Grass carp larvae start feeding on protoza, rotifers and some small Cladocera. After 15-20 days, when the early juveniles are approximately 26 mm TL, they start to ingest duckweed and soon there after feed almost exclusively on macrophytes (Ni and Wang, 1999). Various macrophytes are used to feed grass carp in Asia, including Hydrilla verticillata, Vallisneria asiatica, Potamogeton maackianus, Potamogeton malaianus, Eleusine indica and Ceratophyllum (Venkatesh and Shetty, 1978; Ni and Wang, 1999). Some terrestrial grasses and agricultural by-products such as rice bran, oilseed cakes can also be used as food. Some plants are more palatable than others (Fowler and Robson, 1978; Cassani and Caton, 1983; Feng et al., 2006a).

Almost all ingredients generally used in aquaculture feeds can be used for grass carp. Table 10 shows the digestibility of various feed ingredients (Luo et al., 2001; Lin et al., 2001) and Table 11 lists the apparent amino acids digestibility coefficients for 25 feed ingredients (Ye et al., 2003). Extrusion increases the digestibility of some feed ingredients, especially those ingredients with high carbohydrate levels (Guo et al., 2005). Table 12 provides a summary of the growth performance of grass carp using common, unprocessed ingredients (Wen et al., 2000) fed as single ingredient.

Grass carp is cultured in many countries and hence diet formulation varies with the availability of local ingredients. Chinese grass carp feed formulations usually contain fishmeal (0-10 percent), soybean meal (10-30 percent), rapeseed meal (10-30 percent), rice bran, corn, wheat and other agricultural by-products. Leaf meal and grass meal are also used. Vitamin and mineral premix and feeding attractants comprise around 2-5 percent of the feed.

Grass carp feed formulation has received considerable attention, in particular the replacement of expensive ingredients with cheaper alternatives. Rapeseed meal can successfully replace 30 percent of soybean meal in juvenile feeds (Ma et al., 2005) without any noticeable side effects. 50-75 percent of soybean protein can also be replaced by low glucosinolates, low erucic acid rapeseed protein (Wu et al., 2005). Fishmeal can also be replaced by leather protein meal (by-products from leather industry) although its inclusion results in decreased growth and feed efficiency (Zhao et al., 2003). Dabrowski and Kozak (1979) reported that growth, protein efficiency ratio and apparent net protein utilization of grass carp fry (0.4 g) is optimized when fed a diet containing 40 percent fishmeal. Detoxified castor bean meal can also be used as a protein source for juvenile grass carp but at low inclusion (5 percent) levels (Cai et al., 2005).

Diet formulation affects meat quality. High dietary protein (30 percent) and lipid (4 percent) increases the viscera/body weight ratio (Lin et al., 2006). Supplementary dietary taurine increases the flesh protein content by about 2-3 percent and decreases water content by about 3 percent (Luo et al., 2006). Feeding grass carp on a 60 percent grass: 40 percent formulated pellet combination diet decreases body fat content and increases aromatic amino acid levels in the muscle (Feng et al., 2006b).

Grass carp with “hard” meat (locally known as crisped grass carp) is very popular in southern China. This characteristic is achieved by feeding the fish on horsebean (Vicia faba Linn) about one month before harvesting that results in increased levels of body protein, ash, Fe, K and decreased levels of fat, Na and Zn (Kuang et al., 2004b).

Amino acids, particularly coated lysine, are often added into the diet to improve growth performance (Liu et al., 1999). Vitamin C at 150–300 mg polyphosphate ascorbic acid/kg diet improves growth and feed utilization (Wen and Liao, 1996; Shi et al., 2001; Lin et al., 2003).

Fragment peptides from shrimp waste have also been reported to increase growth, feed utilization and protein retention in grass carp (Feng and Liu, 2005). Chinese medicines are often added as a prophylaxis. For example, addition of 0.5 percent Pulsatilla chinensis to the diet has been found to increase the immune response of grass carp (Tao et al., 2007). Supplementary dietary taurine, at 600mg/kg diet, increases fish growth and protein efficiency ratio, while the inclusion of beta-glucanases (500 IU/kg diet) increases digestibility, somatic growth and decreases FCR (Gao et al., 2006b). Feeding attractants, particularly plant extracts from Potamogeton crispus and Sesamum indicum, are incorporated into commercial pellets to reduce feed waste. Extracts of Lactuca sativa and Heleocharis dulcis are also used as attractants but these are not as efficient as Potamogeton crispus and Sesamum indicum. Extracts of animal origin, particularly grass carp extract as well as extracts from Hemiculter leucisculus, Anodonta sp., Branchiura sp. and Cipangopaludina chinensis also show good attractant properties (Chen et al., 1996). Probiotics may also be used to increase growth and to increase resistance to low dissolved oxygen levels (Xiang et al., 1995). Dietary photosynthetic bacteria have also been shown to increase grass carp growth rate under pond culture conditions (Zhang et al., 1996; Lin, 2001; Chen and Zhang, 2005; Zhang et al., 2007).