Catfish Inventory Losses
Losses of catfish from commercial ponds are a normal part of the production system but accurate estimates of potential losses are difficult to make. The major reasons for catfish losses during the time between stocking and harvesting include: 1) losses over winter; 2) losses due to chronic or acute diseases; and 3) the effect of holding catfish over time. It is possible, by good management methods, to reduce the number of catfish lost from pond inventory.
Winter is a four to five month period of danger to the catfish production system. Catfish growth slows and catfish may actually lose weight if not fed during the winter. Catfish immune systems slow down in cool water. As a result, losses from disease, poor nutrition or cannibalism may occur. Since the winter time is an extended period of slow growth, the catfish make little progress toward market size.
Diseases most likely to effect catfish during the winter include parasitic diseases, fungal diseases and winter kill syndrome. Most diseases are related to poor nutrition or water quality related stress to the catfish. Poor nutrition can occur as the catfish slow down their feeding behavior. Diets with marginal vitamin and mineral supplementation provide fewer nutrients than are required when diet intake is reduced even though the fish may not be growing as fast as when water temperatures are warm. Cannibalism occurs when small catfish are stocked in the fall under larger catfish.
In a study of winter stocking of fingerlings under larger catfish, 4,000 fingerlings per acre were stocked with 1,000 pounds of larger catfish (1.5 lb/fish) and compared to fingerlings alone at 4,000 per acre. Between the months of December and March, all ponds were fed 1% of the fish weight per day. It was evident that diseases caused by protozoan parasites were more common in ponds with both fingerlings and large catfish than in ponds with only fingerling catfish. Fingerling survival averaged 69.3% with large catfish but 76.2% by themselves. Cannibalism appeared to be low, possibly because the fingerlings were 5-7 inches in size. Diseases occurred due to the presence of large catfish as a possible reservoir of the parasites and because of competition for feed between the two catfish size classes. Few of the larger catfish were lost during the study.
Growing Season Losses
Catfish are lost to acute and chronic diseases, water quality stress, harvest and handling injury, predator activity, and theft during the warm months of the year. In Georgia, seven to eight months of the year are warm enough for catfish be actively eating and growing. Bacterial diseases become more important than most parasitic diseases as the weather warms up. Water quality stress can add to the severity of disease outbreaks or poor water quality can kill catfish independently of other causes. Handling catfish during harvest and stocking may lead to fish death by stressing or injuring the fish.
Birds, otters, and snakes are the most common predators of catfish. Birds are usually attracted to ponds with a chronic disease problem and add to the losses. Otters eat all sizes of catfish but are less important as predators in ponds greater than one acre in size. Snakes are important predators when fingerling catfish are present. Theft of catfish is important when ponds are located in remote areas or when uncontrolled access to the ponds exists.
Estimating losses during the growing season can involve counting the number of catfish that die and float at the surface. However, only a portion of the catfish losses are actually observed. If dead fish are observed in the early part of the season, we saw one fish for every nine that died. Dead fish observed during the entire growing season, a chronic disease, accounted for one of every 20 dead fish. If fish were observed in the last part of the growing season, one fish was counted for every three that died.
Percentage of Catfish that are Harvestable
During the first year after a pond is stocked, the catfish in a single size class will reach harvest weight at different times. In nine ponds studied, catfish were stocked at 7,500 per acre with shad, with minnows, or catfish alone. After three months, July, less than 10% of the catfish were of harvestable size. After five months, an additional 38% to 51% of the catfish were harvested, with the highest percentage harvestable from the catfish only ponds. By the seventh month, November, an additional 25% to 40% were harvested. Those ponds with large quantities harvested at five months had fewer harvested in November. An average of 87.9% of the catfish were harvested when the ponds were scrapped at the end of the year. The average weight of harvested catfish was 1.25 pounds.
The longer catfish are held in the pond, the more losses to expect. A loss of 12.1% over seven months amounts to 1.7% loss per month. Assuming that catfish at least 25% of the catfish stocked in a pond are not removed until 18 months have passed, 7.5% additional losses would be expected after the first growing season. Therefore, a reasonable estimate of loss for each age class of catfish would be 12% plus 7.5% or 19.5%.
Catfish Yield Verification
Commercial catfish ponds are stocked at various rates at different times during the year and not drained or scrapped for several years. In order to survey the catfish yield experienced by commercial catfish producers, the University of Arkansas studied four ponds, each approximately 10 acres in size, over a three year period. Stocking density ranged from 5,970 to 7,860 per acre. After three years the average yearly yield was estimated between 3,673 lb/A and 4,782 lb/A. Survival was determined by draining ponds in the third year and counting all harvested catfish. Survival was 84% in Pond A with 5,970 fish/A that experienced fewest disease, stress, or water quality problems. Pond B, 6,295 fish/A had 66% survival with few disease and water quality problems, but the fingerlings were stressed when hauled prior to stocking. Ponds C, 7,860 fish/A, and D, 6,685 fish/A, had disease and dissolved oxygen problems. Diseases included proliferative gill disease, columnaris bacteria, and anemia.
This data was collected between 1993 and 1996, reflecting the catfish culture practices of that time. Yet, the average survival for the four ponds was 65%, close to the range estimated for the catfish industry of 60 to 70%.
How to Improve Catfish Survival
Catfish management must be planned carefully in order to obtain survival percentage higher than 85%. First, the time between stocking and harvesting should be minimized. Catfish should be sold as soon as they reach harvest size. This requires that careful feed records be kept, dependable markets be located, and off-flavor be managed. Stocking large fingerlings will also help minimize the time in the pond as well as reduce the losses from certain stresses and diseases. Careful harvesting will minimize the amount of fish that are carried from one harvest to another. Schedule fingerling stocking for the months of March through September to be sure that the fish have time to grow before the winter months. Winter carry-over should be avoided.
A fish health management program should be developed for the catfish operation. Stress reduction, fingerling quality, feed quality and chemical treatments should be planned for in advance. Catfish losses are usually the result of two or more factors acting together.