti, 1936 is redescribed based on specimens recovered from the bucco-branchial cavity of three species of Carangidae (Pisces, Perciformes), the roughear scad Decapterus tabl Berry, 1968, the whitefin trevally Carangoides equula (Temminck & Schlegel, 1844), and the Japanese jack mackerel Trachurus japonicus (Temminck & Schlegel, 1844) in Japan. The male of the species is described for the first time. The possession of postantennal processes and lateral processes was verified in the genus, next to Nothobomolochus.

Extracting daily isotopic records on fish otolith (Trachurus japonicus) by combining micro-milling and micro-scale isotopic analysis(MICAL-CF-IRMS).

The recent progress in micro-scale isotopic analytical techniques for otoliths has enabled the reconstruction of the experienced water temperature history of fish in every few days resolution using the stable oxygen isotope ratio (δ18 O) of otoliths. We aimed to improve those techniques and extract the daily δ18 O records of otoliths formed during the juvenile period. Growth rings were formed daily in fish otoliths. We precisely distinguished the daily rings in otoliths of Japanese jack mackerel Trachurus japonicus, and milled them along daily growth rings using a high-spatial resolution micromilling system (Geomill326). Then, we determined the stable carbon and oxygen (δ13 C, δ18 O) isotopic compositions using a high-precision micro-scale isotopic analytical system (MICAL3c with IsoPrime 100). We successfully milled each daily ring with width ranging from 14.0 to 62.9μm (average 27.0μm) during the high growth period (30-70 days after hatching), and determined the isotopic compositions of otolith aragonite. Our improved micro-scale analytical method is the first to determine the daily δ18 O history of fish otoliths. By using our method together with the δ18 O - water temperature equation, the daily history of experienced water temperature can be elucidated. Our high-resolution milling and analytical technique can also be applied to high-resolution isotope analysis for stalactites, clams, and corals.

Improved Raman spectroscopy-based approach to assess microplastics in seafood

Microplastics represent an emerging environmental issue and have been found almost everywhere including seafood, raising a great concern about the ecological and human health risks they pose. This study addressed the common technical challenges in the assessment of microplastics in seafood by developing an improved protocol based on Raman spectroscopy and using the green-lipped mussel Perna viridis and the Japanese jack mackerel Trachurus japonicus as the test models. Our findings identified a type of stainless-steel filter membranes with minimal Raman interference, and a combination of chemicals that achieved 99–100% digestion efficiency for both organic and inorganic biomass. This combined chemical treatment reached 90–100% recovery rates for seven types of microplastics, on which the surface modification was considered negligible and did not affect the accuracy of polymer identification based on Raman spectra, which showed 94–99% similarity to corresponding untreated microplastics. The developed extraction method for microplastics was further combined with an automated Raman mapping approach, from which our results confirmed the presence of microplastics in P. viridis and T. japonicus collected from Hong Kong waters. Identified microplastics included polypropylene, polyethylene, polystyrene and poly(ethylene terephthalate), mainly in the form of fragments and fibres. Our protocol is applicable to other biological samples, and provides an improved alternative to streamline the workflow of microplastic analysis for routine monitoring purposes.

Spatiotemporal variability in the occurrence of juvenile Japanese jack mackerel Trachurus japonicus along coastal areas of the Kuroshio Current

AbstractTo understand the population structure of the Japanese jack mackerel Trachurus japonicus in coastal areas adjacent to the Kuroshio Current (referred to as the “CAK”), we analyzed size composition and commercial landing data of juvenile fish in these areas for the period 2005–2015. Trachurus japonicus does not undergo population‐scale spawning migration, and thus, the connectivity between the spawning and juvenile/adult habitat areas is important. Therefore, our primary aim was to assess the origin of juveniles landed in a number of subareas, including those spawned in local spawning grounds in January–May in the western part of the CAK (w‐CAK), those spawned in May–July in the eastern part (e‐CAK), and those spawned in February–March in the remote spawning ground in the southern East China Sea (s‐ECS). Fishing periods starting in spring (spring onset) were commonly observed in the CAK, which involved relatively small size classes (50–100 mm fork length [FL]). Back estimates based on the growth rate of T. japonicus suggested that the contributions from the s‐ECS probably dominated most of the spring onsets in April–June because the smallest size class (50–70 mm FL) occurred almost exclusively in April–May. In autumn, onset signals were associated with the landing of juveniles from the local spawning ground in an eastern subarea of the e‐CAK. Despite the asymmetric transport and migration flows between the habitat areas of T. japonicus, its population levels may be sustained because the local and remote spawning grounds are used in different seasons.

Age and growth from Oita and Miyagi Prefectures of Japanese jack mackerel Trachurus japonicus

The age and growth of Japanese jack mackerel Trachurus japonicus from Oita and Miyagi Prefectures were investigated by means of otolith sectioning. Different types of opaque zones were formed in summer and winter, respectively. The age composition and growth formulas were examined and compared for Oita (2007–2008) and Miyagi (2016–2017) Prefectures from individual age data. We determined that the age–length relationships and parameters for the von Bertalanffy growth function from Oita and Miyagi Pref. were, respectively, L∞ = 342 and 305 mm and k = 0.673 and 0.634 year−1. In Oita Pref., most fish with a fork length (FL) of approximately 180–200 mm were 1+ years of age, while older fish (7+) were rare. In Miyagi Pref., many fish were 3–6+ years of age. Older fish (over 7+ years) accounted for approximately one quarter of the total. These differences in the growth curve and age composition may be reflected by discrepancies in the fishing gears, and multiple life cycle patterns of the Pacific stock which has been unknown.

Annual reproductive cycle and spawning ground formation in Japanese jack mackerel Trachurus japonicus in the Uwa Sea, Japan

To determine the annual reproductive cycle and the formation of spawning grounds in the Japanese jack mackerel Trachurus japonicus in the Uwa Sea, Japan in relation to sea temperature, seasonal changes in the ovary histomorphology and the catch per unit effort (CPUE) of adult fish were analyzed. Japanese jack mackerel in this region initiated vitellogenesis in winter and spawned between late April and early July in 2013–2015, with a quotient analysis suggesting that suitable temperatures for these two processes were 16–20 °C and 16–21 °C, respectively. However, the CPUE of adult fish was consistently high in the central Uwa Sea irrespective of temperature, indicating that the dense distribution of adult fish there is affected by additional parameters, such as phytoplankton productivity and migration. Comparison of the hatching period with the spawning season suggested that individuals recruited to the population in the Uwa Sea are derived not only from the Uwa Sea but also from other sea areas including the East China Sea. Therefore, further research on the hatching sites and recruitment processes of Japanese jack mackerel is required to evaluate the effectiveness of conservation measures for adult fish in the Uwa Sea.

Factors controlling spatiotemporal variations in stable nitrogen isotopes of Trachurus japonicus larvae and juveniles in the East China Sea

To clarify the factors that affect spatiotemporal isotopic variations in fishes, we examined stable carbon and nitrogen isotope ratios (δ13C and δ15N) of Japanese jack mackerel Trachurus japonicus larvae and juveniles sampled in the shelf break region of the East China Sea (ECS) in April during six consecutive surveys (2005–2010). The δ13C values in fish tissues were similar between northern and southern ECS, while δ15N values were higher in the southern ECS, probably because of lower nitrogen fixation and the presence of fish with larger body size occupying a higher trophic level. Interannual variations in δ15N of T. japonicus juveniles might be mainly contributed by the variation in the abundance of the main diet such as Oncaeidae copepodites and Corycaeus. The isotopic overlaps between epipelagic T. japonicus larvae and other dominant mesopelagic fish larvae were negligible, suggesting lesser competition for food resources. Knowledge regarding spatiotemporal variation in stable isotope ratios of T. japonicus can be applied to understand the feeding habits and migrations of fishes in the ECS.

Interannual variations in distribution and abundance of Japanese jack mackerel Trachurus japonicus larvae in the East China Sea

Abstract We examined the interannual variations in distribution and abundance of Japanese jack mackerel Trachurus japonicus larvae <5 mm standard length (SL), based on sampling surveys over a broad area of the shelf break region of the East China Sea (ECS) during late winter and spring for 12 years from 2001 to 2012. Larval abundances in late winter were higher than those in spring. In late winter, ratios (expressed as %) of larval abundance in the southern ECS south of 28°N to the whole study area were highest during the study period, with values ranging from 80.0 to 95.8%. In spring, the ratios in the southern ECS were still high (34.3–88.8%), although the values increased slightly in the northern and central ECS. There was no significant interannual variation in the centre of distribution of the larvae, suggesting that the formation of spawning grounds would be related to topographic rather than hydrographic conditions. Habitat temperature of larvae in the central and southern ECS was ∼3–5°C higher than that in the northern ECS throughout the study period, indicating that larval growth and survival processes may differ between the two areas. In the southern ECS, larval abundances fluctuated largely from year-to-year, and the interannual variations were closely correlated with water temperature and chlorophyll a concentration. However, larval abundance did not correlate with an index of recruited juveniles (∼50–75 mm SL) in the ECS, suggesting that mortality during the late larval and early juvenile stages is responsible for recruitment success or failure.

Target strength spectra of tracked individual fish in schools

Broadband sonar echoes received from individual fish in schools contain information that might be useful for species discrimination. The echo characteristics are closely related to the incident angle of the sound to fish body, corresponding to the apparent tilt angle of a fish from a viewpoint of a transducer. Therefore, it is necessary to isolate individual fish echoes and estimate the incident angles. In this study, a broadband split-beam echo sounder system was used to extract features from free-swimming fish schools. Echoes from individual fish in dense schools were measured and their position was estimated using the system with a downward-oriented acoustic beam. Individual fish were tracked in schools of Japanese jack mackerel Trachurus japonicus, chub mackerel Scomber japonicus, and red sea bream Pagrus major with the system. The target strength (TS) spectra of echoes ranging from 80 to 120 kHz were calculated and sorted on the basis of the incident angle, which was estimated by the tracking result. Using this approach, TS spectra were obtained from entire schools of free-swimming fish, and the obtained TS spectra were found to be dependent on fish species and the incident angles of the individual fish involved.

Revisiting morphological identification of Japanese jack mackerel Trachurus japonicus eggs preserved in formalin

Since formalin-preserved eggs of Japanese jack mackerel Trachurus japonicus have been considered difficult to identify, egg abundance of this species has not been estimated, and subsequently information on their spawning habitat is limited. The present study provides a practical identification of Japanese jack mackerel eggs from formalin-preserved samples based on morphological characteristics with validations through DNA sequencing and a rearing experiment. Eggs obtained by artificial fertilization from mature adults were reared in the laboratory, and developmental changes of morphological characteristics in the formalin-preserved samples were examined. The morphological descriptions were detailed to identify jack mackerel eggs from field-captured egg samples preserved in formalin. Moreover, the identification was validated through DNA sequencing and a rearing experiment. Overall, the diagnostic characteristic for identification was the egg diameter and the segmentation of the yolk, which was maintained in formalin-preserved samples even long after fixation. The presented morphological description with its developmental changes for formalin-preserved eggs is anticipated to promote stock assessments and biological studies for jack mackerel based on the egg and larval surveys.

조리방법에 따른 고등어(Scomber japonicus) 및 전갱이(Trachurus japonicus)의 일반성분 및 지질성분의 변화

Changes in the proximate composition, lipid classes, and fatty acids were studied in chub mackerel Scomber japonicus and Japanese jack mackerel Trachurus japonicus muscles cooked using a frying pan, oven, and microwave oven. The moisture content was high in the raw samples (chub mackerel 65.5%, Japanese jack mackerel 60.5%) and decreased with cooking, especially in the frying pan method (chub mackerel 49.2%, Japanese jack mackerel 49.8%). In contrast, the protein, lipid and ash contents increased significantly with cooking in chub mackerel muscle (P<0.05). However, the lipid content of Japanese jack mackerel muscle showed no significant difference between the samples using the three cooking methods and the raw sample. The dripped lipid contents from the cooked muscles showed the highest levels in the frying pan samples and the lowest levels in the microwave oven samples. The percentage of non-polar lipid (NL) in the total lipid content was over 95% in the muscle lipids (10.43-21.86 g/100 g sample). Prominent fatty acids were 16:0, 18:1n-9, 22:6n-3 (docosahexaenoic acid, DHA), 16:1n-7 and 20:5n-3 (eicosapentaenoic acid, EPA) in both fish muscles and dripped lipids. There was no change in the EPA level in any of the fish muscles, by any cooking method. The percentage of DHA in the muscle of chub mackerel showed the lowest level in the frying pan sample and the highest level in the microwave oven and raw samples, and an intermediate level in the oven sample. However, the percentage of DHA in the Japanese jack mackerel muscle was not significantly different between the various cooking methods. From these results, the microwave oven and oven cooking methods showed relatively low levels of dripped lipid content and loss of n-3 PUFA compared with the frying pan cooking method.

Feeding habits and gill raker morphology of three planktivorous pelagic fish species off the coast of northern and western Kyushu in summer

Feeding habits and gill raker morphology were examined for the three major planktivorous pelagic fishes, Japanese anchovy Engraulis japonicus, Pacific round herring Etrumeus teres and Japanese jack mackerel Trachurus japonicus, off the northern and western coasts of Kyushu, in the north‐eastern part of the East China Sea in the summer months of 2001. Using fishes in the same size range (80–140 mm, standard length), the stomach contents of the three fish species were compared. The diet of the Japanese anchovy mainly consisted of Oncaeidae copepods, while the diets of the Pacific round herring and Japanese jack mackerel were dominated by calanoid copepods at all stations. Comparisons between prey size in the stomach, zooplankton size in the water and gill raker morphology suggested that the stomach contents of the three species were characterized mainly by the difference in the feeding behaviour between Japanese anchovy (filter‐feeding) and the other two species (particulate‐feeding), rather than by the difference in the morphology of feeding apparatus only. It was concluded that behavioural adaptations in the feeding of these pelagic fishes brought about trophic partitioning to some degree in this pelagic ecosystem in summer. Although the diets of these three species overlapped to some extent, there was still little likelihood of competition between the Japanese anchovy and the other two species. The potential for competition between the Pacific round herring and the Japanese jack mackerel is discussed.

Evidence of growth-selective predation on larval Japanese anchovy Engraulis japonicus in Sagami Bay

Growth-selective predation mortality was demonstrated for postlarval Japanese anchovy Engraulis japonicus in field research. The larval anchovy and their predatory fish were simultaneously captured by a trawl in Sagami Bay during October to November 2000. The growth rates analyzed by otolith microstructure were compared between the larvae from the stomach con- tents of the predators (prey larvae) and those from the population of origin (surviving larvae). The mean growth rates of the prey larvae collected on 28 October and 2 to 4 November (mean ± SD: 0.57 ± 0.07 mm d -1 ) and on 23 November (0.50 ± 0.06 mm d -1 ) were significantly lower than those of the corresponding surviving larvae (0.63 ± 0.07 and 0.54 ± 0.06 mm d -1 , respectively). Such significant differences were not explained by size-selective predation, but were due to variations in the mean growth rates at the same larval size (i.e. non-size-related). The mean growth rates of the prey larvae were different among predatory species (barracuda Sphyraena pinguis, Japanese sea bass Lateo- labrax japonicus, white croaker Pennahia argentatus, Japanese jack mackerel Trachurus japonicus, Pacific round herring Etrumeus teres and juvenile anchovy). Comparisons of back-calculated daily growth rates showed that the decrease in growth rates of the prey larvae were consistent from directly after hatching up to predation. The larvae with lower growth rates were more vulnerable to predation, owing to the cumulative decline in growth rates from hatching to each encounter with predators, compared to the larvae with higher growth rates, even if they were the same size, at a given moment in the sea. Therefore, the level of growth rates itself had direct impact on vulnerabil- ity to predation for larval anchovy, independently of both size (size-selective mortality) and time (stage duration). In addition, such impacts could be predator specific. We propose the 'growth-selec- tive predation' hypothesis (mechanism), which is theoretically independent of and synergistic with the existing hypotheses based on size and time under the general 'growth-mortality' concept for the survival process during the early life history of marine pelagic fish.

Confirmation of spawning groups of Japanese jack mackerel Trachurus japonicus in the low stock level period.

Spawning groups of Japanese jack mackerel Trachurus japonicus in the low stock level period were segregated. Segregation was done by the visual examination of monthly changes of the frequency distribution of fork length and/or partly the monthly changes of the mean gonad index. In the Kuroshio Current System, two spawning groups were recognized: the spring spawning group spawns in spring mainly from February to April and distributes from southern Kyushu to Kanto region; the summer spawning group spawns in summer mainly from June to August and is present only in Kanto region. In the East China Sea and Tsushima Current System, two spawning groups are recognized: the winter spawning group spawns in winter mainly December to January and is present in Wakasa Bay and Noto regions; the spring-summer spawning group spawns from spring to summer mainly April to June and is present in northwestern Kyushu region. Comparison of the population structure of both high stock level (former studies) and low level (present study) shows that basically no differences between the two periods exist.

Morphological variations of the Japanese jack mackerel Trachurus japonicus.

Morphological characteristics of four spawning groups of Japanese jack mackerel Trachurus japonicus, spring and summer spawning groups of the Kuroshio Current System and winter and spring-summer spawning groups of the East China Sea and Tsushima Current System were com-pared. Although there are differences of the allometric growth among three length ranges, in general the spring and spring-summer spawning groups are larger than the summer and winter spawning groups respectively in head length and upper jaw length, etc. The larger fish of the summer spawning group is larger than the spring spawning group in head length and upper jaw length, etc. and smaller in body depth and pectoral fin length, etc. Morphological differences seen between spring and summer spawning groups and spring-summer and winter spawning groups were also discussed with the differences between 'kiaji' and 'kuroaji' formerly studied around Wakasa Bay.

Two types of Japanese jack mackerel Trachurus japonicus of summer spawning group in the Sagami Bay region.

Larger individuals of Trachurus japonicus of the summer spawnlng group in the Sagami Bay region have been distinguished into two types, 'nodoguro' and 'maaji' by fishermen, etc. These two types were compared morphologically. There are no significant differences between them for each of nine meristic characters (t-test, p>0.05). Sixteen morphometric characters and the fork length were examined by covariance analysis. In head length, eye diameter, upper jaw length, length from the snout to the origin of unpaired fins, head depth, pectoral fin length and height of anterior scutes, nodoguro type is larger than maaji. While in body depth, length of fin bases and length of posterior part of lateral line, maaji type is larger than nodoguro type.