Growth differentiation among farmed sea urchins (Strongylocentrotus intermedius) poses a significant challenge to aquaculture, with there being a limited understanding of the underlying molecular mechanisms. In this study, sea urchins with varying growth rates, reared under identical conditions, were analyzed for feeding behavior, gut microbiota, and transcriptomes. Large-sized sea urchins demonstrated significantly higher feeding ability and longer duration than smaller ones. The dominant phyla across all size groups were Campylobacterota, Proteobacteria, and Firmicutes, with Campylobacterota showing the highest abundance in small-sized sea urchins (82.6%). However, the families Lachnospiraceae and Pseudomonadaceae were significantly less prevalent in small-sized sea urchins. Transcriptome analysis identified 214, 544, and 732 differentially expressed genes (DEGs) in the large vs. medium, large vs. small, and medium vs. small comparisons, respectively. Gene Ontology and KEGG pathway analyses associated DEGs with key processes such as steroid biosynthesis, protein processing within the endoplasmic reticulum, and nucleotide sugar metabolism. Variations in phagosomes and signaling pathways indicated that size differences are linked to disparities in energy expenditure and stress responses. These findings provide a foundation for future investigations into the regulatory mechanisms underlying growth differences in S. intermedius and provide clues for the screening of molecular markers useful to improve sea urchin production.

This review aims to advance the development of biofloc technology (BFT), providing more sustainable and efficient practices for the farming of the Japanese sea cucumber (Apostichopus japonicus). BFT is a sustainable aquaculture method that promotes nutrient recycling and effective carbon source management, offering significant advantages such as improving water quality, enhancing growth performance, and boosting the physiological activity and disease resistance of cultured animals. In A. japonicus farming, the optimal carbon source is glucose, and the ideal carbon-to-nitrogen (C/N) ratio ranges between 15 and 20. Microbial additives, such as the Bacillus species, have been shown to enhance biofloc formation and growth, as well as the immune responses in A. japonicus. However, the technology also faces limitations, including finding suitable biofloc culture protocols that match the physiological habits of A. japonicus and potential challenges with biofloc stability under varying environmental conditions. Based on existing research, this review discusses these limitations in the farming of A. japonicus. Additionally, it compares biofloc farming models for other economically important aquatic species. By addressing these key aspects, this review offers insights to enhance BFT performance, ultimately contributing to more efficient and sustainable A. japonicus aquaculture practices.

Sea urchin aquaculture has experienced remarkable growth in recent years. However, this growth has been accompanied by increased disease prevalence. Notably, spotting disease has particularly severe impacts. In this study, we isolated the pathogen HZ-3-2 from 10 sea urchins with spotting disease, and it was identified as Vibrio splendidus through morphological observations, 16S rDNA sequencing, and whole-genome sequencing. Subsequently, experimental infection confirmed that V. splendidus (HZ-3-2) is the causative agent of spotting disease in this outbreak. The drug sensitivity confirmed the presence of drug resistance genes, such as CPR, QNRS5, and rsmA, which were identified in the genome. The tests indicated that V. splendidus was sensitive to various antibiotics, including fluoroquinolones and florfenicol. Finally, we used the transcriptome to explore the molecular response of the diseased sea urchin. Compared to the control group, a group of sea urchins immersed in a pathogen suspension with a concentration of 10⁷ CFU/mL (group M) resulted in 439 annotated differentially expressed genes. KEGG pathway analysis indicated significant activation of cholesterol metabolism and starch and sucrose metabolism in the S. intermedius. This study highlights the genes NPC1, AMY2A, and MGAM as critical regulators of energy metabolism, and cholesterol synthesis in infected sea urchins. These findings confirm V. splendidus as the bacterium responsible for spotting disease and provide valuable insights into the intestinal molecular response of S. intermedius to infection.