An Introduction to the Characteristics of Salmon and a Detailed Explanation of Breeding Techniques

Salmon, also known as sanwenyu or damaha fish, is a cold-water, highly migratory fish. Salmon has delicious meat, a very good taste, and is rich in nutrients, making it one of the healthiest fish species in the world.

I. Types and Characteristics of Salmon

There are more than 30 salmon species of commercial value worldwide, but currently only 6 species of salmon and 2 species of trout are the most common. Farmed varieties currently include Pacific salmon, coho salmon, Atlantic salmon, Arctic char, golden trout, triploid trout, and rainbow trout, among others.

Under natural conditions, salmon like to inhabit clear, pollution-free waters. The extreme temperatures for their survival are 0°C and 30°C, and the optimal temperature for growth is 16-18°C. Within the suitable temperature range, they feed vigorously and grow quickly. Below 8°C or above 20°C, their appetite decreases and growth slows. Salmon are fish that prefer countercurrent flow and oxygen-rich water. Abundant water volume and the stimulation of water flow can maintain good material metabolism and promote growth. Therefore, salmon are raised in flowing water. The suitable dissolved oxygen level is above 6 mg/L, and the optimal pH range is 6.5-6.8. They are euryhaline fish, able to live in both seawater and freshwater. Under artificial rearing conditions, they have gradually become omnivorous, can feed well on artificial compound pellet feed, and can be intensively domesticated.

II. Seedling Breeding of Salmon

1. Reproduction

There are many species in the Salmonidae family, but the scale of farming is relatively small. Under pond conditions, the fish can spawn and reproduce naturally. They generally reach sexual maturity in 2-3 years. The spawning water temperature is below 15°C, the suitable water temperature is 4-13°C, and the optimal water temperature is 10-11°C. In the natural environment, mature broodstock often choose river channels with clear water, water flow, and gravel substrate as spawning sites. They spawn multiple times, with each spawning producing 2000-3000 eggs.

① Broodstock cultivation Since the fecundity and egg diameter of broodstock are usually positively correlated with body weight and unrelated to age, fish with strong constitutions and body weights above 0.8-1 kg should be selected as broodstock. For broodstock weighing less than 4 kg, the fecundity is about 2000 eggs per kg of body weight. The ratio of female to male broodstock is 4:1. If the plan is to produce 1 million eggs, then the total weight of broodstock to be raised is 700 kg. The suitable density for broodstock cultivation is 5-10 kg/sq m, the water temperature is controlled at 4-13°C, dissolved oxygen is above 8 mg/L, and the flow rate is 30-50 L/s.

For broodstock cultivation, use a complete compound feed. Crude protein should not be less than 40%, crude fat should not be higher than 6%, and carbohydrates should not be higher than 12%. Use the following feed formula: crayfish 5%, fish meal 20%, trash fish 10%, pig blood 5%, feather meal 3%, brewer's yeast 3%, soybean cake 12%, bran 20%, green feed 2%, plus added fish multivitamins and vitamin E. Raising broodstock this way yields eggs that are all high-quality orange-red eggs, with high average eyed-egg rate and hatching rate. In daily feeding, animal feed accounts for 30%-45%, and plant feed accounts for 55%-70%. One to two months before spawning and for a period after spawning, low-fat animal feed can be fed exclusively, and in winter the amount of vegetables should be increased to 3%-5%. The daily feeding amount is 2% of total weight, and one month before spawning it should be reduced to about 1%. The broodstock pond should be drained of waste in a timely manner to keep it clean. One month before spawning, the water flow should be appropriately increased to promote gonadal maturation.

② Artificial insemination One person holds the fish's head with both hands, and another person grips the caudal peduncle diagonally by hand, with the head upward and the abdomen downward, aiming at a perforated egg-collection basin used for filtration (a beaker, etc., can be used when collecting semen), and squeezes from top to bottom along the abdomen toward the genital pore until most of the eggs have been squeezed out. When the body weight is below 2 kg, a skilled operator can perform the procedure alone. If the eggs are well matured and the operation is done properly, the eggs will flow out very smoothly under squeezing, and the fish can also tolerate this squeezing. When collecting eggs, the water on the fish body surface should be wiped clean to avoid any water droplets from the fish body surface entering the egg-collection basin. The collected eggs need to be rinsed with an isotonic solution (NaCl 90.4 g, KCl 2.4 g, CaCl2 2.6 g, dissolved in sequence in 10 L of water, with a pH of 7 and the temperature adjusted to above 4°C) to wash away the yolk material flowing out of the eggs. Artificial insemination is used, that is, for every 10,000 eggs, add or squeeze in 10 mL of semen, stir quickly and evenly for 1-2 minutes so that the eggs are rapidly fertilized, and then let stand for 1 hour. Then change the water several times and remove excess sperm, bad eggs, egg membranes, blood clots, etc., until the water in the basin is clean and transparent. After the fertilized eggs have fully absorbed water and swollen, transfer them to an incubator for incubation.

③ Incubation management During incubation, light should be avoided and ventilation provided, and vibration and mechanical stimulation should be prevented; at the same time, dead eggs easily breed water mold, so several egg-picking operations need to be arranged during incubation. When the fertilized eggs develop to the eyed-egg stage, the following matters should be noted: prevent hypoxia and suffocation, as eyed eggs have a relatively high oxygen consumption rate, and the eggs cannot be handled in still water, otherwise the eggs are prone to suffocation; control temperature, and after incubation and handling of eyed eggs, strictly carry out the process at 5-13°C; avoid light, as eggs around the eyed stage have the weakest resistance to light, so bright light should be avoided; prevent vibration, as eyed eggs have increased resistance to vibration, so relatively strong vibration should be avoided.

2. Juvenile fish cultivation

Newly hatched larvae rely on absorbing the yolk sac for nutrition. From hatching to 50 mm, fry should use opening feed with extremely small pellet size and a protein content of 45%-50%. This type of feed is specially used for the first feeding of fry. From 50-150 mm, the feed protein content should be about 45%, of which animal protein should not be less than 40%-45%. During the rearing process, once the water temperature exceeds 20°C, cooling measures should be taken. Low water temperature only affects the growth rate of salmon and does not pose danger. Too high a water temperature will cause a decrease in dissolved oxygen content and will directly affect the survival of salmon. The feeding rate is directly related to the body weight of the salmon, the water temperature, and the quality of the feed. At different water temperatures, for the feeding rate of salmon of a certain body weight, dry feed with low moisture content should not exceed 10%, and wet feed with high moisture content should be 20%-50%. Dry feed should be stored under dry and low-temperature conditions, and wet feed should be prepared before feeding; otherwise, mildew will produce toxicity and cause massive death of salmon.

The most effective way to prevent and control diseases is to keep the salmon's growing environment at the cleanest level, use high-quality feed, and adopt reasonable management methods. All tools and equipment for raising salmon should be kept clean when in use, and after use, operators should clean and disinfect them again. Fish ponds should have an automatic waste-cleaning function. Deposited feces and feed residues will compete with the fish for dissolved oxygen and induce the reproduction of harmful bacteria or fungi, which is detrimental to the healthy growth of salmon, and should be improved.

III. Salmon Farming

At present, salmon farming all adopts intensive flowing-water farming methods. The suitable pond area is 80-160 sq m, the stocking density is 15-20 fish/sq m, the water source is cold spring water, the water flow rate is 0.15 cubic meters per second, and the water quality is clear and pollution-free. The pH is 6.8, dissolved oxygen is 11.5 mg/L, and the water temperature is 5.5-11.5°C. Imported adult fish pellet feed can be used until the salmon are marketed. Feed twice a day, and attention should be paid to the feeding amount, which cannot exceed 1% of the fish body weight; otherwise, the fish will become sick. Daily management mainly consists of feeding, water volume adjustment, fish pond waste cleaning, inlet and outlet management, and caretaking. Ensure smooth water flow, clean pond waste once every half month, and keep the water quality clean.