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).     

Two-year surveillance of tilapia lake virus (TiLV) reveals its wide circulation in tilapia farms and hatcheries from multiple districts of Bangladesh

Tilapia lake virus (TiLV) is an emerging pathogen in aquaculture, reportedly affecting farmed tilapia in 16 countries across multiple continents. Following an early warning in 2017 that TiLV might be widespread, we executed a surveillance programme on tilapia grow-out farms and hatcheries from 10 districts of Bangladesh in 2017 and 2019. Among farms experiencing unusual mortality, eight out of 11 farms tested positive for TiLV in 2017, and two out of seven tested positive in 2019. Investigation of asymptomatic broodstock collected from 16 tilapia hatcheries revealed that six hatcheries tested positive for TiLV. Representative samples subjected to histopathology confirmed pathognomonic lesions of syncytial hepatitis. We recovered three complete genomes of TiLV from infected fish, one from 2017 and two from 2019. Phylogenetic analyses based on both the concatenated coding sequences of 10 segments and only segment 1 consistently revealed that Bangladeshi TiLV isolates formed a unique cluster within Thai clade, suggesting a close genetic relation. In summary, this study revealed the circulation of TiLV in 10 farms and six hatcheries located in eight districts of Bangladesh. We recommend continuing TiLV-targeted surveillance efforts to identify contaminated sources to minimize the countrywide spread and severity of TiLV infection.     

Protein Recovery of Tilapia Frame By-Products by pH-Shift Method

The conditions of isolating protein from tilapia frame by-products (TFB) by a pH-shift process were investigated along with their physicochemical and gelling properties. The minimum solubility of TFB protein was observed at pH 5.5 and gradually increased at both acid and alkaline sides. The highest solubility was observed at pH 2 and 12. Protein solubility of TFB increased as the ratio of alkaline extraction medium and extraction time increased. The highest protein extraction was found at the ratio of ground sample to extraction medium of 1 to 9 and extraction time of 15 min. The maximum protein recovery was found at pH 12 with 19.19%. The color of all protein isolate samples obtained from either acid or alkaline extraction was dark brown. Whiteness of a TFB protein isolate extracted at pH 2 was the highest with a value of 14.69. An alkaline pH-shift process effectively removed fat as much as 95%. Breaking force and deformation of recovered protein gel from an alkaline pH-shift were higher than those from the acid counterpart.     

Susceptibility of freshwater rearing Asian seabass (Lates calcarifer) to pathogenic Streptococcus iniae

Asian seabass (Lates calcarifer) has been recognized as an economically important aquaculture species which can be adapted to and cultivated in wide range of salinities. The number of freshwater intensive seabass farms in Thailand is increasing annually. Here, we first describe the susceptibility of Asian seabass, which were cultured in freshwater, to Streptococcus inae (SI) and their pathological changes. Three isolates of putative SI were identified using a combination of standard biochemical assays and species‐specific PCR prior subjected to in vivo challenge. Accumulated mortalities of the fish which received 10⁷ CFU fish^?1 of either SI1J, SI SGSA or SI2J were 90%, 90% and 100% at 7 days‐post infection (dpi), respectively, and mortalities increased sharply between 3 and 5 dpi. Clinical signs such as erratic swimming and opaque eyes were identified from a few infected fish, while most died rapidly without any abnormal signs. Histopathological manifestations were observed in the multiple organs (kidney, liver and brain). Haemorrhage, hyperhemia, cellular degeneration and inflammatory cells infiltration were commonly found within the internal organs. Notably, the formation of numerous encyst‐like lesion aggregated by eosinophilic cells, resembling macrophages, were typically found in the brain of the infected fish. Summarily, this study first revealed that freshwater reared Asian seabass is highly susceptible to SI infection and haemorrhagic septicaemia was a major pathological change that could be found in the infected fish.     

稻米抗性淀粉含量及其环境稳定性分析

【目的】食用高抗性淀粉含量稻米虽利于提高慢性病人群的健康水平,但培育出的高抗性淀粉含量水稻品种还较少。开展水稻种质资源抗性淀粉含量及其环境稳定性的研究,为高抗性淀粉含量水稻种质资源发掘和生产应用提供参考依据。【方法】参照爱尔兰Megazyme公司提供的方法测定稻米抗性淀粉含量,用PAST软件完成种质含量分布作图。通过一年多点试验评价抗性淀粉含量的环境稳定性,利用DPS软件完成含量方差分析。依据国家标准GB/T15683-2008分析了稻米直链淀粉含量。【结果】对1 206份水稻种质稻米抗性淀粉含量分析,结果表明,绝大部分水稻种质稻米抗性淀粉含量低,含量低于2.5%的占87.6%,高于10%的仅占约0.2%。稻米抗性淀粉和直链淀粉含量存在显著正相关,但在高直链淀粉含量种质中未出现抗性淀粉含量高的品系,却在低直链淀粉含量种质中发现3份抗性淀粉含量高于10%的品系,其中1个优质软米品种Diangu2的抗性淀粉和直链淀粉含量分别为10.12%和12.3%,综合农艺性状优良,米饭食味性好。在3个不同环境种植18个不同抗性淀粉含量的品系,结果显示有13个品系的含量不受种植环境差异的影响,另5个品系的含量受环境影响,稻米的抗性淀粉含量除了受基因型影响外,还受种植环境、以及基因型与环境互作的影响。【结论】水稻种质资源稻米抗性淀粉含量普遍很低,抗性淀粉含量与直链淀粉含量虽存在显著正相关,但低直链淀粉含量种质中也可能存在高抗性淀粉的品种,所以培育稻米抗性淀粉含量高且食口性好的品种是可能的。稻米抗性淀粉含量主要受基因型控制,在不同环境中含量高的品种依然高,含量低的品种仍然低,那么高含量的品种可在其适种稻区种植生产大米,其含量不会被明显影响。     

Evaluation of Rice Germplasms for Grain Resistant Starch Content and Its Environmental Stability

【Objective】 It is beneficial for improving the health of chronic patients to eat high resistant starch (RS) content rice, but variety with high grain RS content is still very rare. Evaluations of rice germplasms for grain RS contents and its environmental stability were carried out in this study, and the results could provide a reference for the discovery of rice germplasm resources with high RS contents and its production. 【Method】 Grain RS contents in rice germplasms were detected by the Megazyme method, and used the PAST software to complete the frequency distribution of these contents. The environmental stability of rice RS contents were tested by planting at multiple locations within one year, and its variance analysis were performed with DPS software. Grain amylase contents were tested according to the national standard GB/T15683-2008. 【Result】 The initial evaluations on RS contents of 1206 rice germplasms demonstrated that for most these rice with RS content were very low, and about 87.6% of the rice were less than 2.5%, only about 0.2% were higher than 10%. There was a significant positive correlation between rice RS and amylose content, but high RS variety was not discovered in high amylose germplasms. However, three varieties with RS content higher than 10% were screened in low amylose content germplasms, and one of them was a good quality soft rice variety Diangu2, which has RS and amylose content of 10.12% and 12.3%, respectively. It carried out regional tests for eighteen varieties with different RS contents planting at three very differ environmental conditions. The result of environmental stability analysis indicated that the contents of thirteen varieties were affected by differences in planting area, of the others were affected. Totally, the contents were affected by genotype, planting environment and genotype-by-environment interactions. 【Conclusion】 In this research, most rice resources have low RS content, and also detected a significant positive correlation between rice grain RS and amylase content. Therefore, it is possible to develop rice variety with high RS starch and good taste, according the high RS varieties were identified in low amylose content germplasms. The RS content was mainly affected by genotype, so the varieties with high RS contents were high at different environments, and the lows’ were still low. Then, the varieties with high RS content can grow in its suitable areas to produce rice, and the contents could not be significantly affected.