MOTU analysis of ichthyoplankton biodiversity in the upper Yangtze River, China

Abstract

SummaryIdentification of ichthyoplankton is difficult because fish during early life stages often lack stable morphological characteristics; such difficulty in species identification can be a major hindrance in conducting ichthyoplankton surveys for fish biodiversity investigations. Here, we evaluated the feasibility of a molecular operational taxonomic unit (MOTU) approach for ichthyoplankton investigations, and describe fish biodiversity in the Jinshajiang section of the upper Yangtze River, China. The MOTUs were established by grouping specimens diverging less than 1.00% Kimura two-parameter (K2P) distance units from their nearest neighbor within the same MOTU, based on previous work on between-species divergences of the mitochondrial cytochrome C oxidase subunit I (COI) gene. Taxonomic assignment of the MOTUs was performed by comparing the MOTU sequences with the COI sequences of taxonomic species. Sixty-eight MOTUs were inferred from 818 COI sequences of ichthyoplankton in the Jinshajiang river section. Among those, one MOTU was composed of two identified taxonomic species, and each of the other MOTUs was linked to a single, identified taxonomic species. Only 26 MOTUs were successfully identified to taxonomic species due to the limited reference database. Our results demonstrate that the MOTU approach can be applied successfully for analyzing biodiversity and identifying species of freshwater ichthyoplankton. Compared with previous ichthyoplankton investigations the richness of ichthyoplankton was very high. High diversity of ichthyoplankton noted in our study suggests that the Jinshajiang section should be an important target for fish biodiversity conservation in the Yangtze River.

Patterns of larval fish assemblages along the direction of freshwater input within the southern branch of the Yangtze Estuary, China: implications for conservation

“…The collections were immediately preserved in 4% formalin solution buffered with sodium borate. Larval fish were picked out and identified in the laboratory using combined molecular and morphological analyses (Cheng et al 2013;Ren et al 2016). For larval fish specimens with mitochondrial cytochrome c oxidase subunit I (COI) gene sequences that were not included in the collection of known COI gene sequences, morphological characteristics were used for identification to the lowest possible taxon according to Okiyama (1988) and Cao et al (2007).…”

Potential effects of dam cascade on fish: lessons from the Yangtze River

“…Construction of the dams may fragment their populations. It is suggested that these fragmented populations will have their gene flows blocked, thereby increasing inbreeding, decreasing effective population size, and thus reducing fitness (Alo and Turner 2005;Cheng et al 2013b;Roberts et al 2013). Furthermore, commercial fisheries in the upper Yangtze have been mainly supported by some of these species, such as A. wangi, C. guichenoti, P. pingi, and P. rabaudi among others.…”

The spatial pattern of larval fish assemblages in the lower reach of the Yangtze River: potential influences of river–lake connectivity and tidal intrusion

“…Briefly, specimens were first identified at the species level based on morphology when possible and verified through COI (mitochondrial cytochrome oxidase subunit I) gene sequence analysis by comparing to a collection of COI gene sequences of known species based on adults (Cheng et al, 2013). Specimens that could not be determined of species from morphology were first categorized based on morphological similarity.…”

“…Three to five representative specimens of each morphological category were selected and photographed under a dissecting microscope to record key morphological characteristics. The COI gene sequences of these specimens were then analyzed and compared to the collection of COI gene sequence of known species (Cheng et al, 2013). For specimens with COI gene sequences that were not included in the collection of COI gene sequence of known species, morphological characteristics were used to identify these specimens to the lowest possible taxa using appropriate literature (Cao et al, 2007).…”