Most of the information on the nutritional requirement of rohu has been generated using fingerlings under laboratory conditions. Nutritional information on other life stages is scanty. The major nutrient requirements of rohu are summarized in Table 2 and Table 3.
The optimum protein requirement for larvae and fry varies from 35–45 percent (Sen et al., 1978) and the performance in terms of growth rate, protein utilization and conversion efficiency have been reported to be the best when rohu has been fed with diet having 40 percent protein (Mohanty et al.,1990a&b). The optimum protein requirement for fingerlings has also been reported at 40 percent (Swamy and Mohanty, 1990; Satapathy et al., 2003).
Most importantly, the dietary protein content at which maximal growth occurred under laboratory has been reported to be 45 percent but the economically optimal dietary protein content has been reported to be 31 percent (De Silva and Gunasekera, 1991; De Silva, 1993). This difference has been attributed to the availability natural food in the ponds. The gross protein requirement level have been reported to decrease with increase of age and size of fish and in general, 25–30 percent protein has been reported to be optimum for practical diets for herbivorous fishes like rohu under pond conditions (Mohanty, 2006).
Very few studies have been undertaken to study the nutritional requirements of rohu under field conditions. Nandeeshsa et al. (1994) evaluated the effect of pond fertilization rates (10 and 20 tonnes poultry manure/ha) on protein requirement and growth. They showed that at a fertilization rate of 10 tonnes of poultry manure/ha growth increased with increasing dietary protein up to a level of 25 percent protein. At a fertilization rate of 20 tonnes poultry manure/ha optimum growth was recorded at a dietary protein level of 15 percent. Hence, it is important to consider the contribution by natural food in diet formulation for rohu. Khan et al. (2005) reported that rohu broodstock require a dietary protein level of 25 percent for optimum reproductive performance and egg quality.
Rohu require the same 10 essential amino acids like other finfish. Mohanty and Kaushik (1991) showed that there is no significant difference in the amino acid composition of the three species of Indian major carps. Hence, Mohanty and Kaushik (1991) suggested that under composite Indian major carp culture conditions, it should be possible to develop a common amino acid balanced diet for all three species. The essential amino acid requirements of rohu are presented in Table 2.
The optimum lipid requirement for rohu fingerlings was found to be in the range of 12-15 percent (Gangadhara et al., 1997; Satapathy et al., 2003). However, lipid requirement has been shown to be temperature dependent. Mishra and Samantaray (2004) reported that at 21 oC, the lipid requirement for rohu fingerling was 8 percent, whereas at 31 oC the requirement was 13 percent. Mohanty (2006) considered a range of 7–9 percent dietary lipid to be optimum for Indian major carps including rohu. Under laboratory conditions Anwar and Jafri (2001) reported that rohu fingerlings require 5 percent lipid in a 40 percent crude protein diet with 18.3 KJ gross energy at a carbohydrate to lipid ratio of 8.3.
There is little information on the fatty acid requirements of Indian major carps. However, supplementation of broodstock diet with n-3 and n-6 PUFA has been reported to positively influence gonadal development, egg quality and larval survival (Mohanty, 2006). Supplementing the feed of juvenile rohu with 1 percent n-3 PUFA is reported to enhance immunity against bacterial pathogens (Mishra et al., 2006) and inclusion of dietary phospholipids at 4 percent in larval diets of Indian major carps (including rohu) has been reported to result in better growth and survival (Paul et al., 1998).
Since carps in general, and rohu in particular, are generally herbivorous, carbohydrates can be used as a cheap energy source. It has been reported for rohu fingerlings that a minimum level of 40 percent dietary carbohydrate is required (at a protein level of 35 percent) for optimum growth, feed conversion and nutrient utilization (Saha and Ray, 2001), while Dalal et al. (2001) demonstrated that at a dietary protein level of 40 percent the carbohydrate requirement decreases to 35 percent. In general diets with higher carbohydrate levels lead to improved performance in terms of percent weight gain, specific growth rate, feed conversion ratio and protein efficiency ratio. Diets containing 45 percent gelatinized starch and 30 percent crude protein have been reported to be well utilized by rohu fry (Mohapatra et al., 2003).
The dietary protein and energy ratio has to be optimized to reduce wastage of protein. Sethuramalingam and Haniffa (2001) reported best growth and food conversion ratio in rohu fingerlings at a dietary energy level of 379.72 kcal/100g at 41 percent protein diet (P/E 107.87 and E/P 9.29), while maximum protein utilization and conversion occurred at 383 kcal/100gm) with a dietary protein level of 32 percent.
Except for vitamin A, C and E (Table 3), little is known about the vitamin requirements of rohu. Under semi-intensive polyculture conditions, Chattopadhyaya et al. (2002) reported that there is no added benefit by adding supplementary vitamins to the feed. However, under laboratory conditions the optimum requirements of rohu fry for vitamins A, C and E have been reported to be 2 000 IU/kg, 1 409 µg/g and 131.91 mg/kg dry diet, respectively (Rangacharyulu et al., 1999; Mitra and Mukhopadhyaya, 2003; Sau et al., 2004).
Except for calcium and phosphorus, there is no information on the mineral requirement of rohu. Paul et al. (2006) reported that the optimum calcium and phosphorus requirement of rohu fry are 0.19 and 0.75 percent of the diet, respectively.
