Introduction
In recent decades, global demand for fisheries and aquaculture products has grown exponentially, positioning aquaculture ahead of traditional capture fisheries. This growth has driven the adoption of new trends aimed at ensuring efficient, safe, and sustainable production, both economically and environmentally.
One of the main strategies applied has been the progressive replacement of high-cost animal-based protein raw materials, such as fishmeal, with more competitive plant-based sources (e.g., soybean, rapeseed, corn, etc.).
While feed reformulation using plant-based ingredients has optimized operational costs in aquaculture farms, it also presents major nutritional and health challenges. The increased inclusion of plant raw materials exposes aquatic species to new metabolic and pathological threats, notably a higher risk of mycotoxin contamination.
Mycotoxins are toxic secondary metabolites naturally synthesized by various fungal species. Their entry into the food chain occurs as a result of crop colonization in the field or during the storage of raw materials and feeds (Gruber-Dorninger et al., 2019).
The main effects reported in aquatic species include oxidative stress, histopathological alterations resulting from such damage, immunosuppression, and impaired growth performance, such as reduced weight gain and even mortality in severe cases. The severity of the clinical symptoms depends closely on the animal species and production stage, as well as the type of mycotoxin, dosage, and exposure time (Oliveira et al., 2020).
Furthermore, the impairment of antioxidant and immune systems increases the vulnerability of exposed species to other environmental stressors or co-contaminants, such as heavy metals.
Heavy metal toxicity in aquatic species
Heavy metals, high-density chemical elements, represent a critical threat to aquatic ecosystems due to their high toxicity, non-biodegradable nature, and bioaccumulation capacity along the trophic chain.
The environmental persistence of these compounds has repercussions for animal health, impacting food safety and the global sustainability of the sector (Boularbah et al., 2006).
Although certain compounds are biologically essential (such as copper, which is essential for oxygen transport in crustacean hemolymph), the margin of safety between nutritional requirements and toxicity thresholds is extremely narrow (Amosu et al., 2016).
Exposure pathways for aquatic species are diverse and include the ingestion of contaminated feed, branchial filtration, and even dermal absorption. In turn, the entry of these contaminants into the aquaculture environment derives from industrial effluents, agricultural runoff, and fertilization materials. Upon sedimentation, organic and inorganic matter converted into deposits turns the benthic bed into the primary reservoir of heavy metals in culture systems (Chao et al., 2014).
In aquaculture production, heavy metals have been identified as high-risk elements:
- Mercury (Hg): In aquatic ecosystems, mercury occurs mainly in inorganic form (+2Hg) or as the organic species methylmercury (Balamara et al., 2005). Chronic exposure to these compounds induces severe neurotoxic alterations manifesting as behavioral disorders, accompanied by hepatic and renal dysfunction (Morel et al., 1998). Furthermore, in freshwater species such as the tench (Tinca tinca), concentrations starting as low as 0.1 ppm have been documented to compromise the immune system, significantly increasing susceptibility to infectious diseases (Shah et al., 2005).
- Cadmium (Cd): Chronic sublethal exposure to waterborne cadmium leads to accumulation primarily in the kidneys, liver, and gills of fish (McGeer et al., 2000). At the cellular level, it induces genetic alterations in fish through epigenetic modifications, disrupting critical metabolic pathways and promoting carcinogenesis processes (Liu et al., 2013).
Additionally, other effects have been reported, such as endocrine axis disruptions in Japanese medaka (Oryzias latipes), significantly altering plasma estradiol levels and compromising reproductive function (Tilton et al., 2003).
- Lead (Pb): Integrated into the geochemical cycle, lead occurs in both inorganic species (+2Pb) and derivative organic forms, notably trimethyllead and triethyllead (Bergdahl and Skerfving, 2022).
Exposure to this compound induces severe effects in aquatic organisms: it compromises immune and nervous responses, disrupts hematopoietic processes, and impairs normal growth and development rates (Baker et al., 2015). At the cellular level, it triggers apoptotic pathways, genotoxicity via DNA mutations, and oncogenic processes, with neurobehavioral alterations and cognitive deficits also being reported in study models (Mitra et al., 2017)
In trials conducted on African catfish (Clarias gariepinus), signs of skin pallor resulting from severe hepatotoxicity have been documented, as well as symptoms associated with neurotoxicity, as evidenced by loss of equilibrium and swimming capacity (Olaifa et al., 2003). - Copper (Cu): One of the main pathophysiological mechanisms involved in copper toxicity in aquatic species is the induction of oxidative stress, triggered by copper’s involvement in the production of reactive oxygen species (ROS). Furthermore, copper can interact with the activity of the antioxidant enzymatic system, with a particular impact during acute exposures or the initial stages of chronic exposure (Lushchak, 2011).
In trials conducted on common carp (Cyprinus carpio), these oxidative disorders in hepatic tissue were reflected in a significant increase in key oxidative stress biomarkers, notably alterations in hepatic glutathione peroxidase concentrations (Sevcikova et al., 2016).
Overall, the risk of heavy metals is magnified by their ability to act as triggers for toxic synergisms. Similar to observations with mycotoxins, due to their capacity to induce immunosuppression and chronic oxidative stress, these elements reduce the organism’s tolerance threshold, enhancing the effects of other environmental stressors and feed co-contaminants.
Co-occurrence of mycotoxins and heavy metals in aquafeeds
In the context of aquaculture, the co-occurrence of mycotoxins and heavy metals represents a critical and under-explored threat.
As an example, Tabassum et al. (2025) comprehensively evaluated the co-occurrence of aflatoxins and heavy metals in 48 commercial feed samples in Bangladesh, analyzing 34 batches intended for fish and 14 for shrimp. Fish diets recorded a mean total aflatoxin concentration of 0.055 ppm, with mean heavy metal levels of 0.089 ppm for Cd, 0.864 ppm for Pb, and 58.21 ppm for Cr. Meanwhile, shrimp formulations showed lower aflatoxin contamination (0.006 ppm), but presented significantly higher heavy metal contamination, reaching averages of 0.043 ppm for Cd, 1.89 ppm for Pb, and 95.42 ppm for Cr. Persistent co-contamination compromises the viability of aquaculture production and food safety, highlighting the urgent need to establish strict quality controls and take immediate corrective measures in the feed manufacturing chain.
By sharing key pathophysiological mechanisms, such as the induction of oxidative stress, the interaction between mycotoxins and heavy metals can trigger synergistic or additive effects that exacerbate damage at the hepatic, renal, and intestinal levels (Fu et al., 2022).
However, since research on mycotoxins in aquaculture is relatively recent, the scientific literature regarding combined in vivo exposure in aquatic species remains limited.
From a pathophysiological approach, in vitro assays on intestinal epithelium models exposed to deoxynivalenol (DON) and Cd demonstrated that the combination of both contaminants, starting at doses of 10 µM and 30 µM of each, induces reductions of up to 85% in transepithelial electrical resistance (TEER), accompanied by a massive increase in paracellular permeability after 48 hours of exposure (Luo et al., 2019).
Although these findings stem from laboratory cellular models, they constitute a clear indicator of the high disruptive potential exerted by this combined action on the integrity of the intestinal mucosa in farmed organisms.
Conclusion
Mycotoxins represent an increasingly relevant threat in aquaculture facilities due to the greater use of plant-based ingredients, triggering immunosuppression, oxidative stress, and tissue damage in farmed species.
These impairments of immune and antioxidant defenses reduce the tolerance threshold of production animals, rendering them significantly more susceptible to other contaminants, such as heavy metal toxicity
Therefore, the efficient management of aquaculture facilities requires a global approach, minimizing the impact of mycotoxins through comprehensive solutions and thus mitigating the potential magnified effects of other co-contaminants.
