Morphology of pelagic fish eggs identified using mitochondrial DNA and their distribution in waters west of the Mariana Islands

Fish eggs collected in the West Mariana region of the western North Pacific (7A degrees-18A degrees N, 137A degrees-144A degrees E) were identified using mitochondrial 16S ribosomal RNA (16S rRNA) gene sequences, and their morphology and distribution were analyzed. Of the 5,321 eggs collected, 2,698 live eggs were morphologically divided into 108 types based on the character of shape, diameter, chorion, oil globule, pigmentation, yolk segmentation and perivitelline space. Excluding 20 types of formalin preserved eggs, partial sequences of 16S rRNA gene (1,019-1,190 base pairs) obtained for all remaining 88 types of ethanol preserved eggs were compared with sequences deposited in the DDBJ/EMBL/GenBank using Basic Local Alignment Search Tool. This resulted in 16 species being genetically identified and their morphological characters were observed including the first description of the eggs of three species, Ventrifossa garmani, Diodon hystrix, and Scopelogadus mizolepis. Distribution analysis showed that 52-100% eggs of eight species, Katsuwonus pelamis, D. hystrix, S. mizolepis, Thunnus spp., Xiphias gladius, Cepalopholis spp., Naso spp. and V. garmani were collected around seamounts of the West Mariana region, whereas the other eight species, Lampris guttatus, Oxyporhamphus micropterus, Ranzania laevis, Istiophorus platypterus, Exocoetidae spp., Lactoria diaphana, Tetrapturus angustirostris and Regalecus glesne showed no tendency to be concentrated around the seamounts and were widely distributed through the study area. These distributional patterns of eggs appeared to correspond well with the life histories of each species. The present study suggests that DNA species identification can provide a significant new tool for ecological studies on fish eggs.