Jack Mackerel Trachurus Japonicus Research Articles

A mixed-species shoal including fewer heterospecifics is preferred by jack mackerel Trachurus japonicus juveniles

Mixed-species shoals of fishes were reported from various environments such as coral reefs and temperate lakes. The driving mechanism of forming mixed-species shoal can be either haphazard or a preferential choice by an individual. Here, we tested if jack mackerel Trachurus japonicus, a temperate marine pelagic fish, could choose a shoal composition using vision based on a choice experiment. Shoal preference of jack mackerel juveniles was evaluated by presenting shoals comprising one to four heterospecifics (half-lined cardinal Ostorhinchus semilineatus) out of four shoal members to the focal fish. When both conspecific and heterospecific shoals were presented to a single jack mackerel, the focal fish showed a preference for the conspecific rather than heterospecific shoal, indicating that they can choose a conspecific shoal based on the visual information. However, when a focal fish encountered both conspecific and mixed-species shoals including fewer heterospecifics (one out of four individuals), the latter was preferred. The result implies that jack mackerel can judge a preferable composition of shoal using visual information. The inclusion of fewer heterospecifics may be exploiting oddity effects, whereby minority species are exposed to relatively high vulnerability to predators, as well as resulting in reduced competition for food while maintaining predator vigilance in a shoal.

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.

Environmental DNA preserved in marine sediment for detecting jellyfish blooms after a tsunami

Environmental DNA (eDNA) can be a powerful tool for detecting the distribution and abundance of target species. This study aimed to test the longevity of eDNA in marine sediment through a tank experiment and to use this information to reconstruct past faunal occurrence. In the tank experiment, juvenile jack mackerel (Trachurus japonicus) were kept in flow-through tanks with marine sediment for two weeks. Water and sediment samples from the tanks were collected after the removal of fish. In the field trial, sediment cores were collected in Moune Bay, northeast Japan, where unusual blooms of jellyfish (Aurelia sp.) occurred after a tsunami. The samples were analyzed by layers to detect the eDNA of jellyfish. The tank experiment revealed that after fish were removed, eDNA was not present in the water the next day, or subsequently, whereas eDNA was detectable in the sediment for 12 months. In the sediment core samples, jellyfish eDNA was detected at high concentrations above the layer with the highest content of polycyclic aromatic hydrocarbons, reflecting tsunami-induced oil spills. Thus, marine sediment eDNA preserves a record of target species for at least one year and can be used to reconstruct past faunal occurrence.

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.

Feeding Habits of the Jack Mackerel Trachurus japonicus in the Southern Sea of the Republic of Korea

Feeding Habits of the Jack Mackerel Trachurus japonicus in the Southern Sea of the Republic of Korea

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.

Temperature effect on the maximum swimming speed of jack mackerel Trachurus japonicus through muscle contraction monitoring

Temperature effect on the maximum swimming speed of jack mackerel Trachurus japonicus through muscle contraction monitoring

Biomass-dependent emission of environmental DNA in jack mackerel Trachurus japonicus juveniles.

Environmental DNA (eDNA) from juvenile jack mackerel Trachurus japonicus was detected in tanks with 1, 3, 10, or 30 individuals per tank. Quantitative PCR using a set of species-specific primers and a probe revealed that the concentration of eDNA increased almost linearly with the density of fish. The coefficient of determination (R2 ) in the linear regression was lower than values previously reported for freshwater fishes in similar settings.

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.

Fatigue analysis of the jack mackerel Trachurus japonicus by electrocardiographic monitoring during prolonged swimming

The effect of fatigue on swimming performance was examined by measuring the swimming endurance time and heart rate of the jack mackerel Trachurus japonicus [15.7 ± 0.8 cm fork length (FL), n = 15] during forced exercise in a flume tank at fixed swimming speeds of 4, 5 and 6 FL/s. Electrocardiographic (ECG) monitoring during the experimental process from control (0.8 FL/s) to exercise phase revealed a rapid cardiac response of T. japonicus to the elevation of swimming speed. The heart rate of T. japonicus significantly increased from the control level of 52.9 beats/min at a slow flow speed of 0.8 FL/s to 148.2 beats/min at 4 FL/s, 168.6 beats/min at 5 FL/s and 183.2 beats/min at 6 FL/s. During the fixed speed test, the heart rate of each individual fish was stabilized without any recognizable increase or decrease until the fish failed to swim because of fatigue. Fatigue analysis on endurance time demonstrated that prior swimming experience at prolonged speeds would impair the endurance performance during subsequent swimming exercise. Recovery time of the heart rate after the fish was fully exhausted by prolonged fast exercise increased with increasing swimming endurance time.

Ontogenetic changes of feeding habits of larval jack mackerel Trachurus japonicus in the Kuroshio frontal area of the southern East China Sea

The gut contents of 575 larvae of jack mackerel Trachurus japonicus collected both day and night in seven depth layers (0–10, 10–20, 20–30, 30–40, 40–50, 50–70, and 70–100 m) using a 3 m2 mouth area frame net at Sta. V (27° 50′N, 126° 00′E) on 26–27 February 2003 in the Kuroshio frontal area of the southern East China Sea were examined. Copepods formed 99.0 % of larval gut contents, and larvae less than 5 mm body length (BL) in the 0–10 m layer fed mainly on copepod nauplii and copepod eggs while they hardly fed on highly mobile copepod copepodites which were the same size as eggs. Gut contents of larvae less than 5 mm BL showed differences between the 0–10 m layer and the 10–20 m layer, with potential reasons for such differences relating to visual acuity. Larvae of 5 mm BL or more fed mainly on copepod copepodites and copepod eggs at 0–30 m depth and mainly on copepod copepodites at depth greater than 30 m.

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.

Heart rate and muscle performance during forced swimming of jack mackerel Trachurus japonicus at different temperatures

The physiological condition of jack mackerel [18.3 ± 1.2 cm fork length (FL), n = 24] was simultaneously monitored using electrocardiography (ECG) and electromyography (EMG) techniques during swimming exercise in a flume tank at different temperatures of 10, 15 and 22 °C. To monitor the effect of temperature on the threshold level of the maximum sustainable speed, EMG demonstrated that the initiation of ordinary muscle activity at the lowest temperature (10 °C) occurred at swimming speeds of 3.2–3.5 FL/s, which was slower than the activation speeds at 15 and 22 °C of 4.0–5.4 FL/s. Ordinary muscle became active with increasing swimming speed which subsequently resulted in the frequency, amplitude and duration of burst discharge. ECG and EMG monitoring showed that the heart rate started to increase at the sustained speed level before the threshold and markedly increased up to the maximum level of heart rate at the higher speed. The index of ordinary muscle power output at the lowest temperature of 10 °C was lower than at higher temperatures of 15 and 22 °C. The heart rate increased with the increasing power output of ordinary muscle for all temperatures.

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.

Temperature effect on heart rate of jack mackerel Trachurus japonicus during swimming exercise

The heart rate of jack mackerel [16.5–21.2 cm fork length (FL), n = 24] was examined through forced swimming exercise in a flume tank by 10-min step-ups of speed levels in 1.5–6.0 FL/s range at different temperatures of 10, 15, and 22 °C. Electrocardiograph (ECG) monitoring was conducted by comparing the heartbeat pattern in still water without flow as a control, and continuously during exercise by speed levels until fatigue and during the recovery phase. Average heart rates in the control at each temperature were 36.5 beats/min at 10 °C, 56.1 beats/min at 15 °C, and 75.2 beats/min at 22 °C. The heart rate of jack mackerel significantly increased as the swimming speed was increased in each temperature. At the lower swimming speed of 1.5–2.4 FL/s, the heart rate was the same level as the control value at each respective temperature. The heart rate started to increase at swimming speeds of 2.3–2.5 FL/s at all temperatures. The higher heart rate in the range of 150–200 beats/min was achieved at a swimming speed of 6.0 FL/s at 22 °C. The recovery time after the maximum heart rate at high speed became longer at high temperatures.

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.