Thermal requirements for growth, survival and aerobic performance of weatherfish larvae Misgurnus fossilis

The heat-labile toxin B subunit of E. coli fused with VP6 from GCRV (Grass carp reovirus) was expressed and folded into an active protein in rice calli

Grass carp reovirus (GCRV) is one of the most serious pathogens threatening grass carp (Ctenopharyngon idellus) production in China. VP6 could be suitable for developing vaccine for the control of GCRV. Transgenic plants are an attractive bioreactor for their safety and ability to make economical vaccines. The B subunit of Escherichia coli heat-labile enterotoxin (LTB) fused to VP6 (LTB-VP6) was transformed into rice calli by Agrobacterium tumefaciens-mediated gene transformation. Transgenic rice calli was confirmed by PCR analysis separately. The copy numbers of LTB-VP6 inserted into the rice genome are between 1 and 2. The expression level of LTB-VP6 in rice calli was 0.0005-0.0019%, an average of 0.0011% of the TSP(total soluble proteins). LTB-VP6 was folded and assembled into a pentameric form of approximately 305 kDa capable of binding monosialoganglioside (GM1). The suitable concentration of LTB-VP6 in TSP was 0.4 μg/μl. LTB-VP6 is stable and highly active at room temperature. LTB-VP6 binding to GM1 is affected with different affinities under different temperatures. LTB-VP6 had a strong binding affinity at 25 °C and pH 8.4. Our results showed that LTB-VP6 is capable of forming an active pentameric form protein. It provides an ideal alternative to plant-based vaccines against GCRV in aquaculture.

Rearing of Bitterling (Rhodeus amarus) Larvae and Fry under Controlled Conditions for the Restitution of Endangered Populations

Simple Summary

Among the many species threatened with extinction and covered by protection of species is bitterling Rhodeus amarus. It belongs to ostracophilic fish that place spawn inside live mussels. Bitterlings, such as mussels, belongs to indicator species that testify to the good state of the natural environment. Supporting the populations of these organisms is a necessity in order to preserve the biodiversity of inland waters, which are subjected to severe anthropopression. The development in advance of a method of reproduction and breeding of bitterling under controlled conditions can ensure their survival in the event of an imbalance in the natural environment. These were the first studies of this type, where after 6.5 months of rearing, sexually mature individuals were obtained. In this way, a suitable stocking material of the bitterling was obtained in order to save the endangered populations.

Abstract

Among the several dozen European freshwater fish species, only European bitterling (Rhodeus amarus Bloch) and Rhodeus meridionalis belong to the group of ostrakophilous fish. The embryonic and larval development of the fish in this reproductive group until the time of the yolk sac resorption takes place in the gill cavity of river mussels (Anodonta sp. or Unio sp.). This paper presents the results of the European bitterling Rhodeus amarus being reared under controlled conditions. Bitterling larvae were caught together with river mussels in the natural environment and subsequently placed in a tank for behavioural observations. Bitterling larvae were seen swimming in the water within a week of placing the bivalves under controlled conditions. The bitterling larvae were 8.6 ± 0.11 mm long when they started to swim actively. The rearing was conducted in water at 20 and 26 ± 0.5 °C and lasted for 6.5 months (200 days) in both variants. Initially, the larvae were fed with live nauplii of Artemia salina and subsequently with fodder. The bitterlings in tanks with water at 26 ± 0.5 °C were 66.2 ± 3.0 mm long and weighed 3389 ± 548 mg. For comparison, bitterlings kept in water at 20 ± 0.5 °C were 64.48 ± 3.4 mm long and weighed 3242 ± 427 mg. No larval malformities or mortality were observed during the larvae and fry rearing. The bitterlings had well-developed secondary sexual characteristics and exhibited pre-spawning behaviour at the end of the rearing. This produced suitable bitterling stocking material to be used in the conservation of small or endangered populations.

Thermal Acclimation to the Highest Natural Ambient Temperature Compromises Physiological Performance in Tadpoles of a Stream-Breeding Savanna Tree Frog

Amphibians may be more vulnerable to climate-driven habitat modification because of their complex life cycle dependence on land and water. Considering the current rate of global warming, it is critical to identify the vulnerability of a species by assessing its potential to acclimate to warming temperatures. In many species, thermal acclimation provides a reversible physiological adjustment in response to temperature changes, conferring resilience in a changing climate. Here, we investigate the effects of temperature acclimation on the physiological performance of tadpoles of a stream-breeding savanna tree frog (Bokermannohyla ibitiguara) in relation to the thermal conditions naturally experienced in their microhabitat (range: 18.8-24.6°C). We quantified performance measures such as routine and maximum metabolic rate at different test (15, 20, 25, 30, and 34°C) and acclimation temperatures (18 and 25°C). We also measured heart rate before and after autonomic blockade with atropine and sotalol at the respective acclimation temperatures. Further, we determined the critical thermal maximum and warming tolerance (critical thermal maximum minus maximum microhabitat temperature), which were not affected by acclimation. Mass-specific routine and mass-specific maximum metabolic rate, as well as heart rate, increased with increasing test temperatures; however, acclimation elevated mass-specific routine metabolic rate while not affecting mass-specific maximum metabolic rate. Heart rate before and after the pharmacological blockade was also unaffected by acclimation. Aerobic scope in animals acclimated to 25°C was substantially reduced, suggesting that physiological performance at the highest temperatures experienced in their natural habitat is compromised. In conclusion, the data suggest that the tadpoles of B. ibitiguara, living in a thermally stable environment, have a limited capacity to physiologically adjust to the highest temperatures found in their micro-habitat, making the species more vulnerable to future climate change.

First successful hybridization experiment between native European weatherfish (Misgurnus fossilis) and non-native Oriental weatherfish (M. anguillicaudatus) reveals no evidence for postzygotic barriers

The European weatherfish Misgurnus fossilis (Linnaeus, 1758) is a threatened freshwater species in large parts of Europe and might come under pressure from currently establishing exotic weatherfish species. Additional threats might arise if those species hybridize which has been questioned in previous research. Regarding the hybridization of M. fossilis × M. anguillicaudatus (Cantor, 1842), we demonstrate that despite the considerable genetic distance between parental species, the estimated long divergence time and different ploidy levels do not represent a postzygotic barrier for hybridization of the European and Oriental weatherfish. The paternal species can be easily differentiated based on external pigment patterns with hybrids showing intermediate patterns. No difference in standard metabolic rate, indicating a lack of hybrid vigour, renders predictions of potential threats to the European weatherfish from hybridization with the Oriental weatherfish difficult. Therefore, the genetic and physiological basis of invasiveness via hybridization remains elusive in Misgurnus species and requires further research. The existence of prezygotic reproductive isolation mechanisms and the fertility of F1 hybrids remains to be tested to predict the potential threats of globally invasive Oriental weatherfish species.

Food resource partitioning between juvenile and mature weatherfish Misgurnus fossilis

This study represents a description of the diet composition of one of the largest European cobitids, the weatherfish Misgurnus fossilis. Specimens were collected in a drainage canal, representing a typical habitat for weatherfish, and with gut content analysis conducted with regard to individual total length and maturity stage. Overall, the weatherfish diet mainly consisted of Copepoda, Cladocera, Ostracoda, Oligochaeta, Asellus aquaticus, Chironomidae and Coleoptera larvae, Gastropoda, and detritus. To evaluate size-related patterns of resource use, fish were assigned to two size classes, defined according to size at first maturation. ANOSIM analyses revealed major ontogenetic shifts in feeding strategy, which were related to size and maturity, with a significant ontogenetic shift in feeding pattern, marked by differences in the proportions of the main taxonomic groups of prey consumed. Copepoda and Cladocera dominated in the diet of small and immature individuals, while large weatherfish primarily fed on detritus. Similarly, cluster analysis of diet classified into these food types showed distinct two groups comprising juvenile and mature fish. The weatherfish is a food opportunist using all available resources, but spatially showed a change in feeding sites. Smaller and sexually immature individuals more often use prey caught in the water column and among macrophytes, while larger (sexually mature) individuals occupying the bottom, much more often use detritus as a food base.

Expression and active testing of VP7 from GCRV (Grass carp reovirus) fused with cholera toxin B subunit in rice calli

Grass carp reovirus (GCRV) is one of the most serious pathogens threatening grass carp (Ctenopharyngodon idellus) production and results in high mortality in China. VP7 from GCRV is involved in viral infection and could be suitable for developing vaccines for the control of GCRV infection. To obtain a genetically engineered vaccine and a plant-based oral vaccine and to evaluate their immune efficacy as an oral vaccine against GCRV, cholera toxin B subunit (CTB) of Vibrio cholerae fused to VP7 (CTB-VP7) was transformed into BL21(DE3) for expression. SDS-PAGE and Western blotting showed that the purified CTB-VP7 fusion protein (rCTB-VP7) was approximately 49.0 kDa. Meanwhile, CTB-VP7 was transformed into rice callus cells by Agrobacterium tumefaciens-mediated gene transformation. CTB-VP7 was integrated into the nuclear genome by PCR, and mRNA transcripts of CTB-VP7 were detected. ELISA and Western blot analyses revealed that the CTB-VP7 fusion protein (CTB-VP7) could be expressed in rice callus lines. The level of expression was determined to be 1.54% ± 0.43 of the total soluble protein. CTB-VP7 showed a binding affinity for monosialoganglioside(GM1), a receptor for CTB. CTB-VP7 showed a higher affinity towards GM1 compared to rCTB-VP7. CTB-VP7 bonded to GM1 with different affinities under different temperatures. Maximum binding of CTB-VP7 to GM1 was reported to occur within 2 h at 37 °C, and approximately half of the binding affinity remained at 25 °C. Our results suggest that CTB-VP7 could be produced in rice calli, increasing the possibility that edible plants can be employed in mucosal vaccines for protection against GCRV in aquaculture.

Towards more ecological relevance in sediment toxicity testing with fish: Evaluation of multiple bioassays with embryos of the benthic weatherfish (Misgurnus fossilis)

The effects of sediment contamination on fish are of high significance for the protection of ecosystems, human health and economy. However, standardized sediment bioassays with benthic fish species, that mimic bioavailability of potentially toxic compounds and comply with the requirements of alternative test methods, are still scarce. In order to address this issue, embryos of the benthic European weatherfish (Misgurnus fossilis) were exposed to freeze-dried sediment (via sediment contact assays (SCA)) and sediment extracts (via acute fish embryo toxicity tests) varying in contamination level. The extracts were gained by accelerated solvent extraction with (i) acetone and (ii) pressurized hot water (PHWE) and subsequently analyzed for polycyclic aromatic hydrocarbons, polychlorinated biphenyls and polychlorinated dibenzodioxins and dibenzofurans. Furthermore, embryos of the predominately used zebrafish (Danio rerio) were exposed to extracts from the two most contaminated sediments. Results indicated sufficient robustness of weatherfish embryos towards varying test conditions and sensitivity towards relevant sediment-bound compounds. Furthermore, a compliance of effect concentrations derived from weatherfish embryos exposed to sediment extracts (96h-LC₅₀) with both measured gradient of sediment contamination and previously published results was observed. In comparison to zebrafish, weatherfish embryos showed higher sensitivity to the bioavailability-mimicking extracts from PHWE but lower sensitivity to extracts gained with acetone. SCAs conducted with weatherfish embryos revealed practical difficulties that prevented an implementation with three of four sediments tested. In summary, an application of weatherfish embryos, using bioassays with sediment extracts from PHWE might increase the ecological relevance of sediment toxicity testing: it allows investigations using benthic and temperate fish species considering both bioavailable contaminants and animal welfare concerns.