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Anthocidaris crassispina is a very popular edible sea urchin distributed along the coast of the South China Sea. In this study, we performed whole-genome sequencing and generated a chromosome-level assembly of this species. The total length of the genomic contig sequence was 891.02 Mb, and contig N50 was 808.15 kb when Hifiasm was used for assembly. The Hi-C library was constructed and sequenced, yielding approximately 68.61 Gb of data. After Hi-C assembly, approximately 886.72 Mb of sequence was able to be mapped onto 21 chromosomes, accounting for 99.52% of the total genome length. Among the sequences located on the chromosomes, those for which the order and direction could be determined accounted for approximately 826.82 Mb, or 93.24% of the total length. These results provide valuable resources for further study of A. crassispina at the genetic level. [ABSTRACT FROM AUTHOR]

Monthly changes in sedimentation and sediment properties were studied for three different culture treatments: sea cucumber monoculture (Mc), sea cucumber and scallop polyculture (Ps-c) and scallop monoculture (Ms). Results indicated that the survival rate of sea cucumber was significantly higher in Ps-c cultures than in Mc cultures. Sea cucumber yield was 69.6% higher in Ps-c culture than in Mc culture. No significant differences in body weight and scallop shell length were found between Ps-c and Ms cultures. The mean sedimentation rate of total particulate matter (TPM) was 72.2 g/(m·d) in Ps-c cultures, with a maximum of 119.7 g/(m·d), which was markedly higher than that of Mc (mean value). Sedimentation rates of organic matter (OM), total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) in Ps-c cultures were also significantly higher than those in Mc cultures. TOC and TN contents of sediment increased rapidly in the first 5 months in Ms cultures and remained at a high level. TOC and TN contents in Mc and Ps-c cultures decreased during sea cucumber feeding seasons and increased during sea cucumber dormancy periods (summer and winter). The study demonstrates that co-culture of sea cucumber and scallop in earthen ponds is an alternative way to alleviate nutrient loads and improve water quality in coastal aquaculture systems. Moreover, it provides the additional benefit of an increased sea cucumber yield. [ABSTRACT FROM AUTHOR]

Optimal stocking densities were investigated for the sea cucumber Apostichopus japonicus Selenka under feed-supplement and non-feed-supplement regimes in net enclosures for 333 d. Substantial weight loss occurred during the aestivation phase (AE). Decreased growth rates were also observed during the winter phase (WT). In contrast, sea cucumbers showed rapid growth during the spring (SP) and autumn (AU) phases. Feeding regimes considerably influenced the growth performance, i.e., sea cucumbers grew faster under feed-supplement regime than under non-feed-supplement regime ( P < 0.05). The average survival rates of sea cucumbers under feed-supplement regime were higher than those under non-feed-supplement regime for both the autumn phase and spring phase, but the differences were only significant for the latter phase ( P < 0.05). The fitted B-N curves showed that the optimal stocking densities, in terms of net production, were 22.3 ind. m-2 for feed-supplement regime and 14.1 ind. m-2 for non-feed-supplement regime. [ABSTRACT FROM AUTHOR]