Nutritional requirements

In understanding the nutritional requirements of mandarin fish, it is essential to understand the nutritional composition of the fish. Tests have shown that the nutritional composition (measured in dry weight, the same as below）of the fish is 60–62 percent protein, 15-16 percent fat, 16–18 percent ash and 2–7 percent carbohydrate. Table 6 indicates that the amino acid concentrations at different life stages and shows little difference in both quantity of amino acids and their concentrations. However, research shows that the protein content of mandarin fish is higher than that of grass carp and silver carp. Liang, Cui and Liu (1998) reported that the total amino acids in the muscle from mandarin fish accounted for 78.4 percent, as compared to 67.9 percent for grass carp and 64.1 percent for silver carp, while essential amino acids accounted for 31.1 percent, 28.4 percent and 26.9 percent, respectively. Therefore, the mandarin fish demands a quality protein food higher than that of the other Chinese carps (grass carp, silver carp etc.) it is mostly fish as live foods that can satisfy the needs at different life stages of the mandarin fish. Therefore, development of concentrates for this fish should closely follow the needs of the required nutrients. Protein and amino acid composition of different live foods are given in Table 7.

Grow-out culture

Increased fish size is accompanied by increased feeding capabilities; thus mandarin fish of grow-out size are able to take prey of a wide range of size. The fish prefers strong and healthy live foods. The feeding behavior is quite unique. Mandarin fish generally hides itself, but when it finds prey, it either launches a sudden attack or moves closer before attacking. The fish takes in the live food head first; if feeding is accidently initiated from the belly or dorsal part, the prey is regurgitated and re-swallowed from the head again. Grow-out fish can swallow live foods greater than their own length, the prey being curved in the stomach during the swallowing process. Tests showed that average daily need for live foods is 7.8 percent of the body weight, and that the average FCR is 7.22. However, the daily food requirements decrease with increasing body weight, as the test showed that the food requirement of a mandarin fish of body size of 3.7 cm is 0.75 g per d, or a daily food intake equal to 18.7 percent of the body weight. The live foods are digested and excreted as faeces in 6.5–7.5 h, and it takes 19–27 h to remove all material. Fecal discharge takes place every 2–4 h, a single feeding producing 5–7 discharges of decreasing quantity (Liang, 2002).