Physical Properties
Early experiments demonstated that channel catfish and common carp utilized pelleted feed more efficiently than meal. Many of the small particles were not ingested, resulting in poorer feed conversion and reduced water quality in the ponds. To minimize these undesirable effects, commercial feeds should be processed into pellets that will remain intact in water until consumed by the fish. Pellets with long water stability are especially important for slow-feeding species such as shrimp.
Particle size of fish feeds should be as large as possible to minimize nutrient losses through leaching into the water, but not too large for the fish to consume. Optimum sizes of feed particles for channel catfish, trout, tilapia, and shrimp of various sizes are discussed in chapters on practical feeding of these species. Diet texture is important for some fishes. Most commercially cultured species accept dry feed particles, but some fish, such as eels and young salmon, prefer soft diets.
Catfish farmers in the United States prefer floating feeds. This is a valuable managemet tool when raising fish in ponds because it allows the fish farmer to determine how much the fish are consuming and also on the basis of feeding activity. Most fishes accept surface feeds satisfactorily, but some species, such as penaeid shrimps, prefer sinking feeds.