Behavioral response of farmed Cod to environmental drivers and interaction with feeding practice

Abstract

This study investigated how environmental drivers and feeding practices influence the vertical behavior of farmed Atlantic Cod (Gadus morhua) in a commercial sea cage environment. A 70-day continuous observation was conducted at a farm in northern Norway, utilizing a dual-echosounder setup combined with temperature loggers and model-derived environmental data, including current velocity, salinity, and oxygen profiles. Cod behavior was compared between submerged (5 m) and surface feeding regimes across four sea cages. Fish consistently avoided surface layers above 15^∘C, aggregating at cooler depths, and shifted upward as thermal stratification weakened into autumn. Submerged feeding supported tighter aggregation, stronger rhythmicity, and vertical cohesion, while surface feeding induced anticipatory surfacing, behavioral fragmentation, and increased thermal exposure. These patterns were amplified by Cod’s physoclistic physiology and anatomical predispositions to strain from repeated vertical movement. Signal processing of depth-use patterns revealed stronger behavioral synchronization under submerged feeding, particularly aligned with the 48-hour feeding cycle. Aggregation dynamics were more closely aligned with residual current patterns and deeper water mass structure than with tidal forcing, and air temperature emerged as a reliable and practical proxy for estimating the vertical center of biomass. This study provides critical insight into farmed Cod’s depth preferences and environmental rhythms, which may be essential for enhancing fish welfare, reducing mortality, and improving the sustainability of Cod aquaculture.