Researchers Make Significant Progress on Farm-Bred Bluefin

Sushi is one of the most widely known and loved cuisines in the world, yet one item on the menu may soon disappear. The Southern Bluefin Tuna is highly prized fish, coveted for its fatty belly meat. However, exploitation and overharvesting has driven this species to be classified as Critically Endangered by the IUCN. Although the Bluefin is a streamlined and fast swimming fish that reside in the open waters, technology such as satellite imaging and GPS has allowed fishermen to harvest this fish across its entire migratory route. The most damaging factor is the harvesting technique. In order to produce the sought after belly meat, the Bluefin are caught alive as juveniles and fattened in a pen before being exported to fish markets around the world. These caught Bluefin are never able to spawn, critically decimating its population. Yet, the Southern Bluefin remains one of the most valuable fish in the industry, with a 202kg Bluefin fetching more than $170,000 in 2001 in Japan. Despite quotas set by governing entities, fishermen have been known to catch Bluefin beyond their set limits.

For many years, there has been effort to farm the Bluefin from eggs in aquacultures, which have been successfully accomplished for other fish species such as yellowtail and sea bream. However, several issues make this difficult for the Bluefin. Firstly, they are a very large species, often tipping the scales at a half ton. Also, the Bluefin is built for fast swimming across the open ocean. As a result, they are warm blooded, requiring them to be in constant motion for water to flow across their gills. As a result, they require incredibly large pens.

However, after years of research, there may have been a breakthrough in raising the Bluefin in captivity. Researchers at Kindai University, Japan, believe they have gathered enough information about the species to successfully farm the prized fish. For example, they understood that juvenile tuna could not steer or brake as well as their adult counterparts, as a result often ran into the walls of a square shaped pen, breaking their necks. A circular pen alleviated this problem. They have also identified behavioral triggers for spawning and understanding that the first spawn is related to size rather than age. The researchers and Kindai are selectively breeding the tuna for hardiness and high quality meat by introducing molecular markers for desirable traits. Finally, one of the most unsustainable aspects of fish farming is the feed. As a result, the researchers have successfully weaned the tuna onto plant protein rather than fish feed, which has not been done in other successful fisheries such as farmed salmon. Despite these accomplishments, only about 1% of Bluefin mature from eggs, compared to 60% in sea bream fisheries. A successful Bluefin fishery would not only satiate the market for this prized fish, but scientists also hope to restock the wild population. However, restocking the wild population remains a contentious issue, and the researchers at Kindai admit that several issues need to be resolved before that is a viable solution. 

Article about the Kindai research can be found here: http://www.sciencemag.org/content/324/5932/1260.full