To address airflow leakage from the screw feeder due to the absence of an airlock, compressive breakage caused by rotary airlock valves, and the low conveyance efficiency of conventional Venturi tubes in pneumatic aquafeed conveying, a screw-ejector hybrid positive-pressure conveying system was developed using Haid-brand extruded perch feed as the test material. The conveying performance and parameter optimization were then evaluated for high-efficiency, low-damage operation. Through coupled experiments on screw pitch, rotational speed, and particle size, the optimal operating window for screw feeding was identified as a pitch of 65.4 mm and a rotational speed of 60 r·min−1. Two ejector configurations - a conventional Venturi and an open-intake (atmosphere-type) ejector - were designed, and experiments showed that the latter delivered superior conveyance performance. Pneumatic-conveying breakage tests established the low-damage operating threshold for the No. 6 feed: when the measured empty-line air velocity is ≤ 40 m·s−1, the observed breakage is statistically indistinguishable from the background baseline; at ≥ 50 m·s−1, structural breakage is systematically initiated; a recommended operating air velocity of ≤ 40 m·s−1 is therefore proposed.
As an important structure to improve the habitat environment of aquatic organisms, artificial reefs play an important role in the construction of marine ranching projects. Due to the influence of its own weight and impact during descent, artificial reefs will undergo instantaneous settlement on the seabed during deployment, resulting in a decrease in the usable volume of artificial reefs, and the instantaneous settlement and relative settlement ratio of reefs are also different due to the different reef deployment methods, design structures and seabed sediment conditions in different sea areas. In this study, computational fluid dynamics (CFD) was used to establish a fluid-structure interaction model for artificial reef deployment, and the factors affecting the instantaneous settlement of artificial reefs were analyzed. The results show that: 1) In terms of external influencing factors, the influence of soil internal friction angle φ on instantaneous settlement is more significant than that of soil Poisson's ratio ν and Young's modulus E, the larger the internal friction angle φ, Poisson's ratio ν and Young's modulus E in soil, the smaller the instantaneous settlement of artificial reef and the faster the settlement velocity attenuation, when the soil Poisson's ratio ν increases from 0.1 to 0.28, the relative settlement ratio of the artificial reef, β, decreases by 4.5%, and when the soil Young's modulus E increases from 20 MPa to 40 MPa, The relative settlement ratio of artificial reefs, β, is 3.7% smaller, and when the internal friction angle of clay, φ increases from 20° to 40°, the relative settlement ratio of artificial reefs, β, decreases by 10.85%. 2) In terms of internal influencing factors, the larger the bottom opening ratio of the artificial reef α, the smaller the settlement depth and the faster the decay of the instantaneous settlement velocity, and the relative settlement ratio of the artificial reef β decreased by 5.2% when the bottom opening ratio of the reef α increased from 0.1 to 0.5. The purpose of this study is to provide a reference for the optimal design of artificial reefs and the location of the deployment environment.
This study presents an integrated sustainability assessment, covering environmental performance and economic feasibility, of an innovative vertical haloponic system designed for the co-production of Penaeus vannamei shrimp and salt-tolerant crops (in this case study, Salicornia). Primary data were used for the growth phase of Salicornia and shrimp, electricity and water consumption, and the vertical structures. Environmental performance was assessed in accordance with ISO 14040/44 standards using the ReCiPe Midpoint/Endpoint methodology. Results indicate that electricity consumption is the dominant environmental hotspot across nearly all impact categories, particularly for the midpoint categories of climate change (95,244.52 kg CO2 eq), fossil resource scarcity (30,772.74 kg oil eq), and water consumption (3756.36 m3). Infrastructure materials, especially steel and plastics, are the second-largest contributors, primarily affecting toxicity and mineral resource depletion. Feed and nutrient solutions have moderate but non-negligible impacts, while sludge valorization through vermicomposting yields limited environmental credits. The endpoint results confirm and amplify the patterns identified at the midpoint level. LCC results suggest potential profitability under the modeled baseline conditions, although high initial investments and operational costs remain critical constraints. In particular, at the more conservative discount rate, a Net Present Value (NPV) of €51,619.12 was obtained, with a payback period of 5 years. Overall, the system shows potential as a sustainable food production model, provided that technological optimization and energy transition strategies are implemented.
Recirculating aquaculture systems (RAS) require precise oxygen management to maintain fish performance and system stability, yet oxygen demand varies dynamically with biological and environmental factors. This study quantified the effects of body weight, water temperature, and flow velocity on the oxygen consumption rate (OCR) of spotted knifejaw and developed a multi-factor prediction framework for oxygen management in RAS. A full-factorial experiment (3 ×3 ×3) was conducted using three temperature levels (19, 24, and 29 °C), three flow velocities (0, 40%, and 80% of critical swimming speed, Ucrit), and three body-weight groups (small, medium, and large). OCR increased significantly with temperature from 19 to 24 °C but showed no further significant increase at 29 °C. Body weight exhibited a strong negative allometric relationship with mass-specific OCR (scaling exponent, b = −0.66). Flow velocity showed a non-monotonic effect, with the lowest OCR observed at 40% Ucrit. A multi-factor prediction model integrating temperature, flow velocity, and body weight achieved good agreement with observed OCR values (R² = 0.806). Exploratory 24-h monitoring under fasting conditions revealed temporal variation in OCR; however, the fitted Cosinor model showed low explanatory power, limiting interpretation of circadian rhythmicity. A process-based DO model further demonstrated the potential for integrating metabolic predictions with oxygen dynamics in RAS. These findings provided a quantitative basis for precision oxygen management and highlight the importance of considering environmental and biological interactions in aquaculture systems.
Freshwater integrated multitrophic aquaculture (IMTA) remains less studied than marine systems, particularly regarding how functionally distinct aquatic and horticultural compartments respond to a shared production environment. This study evaluated water chemistry and compartment-specific biological responses in a freshwater IMTA integrating Nile tilapia (Oreochromis niloticus), the detritivorous snail (Pomacea patula catemacensis), the suspension-feeding clam (Rangia cuneata), pepino melon (Solanum muricatum), and chili (Capsicum annuum). A recirculating IMTA system, with water flowing sequentially through fish, snail, clam, and horticultural compartments, was compared over 120 days with independently operated culture units for each aquatic species and a separately fertilized hydroponic control. Both configurations had three independent replicates. Tilapia were stocked at 142 fish m⁻³ , snails at 210 individuals per unit, clams at 30 individuals per unit, and each horticultural unit contained 10 plants of each species. Water chemistry, aquatic productive performance, plant development, and plant sap nutrient composition were evaluated. Lower pH and higher electrical conductivity and several dissolved nutrient concentrations were observed in the integrated aquatic compartments, whereas the independently fertilized hydroponic control showed higher nitrate, potassium, and calcium concentrations than the IMTA horticultural compartment. Tilapia maintained comparable productive performance between systems. The detritivorous snail exhibited numerically higher relative growth under IMTA conditions, whereas the suspension-feeding clam showed numerically higher relative growth in the control; however, these differences were not statistically significant after Holm–Bonferroni correction. Pepino melon maintained comparable final growth between systems, while chili exhibited significantly greater final plant height under IMTA conditions. Branching and flower production were also numerically higher in chili under IMTA conditions but were not statistically significant after adjustment for multiple comparisons. Plant sap nutrient concentrations varied across phenological stages, without significant treatment differences detected within stages. These compartment-specific responses indicate that hydraulic integration was associated with distinct resource environments and biological responses across trophic compartments without uniformly enhancing productivity. The findings suggest that freshwater IMTA performance may depend partly on the functional compatibility between resource availability and the ecological requirements of the organisms incorporated into the system, although resource transfer and nutrient recovery were not directly quantified.
