Potential Aquaculture Problems with Cobia

Potential Aquaculture Problems with Cobia

(This summary was first written 18 Nov 1997 for a potential aquaculture article. It was based on personal experience working with cobia at a research project in Ocean Springs and on display at the J L Scott Aquarium in Biloxi, Mississippi. It was recently found in an old email account and a few changes were made for this publication.)

FISH TB (Mycobacterium marinum)
Susceptible to fish TB. Signs of this disease in cobia are obvious: the fish lose normal gray/black and white markings and become very pale, with a whitish body film/sheen that even covers the eyes, which may appear bloodshot. Fins may also appear pink in color. Since cobia are voracious feeders one must take care that fish fed to them do not carry fish TB. See history of salmon culture where salmon were infected with fish TB after they were fed their dead tank-mates. Due to the dangers of fish TB a pelleted food for cobia should be developed (as they did for salmon).

INGEST SUBSTRATE
Young cobia, at least, do not distinguish between sinking food pellets and crushed coral substrate, or accidentally ingest the coral along with the food pellets, or cannot separate food from coral. See Lawler (1995). Ingestion of substrate can result in impacted intestinal tracts and lost fish. Feed floating pellets or pieces of natural food, or avoid use of substrate in your system.

VORACIOUS FEEDERS
In an Aquarium setting, cobia have been observed to be one of the fastest-growing fish. In our experience, redfish, tripletail, and black drum follow cobia in growth rate. Dolphin (the fish) have one of the fastest growth rates of fishes. One of our cobia grew from about 10 lbs to almost 65 lbs in 28 months (Aug 16, 1988 to Dec 15, l990). Since cobia are voracious feeders and compete vigorously for food one must be aware of three observations made thus far:

1. Cobia can eat so much they can die ( In an aquarium setting I had 3 cobia that darted around tank rapidly, getting as much food as possible. One day after we tried to get food to other fish in the tank by throwing a lot of food into the tank, all three cobia ate a lot, and two were shortly found dead from overeating.) Solution: disperse food over surface of the tank several times a day so they do not ingest too much food at one time.

2. In their feeding frenzy cobia may collide or hit objects in the tank, resulting in internal bleeding and loss of fish. (See Lawler, 1995).

3. Cobia are voracious feeders. I call them the "pigs of the sea" because they will eat almost anything: hardhead catfish, stingrays, eels, crabs, fish, etc. When we were testing our now patented fish attractant, we had a cobia swim up to the stern of the boat and grab the test chum bag containing the attractant.

This habit of eating about anything can result in injury to the fish. In taking internal organ samples at a cobia fishing tournament, it was noticed that spines from catfish and stingrays can penetrate the gut wall and then penetrate various organs: liver, pancreas, spleen. One should probably avoid feeding "spiny" foods to cobia. Some stomachs were noticed to be devoid of food, but contained many spines.

AMYLOODONIUM INFECTION
Cobia are highly susceptible to Amyloodinium ocellatum. See papers by Lawler. Fish will have difficulty in breathing and may rest on the bottom more than normal. Isolate in a treatment tank, use 1.6 grams of Marex per 50 gallons of tank water for 13-18 hours to knock Amyloodinium off. May need more treatments because Amyloodinium caught in gill mucus can re-infect fish. In working with a chief scientist on a cobia project several years ago, I set the protocols at that lab for treatment of cobia for Amyloodinium. One can also use a diatom filter to filter infective dinospores out of the tank water and thus avoid fish loss due to Amyloodinium (see my article on diatom filters).

MONOGENETIC TREMATODE INFECTION
Cobia carry a gill monogenea Dioncus rachycentris Hargis, l955 , which, in tank/confined areas can multiply very rapidly, causing extreme breathing distress in the fish, which must then be given 1:4000 formalin baths of at least 15 minutes duration to knock most of the worms off the gills. This bath may have to be repeated several times as worm eggs in the gill mucus can re-infect the fish. Worm eggs in the water column can be filtered out with a diatom filter.

INTERNAL BLEEDING/MOVING INJURY
From personal experience in moving large redfish, one should take care in moving brood stock cobia, or any large cobia. When no longer supported by water, the forces of gravity take over and "falling" or shifting internal organs can stretch the supporting mesenteries, leading to bleeding from the blood vessels of the mesenteries, and sometimes resulting in shock and death.

　

Adrian R. Lawler, Ph.D. (C) 2012 --


Lawler, A.R. 1995. Some unusual deaths of cobia, Rachycentron canadum, in display tanks. Drum & Croaker 26 (Feb 1995): 9-10.

Lawler, A. R. 2007. Diatom filters. http://www.aquarticles.com/articles/management/Lawler_Diatomfilters.html