Fishes

This study evaluated the effects of water renewal rate and temperature on the growth performance and physiological responses of juvenile Piaractus brachypomus reared in a recirculating aquaculture system (RAS). A total of 336 fish (1.35 ± 0.24 g) were distributed in six RAS units under two water renewal rates (42 and 128 L h⁻¹) and three temperatures (26, 29, and 32 °C) for 45 days. Temperature was the main factor affecting growth, with higher final weight and total length at 29 and 32 °C throughout the experimental period. Water renewal rate significantly influenced feeding efficiency and energy allocation. Higher renewal (128 L h⁻¹) increased dissolved oxygen and daily feed intake and resulted in higher hemoglobin levels and hepatic lipid deposition, particularly at 32 °C, indicating greater metabolic activity. Conversely, the lower renewal rate (42 L h⁻¹) was associated with better feed conversion ratios at 29 °C and higher muscle lipid content at 26 °C, suggesting reduced energy expenditure. Hematocrit, total plasma protein, and cholesterol were primarily influenced by temperature, with higher values at 29 and 32 °C, while glucose, triglycerides, and liver enzymes were unaffected. Overall, temperatures of 29–32 °C optimized growth, while water renewal rate modulated feed utilization, physiological responses, and lipid deposition. These findings highlight the importance of jointly optimizing temperature and water renewal rate in RAS to enhance growth performance and metabolic balance in juvenile P. brachypomus.

China is the world’s leading producer of offshore mariculture, contributing more than 60 percent of global output. Yet the provincial distribution of mariculture space and its economic concentration are still not well described at a comparable national scale. This study draws on a publicly available nation-scale GIS dataset extracted from Landsat 8 imagery from 2018 to map offshore mariculture across nine coastal provinces and to quantify spatial inequality and specialization. The mapped offshore mariculture footprint totals 733,840 ha. The distribution is sharply uneven. Fujian alone reaches 183,025 ha, nearly thirty times the area of Hainan. The Gini coefficient is 0.412, and concentration ratios show that the top three provinces account for 64.0 percent of the total area, and the top five account for 84.5 percent. Location quotient results indicate strong specialization in Fujian, Jiangsu, and Hebei, while Hainan and Guangxi remain marginal. Cluster analysis further identifies three development modes: large-scale expansion, medium-scale and relatively balanced growth, and small-scale dispersed production. Overall, the pattern is consistent with resource endowment, agglomeration effects, and path dependence. The findings point to the need for improved coastal spatial planning, stronger interprovincial technology diffusion, and differentiated governance that balances efficiency with equity and environmental sustainability.

Within the Rajidae family, the blonde ray (Raja brachyura) is considered one of the less resilient species to fishing pressure and other anthropogenic pressures, primarily due to its late maturity and large maximum size, which can exceed 120 cm total length. This is the first study to provide comprehensive insights into the reproductive biology of Raja brachyura in the continental waters of Portugal, with insights into its timing, maturity, and fecundity. It was determined that egg-laying occurs from February to November, with a peak observed between April and September. Males were reproductively active throughout the year, with highest proportions of active males observed between January and May. The length at first maturity was estimated at 95.2 cm for females and 90.0 cm for males, corresponding to 85% of the maximum observed length in each sex. The potential fecundity was estimated at 115 follicles per female per year, and evidence suggests that the species has a determinate fecundity. The findings reinforce the appropriateness of current management measures in Portuguese continental waters, namely seasonal closure when overlapping with the peak of the reproductive season (May and June), and provide valuable scientific support for future conservation and management measures.