Mussel farming in known to enhance coastal habitats by attracting a higher diversity of fish by providing both shelter and feeding opportunities. However, when the feeding opportunities are the cultured mussels themselves, it results in substantial production inefficiencies. In the Firth of Thames region of New Zealand, mussel farmers report predation by fish contributes to mussel losses of up to 100%. However, the species responsible for these losses and the production stage at which they occur remain anecdotal. In this study, remote underwater video (RUV) was used over a 6-month period to observe fish activity at four different stages of production in mussel farms in the Firth of Thames, New Zealand. The RUV enabled the identification of the fish species inhabiting mussel farms, including the two most commonly observed species that were also found to be responsible for consuming cultured mussels, confirming the effectiveness of RUV methods for this research application. Four fish species were identified as frequent inhabitants of the mussel farms, with Australasian snapper (Chrysophrys auratus ) and parore (Girella tricuspidata ) the most abundant at three out of the four mussel farm sites investigated (Figure 1) . Australasian snapper was the most common predator, taking 2880 bites of the mussel dropper lines in a single 11 min 47 sec video recording. Snapper formed feeding aggregations targeting dropper lines holding juvenile mussels (> 20 mm SL) in particular , indicating their potential to remove mussels from nursery farms in a short amount of time. Observations of the feeding behaviour of parore indicated their potential to contribute to the losses of mussels on recently seeded spat farms with these fish recorded tearing apart seeded lines, possibly targeting the macroalgae that is seeded out with the mussel spat. This knowledge can be used to begin to develop mitigation strategies aimed at reducing crop losses in mussel aquaculture.