Effects of Shrimp Shell-Derived Chitosan on Growth, Immunity, Intestinal Morphology, and Gene Expression of Nile Tilapia (Oreochromis niloticus) Reared in a Biofloc System.

Chitosan (CH) shows great potential as an immunostimulatory feed additive in aquaculture. This study evaluates the effects of varying dietary CH levels on the growth, immunity, intestinal morphology, and antioxidant status of Nile tilapia (Oreochromis niloticus) reared in a biofloc system. Tilapia fingerlings (mean weight 13.54 ± 0.05 g) were fed diets supplemented with 0 (CH0), 5 (CH5), 10 (CH10), 20 (CH20), and 40 (CH40) mL·kg-1 of CH for 8 weeks. Parameters were assessed after 4 and 8 weeks. Their final weight was not affected by CH supplementation, but CH at 10 mL·kg-1 significantly improved weight gain (WG) and specific growth rate (SGR) compared to the control (p < 0.05) at 8 weeks. Skin mucus lysozyme and peroxidase activities were lower in the chitosan-treated groups at weeks 4 and 8. Intestinal villi length and width were enhanced by 10 and 20 mL·kg-1 CH compared to the control. However, 40 mL·kg-1 CH caused detrimental impacts on the villi and muscular layer. CH supplementation, especially 5-10 mL·kg-1, increased liver and intestinal expressions of interleukin 1 (IL-1), interleukin 8 (IL-8), LPS-binding protein (LBP), glutathione reductase (GSR), glutathione peroxidase (GPX), and glutathione S-transferase (GST-α) compared to the control group. Overall, dietary CH at 10 mL·kg-1 can effectively promote growth, intestinal morphology, innate immunity, and antioxidant capacity in Nile tilapia fingerlings reared in biofloc systems.

Review of quorum-quenching probiotics: A promising non-antibiotic-based strategy for sustainable aquaculture.

The emergence of antibiotic-resistant bacteria (ARBs) and genes (ARGs) in aquaculture underscores the urgent need for alternative veterinary strategies to combat antimicrobial resistance (AMR). These measures are vital to reduce the likelihood of entering a post-antibiotic era. Identifying environmentally friendly biotechnological solutions to prevent and treat bacterial diseases is crucial for the sustainability of aquaculture and for minimizing the use of antimicrobials, especially antibiotics. The development of probiotics with quorum-quenching (QQ) capabilities presents a promising non-antibiotic strategy for sustainable aquaculture. Recent research has demonstrated the effectiveness of QQ probiotics (QQPs) against a range of significant fish pathogens in aquaculture. QQ disrupts microbial communication (quorum sensing, QS) by inhibiting the production, replication, and detection of signalling molecules, thereby reducing bacterial virulence factors. With their targeted anti-virulence approach, QQPs have substantial promise as a potential alternative to antibiotics. The application of QQPs in aquaculture, however, is still in its early stages and requires additional research. Key challenges include determining the optimal dosage and treatment regimens, understanding the long-term effects, and integrating QQPs with other disease control methods in diverse aquaculture systems. This review scrutinizes the current literature on antibiotic usage, AMR prevalence in aquaculture, QQ mechanisms and the application of QQPs as a sustainable alternative to antibiotics.

Genomics-driven prophylactic measures to increase streptococcosis resistance in tilapia.

Streptococcosis caused by Streptococcus agalactiae and S. iniae is a significant problem that affects the success of tilapia aquaculture industries worldwide. In this critical review, we summarize the applicable practical strategies which may effectively enhance the world tilapia aquaculture development. Recently, the effect of vaccination and selective breeding programmes has been recognized as valuable tools to control the target disease and other consequent negative impacts caused by chemical and drug application. Advances in sequencing and molecular technologies are vital helpful factors with which to develop robust vaccines and increase the selective breeding programme's precision against streptococcosis. The genomic selection for streptococcosis-resistant tilapia strains and crucial genomic application for genomics' contribution to the development of novel Streptococcus vaccine, comparative genomics approach identifying vaccine candidates by reverse vaccinology, and next-generation vaccine design were described. Information from our review is encouraging for practical implementation of the development of vaccination and genomic selection in tilapia for streptococcosis resistance, which may be vital factors to sustain the world tilapia aquaculture industry effectively.

Co-infection of Candidatus Piscichlamydia Trichopodus (Order Chlamydiales) and Henneguya sp. (Myxosporea, Myxobolidae) in Snakeskin Gourami Trichopodus pectoralis (Regan 1910).

The present study describes a simultaneous infection of a novel Chlamydia-like organism (CLO) with a Myxozoa parasite, Henneguya sp. in snakeskin gourami Trichopodus pectoralis in Thailand. A new CLO is proposed "Candidatus Piscichlamydia trichopodus" (CPT) based on 16S rRNA phylogenetic analysis. Systemic intracellular CPT infection was confirmed by histological examination, in situ hybridization, PCR assay, and sequencing of 16S rRNA. This novel pathogen belongs to the order Chlamydiales but differs in certain aspects from other species. The histopathological changes associated with CPT infection were different from the typical pathological lesions of epitheliocystis caused by previously known CLO. Unlike other CLO, CPT localized in the connective tissue rather than in the epithelial cells and formed smaller clumps of intracellular bacteria that stained dark blue with hematoxylin. On the other hand, typical myxospores of the genus Henneguya with tails were observed in the gill sections. Infection with Henneguya sp. resulted in extensive destruction of the gill filaments, most likely leading to respiratory distress. Due to the frequency of co-infections and the unavailability of culture methods for CLO and Henneguya sp., it was difficult to determine which pathogens were directly responsible for the associated mortality. However, co-infections may increase the negative impact on the host and the severity of the disease. Given the commercial importance of the snakeskin gourami and its significant aquaculture potential, the findings of this study are important for further studies on disease prevention.

Tilapia Lake Virus was not detected in non-tilapine species within tilapia polyculture systems of Bangladesh.

Sixteen countries, including Bangladesh, have reported the presence of tilapia lake virus (TiLV), an emerging tilapia pathogen. Fish polyculture is a common farming practice in Bangladesh. Some unusual mortalities reported in species co-cultivated with TiLV-infected tilapia led us to investigate whether any of the co-cultivated species would also test positive for TiLV and whether they were susceptible to TiLV infection under controlled laboratory experiments. Using 183 samples obtained from 15 farms in six districts across Bangladesh, we determined that 20% of the farms tested positive for TiLV in tilapia, while 15 co-cultivated fish species and seven other invertebrates (e.g. insects and crustaceans) considered potential carriers all tested negative. Of the six representative fish species experimentally infected with TiLV, only Nile tilapia showed the typical clinical signs of the disease, with 70% mortality within 12 days. By contrast, four carp species and one catfish species challenged with TiLV showed no signs of TiLV infection. Challenged tilapia were confirmed as TiLV-positive by RT-qPCR, while challenged carp and walking catfish all tested negative. Overall, our field and laboratory findings indicate that species used in polycultures are not susceptible to TiLV. Although current evidence suggests that TiLV is likely host-specific to tilapia, targeted surveillance for TiLV in other fish species in polyculture systems should continue, in order to prepare for a possible future scenario where TiLV mutates and/or adapts to new host(s).

Insight Into Whole Genome of Aeromonas veronii Isolated From Freshwater Fish by Resistome Analysis Reveal Extensively Antibiotic Resistant Traits.

Aeromonas veronii outbreaks in tilapia farming caused relatively high mortalities, and the bacteria was resistant to many kinds of antimicrobials used in Thailand aquaculture. According to the CLSI standard, the determination of antimicrobials efficacy has been limited to phenotypic analyses, and a genomics study is required. This research aimed to analyze the resistome of A. veronii isolated from diseased tilapia in Chainat, Nong Khai, and Uttaradit provinces in Thailand. A total of 12 isolates of A. veronii were identified based on the gyrB sequencing and then, the MIC values to eight antimicrobials (AMP, AML, GEN, ENR, OXO, OTC, SXT, and FFC) were determined. According to the MIC patterns, whole genome sequencing (WGS) of five representatives and resistome analysis were performed, including 15 genomes of A. veronii isolated from freshwater fish available in the NCBI. All tilapia isolates were susceptible to FFC but resistant to AML and AMP while OTC resistance was the most dominant. In addition to the WGS analysis, 4.5 Mbp of A. veronii was characterized. A total of 20 ARGs were detected by resistome analysis and 16 genes were shared among the A. veronii population. In conclusion, A. veronii strains isolated from tilapia exhibited a resistance to several antimicrobials and multidrug resistance (MDR) which was related to the presence of multiple ARGs. Aeromonas veronii shared the ARGs in their population worldwide with a possibility of a plasmid-mediated acquisition due to the presence of resistance islands.

Molecular evidence for homologous strains of infectious spleen and kidney necrosis virus (ISKNV) genotype I infecting inland freshwater cultured Asian sea bass (Lates calcarifer) in Thailand.

Infectious spleen and kidney necrosis virus (ISKNV) is a fish-pathogenic virus belonging to the genus Megalocytivirus of the family Iridoviridae. In 2018, disease occurrences (40-50% cumulative mortality) associated with ISKNV infection were reported in grown-out Asian sea bass (Lates calcarifer) cultured in an inland freshwater system in Thailand. Clinical samples were collected from seven distinct farms located in the eastern and central regions of Thailand. The moribund fish showed various abnormal signs, including lethargy, pale gills, darkened body, and skin hemorrhage, while hypertrophied basophilic cells were observed microscopically in gill, liver, and kidney tissue. ISKNV infection was confirmed on six out of seven farms using virus-specific semi-nested PCR. The MCP and ATPase genes showed 100% sequence identity among the virus isolates, and the virus was found to belong to the ISKNV genotype I clade. Koch's postulates were later confirmed by challenge assay, and the mortality of the experimentally infected fish at 21 days post-challenge was 50-90%, depending on the challenge dose. The complete genome of two ISKNV isolates, namely KU1 and KU2, was recovered directly from the infected specimens using a shotgun metagenomics approach. The genome length of ISKNV KU1 and KU2 was 111,487 and 111,610 bp, respectively. In comparison to closely related ISKNV strains, KU1 and KU2 contained nine unique genes, including a caspase-recruitment-domain-containing protein that is potentially involved in inhibition of apoptosis. Collectively, this study indicated that inland cultured Asian sea bass are infected by homologous ISKNV strains. This indicates that ISKNV genotype I should be prioritized for future vaccine research.

Dissecting the localization of Tilapia tilapinevirus in the brain of the experimentally infected Nile tilapia, Oreochromis niloticus (L.).

Tilapia tilapinevirus or tilapia lake virus (TiLV) is an emerging virus that inflicts significant mortality on farmed tilapia globally. Previous studies reported detection of the virus in multiple organs of the infected fish; however, little is known about the in-depth localization of the virus in the central nervous system. Herein, we determined the distribution of TiLV in the entire brain of experimentally infected Nile tilapia. In situ hybridization (ISH) using TiLV-specific probes revealed that the virus was broadly distributed throughout the brain. The strongest positive signals were dominantly detected in the forebrain (responsible for learning, appetitive behaviour and attention) and the hindbrain (involved in controlling locomotion and basal physiology). The permissive cell zones for viral infection were observed mostly to be along the blood vessels and the ventricles. This indicates that the virus may productively enter into the brain through the circulatory system and widen broad regions, possibly through the cerebrospinal fluid along the ventricles, and subsequently induce the brain dysfunction. Understanding the pattern of viral localization in the brain may help elucidate the neurological disorders of the diseased fish. This study revealed the distribution of TiLV in the whole infected brain, providing new insights into fish-virus interactions and neuropathogenesis.