Wenxuan Cao

Ontogenetic behavior and migration of Chinese sturgeon, Acipenser sinensis

The Chinese sturgeon, Acipenser sinensis, is an anadromous protected species that presently only spawns in the Yangtze River. Using laboratory experiments, we examined the behavioral preference of young Chinese sturgeon to physical habitat (water depth, illumination intensity, substrate color, and cover) and monitored their downstream migration. Hatchling free embryos were photopositive, preferred open habitat, and immediately upon hatching, swam far above the bottom using swim-up and drift. Downstream migration peaked on days 0–1, decreased about 50% or more during days 2–7, and ceased by day 8. Days 0–1 migrants were active both day and night, but days 2–7 migrants were most active during the day. After ceasing migration, days 8–11 embryos were photonegative, preferred dark substrate and sought cover. Free embryos developed into larvae and began feeding on day 12, when another shift in behavior occurred–larvae returned to photopositive behavior and preferred white substrate. The selective factor favoring migration of free embryos upon hatching and swimming far above the bottom may be avoidance of benthic predatory fishes. Free embryos, which must rely on yolk energy for activity and growth, only used 19 cumulative temperature degree-days for peak migration compared to 234 degree-days for growth to first feeding larvae, a 1 : 12 ratio of cumulative temperature units. This ratio suggests that sturgeon species with large migratory embryos, like Chinese sturgeon, which require a high level of energy to swim during migration, may migrate only a short time to conserve most yolk energy for growth.

Comparative ontogenetic behavior and migration of kaluga, Huso dauricus, and Amur sturgeon, Acipenser schrenckii, from the Amur River

We conducted laboratory experiments with kaluga, Huso dauricus, and Amur sturgeon, Acipenser schrenckii, to develop a conceptual model of early behavior. We daily observed embryos (first life phase after hatching) and larvae (period initiating exogenous feeding) to day-30 (late larvae) for preference of bright habitat and cover, swimming distance above the bottom, up- and downstream movement, and diel activity. Day-0 embryos of both species strongly preferred bright, open habitat and initiated a strong, downstream migration that lasted 4 days (3 day peak) for kaluga and 3 days (2 day peak) for Amur sturgeon. Kaluga migrants swam far above the bottom (150 cm) on only 1 day and moved day and night; Amur sturgeon migrants swam far above the bottom (median 130 cm) during 3 days and were more nocturnal than kaluga. Post-migrant embryos of both species moved day and night, but Amur sturgeon used dark, cover habitat and swam closer to the bottom than kaluga. The larva period of both species began on day 7 (cumulative temperature degree-days, 192.0 for kaluga and 171.5 for Amur sturgeon). Larvae of both species preferred open habitat. Kaluga larvae strongly preferred bright habitat, initially swam far above the bottom (median 50–105 cm), and migrated downstream at night during days 10–16 (7-day migration). Amur sturgeon larvae strongly avoided illumination, had a mixed response to white substrate, swam 20–30 cm above the bottom during most days, and during days 12–34 (most of the larva period) moved downstream mostly at night (23-day migration). The embryo–larva migration style of the two species likely shows convergence of non-related species for a common style in response to environmental selection in the Amur River. The embryo–larva migration style of Amur sturgeon is unique among Acipenser yet studied.

Seasonal Variation in Drifting Eggs and Larvae in the Upper Yangtze, China

From 5 March to 25 July 2008, ichthyoplankton drifting into the Three Gorges Reservoir from the upper reaches of the Yangtze River were sampled daily to investigate the species composition, abundance, and seasonal variation in early-stage fishes in this area. Twenty-eight species belonging to five orders and 17 families or subfamilies were identified by analyzing fish eggs and larvae, and a total of 14.16 billion individuals were estimated drifting through the sampling section during the investigation. Among the ichthyoplankton sampled, species in Cultrinae, Cobitidae, Gobioninae and Gobiidae, along with the common carp (Cyprinus carpio Linnaeus), comprised 89.6% of the total amount. Six peaks of drift density were identified during the sampling period, and a significant correlation was found between drift density with water discharge. The dominant species were different in each drift peak, indicating different spawning times for the major species. The total amount of the four major Chinese carps that drifted through the sampling section was estimated as 0.88 billion, indicating an increase in the population sizes of these species in the upper reaches of the Yangtze River after construction of the Three Gorges Dam. Actually, these reaches have become the largest spawning area for the four major Chinese carps in the Yangtze River. The large total amount of eggs and larvae drifting through this section demonstrated that the upper reaches of the Yangtze River provided important spawning sites for many fish species, and that conservation of this area should be of great concern.

Morphological Variability Between Wild Populations and Inbred Stocks of a Chinese Minnow, Gobiocypris rarus

Abstract Gobiocypris rarus, a small, native cyprinid fish, is currently widely used in research on fish pathology, genetics, toxicology, embryology, and physiology in China. To develop this species as a model laboratory animal, inbred strains have been successfully created. In this study, to explore a method to discriminate inbred strains and evaluate inbreeding effects, morphological variation among three wild populations and three inbred stocks of G. rarus was investigated by the multivariate analysis of eight meristic and 30 morphometric characters. Tiny intraspecific variations in meristic characters were found, but these were not effective for population distinction. Stepwise discriminant analysis and cluster analysis of conventional measures and truss network data showed considerabe divergence among populations, especially between wild populations and inbred stocks. The average discriminant accuracy for all populations was 82.1% based on conventional measures and 86.4% based on truss data, whereas the discriminant accuracy for inbred strains was much higher. These results suggested that multivariate analyses of morphometric characters are an effective method for discriminating inbred strains of G. rarus. Morphological differences between wild populations and inbred strains appear to result from both genetic differences and environmental factors. Thirteen characters, extracted from stepwise discriminant analysis, played important roles in morphological differentiation. These characters were mainly measures related to body depth and head size.

Extinction risk and conservation priority analyses for 64 endemic fishes in the Upper Yangtze River, China

It is a global concern to assess extinction risk and set conservation priority for threatened species. In the present study, we assessed extinction risks and conservation priorities for 64 endemic fish species in the Upper Yangtze River, which might be threatened by cascade dams in the Lower Jinsha River. Eight independent criteria were selected and scored to calculate an Extinction Risk Index (ERI) and a Conservation Priority Index (CPI) for each species with a linear rating system. These criteria reflect extinction-prone life-history traits, distribution characteristics, threat extents, and other conservation concerns. Species with high current threats, large body sizes, low fecundity, low historical occurrences and low recent-record rates had high ERIs (i.e. high risk of extinction). High CPIs (i.e. high conservation priorities) were assigned to species (e.g. Yangtze sturgeon) that represented those most in need of conservation in the impacted region given their high extinction risks, high levels of future threat from damming, high economic and genetic values. We recommend habitat protection and other conservation measures should be taken to conserve those endemic fish species with high conservation priorities.

The identification of metallothionein in rare minnow (Gobiocypris rarus) and its expression following heavy metal exposure.

Heavy metal, such as cadmium (Cd), lead (Pb) and copper (Cu) poses serious toxin to aquatic organisms. These exogenous materials affect biological processes including physiology, biochemistry and development. Metallothionein (MT), one of the metal-regulated genes, participates in regulating essential and detoxifying non-essential metals in living animals. In this study, MT EST in rare minnow (Gobiocypris rarus) (GrMT) was obtained from the cDNA subtraction library and the GrMT cDNA was firstly cloned by RACE with a sequence of 379 bp, which can code 60 amino acids. After Cd exposure, the GrMT expression levels dramatically changed in liver, spleen, gill, kidney, intestine, but moderately in muscle. Significantly positive relationships were found between Cd dosages and MT expression levels in liver. And there distinction existed at the GrMT transcript level in fish gender and developmental stages during Cd exposure. While Pb exposure, the expression alteration happened in spleen, gill, intestine, muscle, and moderately in liver. In the Cu treatment test, there were slight changes in intestine and kidney, but more significant changes occurred in spleen, gill, muscle, and liver. This study had investigated the effects of diverse heavy metals on GrMT expression patterns. The results suggest that GrMT would be a potential biomarker to metal contamination monitoring in aquatic environments and rare minnow could be one of the perfect experimental fishes for surveying the freshwater pollution in China.

The identification of apolipoprotein C-I in rare minnow (Gobiocypris rarus) and its expression following cadmium exposure

Cadmium (Cd) is a ubiquitous environment contaminant that has been detected in a variety of terrestrial and aquatic organisms. In our study, rare minnow were exposed to 0.4 mg/L Cd(2+) solution, fish tissues including gill, intestine, kidney, liver, muscle, and spleen were collected at 1, 6, 12, 24 and 48 h after exposure. Differential expression sequence tags (ESTs) were screened and an EST similar to Hemibarbus mylodon apolipoprotein C-I (ApoC-I) was identified. The ApoC-I cDNA had been obtained with the sequence of 583 bp, which can code 84 amino acids. The transcription expression patterns of ApoC-I were compared after Cd exposure with the real-time PCR in the above tissues. ApoC-I regulation was prominent in spleen, muscle, gill and liver and moderate in kidney and intestine. This suggests a complex transcriptional regulation of ApoC-I expression following Cd exposure.

Effects of Environmental Factors on Natural Reproduction of the Four Major Chinese Carps in the Yangtze River, China

The four major Chinese carps are commercially important fish species with high production in China. However, their recruitment decreased sharply in the Yangtze River since the late 20th century. In the present study, to reveal the relationships between spawning activities of the four species and environmental factors, drifting eggs were collected at Yidu City, in the middle reaches of the Yangtze River, from May to July each year between 2005 and 2010. Classification and regression trees (CART) analysis was applied to identify the key factors associated with spawning activities of the four carp species. Twelve predictor variables (hydrological and meteorological variables) and one response variable (egg presence or number of egg) were included in the CART. Our CART analysis showed that water temperature and the diurnal increase of water level were the two most significant factors for the spawning activities. When water temperature was between 18°C and 24°C, especially in association with the diurnal increase of water level greater than 0.55 m·d-1, spawning activities was always favored. Unlike the hydrological factors, meteorological factors seemed to have no influence on initiating the spawning activities. The density of drifting eggs of the four species was mainly influenced by the diurnal variation of water level, the diurnal variation of water discharge, water temperature, humidity, and air pressure. We then related our results to the ecological regulation of the Three Gorge Reservoir in the middle reaches of the Yangtze River. We suggested that, when water temperature was between 18–24°C from May to July, to ensure the successful spawning of the four carp species, the ecological regulation should be managed to create flood peaks and make the diurnal increase of water level greater than 0.55 m·d-1.

Impact of the Three Gorges Dam on reproduction of four major Chinese carps species in the middle reaches of the Changjiang River

Silver carp (Hypophthalmichthys molitrix), bighead carp (Aristichthys nobilis), grass carp (Ctenopharyngodon idella), and black carp (Mylopharyngodon piceus) are the four major Chinese carps and are commercially important aquaculture species in China. Reproduction of these carp has declined since the construction of the Three Gorges Dam (TGD) due to an altered water flow and thermal regime in the Changjiang (Yangtze) River. However, details of the changes in reproduction of the four species are not well understood. To assess the impact of the TGD on reproduction of the four carp, we investigated their eggs and larvae at Yidu City, which is 80 km below the TGD, during 2005–2012. We examined diff erences in larval abundance of the four species in the Jianli section (350 km downstream of the TGD) before (1997–2002) and after (2003–2012) construction of the TGD. Based on these observations, the first spawning date of the four species was delayed a mean of about 25 days after the dam was constructed. Mean egg abundance in the Yidu section of the river was 249 million and mean larval abundance was 464 million, which were significant decreases since the 1980s. Moreover, larval abundance in the Jianli section after the dam was constructed was significantly lower than that before construction (ANCOVA, P<0.05). The observed larval abundance accounted for only 24.66% of the predicted value in 2003 when the dam was first inundated. The present spawning grounds between the TGD and Yidu section of the river are very similar to those described in the 1980s, and some spawning grounds exist upstream of the TGD. Large free-flowing stretches upstream of the TGD and the creation of artificially flooded downstream reaches are needed to stimulate spawning and eff ectively conserve these four major Chinese carps species.

Diet composition and trophic guild structure of fish assemblage in headwaters of the Chishui River, a tributary of the upper Yangtze River, China

In this study, the diet composition and trophic structure of the fish assemblage in the headwaters of the Chishui River were investigated. A total of 1677 fish specimens belonging to 14 species were collected and dissected. Of these specimens, 1063 individuals with undigested food in their stomachs or guts were used for analysis. Our analysis identified thirty-one kinds of prey, which were classified into eight categories, namely, diatoms, chlorophytes, other vegetable prey, aquatic insects, mollusks, other invertebrates, fishes, and unidentified organic matters. Among these categories, diatoms were the most important prey for this fish assemblage. With an ontogenetic dietary shift, the 14 species were subdivided into 16 predator groups, which were categorized into five trophic guilds, namely, algivore (diatoms), algivore (chlorophytes), omnivore, aquatic insectivore, and piscivore. Their diet composition significantly differed from one guild to another (p < 0.05), and an evident overlap was observed in the diet spectrum between predator group in the algivore (diatoms) guild. These results suggested that autochthonous organic carbon was an important nutrient source for the fish assemblage in the headwaters of the Chishui River rather than allochthonous nutrients. For the protection of the fish resources, conservation efforts on the river substratum and the riparian zone in the headwaters of the Chishui River should be prioritized because these places are the main nutrient sources.