Cobia Stripes

Cobia with prominent striping above and dull monocolor below - NOAA Images

Cobia with prominent striping above and dull striping below – NOAA Images

I’ve been seeing lots of cobia pictures lately. I’m acutely tuned into seeing them because cobia is still a bucket list fish for me. And of course this is the time of year when we see them and when anglers are catching them. Recently my friend Robert ask if I knew why some cobia have prominent stripes and others do not. He knows juveniles have darker stripes and as a fish ages the stripes fade. But Robert said if you look at angler photos, you could have two large cobia both the same size and one will be dull and the other with more prominent striping. That was what had him perplexed. And to be honest, I didn’t know the answer. But, I do now!

Before I answer the stripe question, let’s look at this beautiful fish. Cobia, Rachycentron canadum, gets its name from its 7-9 pointed dorsal spines; rhachis is Greek for spine and kentron mean pointed. The first description of cobia occurred in 1766 by a scientist Linnaes who classified it as Gasterosteus canadus, and not from a Canadian specimen as the species name canadus would suggest; his cobia came from the Carolinas. Interestingly, cobia was reclassified and renamed 19 times before its current scientific name was settled on.

Cobia occur worldwide in subtropical, tropical, and warm temperate waters. They range from Nova Scotia to Argentina in the western Atlantic, including the Gulf of Mexico; from Morocco to South Africa in the eastern Atlantic; and in the Indo-West Pacific from East Africa and Japan to Australia.

Cobia grow very quickly and have a moderately long lifespan. In the Gulf of Mexico maximum ages are 9 years for males and 11 years for females. In the Carolinas maximum ages have been reported as 14 years for males and 13 years for females. Though they don’t live quite as long, cobia in the Gulf of Mexico appear to grow more quickly and reach larger sizes than those off the U.S. South Atlantic coast. In the northern gulf, at 1 year, males and females are about 27.9 and 28.1 inches fork length (FL) respectively and at 9 years, 45.5 and 57.5 inches FL respectively. Off North Carolina, males and females are about 22.0 and 24.0 inches FL respectively at age 1, and at age 9, 40.6 and 48.8 inches FL respectively.

Did you know: Cobia lack a swim bladder which means they expend more energy than most fish in order to maintain their position in the water column? Sometimes cobia “rest” on the bottom in order to reduce this energy expenditure.

Cobia become sexually mature at very young ages; 3 years for females and 2 years for males in the Carolinas; In the Gulf of Mexico, males can become sexually mature as young 1 year. Cobia spawn in large aggregations, between June and August in the Atlantic Ocean near the Chesapeake Bay, off North Carolina in May and June, and in the Gulf of Mexico during April through September. There is evidence that spawning occurs both inshore, offshore, and even in estuaries. And unlike many other fish that spawn at night, cobia spawning takes place during daylight hours. During the spawning season, cobia can spawn every 9-12 days. And, here you go Robert – During spawning, cobia undergo changes in body coloration from brown to a light horizontal-striped pattern.

A cobia at two days - Auburn University Image

A cobia at two days – Auburn University Image

Cobia eggs are spherical, averaging about a quarter inch in diameter. Five days after hatching, cobia mouths and eyes develop allowing them to actively feed. A pale yellow streak is visible, extending the length of the body. And, at the end of their first month, cobia juveniles resemble adults with two color bands running from head to tail along each side. As cobia age these color bands fade, except of course during active spawning.

In the Atlantic off South Carolina, scientist have recently confirmed through genetic analysis, that two distinct cobia stocks exist, an offshore, and an inshore population. Genetic studies have yet to be conducted in the Gulf of Mexico, however; research papers dating back to the early 1990s have also hypothesized a two stock structure. In the Gulf, some scientists have suggested an offshore group that over-winters in the Florida Keys, then moves north and west around the Gulf in spring, returning to the Keys in fall; and an inshore group, that over-winters offshore on live-bottom areas, and in the spring moves inshore where it remains through the summer, before returning back offshore in late summer. This later group was specifically mentioned for the northern Gulf of Mexico.

Did you know: In 2013, 746,557 pounds of cobia were landed in Florida? The recreational fishery comprised 82% of the statewide landings with the majority (55%) coming from the Gulf coast.

Sources:

Burns KM, Neidig C, Lotz J, Overstreet R. 1998. Cobia (Rachycentron canadum), stock assessment study in the Gulf of Mexico and in the South Atlantic. Final report for NOAA-NMFS MARFIN Award No. NA57FF0294, St. Petersburg, Florida.

Florida Fish and Wildlife Conservation Commission. 2014. http://myfwc.com/media/194569/cobia.pdf

Florida Museum of Natural History. 2016. https://www.flmnh.ufl.edu/fish/discover/species-profiles/rachycentron-canadum

Franks, J. S., M. H. Zuber, and T. D. McIlwain. 1991. Trends in seasonal movements of cobia, Rachycentron canadum, tagged and released in the northern Gulf of Mexico. J. Miss. Acad. Sci. 36(1):55.

John R. Gold, Melissa M. Giresi, Mark A. Renshaw, and Jin-Chywan Gwo. 2013. Population Genetic Comparisons among Cobia from the Northern Gulf of Mexico, U.S. Western Atlantic, and Southeast Asia, North American Journal of Aquaculture, 75:1, 57-63.

Tanya L. Darden, Matthew J. Walker, Karl Brenkert, Justin R. Yost, and Michael R. Denson. 2014. Population genetics of Cobia (Rachycentron canadum): implications for fishery management along the coast of the southeastern United States, Fish. Bull. 112:24–35.