# Characterizing the Health Status of European Hake (Merluccius merluccius) in Areas with Different Anthropic Impacts (NW Mediterranean Sea)

## TL;DR

This study evaluates the health of European hake in the Mediterranean to see if they can detect local pollution, finding them generally healthy but more useful as regional bioindicators.

## Contribution

The study establishes a baseline for hake health and evaluates their potential as a regional bioindicator for Mediterranean environmental quality.

## Key findings

- Hake showed generally good health across all areas with mostly homogeneous patterns in health indicators.
- Higher levels of detoxifying enzymes and parasitic tapeworms were observed in central and southern areas compared to the north.
- The species' high mobility and wide depth range may limit its ability to detect local-scale pollution impacts.

## Abstract

The Mediterranean Sea is subjected to several human-related (i.e., anthropic) impacts which alter the health of the organisms that inhabit it, including commercial fish like the European hake (Merluccius merluccius). This study assessed hake health along the Catalan coast (about 600 km in length) with varying pollution levels to determine if the species could serve as a local pollution sentinel. We evaluated hake general health status from three areas with different anthropic impacts by measuring different key factors: pollution exposure biomarkers (detoxifying enzymes), cellular stress/damage markers (antioxidant enzymes and lipid peroxidation), and macro-parasite assemblages. Results showed that hake were generally in good health across all areas, with most parameters being homogeneously distributed. Minor differences were observed in the central and south areas, where hake exhibited elevated levels of specific detoxifying enzymes and a higher prevalence of parasitic tapeworms compared to the north zone. The study establishes a baseline for hake health in the Catalan coast. However, the findings suggest that due to the species’ high mobility and wide depth range, the European hake may be limited in detecting local-scale pollution impacts. It is instead proposed as a useful regional bioindicator for monitoring the broader environmental quality of the Mediterranean Sea.

The high incidence of anthropogenic impacts in the Mediterranean basin raises concerns on the health and quality of commercial fish species. This study aims to evaluate the health status of the European hake, Merluccius merluccius, from three areas of the Catalan coast (NW Mediterranean Sea) with different anthropogenic impacts (i.e., chemical pollution, litter, …) and assess if hake could serve as a sentinel species. We measured biomarkers of chemical exposure including B-esterases, antioxidant enzymes (GST, GR, GPx, CAT), biotransformation markers (EROD), lipid peroxidation, and macro-parasite assemblages. Hake showed, generally, a good health status across all areas with homogeneous patterns for most parameters. Tissue-specific differences included elevated gonadal cholinesterases and higher brain and hepatic carboxylesterase activities in the south, and increased hepatic EROD but lower lipid peroxidation in the central Barcelona area. Parasite assemblages were dominated by Digenea, Cestoda, and Nematoda, with higher cestode prevalence in both central and south zones. In summary, despite a greater prevalence of environmental pollution in the central region, there was a homogeneous pattern in hake health indicators throughout the three studied fishing zones. These results establish a baseline for hake health in Mediterranean waters and suggest that the species’ high mobility and wide depth range may limit its utility to detect local-scale pollution impacts, though it may serve as a regional-scale bioindicator.