Impact of Low-Head Dam Removal on River Morphology and Habitat Suitability in Mountainous Rivers.

Dam removal is considered an effective measure to solve the adverse ecological effects caused by dam construction and has started to be considered in China. The sediment migration and habitat restoration of river ecosystems after dam removal have been extensively studied abroad but are still in the exploratory stage in China. However, there are few studies on the ecological response of fishes at different growth stages. Considering the different habitat preferences of Schizothorax prenanti (S. prenanti) in the spawning and juvenile periods, this study coupled field survey data and a two-dimensional hydrodynamic model to explore the changes in river morphology at different scales and the impact of changes in hydrodynamic conditions on fish habitat suitability in the short term. The results show that after the dam is removed, in the upstream of the dam, the riverbed is eroded and cut down and the riverbed material coarsens. With the increase in flow velocity and the decrease in flow area, the weighted usable area (WUA) in the spawning and juvenile periods decreases by 5.52% and 16.36%, respectively. In the downstream of the dam, the riverbed is markedly silted and the bottom material becomes fine. With the increase in water depth and flow velocity, the WUA increases by 79.91% in the spawning period and decreases by 67.90% in the juvenile period, which is conducive to adult fish spawning but not to juvenile fish growth. The changes in physical habitat structure over a short time period caused by dam removal have different effects on different fish development periods, which are not all positive. The restoration of stream continuity increases adult fish spawning potential while limiting juvenile growth. Thus, although fish can spawn successfully, self-recruitment of fish stocks can still be affected if juvenile fish do not grow successfully. This study provides a research basis for habitat assessment after dam removal and a new perspective for the subsequent adaptive management strategy of the project.

Environmentally relevant concentrations of mercury inhibit the growth of juvenile silver carp (Hypophthalmichthys molitrix): Oxidative stress and GH/IGF axis.

Mercury (Hg) is a global environmental contaminant, and excessive mercury levels in water can adversely affect the growth of fish. Silver carp (Hypophthalmichthys molitrix) is one of the important freshwater aquaculture fish in China, and its natural resources have been critically declining. However, the effects of Hg2+ exposure on the growth hormone/insulin-like growth factor (GH/IGF) axis and its toxic mechanism are still unclear. In this study, we systematically evaluated the bioaccumulation, histomorphology, antioxidant status, hormone levels, and GH/IGF axis toxicity of juvenile silver carp after exposure to environmental-related concentrations of Hg2+ (0, 0.05, 0.5, 5, and 50 µg/L) for 28 days. Results showed that the Hg2+ bioaccumulation in the liver increased with a rise in Hg2+ concentration and time of exposure. The body length (BL), body weight (BW), weight growth rate (WGR) and specific growth rate (SGR) all decreased after Hg2+ exposure. The serum levels of growth hormones (GH and IGF) and thyroid hormones (T3 and T4) were significantly decreased, and the expressions of GH/IGF axis-related genes were significantly downregulated after 7, 14, and 28 days of Hg2+ exposure. Correlations between the growth parameters and growth hormones or expression of genes in GH/IGF axis further suggested that environmentally relevant concentrations of Hg2+ could have adverse effects on growth. In addition, with increasing Hg2+ exposure, superoxide activities of dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST)and levels of reduced glutathione (GSH) and malondialdehyde (MDA) were significantly increased, whereas the activity of glutathione peroxidase (GPx) significantly decreased and oxidative stress-related gene significantly changed. Liver lesions were mainly characterized by inflammatory cell infiltration, hepatocyte necrosis and fat vacuolation after exposure to Hg2+. Taken together, the results indicate that Hg2+ exposure leads to growth inhibition and oxidative stress in juvenile silver.

Population genetics and sympatric divergence of the freshwater gudgeon, Gobiobotia filifer, in the Yangtze River inferred from mitochondrial DNA.

The ecosystem and Pleistocene glaciations play important roles in population demography. The freshwater gudgeon, Gobiobotia filifer, is an endemic benthic fish in the Yangtze River and is a good model for ecological and evolutionary studies. This study aimed to decode the population structure of G. filifer in the Yangtze River and reveal whether divergence occurred before or after population radiation. A total of 292 specimens from eight locations in the upper and middle reaches of the Yangtze River were collected from 2014 to 2016 and analyzed via mitochondrial DNA Cyt b gene sequencing. A moderately high level of genetic diversity was found without structures among the population. However, phylogenetic and network topology showed two distinct haplotype groups, and each group contained a similar proportion of individuals from all sampled sites. This suggested the existence of two genetically divergent source populations in G. filifer. We deduced that a secondary contact of distinct glacial refugia was the main factor creating sympatric populations of G. filifer, and climate improvement promoted population expansion and colonization.

Genetic structure of two sympatric gudgeon fishes (Xenophysogobio boulengeri and X. nudicorpa) in the upper reaches of Yangtze River Basin.

BACKGROUND: Xenophysogobio boulengeri and X. nudicorpa are the only two species within the genus Xenophysogobio (Cyprinidae, Cypriniformes), and both are endemic to the upper reaches of the Yangtze River. In recent years, due to human activities, the natural resources available to both species have declined sharply. Sympatric species with overlapping niches inevitably compete for their habitats, and genetic structure and diversity can reflect population history and their potential for adaptation to changing environments, which is useful for management decisions. METHODS: In the present study, microsatellite DNA and mitochondrial DNA (mtDNA) markers were used to investigate the patterns of population genetic structure for X. boulengeri and X. nudicorpa. Microsatellite DNA data, jointly with traditional summary statistics including F ST and F is, were used to assess the population genetic structure by structure analysis. The mtDNA sequences were then used to examine these patterns through time to detect demographic history. RESULTS: Xenophysogobio boulengeri and X. nudicorpa exhibited high levels of genetic diversity in Yangtze River populations, except for two populations of X. nudicorpa in the Jinsha River, which were low in mtDNA diversity. X. boulengeri showed genetic homogeneity among populations, whereas X. nudicorpa appeared to have significant geographic genetic divergence. Both species experienced a late-Pleistocene sudden population expansion in Yangtze River populations, but not in the Jinsha River populations of X. nudicorpa. DISCUSSION: The genetic homogeneity of X. boulengeri populations might result from similar population expansion events and environment features. The geographic genetic subdivision for X. nudicorpa between the Jinsha and Yangtze Rivers might be caused by the geographic isolation in the middle Pliocene, as well as climate and environmental heterogeneity.

Species diversity of drifting fish eggs in the Yangtze River using molecular identification.

The dam constructions greatly changed the hydrologic conditions in the Yangtze River, and then significantly affected the spawning activities of indigenous river fish. Monitoring the species composition of drifting eggs during spawning season is important for protection issues. In this study, we have sampled drifting fish eggs in nine locations from 2014 to 2016. Eggs were identified using the mitochondrial cyt b gene sequence. A total of 7,933 fish eggs were sequenced successfully and blasted into the NCBI database. Thirty-nine fish species were identified, and were assigned to four families and two orders. Approximately 64% of the species identified, and 67% of the eggs, were classified in the Family Cyprinidae. Abundance and Shannon-Wiener diversity index of species were higher in the main river than in tributaries of the river. However, tributaries may be important spawning grounds for some fish species. The Jaccard's similarity index and river-way distances among sampled stations were negatively correlated suggesting the environment shapes species composition in the sampled spawning grounds. These results showed that mitochondrial DNA sequence is a powerful and effective tool for fish egg identification in Yangtze River and these data are useful for conservation efforts.

The mitochondrial genome of Gnathopogon imberbis (Cypriniformes, Cyprinidae).

In the present study, the complete mitogenome sequence of Gnathopogon imberbis is determined using PCR amplification and DNA sequencing, which contains 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes and a non-coding control region with the total length of 16,598 bp. Except for eight tRNA and ND6 genes, all other mitochondrial genes are encoded on the H-strand. The codon usage followed the typical vertebrate mitochondrial pattern (ATG or GTG for start codon and TAA or TAG for stop codon). The overall nucleotide composition was 30.0% A, 27.0% T, 25.8% C and 17.2% G, with an A + T bias of 57.0%. The complete mitochondrial genome sequence will be useful for phylogenetic analysis and studies of population genetics of G. imberbis.

Complete mitochodrial genome of the redlip loach Leptobotia rubrilaris (Teleostei, Cypriniformes: Cobitidae).

In this study, the complete mitochondrial genome sequence of the Leptobotia rubrilaris has been obtained. The genome includes 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes and a non-coding control region with the total length of 16,585 bp. The gene arrangement and composition were identical to other vertebrate. Most of the genes are encoded on heavy strand, except for eight tRNA and ND6 genes. The complete mitochondrial genome sequence of L. rubrilaris would contribute to better understand population genetics and protect its genetic diversity.

[Effects of surgically implanted dummy ultrasonic transmitters on grass carp Ctenopharyngodon idella].

In order to study the effects of surgically implanted dummy ultrasonic transmitters on grass carp Ctenopharyngodon idella, two experiments were conducted from October 2010 to December 2010 and November 2010 to October 2011. The results showed that surgical implantation of dummy ultrasonic transmitters had a significant negative influence on the growth of grass carp within 30 days following the surgery. However, the negative influence after 30 days faded away. One and two fish died during the 60-day and 360-day experiments, equivalent to the mortalities of 4.2% and 6.7%, respectively. All fish incisions were completely healed in 30 days after surgery, and all sutures were lost in 360 days after surgery. Two and one fish expelled the transmitters through the unclosed wound during the 60 days and 360 days, and the discharges were 8.7% and 3.3%, respectively. All the remaining transmitters were encapsulated in fibrous capsules and adhered to body wall, intestinal tract or viscera multiply. The result suggested that surgical implantation of ultrasonic transmitters could be applied to the ultrasonic telemetry research on grass carp. Nevertheless, the grass carp should be given for at least 30 days with the purpose of incision healing and growth recovery from the surgical procedure.

The mitogenome of Leptobotia microphthalma (Teleostei, Cypriniformes: Cobitidae).

The Leptobotia microphthalma belongs to family Cobitidae, which is endemic to the upper reaches of the Yangtze River in China. In this studying, the complete mitochondrial genome sequence of L. microphthalma has been obtained with PCR, which contains 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes and a non-coding control region with the total length of 16,512 bp. The gene arrangement and composition are similar to that of other vertebrates. Most of the genes are encoded on heavy strand, except for eight tRNA and ND6 genes. The complete mitochondrial genome sequence of L. microphthalma would contribute to better understand population genetics and protect its genetic diversity.

The mitogenome of Liobagrus marginatoides (Teleostei, Siluriformes:Amblycipitidae).

Liobagrus marginatoides is endemic to southwest China (Ding, 1994), according to morphological taxonomy, and it is very similar to Liobagrus nigricauda, but its population is much smaller. In this study, the complete mitochondrial genome sequence of L. Marginatoides has been obtained with polymerase chain reaction (PCR), which contains 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and a non-coding control region with the total length of 16,498 bp. The gene arrangement and composition are similar to that of other vertebrates. Most of the genes are encoded on heavy strand, except for eight tRNA and ND6 genes. Just like most other vertebrates, the against bias of G has a universality in different statistics results. The complete mitochondrial genome sequence of L. Marginatoides would contribute to better understand population genetics and protect its genetic diversity.

The mitogenome of Liobagrus nigricauda (Teleostei, Siluriformes: Amblycipitidae).

Liobagrus nigricauda is endemic to the Yangtze River system (Ding 1994, The fishes of Sichuan province. pp. 470-78) and listed as an endangered species (IUCN 2012, Red list of threatened species. http://www.iucnredlist.org ). In this study, the complete mitochondrial genome sequence of L. nigricauda has been obtained with polymerase chain reaction (PCR), which contains 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and a noncoding control region with the total length of 16,512 bp. The gene arrangement and composition are similar to that of other vertebrates. Most of the genes are encoded on heavy strand, except for eight tRNA and ND6 genes. Just like most other vertebrates, the bias against G has a universality in different statistics results. The mitogenome sequence of L. nigricauda would contribute to better understand population genetics and to protect its genetic diversity.

The complete mitochondrial genome of Liobagrus kingi (Teleostei, Siluriformes: Amblycipitidae).

Liobagrus kingi is endemic to southwest China and listed as endangered species (IUCN 2012). Genetic diversity is necessary for conservation issue. In studying this, the complete mitochondrial genome sequence of L. kingi has been obtained with PCR, which contains 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and a non-coding control region with the total length of 16,483 bp. The gene arrangement and composition are similar to that of other vertebrates. Most of the genes are encoded on heavy strand, except for eight tRNA and ND6 genes. Just like most other vertebrates, the against bias of G has a universality in different statistical results. The complete mitochondrial genome sequence of L. kingi would contribute to better understand population genetics and protect its genetic diversity.