Feeding Habits of Fish and Seafood: Implications for Health Effects Associated with Contaminants in Seafood

1. Introduction

Fish are a vital source of protein and nutrients for populations worldwide. However, their feeding habits play a significant role in determining the types and levels of contaminants they may accumulate, which is crucial when considering fish for human consumption.

A review on the types of contaminants that can be found in fish and other foods produced in a marine or freshwater environment, differences between wild caught fish and those produced via aquaculture, regulatory frameworks, risk assessments, and management issues relating to aquatic environments, including the impact of climate change was published in early 2026 [1]. The purpose of this review is to examine the influence of different feeding and other characteristics of various fish species that may influence the type and concentrations of contaminants that may be present in fish.

2. Predatory Fish

Predatory fish play a crucial role in aquatic ecosystems, acting as apex or meso- predators that regulate prey populations and influence food web dynamics. Their feeding habits are shaped by a combination of physiological adaptations, ecological niches, and the availability of prey species in their habitats [2,3].

2.1. Characteristics of Predatory Fish

Predatory fish are typically characterized by streamlined bodies, sharp teeth, and advanced sensory organs that enable them to efficiently detect and capture prey. Many are active hunters, employing strategies such as pursuit, ambush, or stalking to secure food. These species often occupy higher trophic levels and may exhibit territorial behaviour to secure feeding grounds [4].

2.2. Feeding Strategies of Predatory Fish and Examples

One well-known example of a predatory fish is the Atlantic cod (Gadus morhua), which preys on smaller fish, crustaceans, and invertebrates [5]. Another notable species is the northern pike (Esox lucius), an ambush predator that relies on camouflage and sudden bursts of speed to capture prey such as smaller fish and amphibians [6]. In marine environments, the great barracuda (Sphyraena barracuda) is recognized for its opportunistic hunting style, feeding on a diverse range of fish and cephalopods [7].

2.3. Dietary Variation and Ecological Impact

The diet of predatory fish can vary seasonally and geographically, influenced by prey availability and environmental conditions. For instance, largemouth bass (Micropterus salmoides) may shift their diet from insects and crustaceans as juveniles to predominantly fish as adults [8]. This adaptability allows predatory fish to exploit a broad range of food resources, but also makes them susceptible to bioaccumulation of contaminants from lower trophic levels [9].

2.4. Impact of Feeding Habits on Contaminant Profiles in Food

The feeding habits of predatory fish have direct implications for the accumulation of contaminants such as heavy metals and persistent organic pollutants (POPs) in their tissues, which are then transferred to humans when these fish are consumed. Because predatory fish occupy higher trophic levels, they are subject to biomagnification: the process by which concentrations of contaminants increase with each step up the food chain [9,10]. Predators such as tuna, swordfish, and barracuda, which consume large quantities of smaller fish, tend to accumulate higher levels of mercury, polychlorinated biphenyls (PCBs), and other toxic substances compared to non-predatory or lower trophic species [3,4].

Other factors, such as age, fat content, and habitat, can further influence contaminant levels. Older or larger individuals typically have had more time to bioaccumulate toxins, and oily fish can store more lipophilic contaminants in their tissues. Geographic location also plays a role, as fish from polluted waters are exposed to higher concentrations of contaminants. Thus, understanding the feeding habits and ecological characteristics of predatory fish is essential for assessing food safety risks and developing consumption guidelines [9].

2.5. Predatory Fish, Regulatory Limits and Government Advice for Consumption of Predatory Fish

Shark, swordfish and tuna most commonly exceed regulatory limits because they bioaccumulate very high levels of methylmercury, often surpassing the EU maximum level of 1.0 mg/kg for predatory fish. These species are long-lived, high-trophic-level predators, which drives biomagnification of mercury far above levels seen in most commercial fish. For example, in a 10-year EU monitoring dataset (2014–2023), 11.30% of swordfish samples exceeded the EU maximum level for total mercury [11]. In the same EU dataset, 6.48% of shark samples and 3.11% tuna exceeded regulatory mercury limits [11].

Many national agencies (EU, UK, US) therefore advise avoiding shark meat entirely, and to restrict consumption of other predatory fish especially for pregnant women and children, because exceedances are common and predictable.

3. Benthic, Demersal, and Pelagic Fishes

Benthic fishes are species that live on or near the bottom of aquatic environments, typically in close association with the sediment. They often rely on the substrate for food and shelter. Demersal fishes inhabit the water column just above the seabed. While they may venture slightly higher, they are generally found close to the bottom and feed on organisms living in or near the substrate as well as in the water just above it. Pelagic fishes are those that live in the open water column, away from the bottom and the shore. They are adapted to life in the midwater or surface zones and feed primarily on plankton, smaller fish, and other organisms found in these areas.

Note: the terms bentihic and demersal are often used interchangeably, but benthic strictly refers to creatures living directly on or in the sea floor, whereas demersal is a broader category for any fish that lives and feeds near the bottom of a water body. Essentially, all benthic fish are demersal, but not all demersal fish are benthic

3.1. Benthic Fish Feeding Habits

Benthic fishes, such as flounders and some species of cod, feed primarily on organisms living on or within the sediment at the bottom of aquatic environments. Their diet often includes worms, crustaceans, and detritus. Because sediments can act as sinks for contaminants like mercury, lead, and polychlorinated biphenyls (PCBs), benthic feeders are particularly susceptible to bioaccumulating these substances. The ingestion of contaminated sediment and benthic prey results in higher concentrations of certain pollutants in their tissues, which can pose health risks to consumers [12].

Examples of benthic fish include flounder, sole, skates, rays, and tripodfish.

3.2. Demersal Fish Feeding Habits

Demersal fish occupy zones near the bottom but may range slightly above the substrate. Species such as Atlantic cod and haddock exhibit both benthic and pelagic feeding behaviors, consuming prey from the seabed as well as from the water column. Demersal feeders are exposed to contaminants present in both sediments and in suspended particulate matter. Their intermediate position in the ecosystem means they may accumulate a mixture of pollutants, depending on local contamination sources and feeding selectivity [10,13].

Examples of demersal fish include cod, haddock, croakers, and various rockfish.

3.3. Pelagic Fish Feeding Habits

Pelagic fishes, including mackerel, tuna, and herring, feed in the open water column, preying on zooplankton, smaller fish, and squid. These species are less likely to ingest sediment-associated contaminants directly. However, pelagic fish can still accumulate pollutants such as methylmercury and POPs through trophic transfer, especially in higher trophic levels where biomagnification occurs. The migratory nature of some pelagic species may also lead to exposure to diverse contaminant profiles depending on geographic location and water quality [10,14].

Examples of pelagic fish include mackerel, herring, sharks and tuna.

3.4. Implications for Seafood Safety

The foraging strategies of benthic, demersal, and pelagic fishes result in distinct contaminant profiles, which are important considerations for food safety. Benthic and demersal species often present higher risks of sediment-derived contaminants, while pelagic species may be more affected by waterborne and biomagnified substances. Consumers should be aware of these differences, as well as factors such as age, geographic origin, and lipid content, which further influence contaminant levels in fish (see later). Regulatory agencies use this ecological understanding to set guidelines for safe fish consumption and to monitor environmental health [12,14].

4. Filter-Feeding Shellfish

Filter-feeding shellfish, such as mussels, oysters, clams, and scallops, play a crucial ecological role in aquatic environments by filtering large volumes of water to extract their food [15]. This unique feeding strategy, while beneficial for ecosystem health and water clarity, also makes these organisms particularly susceptible to accumulating environmental contaminants [16]. Understanding the relationship between filter-feeding habits and contaminant accumulation is vital for assessing seafood safety and protecting public health.

4.1. Feeding Mechanisms of Filter-Feeding Shellfish

Filter-feeding shellfish acquire nutrients by pumping water across specialized gill structures that trap suspended particles, including phytoplankton, detritus, and microorganisms [17,18]. The efficiency of this process allows shellfish to consume a wide variety of particulate matter present in their environment. However, this non-selective feeding strategy also means that shellfish can inadvertently ingest and concentrate contaminants, such as heavy metals, persistent organic pollutants (POPs), and pathogenic microorganisms, that are attached to or associated with suspended particles [19].

4.2. Types of Contaminants Accumulated by Filter Feeders

The primary contaminants of concern in filter-feeding shellfish include trace metals (e.g., mercury, cadmium, lead, and arsenic), POPs (such as PCBs and dioxins), and microbial pathogens (including bacteria and viruses) [20,21]. Contaminant levels in shellfish are often influenced by local water quality, proximity to pollution sources, and environmental conditions that affect the concentration and availability of harmful substances in the water column [16].

4.3. Bioaccumulation and Food Safety Risks

Due to their filter-feeding habits, shellfish can bioaccumulate contaminants at concentrations significantly higher than those found in surrounding water [19]. Metals and POPs are particularly of concern because they are not easily metabolised or excreted, leading to persistent accumulation in shellfish tissues [20]. When humans consume contaminated shellfish, these substances can pose health risks, ranging from acute poisoning to long-term effects such as neurotoxicity or carcinogenicity [21]. Additionally, outbreaks of shellfish-borne illnesses caused by microbial pathogens highlight the importance of monitoring water quality in shellfish harvesting areas [18].

4.4. Factors Affecting Contaminant Levels in Shellfish

Several factors influence the degree of contaminant accumulation in filter-feeding shellfish, including geographic location, water temperature, salinity, and the specific feeding rates of different species [16]. Areas with higher levels of industrial discharge, agricultural runoff, or urban wastewater are associated with elevated contaminant loads in local shellfish populations [15]. Seasonal variations can also impact contaminant uptake, as changes in plankton abundance and water chemistry affect the types and amounts of particles filtered by shellfish [17].

4.5. Implications for Seafood Safety and Public Health

Given the propensity of filter-feeding shellfish to concentrate contaminants, regulatory agencies have established strict monitoring and management programs for shellfish harvesting. These programs include regular testing for chemical and microbial contaminants and the implementation of closure protocols when unsafe levels are detected [21]. Consumers are advised to source shellfish from reputable suppliers and to follow public health advisories to minimize exposure to harmful substances.

5. Geographical Origin

The geographical origin of fish and seafood plays a critical role in determining the types and concentrations of contaminants present in these foods. Variations in environmental conditions, industrial activities, agricultural runoff, and local regulations all contribute to the unique contaminant profiles observed in seafood from different regions [15,16]. Understanding these geographic influences is essential for assessing food safety risks and making informed choices in seafood consumption.

5.1. Regional Differences in Contaminant Exposure

Marine and freshwater environments vary widely in their exposure to pollutants. Coastal areas near large urban centres or industrial zones are often subject to higher levels of contaminants such as heavy metals and POPs. In contrast, remote regions may have lower anthropogenic input but can still accumulate long-range transported contaminants through atmospheric or oceanic currents. For example, Arctic seafood may contain elevated levels of POPs despite limited local sources due to global distribution patterns [16].

5.2. Influence of Local Practices and Regulations

Local aquaculture practices, wastewater management, and environmental regulations significantly affect contaminant levels in fish and shellfish [15]. Regions with stringent environmental standards and effective enforcement tend to produce seafood with lower contaminant burdens. Conversely, areas with inadequate monitoring or weak regulation may expose aquatic organisms to higher levels of industrial discharges, agricultural chemicals, and untreated sewage, increasing the risk for consumers [18,19].

5.3. Case Studies: Contaminant Profiles by Region

Studies have shown that fish from the Baltic Sea often exhibit higher concentrations of dioxins and PCBs compared to those from the North Atlantic, largely due to historical industrial activity and limited water exchange [16]. Similarly, bivalve molluscs harvested from Chinese coastal waters have been found to accumulate significant levels of heavy metals, reflecting both natural geological inputs and anthropogenic pollution [22]. These examples highlight the importance of considering geographic origin when evaluating seafood safety.

5.4. Implications for Food Safety and Consumer Guidance

The variability in contaminant profiles based on geographical origin underscores the need for region-specific monitoring and risk assessment [21]. Consumers are advised to pay attention to advisories and labelling indicating the source of seafood. Regulatory agencies often set maximum allowable limits for contaminants based on regional data, and international trade standards require documentation of geographic origin to ensure food safety [15].

5.5. Example of Advice Given to Consumers of Fish From the Baltic Sea

Consumers are advised to limit intake of certain Baltic Sea fish—especially fatty species like herring and salmon—because they can contain elevated levels of dioxins, PCBs, and methylmercury which can affect brain development, immune function, and cancer risk with chronic (long-term) exposure. These contaminants have declined sharply since the 1970s–80s but remain high enough in some fish to exceed the tolerable weekly intake (TWI) for some groups. Levels vary widely by fish size, age, and location; older and northern Baltic herring tend to contain more pollutants (balticwaters.org). The strictest restrictions apply to children and women of child-bearing age, while most other adults can safely eat these fish in moderation.

Key advice is given to women of child-bearing age, pregnant and breastfeeding women, children, and adolescents who should: (i) Eat Baltic herring no more than 2–3 times per year; (ii)Limit other fatty Baltic fish similarly, due to the risk of transferring pollutants to the fetus or infant, and (iii) Be aware that even though risks are small, exposure during early development is the main concern. Advice for the general adult population is that: (i) Most adults may eat Baltic herring up to once per week without exceeding health-based guidance values; (ii) For adults over 45 and young men, the health benefits of Baltic herring and salmon (omega-3s, vitamin D, cardiovascular protection) generally outweigh the contaminant risks. Practical consumption advice is given to: (i) opt for smaller, younger herring, which contain significantly lower pollutant levels.; (ii) Recognise that contamination varies by region: in some northern areas, safe consumption may be ~8 meals/year, while in southern areas it may be up to ~100 meals/year without exceeding TWI and (iii) to balance risks and benefits - for many adults, the nutritional advantages of Baltic fish remain substantial and may outweigh risks.

6. Oily and Non-Oily Fish

The distinction between oily (pelagic, high-fat) and non-oily (lean, low-fat) fish is especially important, as it determines not only their nutritional value but also their susceptibility to contaminant accumulation [15,19].

6.1. Feeding Habits of Oily vs. Non-Oily Fish

Oily fish, such as salmon, mackerel, sardines, and herring, are typically pelagic species that inhabit open waters and are characterized by high lipid content in their tissues. Their diets are diverse and often include smaller fish, zooplankton, and crustaceans [15]. These feeding habits place oily fish higher in the aquatic food web, making them more prone to biomagnification of certain contaminants. In contrast, non-oily fish, such as cod, haddock, and pollock, are generally demersal (bottom-dwelling) or benthic feeders. They tend to consume benthic invertebrates, small crustaceans, and detritus, which may expose them to different contaminant sources, particularly those associated with sediments.

6.2. Comparison of Contaminant Profiles

The divergent feeding strategies of oily and non-oily fish result in distinct contaminant profiles. Oily fish, due to their lipid-rich tissues, readily accumulate lipophilic contaminants such as persistent organic pollutants (POPs), including polychlorinated biphenyls (PCBs) and dioxins [23]. These substances are fat-soluble and tend to bio-magnify up the food chain, leading to higher concentrations in top predators. Non-oily fish, having lower fat reserves, accumulate these contaminants to a lesser extent but may still be exposed to significant levels of metals such as mercury, cadmium, and lead, particularly if they feed in contaminated benthic environments [22].

Metals, unlike POPs, do not preferentially accumulate in fatty tissues but can concentrate in muscle and organ tissues [19]. The relative risk posed by these contaminants varies according to species, age, habitat, and feeding behaviour. For example, larger, older oily fish may contain higher levels of both lipophilic and metallic contaminants due to prolonged exposure and biomagnification, whereas non-oily fish may reflect more localized sediment contamination [16].

6.3. Food Safety Implications

Understanding the differences in contaminant profiles between oily and non-oily fish is essential for risk assessment and the development of consumption guidelines. Oily fish provide valuable omega-3 fatty acids but may pose a higher risk for exposure to POPs, especially when sourced from polluted waters. Non-oily fish, though generally lower in fat-soluble contaminants, can still present risks related to metal accumulation [22]. Therefore, regular monitoring of contaminant levels and clear communication of consumption advisories are critical to maximizing the health benefits of fish while minimizing potential hazards.

7. The Relationship Between Fish Age and Contaminant Profiles

As fish grow older, they are exposed to environmental pollutants for longer periods, leading to increased bioaccumulation of contaminants such as heavy metals and persistent organic pollutants (POPs). Biomagnification is particularly pronounced in species that occupy higher trophic levels or have longer lifespans, as they accumulate higher concentrations of contaminants over time.

Older fish generally exhibit greater concentrations of fat-soluble contaminants, including polychlorinated biphenyls (PCBs), dioxins, and certain pesticides, due to their prolonged exposure and the tendency of these chemicals to accumulate in fatty tissues. Similarly, heavy metals such as mercury and cadmium can build up in the tissues of aging fish, sometimes reaching levels that pose health risks to consumers. The rate and extent of accumulation can vary depending on species, habitat, feeding habits, and local environmental conditions.

The relationship between fish age and contaminant load is also influenced by differences in metabolism and growth rates. Younger fish may metabolise certain contaminants more rapidly or exhibit different feeding patterns, leading to variations in contaminant uptake. However, as fish age and grow larger, their slower metabolic rates and increased dietary intake often result in higher contaminant concentrations. This is particularly relevant for predatory species, which may ingest contaminated prey throughout their lives, further contributing to the accumulation of hazardous substances [16,19].

From a food safety perspective, understanding the age-related differences in contaminant profiles is essential for developing effective consumption guidelines and risk assessments. Regulatory agencies often recommend limiting the consumption of older, larger fish, especially for vulnerable populations such as pregnant women and children, due to the elevated risk of exposure to harmful contaminants.

8. Feeding Habits and Contaminant Profiles of Scavenger Versus Non-Scavenger Fish

Scavenger fish, such as catfish and certain species of flatfish, primarily consume dead or decaying organic matter, including other fish, invertebrates, and detritus found on the seabed [24]. In contrast, non-scavenger fish typically feed on live prey such as plankton, small fish, or aquatic plants, following more selective and active foraging strategies [3].

The differences in diet between scavengers and non-scavengers influence the types and concentrations of contaminants that accumulate in their tissues. Scavenger fish are often exposed to higher levels of environmental pollutants due to their consumption of decomposed material, which can contain concentrated residues of heavy metals (such as mercury, lead, and cadmium) and persistent organic pollutants (POPs) like polychlorinated biphenyls (PCBs) and dioxins [9,10]. These contaminants tend to persist in the environment and become more concentrated in dead organisms, making scavengers particularly susceptible to bioaccumulation [25].

Non-scavenger fish, on the other hand, may experience lower contaminant loads depending on their position in the food web and the cleanliness of their prey. However, predatory non-scavenger fish can also bioaccumulate significant levels of contaminants, especially those feeding at higher trophic levels [26]. The type of contaminant—metals, POPs, or others—varies with feeding habits and environmental exposure, but scavengers generally display a broader range of contaminant types due to their less selective diets [27].

From a food safety perspective, these differences are critical. Scavenger fish may present higher risks of contaminant exposure to consumers, particularly regarding fat-soluble compounds and metals that accumulate in tissues over time [28]. Regular monitoring and assessment of contaminant profiles in both scavenger and non-scavenger fish are essential for establishing safe consumption guidelines and protecting public health. Understanding feeding habits provides valuable insight into the potential risks associated with consuming different fish species, guiding regulatory recommendations and consumer choices [29].

9. Differences in Feeding Habits and Chemical Contaminant Risks Between Wild and Aquaculture Fish

The global demand for fish and seafood has led to a significant rise in aquaculture production, complementing traditional wild-capture fisheries. However, the feeding habits of wild fish differ markedly from those of fish raised in aquaculture, influencing both their growth and their exposure to chemical contaminants. Understanding these differences is essential for assessing the risks associated with consuming fish from various sources and for implementing effective food safety strategies [3,29].

Wild fish exhibit diverse feeding behaviours, shaped by ecological availability and competition within natural habitats. Their diets may include a wide range of prey, from plankton and benthic invertebrates to smaller fish and detritus, depending on species, life stage, and trophic position [3]. This dietary diversity exposes wild fish to a broad spectrum of environmental contaminants, such as metals in sediments or persistent organic pollutants (POPs) that biomagnify through food webs [10,26].

In contrast, aquaculture fish are typically fed formulated feeds composed of fish meal, fish oil, plant proteins, and other additives. These feeds are designed to optimize growth and health, but their composition can vary based on economic and regulatory factors. Consequently, the contaminant profile of aquaculture fish is largely determined by the ingredients in their diet, rather than the local aquatic environment [28,29]. The use of terrestrial plant-based feed ingredients has, in some cases, reduced the levels of certain contaminants (such as methylmercury and PCBs) in farmed fish compared to their wild counterparts, although other risks, such as pesticide residues or mycotoxins, may arise depending on feed quality [29].

Wild fish accumulate metals such as mercury and cadmium primarily through their diet and direct contact with contaminated sediments or water. Top predators in wild systems often exhibit higher concentrations of methylmercury due to biomagnification, making trophic level a key determinant of metal burden [24,26]. In aquaculture, the risk of metal contamination is often linked to the sourcing of feed ingredients, especially fish meal and fish oil, which may carry residual metals if derived from contaminated stocks [28,29].

POPs, such as polychlorinated biphenyls (PCBs) and dioxins, persist in aquatic environments and bioaccumulate in animal tissues. Wild fish, particularly those in contaminated habitats or at higher trophic levels, may carry significant burdens of POPs due to their position in the food web [27]. Aquaculture fish, on the other hand, are generally exposed to POPs through their feed. Advances in feed formulation have reduced the use of high-POP fish meal and oil, but the risk remains if these ingredients are sourced from polluted regions [10].

In addition to metals and POPs, aquaculture fish may be exposed to unique contaminants such as veterinary drugs, antibiotics, and antifoulants, which are used to prevent disease and biofouling in intensive farming systems. The presence of such compounds in edible tissues is closely regulated, but improper use or oversight can lead to detectable residues in aquaculture products [29]. Wild fish are less likely to encounter these substances but may be exposed to agricultural runoff, microplastics, and other emerging contaminants depending on their habitat.

The contrasting feeding habits of wild and aquaculture fish result in distinct contaminant exposure pathways. Wild fish are more susceptible to biomagnified contaminants and local environmental pollution, while aquaculture fish are primarily influenced by feed composition and farm management practices (Helfman et al., 2009; Jepson et al., 2016). For consumers, this means that the safety of fish products depends not only on the species and origin but also on the production method and supply chain oversight.

10. Exposure to Micro and Nanoplastics in Fish and Shellfish: Influence of Feeding Habits and Implications for Human Consumption

Microplastics (MPs, <5 mm) and nanoplastics (NPs, <100 nm) are now recognized as pervasive contaminants in aquatic environments [30]. Their presence in marine and freshwater systems raises concerns about ecosystem health and food safety, especially as fish and shellfish are key components of the human diet [28]. While much research has focused on chemical pollutants such as mercury and persistent organic pollutants [27], the unique properties and biological interactions of micro- and nanoplastics warrant specific attention to exposure pathways, accumulation, and potential risks.

10.1. Feeding Habits and Exposure Pathways

The extent of micro- and nanoplastic exposure in aquatic organisms is strongly influenced by feeding strategies [3]. Filter-feeding shellfish such as mussels, oysters, and clams are particularly susceptible to ingesting MPs and NPs, as these particles are readily suspended in water columns and can be trapped during feeding. Studies have shown that bivalves can accumulate significant quantities of microplastics in their tissues, which may subsequently be transferred to humans upon consumption [31].

In contrast, fish species experience varied exposure based on their trophic position and feeding habits. Planktivorous fish, which feed on zooplankton and phytoplankton, are likely to ingest microplastics directly, as these particles can mimic the size and shape of natural prey [3]. Carnivorous and piscivorous fish may accumulate MPs and NPs indirectly through trophic transfer, ingesting contaminated prey and experiencing biomagnification, similar to processes observed for mercury and PCBs [26,27]. Bottom-dwelling and scavenging species may encounter higher concentrations of plastics due to sediment accumulation, particularly in polluted habitats.

10.2. Species-Specific Differences in Accumulation

Shellfish, owing to their sedentary nature and filter-feeding behaviour, tend to show higher concentrations of microplastics compared to most fish species. The efficiency of particle retention and the lack of selective feeding mechanisms contribute to this risk. Among fish, species occupying lower trophic levels (e.g., planktivores and benthic feeders) may exhibit higher initial exposure, while top predators may accumulate plastics through food web transfer, albeit potentially at lower concentrations than chemical contaminants due to partial excretion of indigestible particles [24].

10.3. Consequences for Human Consumption

The presence of micro- and nanoplastics in commercially important fish and shellfish raises concerns for food safety and human health [30]. Consumption of shellfish, which are often eaten whole, may result in direct ingestion of plastics. For fish, the risk depends on which tissues are consumed, as MPs and NPs can accumulate in the gastrointestinal tract and, in some cases, translocate to edible muscle tissues. Although health effects of dietary microplastics in humans are still under investigation, potential impacts include physical tissue damage, chemical toxicity from associated pollutants, and immune responses (www.plasticheal.eu).

Regulatory agencies and public health organizations are increasingly calling for standardized monitoring and risk assessment protocols to quantify micro- and nanoplastic contamination in seafood [30]. The implications for consumers highlight the need for improved waste management, reduction of plastic inputs into aquatic environments, and further research into the biological effects of plastic ingestion at different trophic levels.

11. How are Feeding Habits Important for Specific Classes of Chemical Contaminant?

The feeding habits of fish and shellfish play a crucial role in determining the types and concentrations of contaminants they acquire. Understanding the relationship between diet and contaminant uptake is essential for both ecological risk assessment and public health protection [3,29].

11.1. Feeding Habits and Trophic Position

The trophic position, or the level at which an organism feeds within a food web, along with its life-history traits (longevity, growth rate, lipid content) are the major determinants of contaminant accumulation. Predatory fish occupying higher trophic levels tend to accumulate greater concentrations of certain contaminants, such as methylmercury and PCBs, due to biomagnification [24,26,27]. Medium-trophic, oily fish (salmon, mackerel, herring) have moderate POP burdens but generally lower MeHg than apex predators, offering a more favourable risk–benefit balance. In contrast, species feeding at lower trophic levels, such as filter-feeding shellfish, may be more exposed to contaminants present in suspended particles and sediments, such as certain metals and hydrophobic organic compounds [10], but will typically have lower contaminant levels and are preferred for frequent consumption. Bivalves and benthic feeders (mussels, oysters, carp, catfish) reflect local sediment and water contamination, including metals, PAHs, microplastics and algal toxins; risk is highly site-specific. The diversity of feeding strategies among fish and shellfish thus results in varied contaminant exposure profiles across species [3].

11.2. Metals: Bioaccumulation and Dietary Exposure

Methylmercury(MeHg), the most toxic form of mercury, is efficiently transferred through aquatic food webs and is found at the highest concentrations in top predators [28,29]. Studies have shown that the mercury content in fish is positively correlated with trophic level, as measured by stable nitrogen isotopes (δ15N), underscoring the importance of dietary habits in determining contaminant burdens [26]. Benthic feeders may also accumulate metals from sediments, highlighting the role of feeding substrate in exposure risk [10].

Cadmium (Cd) accumulates in shellfish and can cause kidney damage with chronic exposure. Lead (Pb) affects neurological development in children and cardiovascular health in adults. Arsenic (As) in seafood is mostly organic (less toxic), but inorganic As in some species is a carcinogenic risk.

Regulatory limits for Cd, Pb, and Hg in seafood reflect these risks (e.g., Hg limits 0.5–1 mg/kg depending on species) [32].

11.3. Persistent Organic Pollutants (POPs) and Dietary Pathways

POPs, including polychlorinated biphenyls (PCBs), dioxins, and furans, are hydrophobic compounds that persist in the environment and bioaccumulate in lipid-rich tissues. Fish and shellfish that consume contaminated prey or detritus can accumulate significant levels of these pollutants. Carnivorous fish, especially those at the apex of the food web, often exhibit higher tissue concentrations of POPs compared to herbivorous or omnivorous species [10,27]. Filter-feeding shellfish can also accumulate POPs directly from the water column and suspended particulates, further illustrating the influence of feeding mode on contaminant exposure [10].

11.4. Radionuclides

Radionuclides typically enter the food chain through widespread environmental contamination. As with stable isotopes, radioactive species may be deposited onto terrestrial and aquatic environments via atmospheric fallout or from contaminated water sources. This leads to direct exposure of livestock and aquatic organisms, or alternatively, results in the uptake of radionuclides by plants from contaminated soils or surface deposition. Uptake of radionuclides occurs via contaminated sediments and water; transfer to humans depends on species and trophic level [1]. Examples include radionuclides such as ¹³⁷Cs and ⁹⁰Sr which can enter marine food webs following nuclear releases or chronic discharges. They are taken up by plankton and benthic organisms and transferred to fish and shellfish. Muscle-seeking radionuclides (e.g., ¹³⁷Cs) and bone-seeking radionuclides (e.g., ⁹⁰Sr) pose long-term cancer risks when ingested, although current levels in most regions are generally low compared with natural background. Site-specific monitoring remains essential near nuclear facilities or accident sites.

11.5. Mycotoxins

Mycotoxins are primarily associated with terrestrial crops, but aquaculture feed can be contaminated with aflatoxins, ochratoxin A and other fungal metabolites, leading to transfer into farmed fish tissues at low levels. In parallel, phycotoxins (algal toxins) such as saxitoxin, domoic acid and okadaic acid accumulate in bivalve molluscs through filter feeding, causing paralytic, amnesic and diarrhetic shellfish poisoning in humans. These toxins can produce acute neurotoxic and gastrointestinal syndromes and, in some cases, long-term neurological sequelae. Effective monitoring and harvest closures have substantially reduced major outbreaks in many regions.

11.6. Microplastics and Nanoplastics

Microplastics and nanoplastics are now ubiquitous in marine environments and are ingested by bivalves, crustaceans and small fish. They can act as vectors for sorbed POPs, metals and plasticisers, and may induce local inflammation and oxidative stress in gut tissues. Health concerns from Microplastics and Nanoplastics (MNPs) can be associated with physical particle effects (inflammation, oxidative stress). Smaller sized MNPs may cross biological membranes more readily and hence this is an emerging concern. MNPs can be ingested by filter feeders (mussels, oysters) and small fish resulting in potential trophic transfer.

Barboza et al. [33] concluded that, while current exposure via seafood is likely below thresholds for overt toxicity, the potential for chronic, low-dose effects and systemic translocation of nanoplastics warrants precautionary research and policy [34].

11.7. Microbiological Contaminants

Whilst the focus of this review is chemical contaminants, it is worth noting that fish and seafood is also susceptible to microbiological contamination, especially from organisms such as Vibrio spp., norovirus, hepatitis A, and parasites (e.g., Anisakis). Health implications tend to be acute rather than chronic and include acute gastrointestinal illness. Severe infections in immunocompromised individuals (e.g., Vibrio vulnificus can be a problem and allergic reactions (e.g., Anisakis allergens) are also a problem for affected people. These contaminants are not usually bioaccumulative, but can have higher risk in raw or lightly processed seafood, especially shellfish harvested from contaminated waters. Filter-feeding bivalves are especially vulnerable to faecal contamination and can concentrate enteric pathogens from sewage-impacted waters. Standard controls (depuration, cooking, hygiene) are effective but require robust implementation.

11.8. Other Chemical Contaminants that May Be Found in Fish and Seafood

Pharmaceuticals and personal-care products (antibiotics, antidepressants) have been detected in marine organisms as a result of human use and discharge of waste into rivers and the marine environment. Industrial chemicals (e.g., antifoulants, pesticides) can enter coastal waters and be found in fish and seafood. These are associated mostly with low-level exposure, but long-term effects remain uncertain.

12. Implications for Human Health

Fish and seafood provide essential nutrients including long-chain PUFAs, iodine, selenium, vitamin D) and are consistently associated with reduced cardiovascular risk in adults. However, they are also a major dietary source of several environmental contaminants, notably methylmercury, persistent organic pollutants (POPs), metals, microplastics, radionuclides and microbiological hazards. The net health impact depends critically on species, origin, trophic level, and consumption pattern

The feeding habits of fish and shellfish not only influence their own contaminant loads but also affect the risk to humans who consume seafood. Species known for high trophic positions or specialized feeding strategies, such as large predatory fish or benthic feeders, are often associated with higher levels of contaminants in edible tissues [28,35]. Public health guidelines frequently recommend limiting consumption of certain species to reduce exposure to these contaminants [35].

Table 1 below shows Species specific risks for contaminants in fish and seafood.

12.1. Reducing Adverse Health Effects from Fish and Seafood

12.1.1. Species-Specific Guidance and Consumption Advice

Prioritise consumption of low-trophic, short-lived species (sardines, anchovies, small pelagic species, many farmed species) over other species. Limit intake of apex predators (shark, swordfish, large tuna, some marine mammals), especially for pregnant women, breastfeeding mothers, women planning pregnancy and young children, based on methylmercury and POP levels.

12.1.2. Implement Monitoring and Source Control

Maintain and expand integrated monitoring of metals, POPs, radionuclides, microplastics and microbiological hazards in fish and seafood, with a particular focus on bivalves and benthic species in polluted or eutrophic coastal zones. Reduce emissions of mercury, POPs and PFAS through upstream industrial and agricultural controls, recognising seafood as a key exposure pathway.

12.1.3. Risk–Benefit Communication

Communicate that seafood remains beneficial when consumed as part of a balanced diet, but that species choice and origin matter. Provide simple, evidence-based tools (e.g., traffic-light lists by species and origin) to help consumers and clinicians balance cardiovascular benefits against contaminant risks.

12.1.4. Protection of Vulnerable Groups

Use EFSA and WHO risk assessments as a source of key advice for methylmercury, dioxins/PCBs and other key contaminants, incorporating explicit advice for pregnancy and early childhood. Encourage substitution of high-risk species with lower-risk alternatives that provide similar nutritional benefits (e.g., replacing large predatory fish with small pelagic species or farmed salmon from well-regulated systems).

12.1.5. Research Priorities

Clarify health impacts of micro- and nanoplastics, PFAS and complex contaminant mixtures in seafood. Improve understanding of climate-driven changes in harmful algal blooms, pathogen dynamics and contaminant mobilisation, and integrate these into adaptive monitoring and policy frameworks.

13. Conclusions

Regular monitoring of contaminant levels across different age groups of fish can help inform public health advisories and ensure the safe inclusion of fish in the human diet. Factors that can have an impact on contaminant profile and are thus of relevance to human health have been discussed in this review and include:

13.1. Predatory Fish

Understanding the feeding habits of predatory fish is essential for managing fisheries and conserving aquatic biodiversity. By studying their diet and hunting behaviours, researchers can better predict population dynamics and the potential impacts of environmental changes on aquatic ecosystems, as well as the risks associated with consuming predatory fish as food [3].

13.2. Benthic, Demersal, and Pelagic Fish

The feeding habits of fish—benthic, demersal, or pelagic—directly affect their exposure to environmental contaminants, with significant implications for food safety. Continued research and monitoring are essential to assess risks and to guide public health recommendations regarding seafood consumption [10,13].

13.3. Filter-Feeding Shellfish

Filter-feeding shellfish are an important food source but are also uniquely vulnerable to environmental contamination due to their feeding habits. Continuous monitoring, responsible aquaculture practices, and informed consumer choices are essential to ensuring the safety of shellfish as part of the human diet. Ongoing research into contaminant dynamics and shellfish physiology will further enhance our ability to manage risks and protect public health.

13.4. Geographical Origin

Geographical origin is a key determinant of contaminant exposure in fish and seafood, influencing both the type and concentration of hazardous substances that may be present. By recognizing the significance of regional differences and supporting robust monitoring programs, stakeholders can better manage food safety risks and protect public health.

13.5. Oily and Non-Oily Fish

The feeding habits of oily and non-oily fish significantly influence the type and concentration of contaminants they accumulate. This knowledge is vital for consumers, policymakers, and food safety authorities to make informed decisions regarding fish consumption and public health protection.

13.6. Age of Fish

The age of fish plays a pivotal role in determining the type and concentration of contaminants present in their tissues. Recognizing and addressing these age-related differences is crucial for protecting consumers and maximizing the nutritional benefits of fish while minimizing potential health hazards.

13.7. Scavenger Fish

Scavenger fish may present higher risks of contaminant exposure to consumers, particularly regarding fat-soluble compounds and metals that accumulate in tissues over time

13.8. Wild and Aquaculture Fish

The contaminant profile of aquaculture fish is largely determined by the ingredients in their diet, rather than the local aquatic environment [28,29]. The use of terrestrial plant-based feed ingredients has, in some cases, reduced the levels of certain contaminants (such as methylmercury and PCBs) in farmed fish compared to their wild counterparts, although other risks, such as pesticide residues or mycotoxins, may arise depending on feed quality [29]. Differences in feeding ecology between wild and aquaculture fish have significant implications for the accumulation of chemical contaminants in seafood. While wild fish may face higher risks from environmental pollutants and biomagnified toxins, aquaculture fish are subject to risks associated with feed ingredients and farm management practices. Ongoing monitoring and improvements in both fisheries management and aquaculture feed formulation are essential to ensure the safety and sustainability of fish for human consumption [3,29].

13.9. Influence of Feeding Habits on Chemical Contaminant Accumulation

Feeding habits are a critical factor in the accumulation of chemical contaminants in fish and shellfish. Differences in diet, trophic position, and feeding substrate lead to variability in contaminant profiles, with important implications for ecosystem health and human dietary safety. Continued research into the links between feeding ecology and contaminant dynamics will enhance our ability to manage risks associated with seafood consumption and protect aquatic biodiversity [3,24].

13.10. Micro- and Nanoplastics

Exposure to micro- and nanoplastics varies significantly among fish and shellfish species, primarily as a function of feeding habits and ecological niches. Filter-feeding shellfish and planktivorous fish are at greatest risk, with implications for food safety and human consumption. Addressing these challenges requires interdisciplinary research, public awareness, and policy interventions to mitigate plastic pollution and safeguard the integrity of aquatic food resources.