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An adult Sinocyclocheilus maitianheensis, a surface-dwelling golden-line barbel fish, was collected from Maitian river (Kunming City, Yunnan Province, China) for whole-genome sequencing, assembly, and annotation. We obtained a genome assembly of 1.7 Gb with a scaffold N50 of 1.4 Mb and a contig N50 of 24.7 kb. A total of 39,977 protein-coding genes were annotated. Based on a comparative phylogenetic analysis of five Sinocyclocheilus species and other five representative vertebrates with published genome sequences, we found that S. maitianheensis is close to Sinocyclocheilus anophthalmus (a cave-restricted species with similar locality). Moreover, the assembled genomes of S. maitianheensis and other four Sinocyclocheilus counterparts were used for a fourfold degenerative third-codon transversion (4dTv) analysis. The recent whole-genome duplication (WGD) event was therefore estimated to occur about 18.1 million years ago. Our results also revealed a decreased tendency of copy number in many important genes related to immunity and apoptosis in cave-restricted Sinocyclocheilus species. In summary, we report the first genome assembly of S. maitianheensis, which provides a valuable genetic resource for comparative studies on cavefish biology, species protection, and practical aquaculture of this potentially economical fish.

In our previous work, we reported comparative genomics studies on 3 Sinocyclocheilus fishes, including the surface-dwelling S. graham (Sg), the semi-cave-dewlling S. rhinocerous (Sr) and the cave-restricted S. anshuiensis (Sa). Here, we performed a genomic survey on the immunity differences among the 3 fishes by combination of the genome and transcriptome data. Our results demonstrate that immune-related genetic pathways in Sa and Sr present more similarities than Sg. The innate immune activity in Sa seems to be higher than Sg and Sr, while Sr owns more copy numbers of MHC-related genes (related with the acquired immune system) than Sg and Sa. These differential immune activities in the 3 Sinocyclocheilus species may be due to their differential habitats. Generally speaking, most immunity genes transcribe the lowest levels in Sa when compared with Sg and Sr, which may be associate with a less various microbial environment in the cave-restricted habitat. However, Sr has more members of MHC-related genes than those in Sg and Sa, suggesting a great contribution from the semi-cave-dwelling condition.