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Poly‐β‐hydroxybutyrate (PHB) can promote growth and enhance immunity of aquatic animals such as gibel carp, Carassius auratus gibelio. However, the optimal dietary supplementation level and feeding duration for gibel carp are still unclear. In this study, effects of various PHB supplementation levels on gibel carp growth performance, digestive enzyme activities, immune function, disease resistance, and intestinal mucosal barrier were evaluated. Six experimental diets differing in PHB levels were formulated, that is, 0% (P0 as control), 0.5% (P0.5), 1% (P1), 2% (P2), 4% (P4), and 8% (P8). Results indicated that PHB promoted fish growth performance significantly (p < 0.05). Compared to control group P0, the intestinal lipase, protease, and amylase activities in group P4 were significantly increased after 30 days (p < 0.05). Meanwhile, dietary PHB supplementation at 4% level for 30 days and 0.5% for 60 days upregulated the mRNA expression of immune‐related genes, including IL‐11, ITLN, MPO, KRT‐8, DUSP‐1, and PNP‐5α (p < 0.01). Furthermore, PHB at 4% for 30 days showed positive effects on disease resistance against both viral and bacterial infections and exerted beneficial effects on maintaining epithelial mucosal barrier integrity. In conclusion, 4% PHB supplementation for 30 days or 0.5% for 60 days was recommended for gibel carp culture. [ABSTRACT FROM AUTHOR]

In aquaculture, antibiotics are commonly used to provide protection against pathogens; however, this practice has become controversial due to increased occurrences of microbial resistance, and alternatives are needed. This study aimed to investigate the antimicrobial activity of yeast glycoprotein (YG) against Aeromonas caviae. Pathogens were isolated from liver of diseased Carassius auratus gibelio. Based on morphological and biochemical analysis, together with 16S rRNA gene sequencing, the isolated strains were identified as A. caviae and concluded as clones of a single strain and named L2. Further pathogenicity analysis revealed that A. caviae possessed β‐haemolysis, and its median lethal dose for C. gibelio was 1.33 × 106 CFU/ml. Hepatic adenylate kinase and pyruvate kinase activities of C. gibelio were inhibited post–A. caviae infection. Antimicrobial drug test suggested that A. caviae was a multidrug‐resistant organism but could be inhibited by YG in vitro. Minimum inhibitory and bactericidal concentration of YG was 83.3 mg/ml and 166.7 mg/ml, respectively. Microbiota sequencing results showed that YG supplement could obviously decrease the relative abundance of Aeromonas and increase the microbial diversity. Our study revealed that A. caviae from C. gibelio was a multidrug‐resistant bacteria strain, and could be significantly inhibited by YG in vivo and in vitro, thus providing important insights into ecological control and pathogenesis of A. caviae in aquaculture. [ABSTRACT FROM AUTHOR]

Cyprinid herpesvirus 2 (Cy HV-2) is the main pathogen responsible for causing haematopoietic necrosis disease in Carassius auratus gibelio. Although many nucleic acid-based diagnostic methods have been applied, no stable and sensitive immunological diagnostic approaches have been reported. In this study, to detect Cy HV-2 in clinical samples using immunological methods, recombinant ORF72 protein ( pORF72), encoded by the Cy HV-2 ORF72 gene, was used as a capture antigen to identify blood and tissues infected with Cy HV-2. First, ORF72 gene was amplified from the Cy HV-2 genome and cloned into a PGEX-4t-3 expression vector to produce pORF72 in Escherichia coli. The purified pORF72 was used as an immunogen to prepare monoclonal antibodies. The Western blotting assays revealed that the monoclonal antibody could specifically identify the pORF72. Furthermore, an immunohistochemical protocol and a blood smear method were established to detect Cy HV-2 in carps. The results indicate that the monoclonal antibody against pORF72 could be utilized as an effective detection tool for haematopoietic necrosis disease in Carassius auratus gibelio. [ABSTRACT FROM AUTHOR]

A Thelohanellus species was encountered during a survey on Thelohanellus diversity of Carassius auratus gibelio ( Bloch) in China. The infection is characterized by the presence of large cysts of 1.4-3.2 cm in diameter in the skin of host. Mature spores were ampullaceous in frontal view and testudinate in lateral view, measuring 19.7 ± 0.7 (18.6-20.8) μm long, 7.6 ± 0.4 (6.6-8.4) μm wide and 7.3 ± 0.5 (6.6-8.8) μm thick. The single polar capsule was elongated pyriform, with 11.1 ± 0.5 (10.0-11.9) μm long and 5.3 ± 0.3 (4.3-5.8) μm wide. Polar filaments coiled with 7-8 turns. Scanning electron microscopy revealed a smooth spore surface with flat side and convex side. The sutural line was straight or ' S' like, running near the middle of the valves. Histologically, the large cysts consisting of numerous small plasmodia developed in the dermis of the skin. The BLAST search indicated that the newly obtained ssr RNA gene sequences did not match any available sequences in Gen Bank and phylogenetic analysis placed it in the Thelohanellus clade. Based on morphology and molecular differences with reported Thelohanellus spp., this parasite was described as a new species of genus Thelohanellus. [ABSTRACT FROM AUTHOR]

Infection of a Myxobolus species, previously identified as Myxobolus rotundus, was detected in 182 of 7892 (2.31%) allogynogenetic gibel carp, Carassius auratus gibelio, in a closed pond culture system in China. Morphological and molecular data showed that this myxosporean is a different species from M. rotundus parasitizing Abramis brama in Europe and is thus designated as a new species, Myxobolus turpisrotundus. M. rotundus (s.l.) ex C. auratus auratus is a synonym of M. turpisrotundus. Plasmodia of M. turpisrotundus develop in the subepidermal tissues of the body surface resulting in an unaesthetic appearance and causing severe economic losses. Prevalence of infection with the myxosporean plasmodia varied seasonally, increasing in winter and decreasing in spring. Prevalence was positively correlated to host size, but no host sex-specificity was found. No infection was observed in other fish species (grass carp, bighead carp and yellow catfish) reared in the same pond, suggesting that the parasite has a relatively strict host specificity. Plasmodia grew gradually as the parasite developed, and reached up to a maximum 5.6 mm in diameter. Plasmodia ruptured naturally to release the mature spores and host fish completely recovered with no mortality. Release of spores and regeneration of lesions were not correlated with water temperature. Histology showed that plasmodia developed sub-epidermally, and that the wall of the plasmodia was composed of a multiple complex structure, including layers of fibroblasts, a collagenous membrane, melanophores and a layer of cup-like cells of unknown derivation and function. The cup-like cells are in direct contact with pre-sporogonic stages located in the peripheral parts of the large plasmodia. No severe host inflammatory response was seen. [ABSTRACT FROM AUTHOR]

Myxobolus wulii (= Myxosoma magna) was first described from the gills of goldfish, Carassius auratus auratus, in China. Subsequently, a myxosporean infecting the hepatopancreas of allogynogenetic gibel carp, C. auratus gibelio, was designated as a different species, Myxobolus guanqiaoensis, although the morphological features were almost identical to those of M. wulii. In Japan, an unidentified Myxobolus sp. was found in the gills and hepatopancreas of goldfish. Morphological and molecular analyses in the present study identified these myxosporeans as M. wulii, which was thus shown to use different habitats in the host fish. Phylogenetic analyses of small subunit ribosomal RNA gene sequences showed that M. wulii is closely related to two gill-infecting Myxobolus species, M. ampullicapsulatus and M. longisporus. Fish infected with M. wulii in the hepatopancreas exhibit swollen abdomens and chronic mortality. Hepatopancreas tissues are virtually destroyed and replaced with plasmodia of M. wulii. A remarkable difference in susceptibility to M. wulii between two clones of allogynogenetic gibel carp was observed, suggesting that resistance to the myxosporean infection was established in a clone of fish bred by allogynogenesis. [ABSTRACT FROM AUTHOR]