Controlled infection of Poecilia reticulata Peters (guppy) with Tetrahymena by immersion and intraperitoneal injection

Antiparasitic efficacy of flavonoids identified from Psoralea corylifolia against Tetrahymena piriformis in guppy (Poecilia reticulate)

Tetrahymena piriformis belongs to the ciliated protists (ciliates), causing severe economic losses in aquaculture. Chemical drugs currently used usually have toxic side effects, and there is no specific drug against Tetrahymena. Therefore, it is an urgent need to identify new antiparasitic lead compounds. In the present study, the in vitro parasiticidal activity of ethyl acetate (EtOAc) extracts and water extracts from 22 selected traditional Chinese medicines (TCMs) were evaluated against T. piriformis. The EtOAc extract of P. corylifolia turned out to be the most active with the minimum parasiticidal concentration of 100 mg/L within 3 h. Thus, it was separated into 12 fractions by the first-dimensional (D1) normal phase liquid chromatography (NPLC), meanwhile combining with in vitro antiparasitic tests for activity tracking. Subsequently, 8 flavonoids were identified in the active fractions by the second-dimensional (D2) reverse phase liquid chromatography (RPLC) tandem high-resolution mass spectrometry. According to the results, 5 flavonoids were selected for in vitro antiparasitic test, of which isobavachalcone showed the minimum parasiticidal concentration of 3.125 mg/L in 2 h. Bathing treatment of infected guppies with isobavachalcone could significantly reduce the burden of T. piriformis, obtaining a 24-h median effective concentration (24-h EC50) value of 1.916 mg/L. And the concentration of isobavachalcone causing guppies to die within 24 h is 39 times than that of 24-h EC50. The results demonstrated that isobavachalcone has the potential to be developed into a novel commercial fish drug against T. piriformis.

Aeromonas hydrophila induction method in adult zebrafish (Danio rerio) as animal infection models

Background and Aim: Zebrafish are frequently used as model organisms in scientific research as their genes mirror those of humans. Aeromonas hydrophila bacteria can infect humans and animals, mainly fish. This study aimed to identify the concentration and route of A. hydrophila infection in adult zebrafish. Zebrafish had been used as a challenge test by analyzing their hematological profiles, blood glucose levels, and survival rates. Materials and Methods: Induction of cell supernatant free (CSF) from A. hydrophila bacteria in adult zebrafish was carried out via bath immersion (BI), intraperitoneal injection (IPI), intramuscular injection (IMI), and healthy zebrafish as a control (C). The bacterial concentrations were 107, 109, and 1011 colony-forming units (CFU)/mL. At 24 h post-infection, the outcomes of infection were evaluated based on survival rates, hematological profiles, and blood glucose levels. A one-way analysis of variance with a confidence level of 95% was employed to examine the data. Results: In the BI, IPI, and IMI treatment groups, the survival rate of the fish reached a peak of 100%, 22%–100%, and 16%–63%, respectively, compared with the injection technique. In the IMI2 group, a 109 CFU/mL bacterial concentration was determined to correspond to the lethal dosage 50. All infection groups had lower erythrocyte and hemoglobin counts but higher leukocyte counts than the control group. The blood sugar levels of the healthy and infected groups were not significantly different. Conclusion: The route of A. hydrophila infection through Intramuscular injection with a concentration of 109 CFU/mL indicated a high performance compared to other techniques. This method could be developed as a reproducible challenge test.

Silver nanoparticles are lethal to the ciliate model Tetrahymena and safe to the pike silverside Chirostoma estor

Ciliate ectoparasites are one of the most important groups of pathogens in fish culture, and the traditional treatments are sometimes harmful to the fish and the environment. Thus, the search for novel compounds that are effective at low concentrations and safe for fish are necessary to optimise treatments in aquaculture. The antiprotozoal capacity of silver nanoparticles (AgNPs) against the ciliate Tetrahymena has been documented; however, their toxicity may vary with the synthesis methodology and nanoparticle size. The objectives of this study were a) to evaluate the acute toxicity in vitro of two AgNPs (Argovit™ and UTSA) on Tetrahymena sp., a biological model for ciliated ectoparasites of fish and b) to test the safety of lethal and higher doses of UTSA AgNPs for ciliates on the fish C. estor. Light microscopy and scanning electron microscopy (SEM) were used to determine whether AgNPs affected the structure of the cell surface of Tetrahymena. The mortality, histopathological alterations and metagenomics of the fish were used to determine the major effects of UTSA AgNPs. In Tetrahymena, the median lethal concentration (LC₅₀) for Argovit™ was 2501 ± 1717 ng/L at 15 min and 796 ± 510 ng/L at 60 min, while the LC₅₀ for UTSA AgNPs was 4 ± 2 and 1 ± 0.6 ng/L at 15 min and 60 min, respectively. A concentration of 3300 ng/L Argovit™ and 10.6 ng/L UTSA AgNPs for 15 and 60 min, respectively, was 100% effective against Tetrahymena. After 60 min of exposure to 0.25 and 0.50 ng/L UTSA AgNPs, the number of cilia significantly reduced, there were small holes on the cell surface, and the cellular membrane was ruptured. In fish exposed to lethal (10.6 ng/L) and higher (31.8 and 95.4 ng/L) doses of UTSA, the AgNPs did not affect fish survival after 96 h, and there were no signs of histopathological damage or gut microbial changes. This study is the first report on microscopic and ultrastructural changes in Tetrahymena after exposure to significantly low concentrations of UTSA AgNPs with antiprotozoal efficacy without evidence of harmful effects on fish. These results provide the basis for further studies of both pet aquarium and commercial fish that may validate these findings at a larger experimental scale, taking into account AgNPs bioaccumulation, safety for human consumption and environmental impact.

The effect of tertiary treated wastewater on fish growth and health: Laboratory-scale experiment with Poecilia reticulata (guppy)

Treated wastewater (TWW) constitutes a sustainable water resource and has been used for fish culture in some countries around the world, although there are no comprehensive data on the effect of TWW on fish growth and health in the context of aquaculture production. Our objectives were to examine how fish culture in TWW affected fish growth and fitness, as well as compliance with the international standards for safe consumption. Guppy (Poecilia reticulata) fingerlings were reared in 0%, 50% and 100% tertiary TWW (TTWW), from the age of five days, for a period of four months. In water analyses, 33 out of 67 tested organic micropollutants (OMPs) were detected in the TTWW samples at least once, at concentrations that are typically reported in domestic TTWW. Fish survival ranged between 77-80% and did not differ between treatment groups. Fish growth and mortality following challenge infection with Tetrahymena sp. (which ranged between 64-68%), were similar among treatment groups. Of tested immunological parameters, lysozyme and anti-protease was similar among treatments while complement activity was highest in the 50% TTWW-reared fish. No abnormalities were observed in the histopathological analysis. Levels of heavy metals, polychlorinated-biphenyls (PCBs) and organochlorines (OCs) in fish were below the detection limit and below the Food and Agriculture Organization of the United Nations (FAO) and the European Union EU maximal permitted levels in food fish. Results suggest that the yield of fish grown in TTWW is potentially similar to that in freshwater, and the produced fish comply with the standards of consumer safety. The results are in line with previous studies that examined the feasibility of TWW-fed aquaculture.

Evaluation of guppy (Poecilia reticulata Peters) immunization against Tetrahymena sp. by enzyme-linked immunosorbent assay (ELISA)

Analysis of the effectiveness of guppy (Poecilia reticulata Peters) immunization based on measurements of antibody (Ab) titers suffers from a shortage of reagents that can detect guppy antibodies (Abs). To overcome this problem, we immunized mice with different preparations of guppy immunoglobulins (Igs) and used the mouse antisera to develop a quantitative enzyme-linked immunosorbent assay (ELISA). The most efficient immunogen for mouse immunization was guppy Igs adsorbed on protein A/G beads. Antisera from mice boosted with this immunoglobulin (Ig) preparation were highly specific and contained high Ab titers. They immunoreacted in a Western blot with Ig heavy and light chains from guppy serum, and Ig heavy chain from guppy whole-body homogenate. The mouse anti-guppy Ig was applied in an ELISA aimed at comparing the efficiency of different routes of guppy immunization against Tetrahymena: (i) anal intubation with sonicated Tetrahymena (40,000 Tetrahymena/fish in a total volume of 10 μL) mixed with domperidon, deoxycholic acid and free amino acids (valine, leucine, isoleucine, phenylalanine and tryptophan), or (ii) intraperitoneal (i.p.) injection of sonicated Tetrahymena in complete Freund's adjuvant (15,000 Tetrahymena/fish in total a volume of 20 μL). Negative control fish were anally intubated with the intubation mixture without Tetrahymena, or untreated. ELISA measurement of anti-Tetrahymena Ab titer revealed a significantly higher level of Abs in i.p.-immunized guppies, compared to the anally intubated and control fish. In addition, the efficiency of immunization was tested by monitoring guppy mortality following (i) i.p. challenge with Tetrahymena (900 Tetrahymena/fish) or (ii) cold stress followed by immersion in water containing 10,000 Tetrahymena/mL. Fish mortality on day 14 post-Tetrahymena infection by i.p. injection exceeded 50% in the control and anally intubated fish, compared to 31% in i.p.-immunized fish. Immunization did not protect from pathogen challenge by immersion. The results suggest a direct correlation between the anti-Tetrahymena Ab response and fish resistance to i.p.-injected Tetrahymena, but not to infection by immersion preceded by cold stress.