The sampled fish may have originated from a particularly polluted patch of the Atlantic Ocean.
Microplastics, tiny and highly buoyant plastic fragments, are typically the result of the breakdown of larger plastic items that have entered our oceans.
Due to the low density of these materials, they float at sea surface.
Research conducted by the National University of Ireland in Galway found high levels of plastic from recovered dead deep-sea fish by trawling depths of up to 600m.
One small lanternfish, just 4.5cm long, had 13 pieces of microplastic in its stomach.
PhD candidate and lead author Alina Wieczorek said: "Deep-water fish migrate to the surface at night to feed on plankton [microscopic animals] and this is likely when they are exposed to the microplastics".
Once back on shore, the team examined the stomach contents of the 233 fish they had gathered, which ranged in size from 3.5 to 59 centimetres. The identified microplastics were mostly fibres, commonly blue and black in colour.
The fish were sampled from a warm core eddy, which is similar to ocean gyres that are thought to accumulate microplastics.
The study is just the latest in a series recently highlighting the damage that increasing amounts of plastic are having on marine life and the unknown consequences on other animals, including humans. Of most concern is the additives (such as coloring or flame retardants) in plastics, which can be transferred to animals when they eat them.
Dr Tom Doyle, a co-author of the study from the Ryan Institute at NUI Galway, said: "It's worrying to think that our daily activities, such as washing our synthetic clothes in our washing machines, results in billions of microplastics entering our oceans through our wastewater stream that may eventually end up in these deep-sea fishes".
"This would explain why we recorded one of the highest abundances of microplastics in fishes so far, and we plan to further investigate the impacts of microplastics on organisms in the open ocean", Wieczorek added.