One of the cornerstones of global aquaculture and fisheries research is the Rainbow Trout (Oncorhynchus mykiss). Native to the cold waters of the Pacific Ocean in Asia and North America, this species has become one of the most widely distributed and economically important fish in the world.

Introduced to Europe in the late 19th century, rainbow trout quickly adapted to the continent’s diverse aquatic environments. Today, they are the most produced finfish species in the European Union, by both volume and value,cultivated through various production systems including ponds, raceways, net cages, and recirculating aquaculture systems (RAS). Major producing countries include Denmark, France, Italy, and Spain, where the species is farmed for both aquaculture and recreational sport fishing.

Rainbow trout are known for their:

  • Adaptability: They thrive in freshwater rivers and lakes, but also possess an anadromous form, called Steelhead, which migrates to the ocean before returning to freshwater to spawn.
  • Commercial Importance: Valued for their lean, flaky flesh and mild flavour, they are a cornerstone species in intensive and extensive farming systems across Europe, North America, and beyond.
  • Research Relevance: Due to their relatively short life cycle, ease of breeding, and tolerance for various conditions, rainbow trout are a leading model organism in aquaculture research. They are frequently used to study genetics, nutrition, disease resistance, and sustainable farming practices, generating data that can be applied to many other farmed fish species.
  • Environmental Sensitivity: Rainbow trout are highly responsive to changes in their environment and are often used as bioindicators of water quality, providing early warnings of pollution or ecosystem stress.

Ongoing research projects, such as AQUAEXCEL3.0, have continued to build on this foundation. Within this project, advanced biotechnological approaches have been applied to rainbow trout in RAS systems to enhance sustainability and research precision. The project has implemented a standardised platform based on nanopore sequencing technologies to monitor microbial communities in experimental aquaculture infrastructures. A full pipeline for sampling, data analysis, handling, and storage was also tested.

In addition, cutting-edge genome editing and biotechnological tools have been developed to deepen our understanding of trout biology and improve breeding efficiency. These include CRISPR/Cas9-based genome and epigenome editing, as well as innovative methods using germ stem cell (GSC) transplantation to generate new fish lines from selected parents with unique genotypes, particularly those derived from uniparental inheritance (gynogenesis and androgenesis). Researchers have also explored allelic replacement, single nucleotide mutations, and exon skipping to further refine genetic traits in O. mykiss.

From hatchery innovation to molecular genetics, rainbow trout remains a model species at the forefront of aquaculture science, driving advancements in sustainable production, biotechnology, and environmental monitoring across Europe and beyond.