Farming Cobia, by Stephen Stang

History has taught us that even though the ocean seems to be infinitely large with an extreme abundance of food fish that can be harvested for human consumption, overexploitation of certain fish populations can still occur. As a result, fish farming has been developed in order to create a source to harvest from with minimal to no impact on wild stocks. This is the case with the farming of Cobia. A lot of work that goes into ensuring the efficient production of these large game fish from egg to adult. The farming of cobia commercially is a direct result of the ability of hatchery technicians to successfully raise cobia to adult size in controlled settings. These fast growing sport fish are currently being farmed across the globe in places here in the U.S as well as in the Caribbean and Asia. Cobia hatcheries and grow out stations are always trying to maximize production of these fish while minimizing the impact that they are having on wild ecosystems. 

Cobia in Open Blue Sea Farms' Aquapod off the coast of Puerto Rico. Nicolas Pollock // Open Blue Sea Farms

Cobia are large predatory fish that are exceptionally fast growers, typically reaching sexual maturity in as little as 3 years, and can reach a maximum size of up to 100 pounds and live up to 12 years  according to The University of Southern Mississippi Gulf Coast Research Laboratory. In their wild range, they can be found in the Gulf of Mexico and on the Atlantic coast all the way into the Chesapeake Bay during the summer months. When present in a controlled hatchery environment, cobia continue to show very fast growth rates as well as very low mortality rates and excellent feed conversion rates, resulting in them being very popular candidates for commercial aquaculture systems(Benetti et al., 2007).

Cobia farming began in the United States in the early 1990s when researches first began to hold adult cobia in captivity. There are 2 very large cobia hatcheries located in the U.S, one at the University of Texas’s Marine Science Institute's Fisheries and Mariculture Laboratory in Port Aransas, Texas and the other at the Aquaculture Center of the Florida Keys in Marathon, Florida (The Universtiy of Southern Mississippi Gulf Coast Research Laboratory, “Cobia”). In order to obtain the original brood stock, hatcheries received adult cobia from fisherman that were caught and kept alive in a relaxed state using low concentrations of clove oil mixed with salt water (Benetti et al., 2007). These adult fish were brought back to circular recirculating rearing tanks where they were fed artificial diets that contained fish meal as well as squid, sardines, and shrimp.

Adult cobia are then placed in a 1:1 or 2:1 male to female ratio per tank, and are either injected with hormones or manipulated with light and temperature to induce spawning activity. It has been found that a water temperature of between 25 degrees C and 28 degrees C keeps cobia in a spawning state (Benetti et al., 2007). Fertilization of the eggs occurs naturally between the adults and is induced once a light source is removed from the tanks. The fertilized eggs float to the surface and are removed by hatchery technicians using a mesh skimmer that sits in the middle of the tank. A typical spawning female will produce over 1 million eggs, and in most controlled hatchery settings 85% of the eggs are successfully fertilized (Benetti et al., 2007).

Once the fertilized eggs are collected, they are placed into incubator tanks where they are allowed to hatch, which typically happens 24 hours after fertilization. These larva will absorb their yolk-sac 2 days after hatching, and at this time they are placed into large circular tanks filled with concentrations of microalgae and phytoplankton, a process known as the “green technique”, and the developing larva feed on this phytoplankton source on their own for 15-25 days after hatching until they are weaned onto a diet of small pellets (Benetti et al., 2007). These fish are then raised until they reach fingerling size about 28 days after hatching, depending on feeding rates and water temperature. Disease control and prevention is a major aspect of cobia aquaculture, and the biggest contributor to disease outbreaks in the hatchery is linked to overcrowding, so maintaining proper fish densities is critical to ensuring healthy populations of fish.

Open ocean submersible cage used for Cobia farming. Photo from the NOAA, courtesy of Snapperfarm Inc.

Many of the ecological and environmental impacts that are associated with cobia farming are found during their adult grow out stage. Once the juvenile cobia reach fingerling size, they are shipped to grow out facilities that raise fish to adulthood in closed pens that either float or are suspended in open water environments located off of the coast, a method that is becoming very common in southeast Asia as well as in the Caribbean and off the coasts of the southern U.S (Benetti et al., 2007). Since these fish are being raised in the open ocean, any waste associated with these high concentrations of fish can have impacts on the environment. A large grow out station owned by Snapperfarm Inc has partnered with the University of Miami’s aquaculture program, and is located off of the cost of Puerto Rico. This grow out facility harvests metric tons of cobia weekly and utilizes large sphere shaped pens that are submerged under the water to produce adult cobia. Studies have been conducted to understand the effects that large scale cobia farming has on the environment, and they found that little eutrophication was observed as a result of an increase in fish waste and the impact on the environment, including corals, was minimal (Benetti et al., 2007). This is a result of utilizing proper fish densities that allows water exchange rates to efficiently dilute excess nutrients and waste.

The fact that these predatory fish demand a high protein diet to grow is another concern since most high protein fish diets contain fish meal that is obtained from wild stocks of fish. Cobia, however, are very efficient feed convertors and have excellent feed conversion ratios when raised in this controlled environment, and can reach a size of 6kg in only 1 year (Benetti et al., 2007). A study on the growth of cobia raised in Snapperfarm Inc pens showed that when fed a diet of 50% fishmeal, 1kg of cobia biomass was produced for every 1.8 pounds of feed (Benetti et al., 2007). When comparing these rates with what is observed in the wild, where about 10% of energy is lost between each tropic level, cobia farming has shown that by using fishmeal to produce cobia for human consumption there is a 3.7 times higher conversion factor in controlled grow out facilities than conversion rates found in nature (Bacoat et al., 2007).

Farmed Cobia on ice after harvesting.  Photo D. Benedetti, NOAA. 

We are fortunate to have a fish like the cobia that is fast growing, easy to raise in controlled settings, and has excellent feed conversion rates. Farm raised cobia are a source of fresh seafood that isn’t harvested from wild stocks, and can be raised in a way that has minimal impact on the environment. These characteristics support the possibility that as long as cobia continue to be farmed in efficient and sustainable ways, there is no reason why they can’t become one of the largest farmed marine fish consumed across the globe.

References 

Benetti., D., Bacoat, Donald., D F. Cavalin., B. Denlinger., M. Orhun., K. Palmer., B. Sardenberg., I. Zink,and Brian O’Hanlon. “Aquaculture of Cobia  (Rachycentron canadum) in the Americas and the Caribbean.” 2007. 4/3/2017.

The Universtiy of Southern Mississippi Gulf Coast Research Laboratory. “Cobia” 2017.  4/3/2017