マサバとゴマサバ仔魚の黒色素胞形成および体形の比較：形態による種同定の再検討

抄録

Chub mackerel Scomber japonicus and spotted mackerel S. australasicus are important fishery resources in the western North Pacific and its adjacent seas. Larval morphology of these two species is similar, and no clear conclusion has been reached as to whether it is possible to distinguish larvae of the two species based solely on morphological characteristics. Using specimens fixed and preserved under the same conditions, we compared the larval morphology of S. japonicus and S. australasicus to investigate the possibility of morphological species identification. We used a total of 1,172 Scomber spp. larvae of <9mm in body length (BL) collected in the southern East China Sea during February and March, 2004–2010. After observing morphometric characteristics and pigmentation, the species of each larva was identified by using polymerase chain reaction–restriction fragment length polymorphism analysis of mitochondrial DNA (mtDNA). We identified 590 S. japonicus and 582 S. australasicus larvae. There was no interspecific difference in BL at notochord flexion. In larvae of <7mm BL, the frequency of occurrence of internal melanophores at the nape was significantly higher in S. australasicus than in S. japonicus. In larvae of 3.0–6.9mm BL, the number of melanophores in a series along the ventral midline of the tail was significantly lower in S. australasicus than in S. japonicus. Pre-anal length relative to BL and head length relative to BL were significantly higher in S. australasicus than in S. japonicus in larvae of <4mm BL and4.0–6.9mm BL, respectively. We applied discriminant analysis to use these characteristics to differentiate the species, but the accuracy rate was relatively low (76%) because of large overlaps in ranges of the characteristics for the two species. We conclude that mtDNA analysis is necessary to accurately identify larvae of these two Scomber spp.