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most highly digestible sources of energy that can be used in catfish feeds, are used sparingly because of several negative aspects of using high levels in catfish diets.

Table.3. Minimum dietary vitamin requirement in catfish

Vitamin

Requirement

A

450-900 IU/lb

D

110-450 IU/lb

E

25 -50 ppm

Vitamins

K

R1

Vitamins are a highly diverse group of organic compounds requisite in trace amounts; they are necessary for fish growth and to fight against diseases. They are also required for metabolism of other nutrients in tissue components. Many of the water-soluble vitamins also act as co-enzymes. Fish derive required vitamins from natural food, which become limited in intensive fish culture due to high stocking densities. Qualitative and quantitative vitamin requirements for catfish have been well defined (Table 5). Catfish feeds are generally supplemented with a vitamin premix that contains all essential vitamins in sufficient quantities to meet their requirement; however, vitamin requirements are also affected by fish size, growth rate and stage of sexual maturity, diet formulation, disease, and environmental conditions. Catfish producers and researchers are considering the use of mega dose levels of certain vitamins, particularly vitamin C, to enhance disease resistance in catfish. Early evidence indicated that high levels of vitamin C (10 times or more than the level needed for normal growth) reduced mortality caused by certain bacterial diseases that affect catfish. Mishra and Mukhopadhyay (1996) reported the ascorbic acid requirement of Clarias batrachus to be 69.0 mg/kg diet. Mohammad et al. (2000) reported that biotin deficiencies in Clarias batrachus results in anorexia, dark skin color and convulsion. The

Thiamin

1 ppm

Riboflavin

6 - 9 ppm

Pyridoxine

3 ppm

Pantothenic acid

10-15 ppm

Niacin

7.4 - 14 ppm

Biotin

R1

Folic acid

1.5 ppm

B12

R1

Choline

400 ppm

Inositol

NR

Ascorbic

11-60 ppm

1

R and NR refer to required and not required, respectively.

optimum biotin requirement for maximal growth of C. batrachus is 2.49 mg/kg diet. In Heteropneustes fossilis fingerlings the optimum dietary biotin requirement is 0.25 mg/ kg diet (Mohammad, 2001). Mohamed and Ibrahim (2001) worked out the dietary niacin requirement of Heteropneustes fossilis and the optimum requirement is 25 mg/kg diet.

Minerals Catfish apparently require minerals for osmotic balance of various metabolic processes and for structural functions. Some minerals such as calcium are directly obtained by fish through gill and skin or both, while others are made available from natural food and ingested detritus. Minerals may be classified as macro-minerals or micro-minerals,

depending on the amount required in the diet. Fourteen minerals are considered essential for catfish. Although mineral studies with fish are difficult to conduct; deficiency signs and quantitative requirements for macro- and microminerals have been determined for catfish (Table 6). Minerals like calcium and phosphorous are essential as they are related in metabolism and bone formation in fish. Calcium plays a major role in blood clotting, muscle function and proper nerve impulse transmission while, phosphorous is involved in energy transformation, permeability of cellular membrane, reproduction and growth. Phosphorus is particularly vital in catfish feeds because of the relatively high physiological requisite, the relatively low level of dissolved phosphorus available in natural water. Therefore, catfish feeds