# Water-Column Zone Impacts Non-Essential Heavy Metal Accumulation in Fish Occupying Different Zones

## TL;DR

Fish in different water zones accumulate varying levels of heavy metals, which affects their growth rates.

## Contribution

This study shows for the first time that non-essential heavy metal accumulation in fish depends on their water column zone.

## Key findings

- Demersal fish had highest arsenic and nickel levels, while epipelagic and demersal fish had highest cadmium, lead, mercury, and thallium.
- Mesopelagic fish showed increased weight for length ratios and lowest metal exposure.
- Reduced growth rates were observed in some epipelagic and demersal fish compared to historic data.

## Abstract

The Gulf of Maine and Bay of Fundy have documented increases in heavy metals with specific properties, resulting in differing concentrations throughout the water column. Whether this impacts metal accumulation in fish that occupy different zones of the water column is unknown; as such, this was the focus of this work. Commercially harvested fish spanning the epipelagic, mesopelagic, and demersal zones of the water column had weight for length (LWR) recorded and biopsies taken. Demersal fish had the highest levels of arsenic and nickel, whereas fish in the epipelagic and demersal zones showed the highest levels of cadmium, lead, mercury and thallium. Compared to historic data, LWR was reduced in one epipelagic species (15%) and two demersal species (24%, 25%). Mesopelagic species showed increased LWR (23%) concurrent with overall lowest metal exposure. These findings demonstrate that fish accumulate non-essential metals at levels dependent on location in the water column, impacting their growth.