Lack of initial food size
As 3 to 4-day-old mandarin fish is able to take in feeds, this is quite a critical time. Normally, the feeds are prepared at a size that is 40–50 percent smaller than the fish itself. If the fish is not able or does not happen to consume the feeds until the fifth day, survival will be poor. In this case, higher density and the breeding of the live foods at the appropriate time are recommended so as to meet the initial needs of the mandarin fish.
Fatty liver
Under natural conditions, mandarin fish feeds upon prey that is easily captured. The fish actively searches for food with high consumption of its own energy, thus reducing the accumulation of body fat. However, fish kept under controlled conditions with an abundance of food are inactive. Due to this inactivity, energy is largely accumulated as fat, particularly in the liver. This can lead to poor liver function and lowered metabolism, weakening the fish until it dies. This can be prevented by supplying artificial feeds with L-carnitine so as to accelerate the fat metabolism of the mandarin fish (Liang,. 2002), thus prohibiting the occurrence of the fatty livers.
Insufficient supply of essential elements
In the formulation of artificial feeds, it is not yet clear that all the essential ingredients for mandarin fish are included. As stated above, even though based on the flesh composition and nutritional requirements, the tests showed that the ingredients for fish needs are not evenly balanced. Protein supply is an essential part; the higher this component is, the greater the growth rate that can be expected. However, supplying higher protein content through the use of live foods results in greater mortality because of the unbalanced amino acids, particularly the restricted essential amino acids such as methionine and arginine, which are only present in live foods as half the level required by the fish. Due to the insufficiencies of these amino acids, the metabolic processes become disordered. A careful study on the dead fish found that NH3 and NH4 are not in the right process of normal secretion and discharge; instead, there is a large concentrated accumulation in the kidneys. Thus clinical signs of toxicity are visible on the gills and skin, the whole body turns dark, the fish becomes lethargic, ceases to feed and suffocates to death.
