Malnutrition causes fish diseases

With the rapid development of factory breeding, formula feed is used more and more widely. However, some formula feed can not meet the nutritional needs of fish due to raw material problems or preparation technical problems. In particular, the feed designed and produced by small feed factories and farmers may cause undernutrition or overnutrition, which will lead to the decline of fish physique and, in serious cases, fish death. This paper will explore the causes of fish diseases from the aspect of nutrition, in order to guide farmers to take timely measures to prevent the occurrence of fish diseases in culture production.

1. Deficiency or excess of protein

Protein is the material basis for fish growth and life-sustaining activities. Fish get protein from food and break down into amino acids in the digestive tract, which are used to synthesize fish protein and produce energy. The growth of fish is mainly the accumulation of protein in the body. Low protein content in feed or poor quality of feed raw materials will directly affect the health of fish. The content of protein in feed is too low, the growth of fish is slow, the physique decreases, and the disease resistance decreases. The content and ratio of amino acids in feed is not only an important factor to determine the nutritional value of protein, but also the standard to evaluate feed quality. Therefore, the essential amino acids in feed must meet the needs of fish, otherwise it will also lead to fish disease.

Second, insufficient fat content or deterioration

Fat is the main source of heat energy and is composed of various fatty acids and glycerol. The essential fatty acids needed for fish growth can only be obtained from feed. If there is a lack of essential fatty acids in the feed, it can slow down the growth rate of fish, reduce the survival rate and decrease the feed efficiency. Fatty acids are prone to oxidative deterioration, producing aldehydes, ketones and acids. These substances interact with other nutrients in feed, such as vitamins and proteins, reduce the role of nutrient elements, and cause fish diseases.

III. Excessive carbohydrates

Carbohydrates in feed can not only provide heat, but also participate in many metabolic activities, and are used by fish as precursors for the synthesis of non-essential amino acids and nucleic acids. The high content of carbohydrates in feed leads to the disorder of glucose metabolism in fish, visceral fat accumulation and, in severe cases, fatty liver. In general, choline, inositol and vitamin C can be added to the feed to prevent the occurrence of fatty liver.

IV. Deficiency of vitamins, minerals and trace elements

The vitamin requirements of fish vary greatly according to different species and growth stages. Lack of vitamins will lead to slow growth of fish, decrease of feed efficiency, decrease of food intake, disturbance of substance metabolism and increase of mortality. Minerals and trace elements are important components of fish tissue and are indispensable nutrients for fish to maintain normal material metabolism and physiological function. The lack of certain minerals or trace elements in feed will adversely affect fish. See tables 1 and 2.

Table 1 Vitamin deficiency of farmed fish

Deficiency symptoms of vitamin species in fish

Vitamin A has light skin, exophthalmos, bleeding fins and skin, and deformed operculum.

Vitamin D is not abnormal.

Vitamin E exophthalmos, muscular dystrophy, kyphosis, degeneration of kidney and pancreas

There is no abnormality of vitamin K

Poor growth of vitamin C

Thiamine is easy to frighten, subcutaneous bleeding and light skin color.

Pyridoxine anemia, neurological disorders, decreased hepatopancreatic transferase activity

Pantothenic acid has poor growth, no vitality, skin bleeding, exophthalmos.

Nicotinic acid skin bleeding, death of individual

Biotin is inactive and epidermal mucous cells increase.

Choline, inositol fatty liver, hepatocyte vacuolation

Table 2 Mineral deficiency of farmed fish

Lack of symptoms of mineral fish

Phosphorus has loss of appetite, slow growth, deformity, increased body fat content and decreased water content.

Magnesium poor growth, high mortality, deformities, kidney stones

Poor growth of zinc, high mortality, skin and fin inflammation, erosion, cataract

Poor growth of manganese and motor retardation

Poor copper growth, anemia

Iron anemia

Selenium muscle, abnormal skeletal development and high mortality

Poor growth of iodine, negative thyroid function and mass in the lower Gill.