Genetic pattern and demographic history of cutlassfish (Trichiurus nanhaiensis) in South China Sea by the influence of Pleistocene climatic oscillations.

Trichiurus nanhaiensis is one of the most important commercial fish species in the South China Sea. This study aimed to investigate the level of genetic variation and population genetic structure of T. nanhaiensis in the South China Sea for the first time, using 281 individuals collected from seven locations along the coast of mainland China, Taiwan, and Hainan Island. A high level of haplotype diversity and low nucleotide diversity were detected in the mitochondrial DNA cyt b gene and nuDNA RYR 3 gene. The overall expected heterozygosity (He = 0.693) among the seven populations ranged from 0.681 to 0.706 in microsatellite DNA data, which revealed high levels of genetic diversity. Significant genetic differentiation was found in Taidong populations in Taiwan, revealing the prevention of gene flow caused by the Kuroshio Current. Two major lineages based on the cyt b gene suggested that the Taiwan Strait acted as a geographic barrier for T. nanhaiensis during the glacier periods in the late Pleistocene. The Bayesian skyline plot also revealed that population demographic expansion of T. nanhaiensis was estimated to have occurred in 0.1 Mya. Our results indicated that all populations of T. nanhaiensis had experienced a recent genetic bottleneck following recent expansion based on ABC analysis.

Demographic history and population genetic structure of Anisakis pegreffii in the cutlassfish Trichiurus japonicus along the coast of mainland China and Taiwan.

Studying the genetic diversity of nematode parasite populations is crucial to gaining insight into parasite infection dynamics and informing parasite phylogeography. Anisakiasis is a zoonotic disease caused by the consumption of infectious third-stage larvae (L3) of Anisakis spp. carried by marine fish. In the present study, a total of 206 mitochondrial DNA sequences (cytochrome c oxidase 2, cox2) were used to study the genetic diversity, genetic structure, and historical demography of twelve A. pegreffii populations from Trichiurus japonicas along the coast of mainland China and Taiwan. Two distinct evolutionary lineages of A. pegreffii and no significant genealogical structures corresponding to sampling localities suggested that isolation in the marginal seas shaped their patterns of phylogeographic distribution along the coast of mainland China and Taiwan during glaciation with lower sea levels. Furthermore, pairwise FST values and AMOVA did not indicate any significant genetic differentiation among groups with no relation to the geographic area, which might be attributed to fewer barriers to gene flow as well as large population sizes. The results of the neutrality test, mismatch distribution, and Bayesian skyline plot analyses showed that entire population underwent population expansion during the late Pleistocene. Analysis of the demographic history revealed that A. pegreffii underwent historical lineage diversification and admixture due to secondary contact based on ABC analysis. The present research represents the first definitive population structure and demographic history across sampling locations of A. pegreffii along the coast of mainland China and Taiwan.

Complete mitogenomes of four Trichiurus species: A taxonomic review of the T.lepturus species complex.

Four Trichiurus species, T.japonicus, T.lepturus, T.nanhaiensis, and T.brevis, from the coasts of the China Seas, have been identified and their entire mitochondrial genomes (mitogenomes) have been sequenced by next-generation sequencing technology. A comparative analysis of five mitogenomes was conducted, including the mitogenome of T.gangeticus. The mitogenomes contained 16.568-16.840 bp and encoded 36 typical mitochondrial genes (13 protein-coding, 2 ribosomal RNA-coding, and 21 transfer RNA-coding genes) and two typical noncoding control regions. Although tRNAPro is absent from Trichiurus mitogenomes, when compared with the 22 tRNAs reported in other vertebrates, the gene arrangements in the mitogenomes of the studied species are consistent with those in most teleost mitogenomes. The full-length sequences and protein-coding genes (PCGs) in the mitogenomes of the five species had obvious AT biases and negative GC skew values. Our study indicate that the specimens in the Indian Ocean are neither T.lepturus nor T.nanhaiensis but they are T.gangeticus; the Trichiurus species composition in the Indian Ocean is totally different from that in Pacific and Atlantic oceans; there are at least two Trichiurus species in Indian Ocean; and the worldwide systematics and diversity of the genus Trichiurus need to be reviewed.

Changes in the trophic niche of Trichiurus japonicus in the Beibu Gulf in different periods.

We measured stable carbon and nitrogen isotopes and calculated trophic level and trophic niche of Trichiurus japonicus, with samples collected from the Beibu Gulf from 2008 to 2009 and 2018. The differences between two periods were compared and analyzed to explore the changes of its ecological adaptation. The results showed that value of δ13C varied substantially between the two periods. The narrowed range and the smaller mean value of δ13C in 2018 suggested that their food source changed from upper-middle to lower-middle waters. The values of δ15N were stable, and the range and mean values of trophic level (3.38-3.43) did not change significantly, which indicated a stable trophic level of T. japonicas in the past decade. The correlation between δ13C and preanal length was not significant, but a positive correlation between δ15N and preanal length. In terms of trophic niche, the indicators had decreased in different degrees in 2018 with 1.1%-32.1%. The value of total area and standard ellipse area decreased from 20.20 and 4.68 to 14.20 and 3.18, respectively, indicating that the niches of T. japonicas in the Beibu Gulf had varied obviously and that their ability to use resources and adapt to the environment had declined. It was speculated that in the past decade, the mean trophic level of T. japonicas in the Beibu Gulf had not changed significantly. Due to the change of food sources, however, the diversity of trophic sources had decreased, and the trophic niche had become smaller.

[Trophic structure of pelagic fishery organism assemblage in the central and western South China Sea in spring revealed by carbon and nitrogen stable isotope analysis]. / åŸºäºŽç¢³æ°®ç¨³å®šåŒä½ç´ çš„å—æµ·ä¸­è¥¿éƒ¨æµ·åŸŸæ˜¥å­£ä¸­ä¸Šå±‚æ¸”ä¸šç”Ÿç‰©ç¾¤è½è¥å »ç»“æž„.

Carbon and nitrogen stable isotope analysis was carried out on pelagic fishery organisms caught in light traps and falling nets in the central and western South China Sea in the spring of 2018. The stable isotope values of the sampled individuals were used to elucidate the isotopic variations for the pelagic fishery organisms, to classify species into trophic functional groups, and to compare the differences of trophic structure among the classified trophic functional groups. The results showed that among 23 fishery species the mean δ13C value of Coryphaena hippurus was the lowest (-17.58‰±0.21‰), and that of Grammistes sexlineatus was the highest (-19.86‰±0.33‰). The mean δ15N values ranged from 8.31‰ in Psenes cyanophrys to (12.46±0.74)‰ in Chirocentrus dorab. The continuous trophic spectrum indicated that the trophic level (TL) for the sampled pela-gic fishery organisms ranged from 3.01 to 4.23, of which 19 species (83% of the total) fell between TL 3.0 and 4.0. The 23 species of fishery organisms were classified into three trophic functional groups, i.e., plankton feeding functional group (PFFG), nekton feeding functional group (NFFG), and mixed feeding functional group (MFFG). The analysis of standard ellipse area (SEA) showed that the PFFG occupied the largest trophic niche width (SEA=1.56‰2), followed by the MFFG (SEA=0.99‰2) and NFFG (SEA=0.31‰2). The MFFG overlapped with PFFG and NFFG in the trophic niche, with a relative percentage of 17% and 26%, respectively. There was no overlap between PFFG and NFFG.

[The breadth and overlap of ecological niche of major fish species in the Minjiang River Estuary, China.] / é—½æ±Ÿå£ä¸»è¦æ¸”èŽ·é±¼ç±»çš„ç”Ÿæ€ä½å®½åº¦ä¸Žé‡å .

Based on the seasonal bottom trawl surveys in the Minjiang River Estuary in 2015, the breadth and overlap of ecological niche of major fish species were analyzed. Those fish species were identified based on the index of relative importance (IRI). A total of 137 species belonging to 37 families and 16 orders were collected. Fifteen major fish species were determined by the IRI, including six dominant species Polydactylus sextarius, Harpadon nehereus, Pennahia argentata, Secutor ruconius, Cynoglossus abbreviates, Coilia mystus, and nine important species Collichthys lucidus, Amblychaeturichthys hexanema, Upeneus japonicas, Lagocephalus spadiceus, Pampus argenteus, Larimichthys crocea, Thryssa kammalensis, Takifugu oblongus, Lepturacanthus savala. Seven species whose spatio-temporal niche breadth was higher than 1 in a declining order were C. abbreviates, C. lucidus, S. ruconius, A. hexanema, T. kammalensis, C. mystus, H. nehereus. The ecological niche of major fish species in the Minjiang River Estuary showed obvious seasonal dynamics. The percentage of species pairs with spatio-temporal niche overlap at the meaningful level was as high as 81.9%. Six species pairs reached significant ecological niche overlap, indicating that major fish species had similar distribution at the spatial and temporal scales and the existence of resource utilization competition. The species pairs of U. japonicus-L. savalawas had the highest spatio-temporal niche overlap value, whereas U. japonicus-C. lucidus had the lowest niche overlap value. The spatio-temporal niche overlap of major fish species in the Minjiang River Estuary had substantial seasonal variation.

[Applying multi-model inference to estimate growth parameters of greater lizard fish Saurida tumbil in Beibu Gulf, South China Sea].

Age and growth parameters are key parameters in fish stock assessment and management strategies, thus it is crucial to choose an appropriate growth model for a target species. In this study, five growth models were set to fit the length-age data of greater lizard fish Saurida tumbil (n = 2046) collected monthly from December 2006 to July 2009 in the Beibu Gulf, South China Sea. The parameters for each model were estimated using the maximum likelihood method under the assumption of the additive error structure. Adjusted coefficient of determination (R2adj), root mean squared error (RMSE), Akaike's information criterion (AIC), and Bayesian information criterion (BIC) were calculated for each model for fitness selection. The results indicated that the four statistical approaches were consistent in selection of the best growth model. The MMI approach indicated that the generalized VBGF was strongly verified and made up 95.9% of the AIC weight, indicating that this function fitted the length-age data of the greater lizard fish well. The growth function was Lt = 578.49 [1-e -0.05(t-0.14) 0.361.

[Feeding habits of Trichiurus lepturus in Beibu Gulf of South China Sea].

From August 2008 to September 2009, the feeding habits of Trichurus lepturus L. in Beibu Gulf of South China Sea were studied by monthly sampling and stomach content analysis. In study area, T. lepturus was euryphagous, which fed on fish, cephalopoda, benthic crustacean, and zooplankton, etc., among which, Bregmaceros rarisquamosu, Decapterus maruadsi, and Acetes chinensis were the main prey components, accounting for 37.99%, 16.42%, and 10.03%, respectively. D. maruadsi and Anchoviella heteroloba appeared throughout the Beibu Gulf all year round, and could be served as the index species for the migration and fishing ground distribution of T. lepturus. The indices feeding intensity and stomach fullness differed significantly among seasons (P < 0.001); while the index prey diversity had no significant seasonal difference (P > 0.05), which peaked in autumn and had an annual average value of 1.97. Cluster analysis revealed that when the preanal length of T. lepturus was 190 mm, i. e., at 50% of maturity length, a clear diet shift happened, from small zooplankton, pelagic fishes, and crustacean for the juveniles to predominantly larger fish and cephalopoda for the adults.