Tun, Thein ThanHuang, LoulinPreece, Mark Anthony2025-07-242025-07-242025-07-24Ocean Engineering, ISSN: 0029-8018 (Print); 1873-5258 (Online), 340. doi: 10.1016/j.oceaneng.2025.1221370029-80181873-5258http://hdl.handle.net/10292/19602Unmanned underwater vehicles are deployed to automate the production processes in offshore aquaculture, but the onboard power supply with limited energy capacity constrains the operational range and time. In this paper, a nonlinear energy-optimal Model Predictive Control (EO-MPC) is proposed to perform a 4-degree-offreedom 3D fish net-pen visual inspection trajectory tracking while minimizing energy consumption. The EOMPC problem with explicit energy-related terms in the performance index (PI) is transcribed into a nonlinear programming problem (NLP), solved via IPOPT, the open-sourced primal-dual interior point solver. Using the specifications of Blue Endeavour Project (the upcoming first-of-its-kind offshore salmon firm in New Zealand) of the New Zealand King Salmon Company and the work-class ROV called RexROV 2, theoretical fundamentals and practical implementation aspects are detailed, and four controllers are tested in high-fidelity simulation using Robot Operating System and Gazebo Physics Engine. In a general constrained operational working environment, the proposed EO-MPC controller saves 3.1% - 21.4% more energy than the conventional MPC (CO-MPC) while achieving better or equivalent trajectory tracking performance under different underwater current disturbance speeds (0.0m∕s, 0.5m∕s and 0.9m∕s).© 2025 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).http://creativecommons.org/licenses/by/4.0/0405 Oceanography0905 Civil Engineering0911 Maritime EngineeringCivil Engineering4005 Civil engineering4012 Fluid mechanics and thermal engineering4015 Maritime engineeringEnergy-optimal model predictive control (EO-MPC)Nonlinear programming (NLP)Unmanned underwater vehicle (UUV)Fish net-pen visual inspection (FNVI)Offshore aquacultureRobot operating system (ROS)Gazebo physics engineJournal ArticleOpenAccess10.1016/j.oceaneng.2025.122137