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Simple Summary: Two subspecies of largemouth bass (Micropterus salmoides, LMB) with different thermal tolerance, northern largemouth bass (NLMB) and Florida largemouth bass (FLMB), were subjected to acute and chronic thermal stress at 33 °C. Then, variations of 12 candidate biomarkers between NLMB and FLMB were analyzed. Compared to NLMB, FLMB exhibited a lower plasma cortisol level and a higher expression of hsp90 under acute thermal stress. Additionally, lower expression of hsp70 in FLMB was observed under chronic thermal stress. The differences in plasma cortisol levels and hsp expression represent variations in thermal tolerance between the two subspecies of LMB, providing valuable information for the identification and breeding of LMB varieties with better thermal tolerance in the future. Affected by the continuously rising temperature, thermal stress leads to a delinked growth rate and resistance to stress in cultured largemouth bass (Micropterus salmoides, LMB) in China. Identification of LMB with better thermal resistance will benefit the breeding of new varieties. However, there has been limited reporting on the evaluation to identify LMB with better thermal resistance. LMB consists of the northern LMB (Micropterus salmoides salmoides, NLMB) and the Florida LMB (Micropterus salmoides floridanus, FLMB). Due to their different geographical distributions, it has been suggested that FLMB exhibit better thermal resistance compared to NLMB. In this study, NLMB and FLMB were subjected to thermal stress for 3 h (acute) and 60 d (chronic) at 33 °C, respectively. Subsequently, the variations of 12 candidate biomarkers between NLMB and FLMB were analyzed. Exposure to acute thermal stress significantly increased plasma cortisol, blood glucose, and lactate levels; activities of superoxide dismutase (SOD), glutathione peroxidase (GPX), catalase (CAT), glucose kinase (GK), pyruvate kinase (PK), lactate dehydrogenase (LDH), and glucose 6 phosphatase (G6Pase); and the expressions of hsp70 and hsp90 in both NLMB and FLMB (p < 0.05). Compared to NLMB, FLMB exhibited a lower plasma cortisol level and a higher expression of hsp90 under acute thermal stress (p < 0.05). Exposure to chronic thermal stress significantly increased plasma cortisol and blood glucose levels, as well as activities of GK, PK, LDH, and G6Pase, as well as expressions of hsp70 and hsp90 in both NLMB and FLMB (p < 0.05). Additionally, FLMB showed a lower expression of hsp70 compared to NLMB (p < 0.05). In conclusion, our results showed that LMB with lower plasma cortisol level and higher expression of hsp90 under acute thermal stress, as well as lower expression of hsp70 under chronic thermal stress were suggested to have better thermal resistance. Our study provides valuable information for identifying and breeding LMB varieties with better thermal resistance in the future. [ABSTRACT FROM AUTHOR]

Acceptance of artificial pelleted diets contributes to increasing the cultured areas and output of carnivorous fish. However, the mechanism of acceptance of artificial pelleted diets remains largely unknown. In this study, the easy acceptance of artificial pelleted diets (EAD) group and the not easy acceptance of artificial pelleted diets (NAD) group of Largemouth bass (Micropterus salmoides) were divided based on the ratios of stomach weight/body weight (SB) after 0.5 h feeding, which was bigger than 18% in the EAD group and ranged from 8 to 12% in the NAD group. Through transcriptome and proteome sequencing, a total of 2463 differentially expressed genes (DEGs) and 230 differentially expressed proteins (DEPs) were identified, respectively. Integrated analyses of transcriptome and proteome data revealed that 152 DEPs were matched with the corresponding DEGs (named co-DEGs-DEPs), and 54 co-DEGs-DEPs were enriched in 16 KEGG pathways, including the metabolic pathways, steroid biosynthesis, fatty acid biosynthesis, etc. Furthermore, 3 terpenoid backbone biosynthesis-related genes (Hmgcr, Hmgcs, and Fdps) in metabolic pathways, 10 steroid biosynthesis-related genes (Fdft1, Sqle, Lss, Cyp51a1, Tm7sf2, Nsdhl, Hsd17b7, Dhcr24, Sc5d, and Dhcr7), and 3 fatty acid biosynthesis-related genes (Acaca, Fasn, and Ascl) were all up-regulated in the EAD group, suggesting that the lipid metabolism pathway and steroid biosynthesis pathway play important roles in early food habit domestication in Largemouth bass. In addition, the detection results of randomly selected 15 DEGs and 15 DEPs indicated that both transcriptome and proteome results in the study were reliable. Our study provides useful information for further research on the mechanisms of food habit domestication in fish. [ABSTRACT FROM AUTHOR]

The largemouth bass is an important species, and its culture has risen sharply with the surge in fish aquaculture in China. Due to the lack of selective breeding technology for the largemouth bass, the growth rate and disease resistance are low, its sexual maturation is slow, and other serious problems are contributing to a sharp decline in the safety and quality of largemouth bass products in recent decades. Therefore, comprehensive breeding programs to improve the economic performance and promote the modern industrial development of largemouth bass must be considered a priority. Here, a total of 152 adult largemouth bass, including two parents and 150 progenies, were selected to produce the genetic mapping family. Then, a high-density linkage map was constructed based on restriction site–associated DNA sequencing using 6,917 single-nucleotide polymorphisms (SNPs) located in 24 linkage groups (LGs). The total genetic length of the linkage map was 1,261.96 cM, and the length of each LG varied from 24.72 cM for LG02 to 117.53 cM for LG16, with an average length of 52.58 cM and an average SNP number of 286. Thirteen significant quantitative trait loci (QTLs) for sex determination were located on LG04, LG05, LG08, LG12, LG15, LG21, and LG23. An informative QTL cluster that included six QTLs was detected on LG12. However, one notable QTL, which accounted for 71.48% of the total phenotypic variation, was located in the region of 1.85 cM on LG05. In addition, 32 identified QTLs were related to growth, including body weight, body length, body height, and head length. The QTLs for these growth-related traits are located in 13 LG regions and have little effect on phenotypic variation. This high-density genetic linkage map will enable the fine-mapping of economic traits and support the future genome assembly of the largemouth bass. Additionally, our study will be useful for future selective culture of largemouth bass and could potentially be used in molecular-assisted breeding of largemouth bass for aquaculture. [ABSTRACT FROM AUTHOR]

Abstract: During June through October 2008, numerous cultured largemouth bass (Micropterus salmoides) died in the Foshan area of Guangdong Province, China. Affected fish had ulcerations on the skin and muscle. Epithelioma papillosum cyprini (EPC) cell cultures inoculated with filtrates of muscle homogenates from the diseased fish developed the cytopathic effect (CPE) 5days after inoculation at the primary passage. Transmission electron microscopy of the ulcerative muscle tissue and the infected EPC cells revealed a cytoplasmic, icosahedral virion that averaged 145nm in diameter. Intramuscular injection of the virus (≥107.82 TCID50 ml−1) resulted in clinical signs of the disease and caused 100% mortality of healthy largemouth bass. In addition, the mandarinfish (Siniperca chuatsi) was susceptible to the virus after intramuscular injection of the virus (0.2ml of 109.82 TCID50 ml−1), and the mortality was 20%. However, no death or clinical signs were found in grass carp (Ctenopharyngodon idella), bighead carp (Aristichthys nobilis), Nile tilapia (Oreochromis niloticus), crucian carp (Carassius carassius), common carp (Cyprinus carpio), and fancy carp (C. carpio) after experimental infection. DNA fragments of the viral major capsid protein (MCP) and DNA methyltransferase (MTase) were amplified and sequenced. Subsequent multiple alignment and phylogenetic analysis revealed that the virus is identical to doctor fish virus (DFV) and closely related to largemouth bass virus (LMBV). [Copyright &y& Elsevier]

Sex dimorphism of economic traits such as growth rate and body size have potential breeding value in aquaculture. Largemouth bass (Micropterus salmoides L.) is an important freshwater cultured fish in China and the females live longer and reach larger sizes than males. However, the lacking of sex-specific makers and the unclear sex determination mechanism inhibits the development of all-female breeding. In this study, 5 females and 5 males were randomly selected and sequenced with whole-genome re-sequencing technology. In total, 1394 filtered SNPs and 425 filtered InDels were finally identified, and most of these makers were located at Chr7 and Chr18. The validation of the 35 SNPs located at Chr7 in three distinct population (n = 72) indicated that 2 SNPs (S4 and S6) could distinguish the females and males with 100% accuracies, which were genotyped as CC and CG, AA and AT in the females and males, respectively. Further, 10 and 6 InDels with sizes more than 18 bp were finally screened out on Chr7 and Chr18. 2 male-specific InDels (rs3394676 and rs3496814) located at Chr7 could effectively distinguish the above females and males with a PCR-based agarose gel electrophoresis, which performed as one band in the females and two bands in the males, respectively. These results suggested the Chr7 might be the sex chromosome and a XX/XY sex determination system in largemouth bass. In conclusion, a whole-genome re-sequencing method was first conducted to provide usefulness sex-specific makers and a XX/XY sex determination system in largemouth bass, which contributes to study of the sex determination mechanisms and the development of mono-sex population breeding. • Whole-genome re-sequencing were first conducted to explore the genetic differences between males and females in largemouth bass. • Two male-specific SNPs and two male-specific InDels were developed to distinguish genetic sex of largemouth bass. • The chromosome 7 was the sex chromosome in largemouth bass. • The sex determination system was a XX/XY determination system in largemouth bass. [ABSTRACT FROM AUTHOR]