Zooplankton (copepods and cladocerans) is the primary food of cultured catfish fry during the first 3–4 weeks of culture, after which external feeding will be imperative (Mischke, Wise an d Lane, 2003). Therefore, the main goal of fertilizing catfish fry ponds is to establish a phytoplankton bloom that will produce large stocks of copepods and cladocerans for feeding catfish fry during the first 3–4 weeks after stocking (Mischke, Wise and Lane, 2003; Mischke and Zimba, 2004). However, limited research has been conducted on fertilization practices specific to channel catfish nursery ponds.
Catfish feed coming out from a dryer on a belt at a feedmill in Mississippi.
Therefore, fertilization regimes and practices applied to channel catfish nursery ponds vary widely. Tucker and Robinson (1990) recommended fertilizing fry ponds with liquid inorganic fertilizers at rates of 2.2–4.5 kg/ha of 10–34–0 or 13–38–0 (0.2–0.6 kg/ha N; 0.3–0.8 kg/ha P) every 2 days until a bloom develops. Much higher application rates of inorganic and organic fertilizers are recommended for fry ponds. Ludwig, Stone and Collins (1998) recommend an initial application of 54 kg/ha of liquid 10–30–0 (5.4 kg/ha N; 7.1 kg/ha P) and 280 kg/ha organic fertilizer (rice bran, cottonseed meal or alfalfa pellets), followed by weekly applications of half the initial rate of inorganic and a fifth the organic rate of fertilization. However, Mischke (2009) reported that despite the benefits of organic fertilizers in catfish fry ponds, these fertilizers are more labour intensive to apply, and they also cause an additional oxygen demand in the pond. The author suggested that the desirable zooplankton for channel catfish fry culture can be increased through the use of inorganic fertilizers.
Commercial Feeds
Various types of floating and sinking catfish feeds (Figure 3) are currently produced at commercial scale. Pellet size depends on fish size and grow-out stage. Commercial feeds generally contain a mixture of plant and animal proteins. Major protein sources used in catfish feeds include fishmeal, soybean meal, cottonseed meal and animal by-product meal (meat and bone and blood meal). Catfish fry in hatcheries are generally fed finely ground meal containing 45–50 percent protein. Fines or crumbles containing 28 to 32 percent protein for grow-out stage are suitable for fry stocked in nursery ponds until they reach 2.5 to 5 cm in length. Larger fingerlings should be fed small floating pellets (0.3 cm diameter) containing 35 percent protein. Larger fingerlings (12–15 cm) are generally fed a floating feed of about 0.4–0.5 cm in diameter containing 28–32 percent protein. Some producers switch to a slow-sinking feed during the winter.
Examples of practical diets for channel catfish are presented in Table 5. These formulations have been used with good results in commercial culture.