Xin Zhan

In aquaculture, reduced water exchange helps constrain exogenous pathogen invasion, lower pumping costs, and improve management efficiency; nevertheless, its effects on the growth of cultured aquatic animals remain poorly characterized. This study compared two daily water-exchange rates (100% and 0%) to evaluate growth and associated intestinal responses in Babylonia areolata (ivory shell). Growth performance and intestinal enzyme activities were measured, while 16S rRNA gene sequencing and untargeted metabolomics were used to characterize microbial composition and metabolite profiles. The low-water-exchange group exhibited significantly lower weight gain rate (WGR, p < 0.0001), specific growth rate (SGR, p < 0.0001), daily increments in shell length (DISL, p = 0.0060), and shell width (DISW, p = 0.0012). Intestinal total superoxide dismutase (T-SOD, p < 0.0001) and lipase (LIP, p = 0.0011) activities were also significantly lower. The relative abundances of Vibrio, Halodesulfovibrio, and Fusibacter were higher, whereas that of Christensenellaceae_R-7_group was lower. Lipid-related metabolic pathways showed the most pronounced intestinal differences. Intestinal levels of prostaglandins (PGs), leukotrienes (LTs), and sphingosine (Sph) were significantly higher under low-water-exchange conditions. The relative abundance of Halodesulfovibrio correlated positively with PGs and LTs but negatively with lysophospholipids (Lpc) and T-SOD activity. The relative abundance of Christensenellaceae_R-7_group correlated positively with LIP activity and was significantly associated with metabolites involved in primary bile acid biosynthesis. Overall, low-water-exchange conditions were associated with coordinated changes in growth, intestinal enzyme activities, microbial composition, and metabolite profiles, although the underlying mechanisms require functional validation. These findings provide new insights into intestinal microbiota–metabolite responses to low-water-exchange conditions and may guide future validation and intervention studies in RAS-based ivory shell culture.

Phosphorus (P) availability in soil is paradoxical, with a significant portion of applied P accumulating in the soil, potentially affecting plant production. The impact of biochar (BR) and fishpond sediments (FPS) as fertilizers on P fixation remains unclear. This study aimed to determine the optimal ratio of BR, modified biochar (MBR), and FPS as fertilizer replacements. A pot experiment with maize evaluated the transformation of P into inorganic (Pi) and organic (Po) fractions and their contribution to P uptake. Different percentages of FPS, BR, and MBR were applied as treatments (T1–T7), T1 [(0.0)], T2 [FPS (25.0%)], T3 [FPS (25.0%) + BR (1%)], T [FPS (25%) +MBR (3%)], T5 [FPS (35%)], T6 [FPS (35%) +BR (1%)], and T7 [FPS (35%) + MBR (1%)]. Using the modified Hedley method and the Tiessen and Moir fractionation scheme, P fractions were determined. Results showed that various rates of MBR, BR, and FPS significantly increased labile and moderately labile P fractions (NaHCO₃-P_i, NaHCO₃-P_o, HCl_D-P_i, and HCl_C-P_i) and residual P fractions compared with the control (T1). Positive correlations were observed between P uptake, phosphatase enzyme activity, and NaHCO₃-Pi. Maximum P uptake and phosphatase activity were observed in T6 and T7 treatments. The addition of BR, MBR, and FPS increased Po fractions. Unlike the decline in NaOH-Po fraction, NaHCO₃-Po and HClc-Po fractions increased. All Pi fractions, particularly apatite (HCl_D-Pi), increased across the T1–T7 treatments. HCl_D-P_i was the largest contributor to total P (40.7%) and can convert into accessible P over time. The T5 treatment showed a 0.88% rise in residual P. HCl_D-P_i and residual P fractions positively correlated with P uptake, phosphatase activity, NaOH-Pi, and NaOH-Po moderately available fractions. Regression analysis revealed that higher concentrations of metals such as Ca, Zn, and Cr significantly decreased labile organic and inorganic P fractions (NaHCO₃-Pi, R^2 = 0.13, 0.36, 0.09) and their availability (NaHCO₃-Po, R^2 = 0.01, 0.03, 0.25). Excessive solo BR amendments did not consistently increase P availability, but optimal simple and MBR increased residual P contents in moderately labile and labile forms (including NaOH-Pi, NaHCO₃-Pi, and HCl_D-Pi). Overall, our findings suggest that the co-addition of BR and FPS can enhance soil P availability via increasing the activity of phosphatase enzyme, thereby enhancing plant P uptake and use efficiency, which eventually maintains the provision of ecosystem functions and services.

The effect of low salinity levels on byssal re‐attachment behavior in Pteria penguin juveniles was observed in the laboratory. Juvenile pearl oysters were submerged in seawater blended to 8.0, 12.0, 16.0, 20.0, 24.0, 28.0, and 32.0 salinity levels for a period of 48 hr. The sub‐lethal salinity level was greater than 20.0 psu. Although salinity levels of 20.0 and 24.0 psu did not affect the oyster survival, the observed byssogenesis activity was significantly reduced and locomotion activity was delayed. Description of the effects of low salinity levels on the byssal re‐attachment behavior of P. penguin juveniles provides a foundation for the design of more complex experiments and approaches to further the exploration and development of improved pearl production techniques.