Excess total ammonia nitrogen (TAN) and its oxidized forms, nitrite and nitrate, pose significant risks to marine aquaculture. This study evaluated the feasibility of adsorption-based technologies for nitrogen removal under seawater aquaculture conditions. Three synthesized adsorbents—chitosan hydrogel (Cht-HG), p -hydroxybenzoic acid-modified Cht-HG (M-Cht-HG), and alginate–hydrogel–metal–zeolite (Al-H-M-Z)—were benchmarked against a moving bed biofilm reactor (MBBR) and commercial zeolite. In pilot-scale fish tanks, Al-H-M-Z achieved rapid physicochemical TAN removal, with 75.6% efficiency within 24 h, reducing concentrations from 0.023 mg L –1 to 0.006 mg L –1 . Furthermore, it maintained TAN and nitrite levels below 0.20 mg L –1 for 7 days, demonstrating stable performance. In contrast, M-Cht-HG was effective for only 2 days, after which TAN levels exceeded 1.62 mg L –1 . At an initial concentration of 300 mg L –1 , a long short-term memory (LSTM) deep learning model predicted that Al-H-M-Z would remove 80.1 mg L –1 TAN (26.7%) and 86.5 mg L –1 nitrite (28.8%) within 24 h. This study provides a foundation for integrating advanced adsorbents with predictive modeling to improve nitrogen treatment strategies for sustainable marine aquaculture. • Various adsorbents, including hydrogels and coated zeolites, were developed. • Al-H-M-Z outperformed other adsorbents in aquaculture applications. • Al-H-M-Z exhibited 2.14- and 1.11-fold higher removal of TAN and nitrite vs. MBBR over 7 days. • LSTM predicted Al-H-M-Z can adsorb 80.1 mg L –1 and 86.5 mg L –1 of TAN and nitrite in seawater.

This study investigated the influence of submerged versus surface feeding strategies on behavior and growth performance in farmed Atlantic Cod ( Gadus morhua ) in a full-scale, surface-based open cage system in northern Norway. Cod receiving submerged feed consistently occupied deeper and more stable vertical positions than surface-fed fish, particularly under elevated surface temperatures ( > 15 ° C ). While both groups exhibited diurnal vertical migrations, submerged-fed Cod displayed tighter vertical cohesion and reduced surface avoidance. The SGR was slightly higher in the submerged-fed group ( 0 . 39 % day − 1 vs. 0 . 35 % day − 1 ), likely reflecting reduced thermal stress and better alignment with the species’ natural foraging depth. However, FCR was marginally poorer (1.23 vs. 1.20), possibly due to increased feeding competition caused by localized feed delivery. In contrast, surface feeding provided more uniform feed dispersion, resulting in lower competition and more efficient feed utilization. Mortality rates were comparable between treatments (24.2% submerged vs. 23.4% surface), with peaks observed during a warm-water starvation phase. Principal component analysis identified feed availability as the primary driver of behavioral dynamics, followed by temperature and biomass. Submerged feeding also promoted greater behavioral synchrony and depth targeting under thermally stratified conditions. These findings highlight a trade-off between growth potential and feed efficiency, shaped by the spatial and competitive dynamics of feeding depth. They underline the importance of species- and site-specific feeding strategies, particularly in environments subject to thermal stress. The results can inform the optimization of feeding depth, scheduling, net pen configuration, and feeder design and placement. Furthermore, they support the development of behavior-informed, adaptive management tools aimed at improving production efficiency and fish welfare in Cod aquaculture.