Although not popular as a food fish in most of the United States, eels are considered a delicacy in many European and Asian countries. Traditionally, these fish have been harvested from the wild already at marketable size, but young eels are now widely captured and cultured to market size. Globally, most eel production is attributed to aquaculture of wild-caught young. Whether in Europe, Asia or North America, eel farming must rely on wild-caught juveniles because it is difficult or impossible to produce viable offspring in commercial quantities using captive spawning methods.
Eel species have provoked little commercial interest in the United States in recent decades although a few farms have been established. The reliance of eel aquaculture on a supply of wild seed stock has proven to be a serious constraint for commercial operations. Regulatory limits on larval and juvenile collections are expanding due to concern over the conservation status of most wild populations. Because most of the world considers eel a gourmet item, and they are in high demand in many ethnic markets, this species could potentially be a high-value export and niche market product.
The distribution of the American eel (Anguilla rostrata) includes the entire eastern seaboard of the United States, southeastern Canada and the Gulf of Mexico. Eels can be found as far inland as the Great Lakes. Eels are referred to as a catadromous (the opposite of anadromous) and amphihaline species, meaning that they spend part of their life in the ocean, then part of their life in freshwater, and then they migrate from freshwater back to the ocean once more to spawn. Adult eels move from rivers into the ocean in the fall, traveling to a region in the southwest part of the North Atlantic, east of the Bahamas and south of Bermuda, called the Sargasso Sea.
After spawning, adults die at sea while the larvae travel on ocean currents back toward the mainland, feeding and growing along the way. Eel larvae undergo three stages during this oceanic period, reaching the coast as “glass eels” and “elvers.” Elvers are migratory, reaching estuaries and stream mouths in the spring and then eventually traveling up rivers. Eels may spend anywhere from 8 to 30 years in freshwater as they grow and ultimately mature.
Catches of the American eel, and those of related species in Europe and Asia, declined rapidly over the latter part of the twentieth century, and most experts agree these species are in jeopardy. Nonetheless, a status review of Atlantic coast populations of the American eel by the Atlantic States Marine Fisheries Commission in 2015 determined that those populations were not threatened or endangered. There are several eel fisheries in the U.S., focusing on glass eels and elvers (for export as stocking animals for commercial farms primarily in Asia and Europe), juveniles (yellow eels), and adults moving downstream to return to the sea (silver eels).
International trade in glass eels has exploded over the past two decades as eel farms in Japan and other Asian countries exhausted supplies of their local species, Anguilla japonica. Glass eel fisheries still persist in several locations in North America, with an annual quota of 9,688 pounds in Maine.
Aquaculture production of juvenile eels for grow-out to adult fish for meat products is a well-established industry in many European and Asian countries. Glass eels are preferred over elvers for stocking, primarily because they are easier to transport and to wean unto artificial diets. Roughly 2.5 kg of glass eels are required to produce one metric ton of marketable live eels, at a preferred market size of seven eels per kg (averaging about 1/3 pound each). Glass eels must be gradually weaned off of natural food (minced fish or fish eggs) and trained to artificial diets. Under optimum conditions, when stocked as glass eels, farmed eels can reach market size in 18 months or less. To attain these results, high-protein (42-49 percent) diets are required, but feed conversions are very economical, generally in the range of 1.0 to 1.8.
Eel farming takes one of two general forms – high-intensity recirculating aquaculture systems (RAS), which are typically indoor facilities, or intensive pond-based operations, often incorporating greenhouse covers during colder months of the year. Open-pond grow-out of eels can be successful under a variety of conditions. In temperate regions of Japan, eel prices actually justify the cost of covering ponds with greenhouse structures and even heating the water during winter months. Pond production densities may reach as much as 20 kg/cubic meter, and aeration is generally utilized to maximize yields. A good rule of thumb for this type of intensive pond culture is to have a water exchange capacity of 4000 cubic meters per day (an average flow of 730 gallons per minute) for every 100 metric tons (220,000 pounds) of production. Much lower exchange rates can still result in profitable production, however.
Recirculating systems are well-suited for eel production, especially since eels tend to tolerate very high densities and associated high levels of ammonia and comparatively low pH conditions. In Europe, where most production relies on RAS, densities of up to 120 kg of eels per cubic meter are not uncommon. Exchange rates are typically in the range of 5 to 8 percent daily. Investment costs, and risk, are high with this type of enterprise, but technology suitable for recirculating production of eels is available and can be employed virtually anywhere one can find a reliable supply of electricity and suitable make-up water. The economics of this production approach depend, however, on a dependable supply of glass eels or elvers, access to inputs such as high protein diets and approved health management products, and suitable market demand within 1 to 2 days transport time. In most of the U.S., these markets will be comprised of urban populations of Asian and European ancestry with an appreciation for eels as a delicacy.
Eel farmers must manage their systems to avoid both diseases and cannibalism. Cannibalism can be addressed through regular grading, but this requires adequate system design to allow graders to be deployed efficiently. Diseases are more problematic, since wild glass eels are brought into these facilities every year. Quarantine practices are essential for biosecurity and profitability.
The USDA Census of Aquaculture reported 7 eel farms across the U.S. in 2018. Sales volume and value numbers were not available due to confidentiality constraints. Florida, Maine and Pennsylvania each reported two farm operations, and Delaware reported one.
Eel is probably not in demand as a mainstream U.S. seafood product partly due to its “snake-like” appearance and a lack of educated consumers. However, the size and buying power of the Asian-American consumer market continues to grow, and eels are certainly considered a high-value delicacy among this market segment. Eels have the potential to become one of the highest-quality, highest-value aquaculture products because the science for raising the fish is well established. The most promising approach for U.S. producers would probably involve establishment of recirculating production facilities near large ethnic Asian or European markets. In certain regions, economical production might be accomplished with outdoor facilities, but in most the preferred technology would involve indoor closed loop systems, as has been successfully demonstrated with North American live markets for tilapia.
Prepared by C. Greg Lutz, Louisiana State University Agricultural Center