The chub mackerel Pneumatophorus japonicus distributes in Indo-Pacific Oceans and occurs along coastal waters of China, including the East China, South China and Yellow Seas. With the fishery collapses of the three top commercial marine fishes (the large yellow croaker Pseudosciaena crocea, the little yellow croaker P. polyactis and the largehead hairtail Trichiurus lepturus), the fishery of P. japonicus has become important since the 1980s. Based on the migration pattern, morphological and biological characteristics, and tagging experiment, two populations of P. japonicus were initially identified in the Taiwan Strait, i.e. the East China Sea population in eastern Fujian and population in Southern Fujian-Estern Guangdong.
Knowledge on population structure is essential for developing fisheries management and conservation measures. In this study, specimens of P. japonicus were sampled from eastern and southern Fujian waters in 2009-2010, with total lengths of 204.7-300.2 mm (n =30) and 214.1-311.5 mm (n =30), respectively. Amplified fragment length polymorphism (AFLP) was used to analyze the genetic diversity and variation of the East China Sea and Southern Fujian-Estern Guangdong populations in the Taiwan Strait and its adjacent waters. AFLP bands were scored for presence (1) or absence (0) and transformed into 0/1 binary character matrix. AMOVA was performed in Arlequin 3.1. Number of polymorphic loci, Nei genetic diversity, Shannon genetic diversity index, genetic similarity and genetic distance between populations, coefficient of gene differentiations (G _st), gene flow (N_m) and dominant gene frequency were conducted in POPGENE 1.31.
A total of 497 loci ranging in size from 100 bp to 1000 bp were detected from 60 specimens of P. japonicus based on eight primer combinations, of which 343 were polymorphic; however, no population specific band was found. The number of bands per primer combination varied from 50 to 81 and the polymorphic bands per primer combination ranged from 60.00% to 94.29%. The proportion of polymorphic loci, the Nei genetic diversity and Shannon genetic diversity index had no significant difference (P >0.05) between the two populations with 57.75%, 0.1779 and 0.2725 in eastern Fujian waters, and 64.59%, 0.2123 and 0.3228 in southern Fujian waters, respectively. The G _st value, Shannon genetic diversity index and AMOVA analysis showed that the genetic variation mainly existed among individuals within population. N_m showed the frequent gene flow between the two populations. Dominant gene frequency revealed that both populations had a similar genetic structure. This study reveals that the genetic diversity of the two initially proposed populations is at the same level. We propose that the stocks of P. japonicus in the Taiwan Strait belong to the same population. Further studies using co-dominant markers are needed for a better understanding of the population genetics of P. japonicus.
The genetic diversity of P. japonicus in the Taiwan Strait is considerably higher than some commercially important marine fishes in coastal waters of China, such as the Hong Kong grouper Epinephelus akaara, Yellow drum Nibea albiflora, Barfin flounder Verasper moseri and Silver pomfret Pampus argenteus. Wide distribution and short reproductive cycle may contribute to high genetic diversity of P. japonicus. Annual migrations and larval drift in the ocean currents can explain the genetic homogeneity in the studied areas. Currently, the fishery of P. japonicus in southern Fujian waters remains stable; however, it shows a decline in eastern Fujian waters. Therefore, timely and effective management can ensure the sustainable use of P. japonicus wild stocks in China.