What diseases are fish prone to when suffering from malnutrition?

With the rapid development of factory farming, the use of compound feed is becoming more and more widespread. However, some compound feeds cannot meet the nutritional needs of fish due to raw material problems or formulation technical problems. In particular, feed designed, formulated, processed and produced by small feed mills and farmers themselves may cause nutritional deficiencies or excesses, weakening the fish's constitution and, in severe cases, causing fish death. This article will discuss the causes of fish diseases from the nutritional aspect, in order to guide farmers to take timely measures in breeding production to prevent the occurrence of fish diseases.

I. Protein deficiency or excess

Protein is the material basis for fish growth and the maintenance of life activities. Fish obtain protein from food, break it down into amino acids in the digestive tract, and use them to synthesize fish body 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. If the protein content in feed is too low, fish grow slowly, their constitution declines, and disease resistance decreases. The content and ratio of amino acids in feed are important factors determining the nutritional value of protein, and are also standards for evaluating the quality of feed. Therefore, the essential amino acids in feed must meet the needs of fish, otherwise it will also cause fish disease.

II. Insufficient or deteriorated fat content

Fat is the main source of heat energy, composed of various fatty acids and glycerol. The essential fatty acids needed for fish growth can only be obtained from feed. If the feed lacks essential fatty acids, it can lead to slowed growth, reduced survival rate, and decreased feed efficiency in fish. Fatty acids are prone to oxidative deterioration, producing aldehydes, ketones, and acids. These substances interact with other nutrients in the feed such as vitamins and proteins, reducing the effect of nutritional elements and causing fish diseases.

III. Excessive carbohydrates

Carbohydrates in feed can not only provide heat, but also participate in many metabolic activities of the body, and are utilized by fish as precursors for synthesizing non-essential amino acids and nucleic acids. If the carbohydrate content in feed is too high, it causes disorder of carbohydrate metabolism in fish, accumulation of visceral fat, and in severe cases, fatty liver. Under normal circumstances, adding choline, inositol and vitamin C to the feed can prevent the occurrence of fatty liver.

IV. Deficiency of vitamins, minerals and trace elements

The vitamin requirements of fish vary greatly depending on species and growth stage. Vitamin deficiency will lead to slow growth, reduced feed efficiency, decreased food intake, disorders of material metabolism, and increased mortality in fish. Minerals and trace elements are important components of fish body tissues and are indispensable nutrients for fish to maintain normal material metabolism and physiological functions. Lack of a certain mineral or trace element in feed will have adverse effects on fish. See Table 1 and Table 2.

Table 1 Vitamin deficiency symptoms of farmed fish

Vitamin type | Deficiency symptoms in fish

Vitamin A: light skin color, exophthalmos, bleeding of fins and skin, deformed operculum

Vitamin D: no abnormalities observed

Vitamin E: exophthalmos, muscular dystrophy, lordosis, degeneration of kidney and pancreas

Vitamin K: no abnormalities observed

Vitamin C: poor growth

Thiamine: easily startled, subcutaneous hemorrhage, light skin color

Pyridoxine: anemia, nervous disorder, decreased transaminase activity in liver and pancreas

Pantothenic acid: poor growth, inactivity, skin hemorrhage, exophthalmos

Niacin: skin hemorrhage, occurrence of dead individuals

Biotin: inactivity, increased epidermal mucous cells

Choline, inositol: fatty liver, vacuolation of liver cells

Table 2 Mineral deficiency symptoms of farmed fish

Mineral | Deficiency symptoms in fish

Phosphorus: loss of appetite, slow growth, deformity, increased body fat content, decreased water content

Magnesium: poor growth, high mortality, deformity, kidney stones

Zinc: poor growth, high mortality, inflammation and erosion of skin and fins, cataracts

Manganese: poor growth, slow movement

Copper: poor growth, anemia

Iron: anemia

Selenium: abnormal muscle and bone development, high mortality

Iodine: poor growth, impaired thyroid function, lumps appearing on the lower part of the gills