Paramisgurnus Research Articles

Initial Alterations of Fish Community Structure and Diversity Following Fishing Cessation in Qilu Lake, China.

The Qilu Lake is an eutrophic shallow lake located in Yunnan Province, China. An ecological fishery project was initiated in the lake from 2011 to 2021 to introduce filter-feeding fish species that feed on algae, with the aim of improving water quality. In January 2022, when the ecological fishery project expired, all fisheries-related activities (including fish stocking and fishing activities) ceased in the lake. To comprehensively evaluate the initial alterations in fish community structure and diversity resulting from the fishing cessation in the Qilu Lake, the present study conducted field surveys within the one year before the fishing cessation (referred to as BFC) and the one year after the fishing cessation (referred to as AFC). A total of twenty-one fish species were collected, including four native species. Four species were recorded in the lake for the first time, including Pelteobagrus fulvidraco, Pelteobagrus vachelli, Paramisgurnus dabryanus, and Hyporhamphus intermedius. The number of fish species decreased from 21 to 13 following the fishing cessation. The fishes collected in both BFC and AFC are mainly omnivorous-feeding and of bottom-dwelling habits. The mean size of the fishes in the AFC sample shows a significant decrease compared to those in BFC. After the fishing cessation, the Shannon-Wiener diversity index and Margalef richness index of the fish slightly declined. The fish community structure of the Qilu Lake exhibits a high degree of similarity to adjacent lakes in central Yunnan. Our study demonstrates a significant shift in the fish community of the Qilu Lake following the fishing cessation, one which may adversely impact the stability of the lake ecosystem. To enhance fish species diversity in the Qilu Lake, it is recommended that policies be implemented to promote the ecological fishery project and improve habitat restoration for native fish species, while also regulating fish community structure.

Assessing the Effects of Dietary Tea Polyphenols on the Gut Microbiota of Loaches (Paramisgurnus dabryanus) under Chronic Ammonia Nitrogen Stress

This study examined the impact of tea polyphenols (TPs) on the intestinal flora of loaches (Paramisgurnus dabryanus) under chronic ammonia nitrogen stress using high-throughput sequencing. Two groups of 600 loaches were studied over one month, and they were separated into a control group and tea polyphenol group. Alpha and beta diversity analyses showed diverse bacterial communities, with significant differences in the abundance and uniformity observed initially but not between sampling time points. Cluster analyses revealed distinct differences in microbial communities between groups. A predictive function analysis indicated enrichment in pathways related to amino acid and nucleotide biosynthesis. These findings offer initial insights into how tea polyphenols may affect intestinal microbial communities in loaches under ammonia nitrogen stress.

Dietary Nanometer Selenium Enhances the Selenium Accumulation, Nutrient Composition and Antioxidant Status of Paramisgurnus dabryanus spp.

Selenium, an essential trace element, exerts beneficial effects on aquatic animals when present in suitable concentrations. This study investigates the effect of dietary nanometer selenium (Nano-Se) on the muscle selenium accumulation, nutrient composition, and antioxidant ability of Paramisgurnus dabryanus spp. Nano-Se was supplemented in the basal diets at levels of 0, 0.1, 0.2, 0.4, and 0.6 mg/kg. Three hundred fish, averaging 5.21 ± 0.06 g, were randomly divided into five groups and fed the experimental diet for 6 weeks. Fish with a dietary Nano-Se supplement of 0.2 mg/kg exhibited activities of SOD, GSH-Px, AKP, and CAT in the liver, which were significantly higher (p < 0.05) compared to the control diet, while MDA content was significantly lower (p < 0.05) in the 0.2 mg/kg group. The muscle selenium content significantly increased (p < 0.05) at ≥0.2 mg/kg Nano-Se levels. The highest levels of essential amino acids, EAA/TAA, and EAA/NEAA ratios were observed in fish fed 0.2 mg of Nano-Se. Thus, this study recommends incorporating 0.2 mg of Nano-Se per kg in the diet to enhance antioxidant defense, selenium content, and nutrient composition.

Metabolomic and transcriptomic profiling reveals the effect of dietary protein and lipid levels on growth performance in loach (Paramisgurnus dabryanus).

The subject of this study was to explore the optimum requirements of loach (Paramisgurnus dabryanus) regarding dietary proteins and lipids and discuss the underlying mechanism. We designed nine diets to determine the effects of different levels of dietary crude protein (CP: 30%, 35%, and 40%) and ether extract (EE: 6%, 10%, and 14%) on the growth performance and metabolism of P. dabryanus. In total, 2160 healthy P. dabryanus (5.19 ± 0.01g) were divided into nine groups with four replications at 60 fish per barrel stocking density. The trial lasted for eight weeks. Serum and liver samples were gathered for metabolomic and transcriptomic analyses. The results showed that the specific growth rate of P. dabryanus in the CP40EE10 group was the fastest and notably higher than that in other groups (P< 0.05). Analysis of the metabolome results found that the mTOR signaling pathway, glycerophospholipid metabolism, D-arginine and D-ornithine metabolism were significantly enriched pathways in the CP40EE10 group compared with the other groups (P< 0.05). Moreover, the transcriptomic analysis of differentially expressed genes (DEGs) showed that the expression of ARG (arginase) involved in protein synthesis was significantly upregulated in the CP40EE10 group compared to the slowest growing group (P< 0.05). Additionally, the expression of SPLA2 (secretory phospholipase A2) involved in lipid metabolism and FBP (fructose-1,6-bisphosphatase) involved in glucose metabolism were all significantly downregulated in the CP30EE6 group compared with the CP40EE10 group (P< 0.05). Furthermore, the analysis of differentially expressed metabolites (DEMs) and DEGs co-enriched in the KEGG pathway revealed that the significantly enriched pathways were arginine and proline metabolism, glycerophospholipid metabolism, and glycolysis/gluconeogenesis in CP40EE10 compared with other groups (P< 0.05). We conclude that including 40% CP and 10% EE in the P. dabryanus diet could result in a better growth rate. We hypothesized from metabolomic and transcriptomic analyses that the CP40EE10 diet might promote the growth of P. dabryanus by promoting protein synthesis, lipid metabolism, and energy production.

Effects of different protein and lipid levels on the growth performance and intestinal microflora of loach (Paramisgurnus dabryanus).

The aim of this study was to examine the effects of dietary protein and lipid levels on the growth performance and homeostasis of the intestinal flora in Paramisgurnus dabryanus. An 8-wk 3×3 two-factorial experiment was conducted to investigate the interaction between dietary crude protein (CP: 30%, 35%, 40%) and ether extract (EE: 6%, 10%, 14%) on the growth rate and the intestinal microflora of P.dabryanus. A total of 2,160 fish (5.19±0.01g) were randomly allotted to 36 aquariums each with 60 fish. Fish were fed the experimental diet twice daily. Results revealed that weight gain rate (WGR), specific growth rate (SGR), protein efficiency ratio and net protein utilization significantly increased when increasing protein levels from 30% to 40% (P<0.05). Both WGR and SGR enhanced first but reduced thereafter with maximum value at 10% lipid level as dietary lipid increased from 6% to 14% (P<0.05). Significant interactions between protein and lipid were found with feed conversion rate, lipid efficiency ratio and net lipid utilization (P<0.05). At the phylum level, Proteobacteria and Actinobacteria were the dominant bacteria; at the genus level, Burkholderia-Caballeronia-Paraburkholderia was the dominant bacteria. Fish fed the diet containing 10% lipid had a higher abundance of Proteobacteria and unclassified_f_Eenterobacteriaceae than those fed the 14% lipid diet, and a higher abundance of Rhodobacter than those fed the 6% lipid diet (P<0.05). Analysis of the predicted functions showed that metabolism in the intestine of fish in the CP40EE10 group was more active than that in CP30EE14 group. Polynomial regression analysis found that a diet containing 40.87% protein and 9.88% lipid can be considered optimal for P.dabryanus.

Inhibition of the NF-κB signaling pathway affects gonadal differentiation and leads to male bias in Paramisgurnus dabryanus

In recent years, sex-controlled breeding has emerged as an effective strategy to enhance the yields of economic animals with different growth characteristics, while increasing the economic benefits of aquaculture. It is known that the NF-κB pathway participates in gonadal differentiation and reproduction. Therefore, we used the large-scale loach as a research model for the present study and selected an effective inhibitor of the NF-κB signaling pathway (QNZ). This, to investigates the impacts of the NF-κB signaling pathway on gonadal differentiation during a critical period of gonad development and after maturation. Simultaneously, the sex ratio bias and the reproductive capacities of adult fish were analyzed. Our results indicated that the inhibition of the NF-κB signaling pathway influenced the expression of genes related to gonad development, regulated the gene expression related to the brain-gonad-liver axis of juvenile loaches, and finally impacted the gonadal differentiation of the large-scale loach and promoted a male-biased sex ratio. Meanwhile, high QNZ concentrations affected the reproductive abilities of adult loaches and inhibited the growth performance of offspring. Thus, our results deepened the exploration of sex control in fish and provided a certain research basis for the sustainable development of the aquaculture industry.

Transcriptomic analysis of regenerated skins reveals key genes involved in skin immune response and air-breathing of loach (Paramisgurnus dabryanus)

Fish skin acts as the first immune barrier against pathogens from external environments. Recently, fish skin immunity research has gradually become a hot topic in aquaculture disease control. Interestingly, the skin can do air-breathing in some bimodal respiration fish. However, there is no comprehensive understanding of these two functions. In this study, the skin regeneration of loach (Paramisgurnus dabryanus) was investigated through morphological and histological observations. Then, original skins (OS) and the regenerated skins (RS) when their capillaries were the most abundant during healing, were collected for transcriptomic analysis. 285,899,386 clean reads with a total length of 42.34 Gb were obtained. A total of 1282 differentially expressed genes (DEGs) were detected, including 1030 DEGs up-regulated and 252 DEGs down-regulated in the comparison of RS vs. OS. Fc gamma R-mediated phagocytosis (containing gelsolin (Gsn)), chemokine signaling pathway (containing C–C motif chemokine ligand 28 (Ccl28)), and B cell receptor signaling pathway (containing CD80 molecule (Cd81)) were closely related to skin immune response of the loach. PI3K-Akt signaling pathway [containing fibronectin 1 (Fn1) and lysyl oxidase-like 2b (Loxl2b)], TGF-beta signaling pathway [containing thrombospondin 1 (Thbs1)], ECM-receptor interaction [containing integrin alpha 7 (Itga7), Itgb8, Itgb10 and Itgb5], and dilated cardiomyopathy [containing laminin subunit alpha1 (Lama1)] were closely associated with skin air-breathing of the loach. This study is conducive to explore the molecular mechanisms of skin immune response during its regeneration and air-breathing of bimodal respiration fish. This study will benefit for the aquaculture of P. dabryanus and its related species.

Population genetics and phylogeography of Paramisgurnus dabryanus (Cypriniformes: Cobitidae) in six river basins of China

Population genetics and phylogeography of Paramisgurnus dabryanus (Cypriniformes: Cobitidae) in six river basins of China

Impacts of dietary supplementation of bamboo vinegar and charcoal powder on growth performance, intestinal morphology, and gut microflora of large-scale loach Paramisgurnus dabryanus.

Although accumulating data demonstrate that dietary supplementation of bamboo vinegar and charcoal powder (BVC) can significantly strengthen the immunity and boost the growth of domestic animals, its application potency still awaits verification in commercial fish species such as the large-scale loach Paramisgurnus dabryanus. The impacts of 90-day dietary supplementation of 1% and 2% BVC on survival and growth performance of the loach, and on the intestinal morphological characteristics and gut microflora were analyzed. Our data show that the large-scale loach supplied with BVC at the experimental doses had significant higher survival rates and better growth performance (indicated by greater weight gain (1.13-1.14 times), higher specific growth rate (1.04 times), and lower feed conversion ratio (0.88-0.89 times)) compared to that of the control (P<0.05). Histological examination revealed significant longer villus (3.22-5.54 times), deeper crypt (1.77-1.87 times), and thicker muscle (1.59-3.17 times) in the intestines of large-scale loach fed with BVC (P<0.05). Furthermore, we found that the gut microflora consisted of significantly fewer proportions of potential pathogenic bacterial species (Aeromonas veronii and Escherichia coli), but significantly greater proportions of beneficial microbes (Lactococus raffinolactis and Faecalibacterium prausnitzii). Therefore, dietary intake of BVC can promote intestinal tract development and optimize gut microflora, by which the survival and growth of large-scale loach may be improved.

QNZ exposure induces development toxicity and mechanisms of hatching inhibition in large-scale loach (Paramisgurnus dabryanus) embryos

QNZ is a quinazoline-type NF-κB inhibitor and is one of the hot anti-inflammatory drug candidates in recent years. With its development and application, QNZ will inevitably enter the aquatic environment posing a threat to aquatic organisms. To investigate the potential toxicity of QNZ in the early life stages of the organism, this study exposed embryos of large-scale loach (Paramisgurnus dabryanus) to 0, 20, 40, 60, and 80 nM of QNZ. The hatching of embryos was significantly inhibited and hatching time was delayed. We explored the mechanism of hatching delay and failure. The results suggested that QNZ exposure reduced the number of hatching gland cells (HGCs) and hatching enzyme activity. Also, the frequency of spontaneous movements was inhibited by interfering with the expression of genes related to the cholinergic system and skeletal muscle development. Further, QNZ exposure induces a series of morphological changes (spine deformation, pericardial edema, tail deformation, and yolk sac edema) in embryos and newly-hatched larvae, and finally increased the deformity rate and mortality rate of newly-hatched larvae. The information presented in this study will provide a scientific basis for further studies into the potential toxicity of QNZ on aquatic organisms.

Invaders they are a‐changing†: A recent, unexpected surge of invasive loaches in Catalonia

Abstract Risk analyses for invasive species often assume that the characteristics of future invaders will resemble those already successful, but these features may change. Here, we use data from more than 3,500 fish sampling events, sequencing of mitochondrial and nuclear genes and analyses of several traits describing non‐native fish to describe the irruption and rapid expansion of non‐native loaches in Catalonia, north‐east Iberian Peninsula, and framing this surge in the knowledge of previous invasions. We report the establishment of at least five (Cobitis bilineata, Misgurnus anguillicaudatus, Misgurnus bipartitus, Paramisgurnus dabryanus, and a yet undescribed Barbatula species) non‐native loach species in Catalonia, most of which are currently spreading. Furthermore, one of the two regionally native loach species (Cobitis paludica) has been introduced and is spreading through river basins where it is not native. Genetic analyses were fundamental to understand loach invasions, by clarifying specific statuses, identifying the origin of non‐native populations and/or detecting independent introduction events. Genetic results also highlighted the unresolved taxonomy of loaches, particularly for European Barbatula. Loaches are recent, diverse, and successful invaders whose traits differ from those of most previously established invasive fish species, signalling potential weaknesses of prevention of biological invasions based on prohibited species lists. We call for the development of more flexible management tools (e.g. based on fish traits and not only on species identities) and prioritising prevention and rapid responses to new introductions.

The background adaptation of the skin color in the loach Paramisgurnus dabryanus

Body color change is one of the most important manifestations of fish adaptation to the environment. In this study, the body color change of two kinds of loach (Paramisgurnus dabryanus) with different body colors under five different background colors was first studied. It was found that the color of dorsal skin of gray-black loach changed more than that in the abdominal skin, and the L* value of the dorsal skin on the red, yellow and white backgrounds changed significantly (P < 0.05). Compared with the gray-black loach, the body color of golden loach changed less, and the L* value of the back skin and the abdomen skin did not change significantly (P > 0.05). Furthermore, the dynamic change characteristics and adaptive mechanism of body color in different background colors was studied in a black-white background conversion model. The results showed that the greyscale color decreased from 72.33 ± 2.55–38.22 ± 2.33, the melanocytes changed from dendritic to mass, and the L* value of the back skin increased significantly (P < 0.05) after transferring the loach from a black background to a white background. The concentration of plasma ATCH decreased significantly (P < 0.05), and that of MCH increased significantly (P < 0.05). When transferring the loach from a white background to a black background, these indicators showed an opposite trend. This study provides a scientific basis for healthy farming of loach and understanding the background color adaptation mechanism of fish.

Ontogenetic Development of Gill and Na+/K+ ATPase in the Air-Breathing Loach

This study aimed to explore the gill developmental mechanism of the high mortality rate of Paramisgurnus dabryanus larvae in the early life-history process. Based on histological observations with a optical microscope, we studied the ontogeny of the gill of P. dabryanus. The result indicated that external gills first appeared 12 h after hatching. The number of external branchial filaments greatly increased at 2 d after hatching (DAH). The internal branchial filament primordial was formed in the oropharyngeal cavity at 5 DAH. At 9 DAH, none of external branchial filaments were observed outside, but the fish operculum was completed covered. From 15 DAH forward, the filaments and lamellae of gills increased in number and length prominently, and the gills of the larvae were similar to those of juvenile fish. The specific activities of Na+/K+-ATPase steadily increased from 0 to 12 DAH and peaked at 15 DAH. After 15 DAH, the specific activities of Na+/K+-ATPase slightly decreased and then tended to remain steadily stable until the end of the experiment. There were abundant gill lamellae on the gill filaments at 40 DAH. The sensitive period of the development of larval and juvenile P. dabryanus was from 6 to 15 DAH. Our results provide information that may be useful for improving our understanding of the life history and ecology of loaches.

Reproductive toxicity and cross-generational effect of polyethylene microplastics in Paramisgurnus dabryanus

Pollution of microplastics (MPs) has become a global environmental issue due to the difficulty in its degradation and may cause unexpected ecological effects. Nevertheless, little is known about the potential effects of MPs on reproduction toxicity in aquatic species. In this study, adult loach (Paramisgurnus dabryanus, F0 generation) were exposed to two concentrations (1 and 10 mg/L) of polyethylene MPs (PE-MPs) for 15 or 30 days, and the toxic effects in parental loach and the offspring (F1 generation) were examined. Our results showed that PE-MPs exposure could change the indicators content of antioxidant system in the brain, liver, and gonad. PE-MPs can accumulate in the gonads, disrupt the transcription of HPG-axis related genes, alter sex hormone levels, increase cell apoptosis and gonadal pathological lesions, lead to the damage of biological characteristics of semen, and affect the reproduction in F0 generation. PE-MPs remaining in the parental gonads can be transferred to the F1 generation embryos and accumulated on the embryonic chorionic membrane, increasing mortality and malformation rates, accelerating hatching time, and decreasing hatching rate and body length. These results suggest that PE-MPs leads to a potential adverse influence on reproduction and serious impacts on population sustainability. This work provides a new perspective into the effects of MPs on reproductive damage and cross-generational effects in teleost fish, which have implications in fields of freshwater ecology and environmental toxicology.

Regulation of Rhesus glycoprotein-related genes in large-scale loach Paramisgurnus dabryanus during ammonia loading.

Waterborne ammonia is one of the crucial issues that limited production and animal health in aquaculture. Ammonia-tolerant varieties are highly desired in intensive fish farming. Screening for the key regulatory genes of ammonia tolerance is essential for variety breeding. According to the previous hypothesis, Rh glycoproteins play an important role in ammonia excretion in teleosts. However, the ammonia defensive mechanisms are not well described at present for large-scale loach (Paramisgurnus dabryanus), a typical air-breathing and commercially important fish in East Asia. Here we show that the transcription of Rh glycoprotein-related genes was significantly affected by ammonia exposure in this species. Probit analysis showed that 96h-LC50 of NH4Cl at 23℃ and pH 7.2 was 92.64mmol/L. A significant increase of Rhcg expression in gills was observed after 48h of 60mmol/L and 36h of 80mmol/L NH4Cl exposure, suggesting that Rhcg present on the apical side of the branchial epithelium facilitates NH3 excretion out of gills. A high concentration of acute ammonia exposure induced elevated Rhbg transcript in the gills of large-scale loaches, while a slight change in Rhbg expression was observed in response to lower ammonia, suggesting that transcriptions of Rhbg genes are activated by a considerably high level of ambient ammonia to eliminate excessive endogenous nitrogen. The Rhag mRNA level in gills of large-scale loaches increased markedly with the prolonging of exposure time from 0 to 36h of ammonia loading, suggesting Rhag localized in gills may be primarily associated with ammonia handling. During 7-21 days of ammonia exposure, the expression of most Rh glycoproteins-related genes in the gills decreased, indicating that the functional role of Rh glycoproteins is not primarily associated with ammonia defense over a long period (more than 7 days). Although a significant transcript of Rhbg was found in the skin of a large-scale loach, the lack of Rhcg and down-regulation of Rhag may indicate that the skin is not an essential location of ammonia excretion, at least when submerged to high levels of ammonia in the environment. In conclusion, Rh glycoproteins localized in gills as ammonia transporters play a momentous role in ammonia detoxification in this species during acute ammonia loading. However, it does not show a positive function during long-term ammonia exposure. Furthermore, the physiological function of Rh glycoproteins localized in the skin is still unclear and deserves further study.

Aquaporins1 and 3 in the tissues of Paramisgurnus dabryanus and their expression profiles in response to ammonia and drought

Aquaporins (Aqp)1 and Aqp3 are the representatives of two types of aquaporins (classical aquaporin and aquaglyceroporin) and have been proven to potentially facilitate ammonia detoxification in air-breathing fishes. Paramisgurnus dabryanus is one of East Asia’s most important commercially farmed species and can breathe air directly through its hindgut. Besides, excellent ammonia tolerance was reported in this species. However, the mechanisms of its tolerance of high ammonia are still unclear. To explore the physiological roles of Aqp1 and Aqp3 in Paramisgurnus dabryanus, we detected the expression pattern of these two Aqps in several tissues and their transcriptional changes in response to different levels (30, and 70 mmol L-1 NH4Cl) and periods (0, 12, 48, and 96 h) of ammonia exposure and different periods (0, 12, 48, and 96 h) of drought stress. The aqp1 mRNA showed a high abundance in the brain and the osmoregulatory tissues, such as the intestine and kidney. While aqp3 was mainly expressed in the epithelium of skin and gills that were directly exposed to the environment. The expression level of aqp3 in gills was more responsive than aqp1 to ammonia challenges, although both of them were up-regulated. Considering the wide difference between aqp1 and aqp3 in the skin, aqp3 increased significantly after 12 h of air exposure. The changes of the two aqps in the intestine of P. dabryanus were relatively stable after ammonia stress. After drought stress, intestinal aqp1 increased significantly, while aqp3 decreased. Combined with the effects of tissue location and environmental stress on Aqps, it was suggested that Aqp1 was mainly involved in osmotic regulation, providing water as raw material for body metabolism. Accordingly, our results suggest that Aqp3 has the positive function of assisting ammonia transportation and epidermal moisturizing.

Comparative study on body index, nutrient composition, and digestive enzyme activity of Misgurnus anguillicaudatus, Paramisgurnus dabryanus, and Paramisgurnus dabryanus ssp

The current research work was undertaken to compare and analyze the body index, nutrient composition, and digestive enzyme activity of Pond loach (Misgurnus anguillicaudatus), large-scale loach (Paramisgurnus dabryanus), and Taiwan loach (Paramisgurnus dabryanus ssp). Viscerosomatic ratio (VR), condition factor, (CF), W/L and H/L were highest in Taiwan loach (P &lt; 0.05). Muscle protein content was highest, whereas lipid content was lowest in pond loach (P &lt; 0.05). The content of total amino acids (TAA), total essential amino acids (EAA), and delicious amino acids (DAA) in the muscle of pond loach was highest (P &lt; 0.05). The content of polyunsaturated fatty acids (PUFA), monounsaturated fatty acids (MUFA) and linoleic acid was highest in pond loach, Taiwan loach and large-scale loach, respectively (P &lt; 0.05). The trypsin activities and amylase activities of the pond loach were significantly higher than those of the large-scale loach and Taiwan loach in the intestine and liver (P &lt; 0.05). These results indicate that the three kinds of loaches are of high nutritional value and have breeding prospects, among which pond loach has higher nutritional value.

Effects of carbonate alkalinity on branchial gene expression in the large-scale loach (Paramisgurnus dabryanus)

Elucidating the mechanisms of alkaline tolerance in freshwater teleosts will help in the development of commercial saline-alkaline aquaculture. The large-scale loach (Paramisgurnus dabryanus) is a viable species for such aquaculture, but the mechanisms of its tolerance of alkaline water are unclear. Large-scale loach was exposed to 40, 50, and 60 mmol L-1 NaHCO3 for 12, 48, and 96 h to evaluate the transcriptional changes of branchial Rhesus (Rh) glycoproteins, and aquaporins (Aqp)1 and Aqp3. Rhag transcript levels increased with longer exposure times. Rhag expression also rose considerably at higher carbonate alkalinities. Rhbg mRNA levels declined significantly under carbonate alkalinity exposure. A marked up-regulation of Rhcg was observed in the gills of the loach. Exposure to 60 mmol L-1 NaHCO3 also induced a significant up-regulation of aqp1. By contrast, aqp3 expression was significantly lower after 48 h exposure. The current findings reveal that the large-scale loach up-regulates Rhag and Rhcg to enhance ammonia efflux from the gills when exposed to high alkalinity. It is proposed that this species maintains appropriate osmolality when adapting to an alkaline environment by down-regulating aqp3 (to impede urea removal) and up-regulating aqp1 in the gills (to excrete excessive internal water).

Development of multiplex species-specific PCR for the simultaneous identification of three closely related species in the genera Misgurnus and Paramisgurnus

We aimed to develop a multiplex PCR method for the simultaneous detection of the three most consumed commercial loaches in East Asia: Misgurnus mizolepis, Misgurnus anguillicaudatus, and Paramisgurnus dabryanus. Phylogenetic analysis of genetic divergence and a phylogenetic tree based on the cytochrome oxidase I gene enabled successful genetic identification of the 3 species of loach. Multiplex species-specific PCR (MSS-PCR) primers designed based on single nucleotide polymorphisms were able to differentiate the species and generate PCR products among species that differed in size by at least 150 bp. The lengths of the amplified fragments were 818 bp for P. dabryanus, 669 bp for M. mizolepis, and 486 bp for M. anguillicaudatus, which could be clearly distinguished by gel electrophoresis. The three sets of PCR primers were mixed and applied to simultaneously detect the three loaches. The MSS-PCR markers designed in this study will be useful for the detection and identification of M. mizolepis, M. anguillicaudatus, and P. dabryanus.

Enrichment of polystyrene microplastics induces histological damage, oxidative stress, Keap1-Nrf2 signaling pathway-related gene expression in loach juveniles (Paramisgurnus dabryanus)

Polystyrene microplastics (PS-MPs, particle size<5 mm) cause great harm to aquatic organisms. However, their precise effects are not completely understood. In China, placing plastic film at the pond bottom has become an important loach aquaculture mode. In this mode, MPs will affect loach health. This study investigated the enrichment of PS-MPs and its effects on the growth, liver histomorphology, antioxidant enzymes, and Keap1-Nrf2 signaling pathway-related gene expression in loach juveniles (Paramisgurnus dabryanus). The loach juveniles were raised at the concentration of 1000 μg/L fluorescent polystyrene microplastics (PS-MPs) with particle size of 0.5 µm or 5 µm for seven days, the results showed that fluorescent PS-MPs were found to be enriched in liver, intestine, and gill, and the enrichment amount was higher in liver than in gill and intestine (P < 0.05). Furthermore, the enrichment amount of different-sized PS-MPs was different in liver, gill, and intestine. The loach juveniles were cultured for 21 days in the water of the concentration of 100 or 1000 μg/L PS-MPs with particle size of 0.5 µm or 5 µm, the results showed that the survival rate, weight gain rate, and specific growth rate of loach juveniles were significantly reduced. The histological analysis revealed that PS-MPs caused liver damage. The activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-PX), and acetylcholinesterase (AChE) were decreased with the extended exposure to PS-MPs. Generally, the expressions of Nrf2 and Keap1 showed the similar change trend. From 7–14 day, the expression trend of oxidative stressed-related genes was not completely consistent with that of Nrf2 gene, but on day 21, the gene expression trend of oxidative stress-related SOD, CAT, and GSH-PX in the downstream of Keap1-Nrf2 signaling pathway was roughly consistent with that of Nrf2 gene. Basically, the change trends of these three gene expression were similar to those of their corresponding enzyme activities. This study provides theoretical basis for the toxicological effects of PS-MPs on freshwater fish.