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We report on novel chromosomal characteristics of Haliotis discus hannai from a breeding population at Fujian, China. The karyotypes of H. discus hannai we obtained from an abalone farm include a common type 2n = 36 = 10M + 8SM (82%) and two rare types 2n = 36 = 11M + 7SM (14%) and 2n = 36 = 10M + 7SM + 1ST (4%). The results of silver staining showed that the NORs of H. discus hannai were usually located terminally on the long arms of chromosome pairs 14 and 17, NORs were also sometimes located terminally on the short arms of other chromosomes, either metacentric or submetacentric pairs. The number of Ag-nucleoli ranged from 2 to 8, and the mean number was 3.61 ± 0.93. Among the scored interphase cells, 41% had 3 detectable nucleoli and 37% had 4 nucleoli. The 18S rDNA FISH result is the first report of the location of 18S rDNA genes in H. discus hannai. The 18S rDNA locations were highly polymorphic in this species. Copies of the gene were observed in the terminal of long or/and short arms of submetacentric or/and metacentric chromosomes. Using FISH with probe for vertebrate-like telomeric sequences (CCCTAA)3 displayed positive green FITC signals at telomere regions of all analyzed chromosome types. We found about 7% of chromosomes had breaks in prophase. A special form of nucleolus not previously described from H. discus hannai was observed in some interphase cells. It consists of many small silver-stained nucleoli gathered together to form a larger nucleolus and may correspond to prenucleolar bodies. [ABSTRACT FROM AUTHOR]

The prevalence of juvenile Pacific abalone disease without apparent external lesions in the Chinese province of Fujian has led to mass mortality in 2018. A novel method for screening abalone pathogen was developed based on the importance of mucus in innate immunity. We identified the pathogenic bacterial strain of abalone by bacterial isolation, sequence analysis, and experimental challenges in vitro and in vivo. We verified that the abalone mortality rates were high when exposed to Pseudoalteromonas shioyasakiensis strain SDCH87 at 28 °C. This opportunistic pathogen had an outstanding growth ability in mucus and disrupted the first line mucosal immunity in the pedal within three days. To our knowledge, this is the first report that P. shioyasakiensis is a severe opportunistic pathogen of abalone, which indicated pedal was the lesion, in the context of a heatwave. • A novel method was developed for screening abalone pathogens, based on the important role of mucus in the innate immunity. • P. shioyasakiensis strain SDCH87 is a significant opportunistic pathogen of abalone during a record-breaking heatwave. • Histopathology and the distribution of bacterial strains indicated pedal was the lesion. [ABSTRACT FROM AUTHOR]

China is the largest producer and consumer of abalone worldwide, harvesting nearly 140,000 tons in 2016. Due to rising temperatures, intensive culture patterns, and other factors, hypoxia has become a serious problem for Chinese abalone aquaculture, especially in Fujian Province. A hypoxia-tolerant strain is needed for the sustainable development of abalone farming. However, it is problematic to evaluate hypoxia tolerance in abalone. Usually, the traditional analyses cause severe damages to the sampled individuals, possibly including disorders in gonad development or death and these samples could hardly be used for breeding. Here, it was found that abalone heart rates characteristically exhibited a sharp decline below a certain DO threshold, which can be referred to as the breakpoint of dissolved oxygen (BPDO). The BPDOs were sensitive to temperature – the higher acclimation temperature or experimental temperature would increase BPDO. To verify the utility of BPDO as an indicator of hypoxia tolerance in abalone, an acute stress test was conducted with 32 abalone individuals under severe hypoxia (~0.5 mg/L) and significant negative correlations between BPDO and attachment duration, and between BPDO and survival time were found. The BPDO method was advantageous, as it supported individual detection and survival, which allows the selection and retention of hypoxic-tolerant individuals for further genetic breeding. BPDOs at different temperatures also provide important references for abalone aquaculture. • A new indicator (BPDO) of hypoxia tolerance in abalone was found, which was based on cardiac performance. • The BPDO is highly susceptible to temperature and the higher value of BPDO mean less resistance to hypocia. • The BPDO method demonstrated advantages in individual detection and animal survival. [ABSTRACT FROM AUTHOR]