Selective breeding of saline-tolerant striped catfish (Pangasianodon hypophthalmus) for sustainable catfish farming in climate vulnerable Mekong Delta, Vietnam

peer reviewedStriped catfish (Pangasianodon hypophthalmus), a freshwater species cultured mainly in the Mekong Delta region in Southern Vietnam, is facing a significant challenge due to salinity intrusion as a result of climatic changes. Given these evolving environmental conditions, selecting new strains with a higher salinity tolerance could make production of striped catfish economically feasible in brackish environments. In this study, we carried out a selection program aimed at developing a striped catfish strain able to survive and grow fast in a saline environment. To implement the selection program, we first collected males and females from different provinces in the Mekong delta. We next performed a factorial cross of these breeders to produce half- and full-sib families. When fish reached fry stage (47 dph), we put them in a saline environment (10 ppt) and subsequently kept 50 % of the fastest-growing fish after 143 days post hatching (dph). We repeated this mass selection procedure after 237 dph and 340 dph. We maintained in parallel a randomly selected group in saline conditions and a group of fish reared in freshwater to serve as controls. After crossing the selected individuals, we performed several tests on the next generation of fish to evaluate the effectiveness of selection after one generation in saline conditions. Average direct responses to selection were 18.0 % for growth and 11.4 % for survival rate after one generation of selection. We estimated a moderate realized heritability (0.29) for body weight. The genetic gains obtained in our study for body weight and survival rate after one generation of selection under saline conditions suggest that selection can be effective to improve ability of striped catfish to cope with saline stress. We conclude that our selection program has succeeded in developing a productive strain of striped catfish with better tolerance to salinity. © 2022 The Author

A High-Quality Genome Assembly of Striped Catfish (Pangasianodon hypophthalmus) Based on Highly Accurate Long-Read HiFi Sequencing Data

The HiFi sequencing technology yields highly accurate long-read data with accuracies greater than 99.9% that can be used to improve results for complex applications such as genome assembly. Our study presents a high-quality chromosome-scale genome assembly of striped catfish (Pangasianodon hypophthalmus), a commercially important species cultured mainly in Vietnam, integrating HiFi reads and Hi-C data. A 788.4 Mb genome containing 381 scaffolds with an N50 length of 21.8 Mb has been obtained from HiFi reads. These scaffolds have been further ordered and clustered into 30 chromosome groups, ranging from 1.4 to 57.6 Mb, based on Hi-C data. The present updated assembly has a contig N50 of 14.7 Mb, representing a 245-fold and 4.2-fold improvement over the previous Illumina and Illumina-Nanopore-Hi-C based version, respectively. In addition, the proportion of repeat elements and BUSCO genes identified in our genome is remarkably higher than in the two previously released striped catfish genomes. These results highlight the power of using HiFi reads to assemble the highly repetitive regions and to improve the quality of genome assembly. The updated, high-quality genome assembled in this work will provide a valuable genomic resource for future population genetics, conservation biology and selective breeding studies of striped catfish

Challenges and Lessons Learned in the Development of a Participatory Learning and Action Intervention to Tackle Antibiotic Resistance: Experiences From Northern Vietnam

Antibiotic use in the community for humans and animals is high in Vietnam, driven by easy access to over-the counter medicines and poor understanding of the role of antibiotics. This has contributed to antibiotic resistance levels that are amongst the highest in the world. To address this problem, we developed a participatory learning and action (PLA) intervention. Here we describe challenges and lessons learned while developing and testing this intervention in preparation for a large-scale One Health trial in northern Vietnam. We tested the PLA approach using community-led photography, and then reflected on how this approach worked in practice. We reviewed and discussed implementation documentation and developed and refined themes. Five main themes were identified related to challenges and lessons learned: understanding the local context, stakeholder relationship development, participant recruitment, building trust and motivation, and engagement with the topic of antibiotics and antimicrobial resistance (AMR). Partnerships with national and local authorities provided an important foundation for building relationships with communities, and enhanced visibility and credibility of activities. Partnership development required managing relationships, clarifying roles, and accommodating different management styles. When recruiting participants, we had to balance preferences for top-down and bottom-up approaches. Building trust and motivation took time and was challenged by limited study team presence in the community. Open discussions around expectations and appropriate incentives were re-visited throughout the process. Financial incentives provided initial motivation to participate, while less tangible benefits like collective knowledge, social connections, desire to help the community, and new skills, sustained longer-term motivation. Lack of awareness and perceived importance of the problem of AMR, affected initial motivation. Developing mutual understanding through use of common and simplified language helped when discussing the complexities of this topic. A sense of ownership emerged as the study progressed and participants understood more about AMR, how it related to their own concerns, and incorporated their own ideas into activities. PLA can be a powerful way of stimulating community action and bringing people together to tackle a common problem. Understanding the nuances of local power structures, and allowing time for stakeholder relationship development and consensus-building are important considerations when designing engagement projects

Effects of immunostimulants on the immune response and resistance of striped catfish (Pangasianodon hypophtalmus) to bacterial disease : in vitro and in vivo approaches.

The striped catfish (Pangasianodon hypophthalmus) farming system in the Mekong Delta of Viet Nam has been vigorously developed in recent years. It has resulted from expansion of farming areas, application of new farming techniques and an increase of intensification level. As in other developing striped catfish culture venture, health problems including disease outbreaks have been encountered. The use of chemicals and antibiotics in striped catfish farming has increased for prevention and treatment of diseases. These compounds have attracted criticism because of a potential hazard for fish health, environment risk and human consumers. The present study aimed to evaluate the efficiency of different immunostimulating compounds in striped catfish farming in order to reduce the use and impact of antibiotics and chemicals by alternative method of immunostimulation. A combination of in vitro and in vivo approaches was used to investigate the effects of Lipopolysaccharide (LPS) on immune responses of striped catfish. Some potential results of this research were highlighted. The innate immune system of striped catfish was significantly stimulated by LPS injection or feeding through the increase of respiratory burst, lysozyme and complement activities. Total of immunoglobulins was also enhanced in LPS treatment. A challenge test with a common bacterial pathogen (Edwardsiella ictaluri) for striped catfish was performed and documented that LPS could significantly reduce the cumulative mortality of fish, especially in low dose such as 3 mg LPS/kg fish for injection and 0.01% of LPS for oral. Proteomic analysis performed in both approaches suggested that LPS could stimulate the over-expression of several immune proteins such as complement component, lysozyme precursor, transferrin, immunoglobulin,… In addition, the results from in vitro also showed that the response of striped catfish to LPS involved an increase of many protein expression related in cytoskeleton, stress response, cell signaling, carbohydrate metabolic process as well as muscle contraction. All these protein responses result in an increase of the ability of striped catfish peripheral blood mononuclear cells (PBMC) to produce and secrete pro-inflammatory mediator, which is fundamental to fight against a pathogen invasion. Comparing the efficiency of different immunostimulants on immune responses and bacterial resistance of striped catfish was also investigated. The results suggested that all tested immunnostimulants (β-glucan, bovine lactoferrin, chitosan, levamisole and vitamin C) could significantly enhance the immune response in striped catfish and protect fish from bacteria damage. Among them levamisole at the dose 5 mg/kg fish performed as the best immunostimulant. From above results, levamisole and LPS were selected as immunostimulant in a comparative experiment aiming to evaluate whether these compounds could efficiently replace an antibiotic treatment in infected striped catfish by E. ictaluri. Both LPS and levamisole stimulated the immune system of striped catfish and reduce the cumulative mortality after challenge with bacteria. The fish mortality in treatments LPS and levamisole without anitibiotics did not significantly differ with the one of control (without immunostimulants) treated with antibiotics. These results are good evidences to support that LPS and levamisole can replace antibiotic treatment to protect striped catfish against Edwardsiella ictaluri. However, validation in field trials needs to be performed before advocating the use of LPS and levamisole in intensive striped catfish culture practices. Overall, the use of immunostimulants in striped catfish aquaculture appears as an excellent method to enhance the immune system and increase the bacterial resistance of this fish species, supporting the replacement of antibiotics by alternative method such as the immunomodulation.(DOCSC03) -- FUNDP, 201