The study aimed to investigate the effects of temperature and dissolved oxygen on juvenile largemouth bass during transportation. The experiment involved four temperature groups: 20, 15, 10, and 5 °C. We analyzed the effects of acute and uniform cooling on fish behavior to determine the optimal approach for cooling. Then, we simulated transport under different temperature conditions while measuring the dissolved oxygen level and metabolic rate until all the fish died. The results showed that acute cooling significantly influenced the tail-beat frequency of fish compared with uniform cooling, while abnormal behaviors such as increased swimming, attempted jumping out of the water, and loss of balance were observed. As the transport temperature reduced, the oxygen consumption rate of fish significantly changed at 10 °C, being 2.6 times lower than at 15 °C, with values of 0.10 ± 0.02 and 0.47 ± 0.07 mg·g⁻¹·h⁻¹, respectively. The critical oxygen threshold (P_crit) of fish were 1.90 ± 0.12, 1.61 ± 0.04, 1.15 ± 0.09, and 1.12 ± 0.25 mg·L⁻¹ at 5, 10, 15, and 20 °C. In addition, below P_crit, hypoxia-led behavior changes and oxygen consumption rate reduction were observed at every transport temperature. The findings suggest that the optimal low temperature can reduce metabolism and improve the hypoxia tolerance of juvenile largemouth bass. We recommend transporting largemouth bass at an optimal low temperature (15 °C), monitoring fish behavior, and maintaining oxygen levels above P_crit during transport to prevent stress.

To investigate the effects of the interaction between water quality and gill function of large yellow croaker during transportation in packaging bags, a total of 186 large yellow croakers weighing 120.0 ± 28.0 g were randomly divided into two groups: a control group (tanks with a water treatment system to maintain normal water quality) and treatment groups subjected to simulated transport for 0, 6, 12, 18, and 24 hours at a temperature of 20°C. The results revealed that prolonging the transport duration (beyond 6 hours) caused significant changes in dissolved oxygen (DO), total ammonia nitrogen (TAN) and pH levels in the water. Beyond 6 hours of transport, gill tissue damage increased, and the histomorphological characteristics of the gills were altered. Regarding osmoregulation, the activities of Ca²⁺/Mg²⁺-ATPase and Na⁺/K⁺-ATPase were notably reduced in the treatment groups, indicating compromised osmoregulatory function of the gill tissue during transport. However, changes in lactic acid (LD) and lactate dehydrogenase (LDH) were not statistically significant, and fish did not experience hypoxia during packaging bag transport. In terms of antioxidant activity, the treatment groups exhibited significantly lower activities of catalase (CAT) and superoxide dismutase (SOD) after 24 hours, as well as increased malondialdehyde (MDA) content after 18 hours. This reduction in antioxidant capacity led to cellular membrane damage in the gill tissue. Furthermore, acid phosphatase (ACP) activity showed a notable decline from 12 hours onwards in immune indicators, while lysozyme (LZM) activity experienced a substantial decrease at 24 hours. Correlation analysis revealed a significant correlation between the osmoregulation, antioxidant capacity, and immune response of gill tissue with elevated TAN levels and reduced pH. In conclusion, the levels of TAN and pH experience notable alterations after 6 hours of transportation, which may lead to impairment of gill function in large yellow croakers. Hence, we advise limiting the transportation of large yellow croakers to less than 6 hours at 20°C.

Sargassum thunbergii is a dominant seaweed species in the intertidal zone along the coast of China. It provides various ecological services, such as primary productivity, marine carbon sequestration, and water purification. To investigate the population structure characteristics of Sargassum thunbergii, the Hegyi competition model was employed to quantify intraspecific competition within populations in the intertidal zone of Luhua Island, China. The results showed that the competition intensity decreased as a power function (y = 1.93x^−0.89, R² = 0.28) with increasing seaweed height. Intraspecific competition had minimal effects on seaweeds taller than 50 cm. Seaweeds at lower population levels exhibited more stable competition indices. Therefore, the model can reliably predict intraspecific competition intensity in Sargassum thunbergii. The sample circle method was applied to identify an optimal intraspecific competitive range of 50 cm for intertidal populations of Sargassum thunbergii. This study provides scientific guidance for seaweed spacing and rational harvesting during ecological restoration. Moreover, it offers valuable insight for conserving other macroalgae, such as Sargassum fusiforme, and restoring seaweed beds ecologically.