The wide range of natural food and man-made feeds consumed by common carp in pond culture helps to protect the fish from contracting deficiency diseases. However as stocking intensity increases in ponds or when common carp are reared in tanks or cages, the chance for nutrition-related diseases to occur sharply increases (Tacon, 1986, 1990, 1992, 1995; Hasan et al., 2007; Hoole et al., 2011). For this reason, recognizing the clinical signs of the most common nutritive deficiency diseases is of vital importance for fish producers (Table 10.1, Table 10.2 and Table 10.3).
Signs of certain deficiencies in farmed common carp can be observed when fish are fed with deficient diets, a situation that occurs mainly in intensive pond culture or in tank or cage culture. Essential amino acid (EAA) deficiency in common carp is rare, if occurring at all (Table 10.1). The limited relevant data available are controversial. Therefore further investigations are needed in this field.
Dietary EAA deficiencies may arise from the chemical treatment of feed proteins with acids (silage production) or alkalis, due to the loss of free tryptophan and lysine/cystine, respectively (Tacon, 1992). Dietary EAA deficiencies may arise also from the leaching of free and protein-bound amino acids into the water when frozen or freeze-dried zooplankton is fed. This leakage of free amino acids upon thawing may be more than 20 percent.
Although the clinical signs related to deficiency of essential fatty acids (EFA) cannot be easily detected in common carp, poor growth, high mortality and skin depigmentation are related to this deficiency disease (Table 10.1). The role of medium-chain triglycerides (MCT) in the nutrition of carp larvae has been recently studied and found to be important. Phospholipids (PL) have numerous roles in larval feeding, including an influence on the texture, resistance to oxidation and water stability of food particles. So, much attention should be paid to an adequate dietary PL supply when carp larvae are offered artificial diets instead of PL-rich live food. Dietary PL deficiency results in an accumulation of fat droplets in the enterocytes of the anterior intestine, an increase in the height of the mucosal epithelium and a reduction in mean hepatocyte volume (Takeuchi, Satoh and Kiron, 2002).
Mineral deficiencies (Table 10.2) are difficult to assess in common carp since most trace elements are obtained from both the dietary ingredients and from the culture water by extra-oral ways. For example, some dissolved minerals, such as calcium, can be exchanged between the body fluids and the surrounding water across the gill membranes. However, some minerals are essential in the diet; consequently feeds compiled for intensive rearing systems (tank and cage) must contain the necessary macro (Ca, P, Mg) and micro elements (Fe, I, Co, Cu, Mn, Se, Zn) in easily absorbable form. Known and suspected deficiencies include low growth rate, poor appetite and skeletal deformities (Table 10.2).
Vitamin deficiency of carp is very well reviewed (Tacon, 1992; Takeuchi, Satoh and Kiron, 2002) and is summarized in Table 10.3. However, it must be noted that under pond-culture conditions, signs of vitamin deficiency can rarely be observed in common carp. This is because vitamins can be obtained from natural food, and the microbial biosynthesis of some vitamins in the intestine certainly contributes significantly to the vitamin requirements of common carp. On the other hand, some evidence suggests that the dietary vitamin requirement of fish may be higher under "stressed" or adverse environmental conditions (Tacon, 1992). For the above reasons, environment and management-related diseases which increase stress in fish should be reduced as much as possible. Consequently, stressing fish with thermal shock, overcrowding and traumas occurring during handling and transport, as well as irregular and/or inadequate feeding must be avoided.
