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Small omnivorous fish often dominate in subtropical shallow lakes, and they may affect the community structure of aquatic organisms on at least two trophic levels. However, in the study of aquatic food webs in subtropical lakes, most ecologists have focused on the effects of large-sized omnivorous species (e.g. common carp), studies of small-sized species being scarce. We conducted a mesocosm experiment with two treatments (fish presence and absence) to examine the effects of a small-sized omnivore, bitterling (Acheilognathus macropterus), on phytoplankton, zooplankton and benthic macroinvertebrates. Our results showed that bitterling presence significantly increased the chlorophyll a concentration and biomass of phytoplankton, which became dominated by cyanobacteria (mainly Aphanizomenon spp.) that accounted for >99% of both total phytoplankton abundance and biomass. Both the abundance and biomass of zooplankton were also higher in the fish-present treatment, but small rotifers became dominant, and the zooplankton:phytoplankton biomass ratio decreased, indicating less grazing on phytoplankton. Moreover, both the abundance and biomass of benthic macroinvertebrates (tubificids) were higher in the bitterling-present treatment than in the controls, which is opposite to the situation found when omni-benthivorous fish (e.g. crucian carp) dominate. Higher biomass of tubificids may, in turn, result in higher sediment nutrient release. Our study suggests that A. macropterus, and maybe also other bitterling species, can alter both pelagic and benthic assemblages via both top-down and bottom-up control effects and lead to more turbid water in eutrophic lakes. Thus, more attention should be paid to these small omnivorous species in the restoration and management of shallow subtropical lakes.

The knowledge of prey small fish stock, distribution and abundance is necessary to guide stocking of piscivorous fish for the biomanipulation in domestic tap water lakes. This study describes the current status of small fish community in Lake Kuilei (China), and examines the spatial and seasonal variations of the community in relation to key environmental factors. Based on submerged macrophyte cover and water depth, the lake was divided into five major habitats: (1) macrophyte covered shallow habitat of water depth < 2.00 m, (2) uncovered or less-covered shallow habitat (2.00 m–3.50 m), (3) uncovered medium shallow habitat (3.50 m–5.00 m), (4) uncovered medium deep habitat (5.00 m–6.50 m) and (5) uncovered deep habitat (6.50 m–8.50 m). The abundance and composition of small fish were monitored by benthic fykenet sampling from April 2013 to January 2014. A total of 2881 individuals belonging to 5 families and 21 species were collected. Based on their abundance (accounted for 88.96% of the total) and occurrence (more than 33.33%), Acheilognathus chankaensis, Acheilognathus macropterus, Microphysogobio microstomus, Pseudorasbora parva and Rhinogobius giurinus were recognized as dominant small fish species. The results of correlation analysis identified that species richness ( Sr ), Shannon-Wiener diversity index ( H′ ) and Margalef′s richness index ( D ) were significantly negatively correlated with water depth, but positively correlated with biomass of submerged macrophytes.Redundancy analysis (RDA) revealed that the spatial distributions of most small fishes were negatively associated with water depth. The details of these findings are beneficial to understanding the adaptation of the small fishes in degraded environments, and to developing suitable biomanipulation strategies for the management of fish resources and water quality in the lakes along the lower reach of the Changjiang (Yangtze) River basin.

Omnivorous fishes are prevalent in warm waters and may have strong impacts on water quality by excreting nutrients and reducing periphyton biomass. However, most studies have focused on large-sized species and overlooked the role of small omnivores. Filter-feeding mussels may modulate the negative effects of small omnivorous fishes on water quality, and stocking of mussels has been frequently used in shallow eutrophic freshwaters in China to improve the water clarity. However, the mechanisms behind such management practices are poorly studied. We conducted a mesocosm experiment to examine the ecosystem effects of the bitterling Acheilognathus macropterus as modulated by the mussel Sinanodonta woodiana, one of the mussels upon which it relies for breeding. We hypothesized that bitterling would exert negative effects on the lake environment, specifically higher phytoplankton biomass and lower water clarity, but that these effects might be alleviated by the filter-feeding activities of S. woodiana. In a 56-d mesocosm experiment with and without bitterling in the presence and absence of mussels, we found interactive effects of bitterling and mussels. In mesocosms with bitterling, nutrient concentrations, phytoplankton biomass, and total suspended solids (TSS) increased, but there were no changes in periphyton biomass in the mussel-free treatments. In contrast to the effects of large-sized omnivorous fishes reported from the literature, bitterling mainly affected TSS levels by increasing organic suspended solids rather than inorganic solids, indicating weak effects on sediment resuspension. However, the presence of mussels alleviated the negative effects of bitterling by decreasing nutrient levels, phytoplankton biomass, and TSS concentrations. Mussels alone had no effects on periphyton biomass, but the mussel–bitterling interactions boosted the growth of periphyton. Our study suggests that the negative effects of bitterling on water quality (e.g., increased nutrient concentrations and phytoplankton biomass) are alleviated by the presence of filter-feeding mussels, but the stimulatory interactive effects of mussels and bitterling on periphyton may impair the recovery of submerged macrophytes.

Transplantation of submerged macrophytes has been widely used to improve water quality in restoring shallow lakes in China. However, in some lakes, small omnivorous fish predominated the fish assemblages and fed mainly on submerged macrophytes. Despite significant research examining grazing selectivity in herbivorous fishes, macrophyte feeding preferences of small omnivorous fishes are poorly understood. We conducted a mesocosm experiment to examine the effects of a prolific small omnivorous bitterling fish Acheilognathus macropterus on the relative growth rate (RGR) and biomass of submerged macrophytes (Ceratophyllum demersum, Myriophyllum spicatum, Vallisneria denseserrulata, and Hydrilla verticillata). Our results showed that the presence of A. macropterus significantly increased nutrient concentrations (e.g. total nitrogen and total phosphorus). The RGR of C. demersum in the bitterling-present treatment was significantly lower than the controls, in the presence of other macrophyte species. Further, total biomass of the four species of macrophytes in the fish-present mesocosms was markedly lower than in the fish-absent treatment, suggesting considerable consumption of macrophytes by bitterling. Moreover, the percent biomass of V. denserrulata and H. verticillata were significantly enhanced by the presence of bitterling. Our findings suggest that A. macropterus may increase nutrient concentrations through excretion and reduce the biomass and RGR of certain submerged macrophytes which may shift macrophyte community structure via selective grazing.

The Yangtze River is the longest river in China and is divided into upstream and mid‐downstream regions by the Three Gorges (the natural barriers of the Yangtze River), resulting in a complex distribution of fish. Dramatic changes to habitat environments may ultimately threaten fish survival; thus, it is necessary to evaluate the genetic diversity and propose protective measures. Species identification is the most significant task in many fields of biological research and in conservation efforts. DNA barcoding, which constitutes the analysis of a short fragment of the mitochondrial cytochrome c oxidase subunit I (COI) sequence, has been widely used for species identification. In this study, we collected 561 COI barcode sequences from 35 fish from the midstream of the Yangtze River. The intraspecific distances of all species were below 2% (with the exception of Acheilognathus macropterus and Hemibarbus maculatus). Nevertheless, all species could be unambiguously identified from the trees, barcoding gaps and taxonomic resolution ratio values. Furthermore, the COI barcode diversity was found to be low (≤0.5%), with the exception of H. maculatus (0.87%), A. macropterus (2.02%) and Saurogobio dabryi (0.82%). No or few shared haplotypes were detected between the upstream and downstream populations for ten species with overall nucleotide diversities greater than 0.00%, which indicated the likelihood of significant population genetic structuring. Our analyses indicated that DNA barcoding is an effective tool for the identification of cyprinidae fish in the midstream of the Yangtze River. It is vital that some protective measures be taken immediately because of the low COI barcode diversity.

Fish assemblage will change along with the river habitat environment. In order to find the response degree of fish assemblage to fish culture within low-head-dam water,two low-head dams( including the upstream and downstream dams) of the Wulong River( a tributary of the lower reach of the Yangtze River,China) were selected as sampling sites,where the habitat variables,the fish diversity and fish assemblage structure were surveyed for 6 times from 2013 to 2014 in these wadeable reaches of the sampling sites. A total of 24 fish species which belong to 5 orders,21 genera and 24 species were caught,with dominant Cyprinidae accounting for 58. 3% of the total. After an analysis on the influences of temporal changes and local habitat conditions upon the fish assemblage,seasonal factors were found to have no apparent effect on the fish assemblage structure. The spatial location( the upstream dam or the downstream dam) affected the assemblage's structural differences significantly,which were determined by the abundance of Hemiculter leucisculus,Abbottina rivularis,Rhodeus sinensis,Acheilognathus macropterus in the upstream site,and the abundance of Gambusia affinis in downstream site. Besides,all the three habitat variables including dissolved oxygen,conductivity and current velocity exerted a great impact on the fish assemblage. The differences in habitat environment bring about some great influences on the fish assemblage,showing in the dramatic decrease of capture weight,quantity,density and diversity of fish in the sampling sites of the downstream dam,which are probably caused by the fish culture within the low-head dam.

A new species of the bitterling genus Acheilognathus, Acheilognathus changtingensis sp. nov., was recently discovered from Changting County in Hanjiang River, Fujian Province, Southeastern China. It can be diagnosed by the following combination of characters: dorsal fin with three simple and 15 (occasionally 14) branched fin rays, anal fin with three simple and 12 (occasionally 11) branched fin rays; dorsal fin pale and anal fin slightly pale; white spots on anal-fin rays forming a transverse band, and anal fin margined with white band in males. Its unique characters are the many dispersed black spots on the dorsal, anal, pelvic, caudal fins, and on the head. Using the mitochondrial cytochrome Jb gene as a molecular marker, we reconstructed phylogenetic trees of A. changtingensis sp. nov. and other species in Acheilognathus to confirm its taxonomic status and study its speciation. Analyses of both morphological and molecular data consistently indicated the taxonomic status of the present new species. The results also show that A. changtingensis sp. nov. and Acheilognathus macropterus are sister species that diverged about 14.50 MYA by geographical isolation.

In this study, thirty-six individuals of Acheilognathus macropterus were collected from the Heilongjiang River, the Yangtze River, and the Nandujiang River. Partial mitochondrial cytochrome b gene region (636 base pair) was sequenced to these samples and 22 haplotypes were found. With A. chankaensis and A. tokinensis as outgroups, their relationships were analyzed. The p-distances were calculated with Mega software and a molecular phylogenetic tree was constructed using the neighbor-joining (NJ) method. The proportions of main morphological characters were compared as well. P-distances showed that the genetic differences in A. macropterus samples were far smaller than those between these samples and the outgroups. The molecular phylogenetic tree shows that samples with barbels and those without barbels were intermingled. There was no distinctive difference in proportions of morphological characteristics among them. These results suggested that samples with barbels and those without barbels (formally identified as A. taenianalis) are the same species; A. taenianalis is synonymous with A. macropterus. The thirtysix individuals were grouped into five clades and the positions of the samples in the clades were correspondingly grouped within their geographical distributions. Among the five clades, clades 1 and 5 included samples from the Heilongjiang River and Nandujiang River respectively. The samples from the Yangtze River scattered into clades 2, 3, and 4. There were distinctive genetic differences (>5%) among them. Interestingly, the distributions of the 21 samples in these three clades were not correlated to their geographical distributions. It is postulated that these genetic differences were due to the bitterlings’ mating choice mechanism, the prozygotic isolation. The genetic differences between the fish from Nandujiang River and those from the mainland indicated that they were separated early. However, the small genetic differences among the samples and the positions of the fish from the Heilonjiang River in the molecular phylogenetic tree indicate that fish in Heilongjiang River might have dispersed from the Yangtze River to that area much later.

In bitterlings (Acheilognathinae) C- and Ag-banding karyotypes of 6 species-subspecies collected in China and South Korea were analyzed. The chromosomal constitution of 2n =46 (4 SM + 42 ST) in Rhodeus atremius fangi was quite different from that of 2n = 48 (8 M + 20 SM + 20 ST) in other species-subspecies in Rhodeus. It was concluded from the analysis of banded chromosomes that the increase in number of ST during the karyotype change from 2n = 48 to 2n = 46 was achieved by a series of pericentric inversions from 24 M-SM to 24 ST, and the decrease in the diploid number was caused by an additional tandem fusion of 4 ST chromosomes, forming a new ST pair in the 2n = 46 karyotype. The karyotype of Tanakia koreensis, T. signifer, and Acheilognathus macropterus is 2n = 48 (8 M + 20 SM + 20 ST), 2n = 48 (8 M + 20 SM + 14-16 ST + 4-6 A), 2n = 44 (14M + 16 SM + 14 ST), respectively. In R. ocellatus ocellatus, T. koreensis, T. signifer and A. macropterus, karyotype changes from 2n = 48 to 2n = 44 due to centric fusion and inversion have also been estimated. It was suggested that C-banding heterochromatin was greatly concerned with the karyotype evolution in bitterlings.

Summary The length-weight relationships (LWRs) are presented for eight freshwater fish species (Acheilognathus macropterus, Saurogobio dabryi, Saurogobio gymnocheilus, Sinobdella sinensis, Pelteobagrus eupogon, Rhinogobius cliffordpopei, Neosalanx jordani, and Silurus meridionalis) from the Yangtze River and Lake Taihu. A total of 1044 specimens were sampled and measured between July 2012 and June 2014. Among the eight species, five species have no LWR estimates in FishBase.

The complete mitochondrial genome was sequenced from one of the endemic bitterling fish in China. The mitochondrial genome sequence was 16,575 bp in size, and the gene order and contents were identical with the species of the same subfamily like T. lanceolata, T. limbata, Acheilognathus macropterus and A. yamatsutae. Five genes (COII, COIII, ND3, ND6, and CYTB) had an incomplete stop codon. Base composition of the genome is A (29.2%), T (27.4%), C (26.2%), and G (17.2%) with an A+T-rich feature (56.6%) as that of other vertebrate mitochondrial genomes.