Plastic debris has been identified as a major global environmental threat, with microplastics now recognized as a pervasive contaminant in marine ecosystems. These particles, ranging from 0.15 to 5 millimeters, are found across all oceans, with concentrations varying between 0.002 and 62.50 items/m³ and a global mean abundance of 2.76 items/m³ (Mutuku et al., 2024). Their effects extend across marine organisms and humans, raising growing concerns for aquaculture.
The dominant plastic types in marine environments are polystyrene (28%), polypropylene (24%), polyphthalamide (22%), polyethylene (15%), and polyethylene terephthalate (11%). Between 5 or 12 million tons of microplastics enter the oceans annually, with more than half of all production and release occurring since 2000.
Aquaculture species are exposed to microplastics through direct contact with water, nets, and cages, as well as indirectly through contaminated feed ingredients, particularly fishmeal.
Evidence of contamination in aquafeeds
Research led by Tufan Eroldoǧan, Professor at Çukurova University, has demonstrated the extent of microplastic contamination in fishmeal. In a global survey, samples were collected from 26 producers across 11 countries and four continents, including the Arctic. The findings, published in 2021, confirmed widespread contamination, with plastics ranging from 0 to 526.7 n/kg. Higher levels were reported in fishmeal from China and Morocco, while Antarctic krill meal showed no detectable plastics.
A risk assessment based on feed conversion ratio (FCR) revealed that carnivorous species, such as eels, with high fishmeal inclusion in diets, are particularly vulnerable to plastic ingestion.
Figure 1. Examples of extracted plastics from some of the tested fishmeal samples. Credits: Tufan Eroldoǧan
Experimental studies on aquaculture species
In 2022, Eroldoǧan’s team collaborated with IFFO – The Marine Ingredients Organisation to evaluate microplastic contamination in fishmeal and other feed ingredients, as well as their physiological effects on aquaculture species.
A 15-day trial with Atlantic salmon (initial weight ~300g) fed diets containing 2.5% microplastics (PEPT, PET, and polyethylene) showed no significant difference in feeding rate, final weight, or digestible parameters. However, higher microplastic levels were detected in the liver compared to those in the muscle.
Further analysis of standard Atlantic salmon feed ingredients revealed that guar meal had the highest microplastic contamination, while sunflower meal had the lowest.
In a trial with European seabream, preliminary analyses of liver and intestine samples showed that microplastic inclusion depressed certain Interleukin (stress) genes, indicating that fish could tolerate the stress from microplastics, but some groups experienced "cytokine storms," similar to those seen in COVID-19. Microbiome analyses also indicated negative effects, with specific bacterial groups like Porcelainomonas and Bacillota dominating in affected fish.
Future directions
These findings confirm that microplastic contamination is widespread in aquafeed ingredients and may cause subtle but significant impacts on fish health. While fish can survive moderate levels of exposure, risks include immune disruption, altered gut microbiota, and organ accumulation.
Ongoing research aims to clarify dose-response relationships, long-term impacts, and species-specific vulnerabilities. The evidence to date suggests that nearly all feed ingredients may carry some level of microplastic contamination, with regional variability in fishmeal being particularly critical.
Microplastics represent a complex challenge for aquaculture. They originate from multiple sources, ocean water, farming equipment, and feed ingredients, making mitigation difficult. As Eroldoǧan notes, “understanding their impacts and developing solutions is critical for the industry’s future.” Addressing this issue will require joint efforts across research, feed manufacturing, and farming practices to safeguard fish health and the sustainability of aquaculture.
