Grow-out of channel catfish to market size takes a little less than two years after hatching, or one year from the fingerling stage. The usual market size is 500g to 1.4kg, though many are harvested at 450 to 600g size. Fingerlings aregenerally stocked in grow-out facilities in the spring, and harvested in about seven months in October or November.
The most common grow-out facilities are pond farms and they generally seem to be more cost-effective than other systems.The ponds are prepared for stocking by eradication of weed fish by application of rotenone. New ponds are fertilized with 16–20–4 or 16–2–0 NPK fertilizer at the rate of 56kg/ha. The stocking density depends mainly on the quantity and quality of the water supply and the desired size of the market fish. In ponds with a dependable water supply, a stocking density of about 3700–4900/ha is common. At the lower range of this density, the fish would weigh 500–600g at the end of the growing season. To obtain a fish of about 1.2kg weight, a third year of growth is needed. A stocking density of 2000–2500/ha is recommended for this purpose. Producers very often thin out the stocks from their stocking ponds after the second year of growth and maintain the lower density required for a third year of growth.
The use of commercially produced formulated feeds is a common practice in the catfish culture in the USA. In ponds where the fish have access to natural food, a feed containing 25 per cent protein may be enough, whereas in others a complete feed containing 30 per cent protein is required. Commercial catfish diets are made in different forms, the most common one being the extruded or hard pellet. Other forms used are dry meals and crumbles for feeding fry, floating pellets, semi-moist pellets containing 25–30 per cent water, and agglomerates prepared by rolling finely ground dry formulated feed into balls for fingerling and adult feeding.
The most common methods of feeding are hand feeding and self or demand feeding. Many farmers prefer the former practice, mainly because they can regulate the feeding more easily and closely observe the feeding activity. Self or demand feeders permit the fish to obtain feed when they want and reduce over-feeding, which appears to be a common problem in channel catfish culture. Blow feeders, or low-flying aeroplanes that dispense feed, are made use of in extensive farms. Feed conversion in commercial grow-out facilities during the second year of growth is generally 2kg feed for
1kg fish, although better conversion has been achieved with improved feeding and management. An average production in commercial pond farms is around 1500kg/ha, although production of up to 3000kg/ha has been reported.
Raceways with an adequate flow of water that allows an exchange twice every hour in each segment can produce much greater quantities of fish than ponds. The stocking density depends on the size to which the fish are to be grown. The usual rate is about 2000 fingerlings per 120m3 raceway, where with proper feeding and exchange of water about 1 ton of fish can be produced in 180–210 days. In raceways with a lower water flow, only lower densities of fish can be raised. For example, with a flow of 9.5l/s, only 3500–5000 fingerlings can be stocked. Stocking is carried out in spring and early summer, with advanced fingerlings of 15–20cm size. A complete feed, nutritionally richer than the feed used in ponds, is provided in raceways. The rate of feeding is usually 4–5 per cent of body weight twice a day, for two months after stocking, after which it is gradually reduced to about 3 per cent.
Tank culture of catfish, though only introduced comparatively recently, is reported to give very satisfactory results. Farmers who have adopted this technique report that a circular tank of 6m diameter and 0.6m depth gives the same production as a 0.4ha pond. High rates of stocking are possible if the tanks are provided with aerators. Complete feeds at the daily rate of 3 per cent of the body weight are fed twice a day. Protection from bright light appears to give better growth rates and so the tanks are either covered or housed indoors.
Cage culture of catfish is of greater value when the cages are installed in open waters rather than in ponds. The stocking rate is about 65 fingerlings per m3. Complete floating feeds are usually given at the rate of 3.5 per cent of body weight per day. This is gradually reduced to 2 per cent, depending on the quantity consumed.