Salmon trout culture technology

Salmonidae fish, customarily known as salmon, some called trout, collectively known as salmon trout. Cold-water fish are called cold-water fish because they can reproduce for generations in low-temperature environments where other fish cannot reproduce and grow. Rainbow trout farming industry was developed in China in the 1950s from the introduction of technology.

I. Biological characteristics of salmon trout

Salmon trout differs from other fish in its biological characteristics of reproduction, growth and normal growth in low-temperature waters with very low upper water temperature and no distinct lower water temperature.

1. Salmon trout is a short-day fish. In autumn and winter, when the natural light time is shorter and the water temperature is lower day by day, the sexual cells mature. Gonad development is sensitive to the change of light time, which can change its maturity. People use this characteristic to change the light method to make it spawn and reproduce in the period of need.

2. The breeding season is mostly from November to February of the next year, and the peak period of reproduction is from December to January of the next year. In areas with long freezing periods, some species begin to thaw in streams and feed organisms begin to multiply in spring. The water temperature of reproduction is below 8 C.

3. The upper limit of water temperature for gonad development, maturation, fertilization, embryo development and juvenile hatching is 13 C. Abnormal gonadal development over 13 C increased the malformation rate of juvenile fish.

4. There is no obvious lower limit temperature for gonad maturation, fertilization, embryo development, hatching and development of juvenile fish. Embryos can still develop and hatch normally at 0.5 C.

5. After fertilization, the embryo develops up to 300-600 degrees per day. When the larvae reach the juvenile stage, they hatch the membrane. Once they hatch, they are juveniles, which are called hatched juveniles.

6. The optimum water temperature for growth is 8-20 C, which is higher than 21 C. Metabolic strength, feed efficiency and disease resistance decrease, and death will occur quickly at 25 C.

7. There is no obvious lower growth limit water temperature, as long as water does not change into ice, it can feed and grow.

8. Lifelong habitat in high transparency, high dissolved oxygen flowing water environment.

9. Except humpbacked salmon and rock salmon, other salmon trout have 7-12 juvenile salmon markers (parr. mark) on the side of juvenile fish, which are 0.2-15g. The young salmon spotted trout, which belongs to river remnants and freshwater salmon, will not disappear for a lifetime and will last for a lifetime in its immature form.

2. Species of Salmon Trout Culture

There are about 16 species of salmon trout in the world that can be cultured completely in the sea and freshwater areas. The sea trout culture in China has achieved preliminary results, but it has not yet been popularized. At present, almost all of them are freshwater culture. There are four main types of complete artificial breeding techniques which have been developed and have been widely cultivated or are expanding.

1. Rainbow Trout

Rainbow trout is the first fish of salmon family to be developed into aquaculture species. So far, it has been cultured for more than 120 years. The aquaculture area has spread over more than 1 to 20 countries and regions. Two years of sexual maturity, life can be multiplied. The average annual water temperature is below 1-2 C, and the body weight of 2-year-old can reach 1 kg. The largest individual in pond culture is 7 kg. Running pond culture can produce more than 25 kilograms per square meter. The main diseases affecting survival are viral diseases and vibriosis.

2. Golden Trout

Golden trout is a golden yellow line bred from the body color mutant of rainbow trout. Introduced from Japan in 1996, it has become an excellent breed widely cultivated all over the country. The biological characteristics, growth rate and yield per unit area of rainbow trout are similar to those of rainbow trout. It has both edible, fishing and ornamental value. Its golden yellow body color is a dominant genetic trait, which has important germplasm value for breeding science research. Because of its rich and elegant golden body color, the market price is higher than rainbow trout.

3. Mountain trout

Originated in Japan, it was developed into a breeding species more than 50 years ago. It is one of the two freshest meat species in salmon family. Its market price is 3-8 times that of rainbow trout. It is suitable for fishing in ponds and streams. Sexual maturity in 2 years, reproduction only once in life. Most of the 2-year-old fish weighed 400-700 grams and the largest individual weighed 900-1000 grams. Strong disease resistance, generally not infected with viral diseases. The survivability and feeding intensity of rainbow trout were better than those of rainbow trout at water temperature of 22-25 C. In 1996, the whole artificial breeding technology, including human propagation, was introduced into China, and now it is being popularized.

4. Solar white-spotted salmon

Originated in Japan, farming has a history of more than 50 years. Two years of sexual maturity, life-long reproduction can be repeated, suitable for fishing. Cooked fish dishes are famous for sashimi, and the market price is 2-3 times that of rainbow trout. In 1996, it was introduced into China. The average annual water temperature was 12 C. The body weight of 12-month-old fish was 110-130 g and that of 2-year-old fish was 500-1000 G. The largest individual is more than 2000 grams. The survival vigor and feeding intensity of rainbow trout were better than those of rainbow trout. He likes to eat sunken artificial bait as well as sunken bottom bait. Strong disease resistance, basically not infected with viral diseases.

In addition, aboriginal species of fine-scaled salmon, Far Eastern jellyfish, lamb red-spotted salmon and introduced species of river trout, Arctic red-spotted salmon, silver salmon, Atlantic salmon, brown trout are under experimental cultivation.

III. Aquaculture Environmental Conditions

1. Water temperature

Freshwater or mariculture requires a low-temperature water environment. Water temperature in summer does not exceed 22 C, the highest does not exceed 24 C, winter does not freeze or freeze in a short period of time, pollution-free, clear and transparent sea and fresh water can be used for the cultivation of salmon trout. Water temperature is an important factor affecting the effect of aquaculture. When the water temperature reaches 22 C, the dissolved oxygen in the water will drop to 5-6 mg/l. At this time, there are two unfavorable factors in the water environment: high water temperature and low oxygen content. The metabolic intensity and feed efficiency of fish will be reduced, which will seriously affect the growth and even cause death in the long run. The growth is generally unaffected by water temperature and dissolved oxygen when the water temperature is below 18 C.

2. Dissolved oxygen

Salmon trout like to live in high dissolved oxygen water. Generally speaking, the critical value of Dissolved Oxygen safety for rainbow trout is 3.15 mg/l. The critical value of Dissolved Oxygen safety for fish fed under hypoxic environment for a long time falls to about 2.45 mg/l. When dissolved oxygen is less than 5 mg/l, the respiratory rate of rainbow trout accelerates and swims slowly when dissolved oxygen is less than 4 mg/l. When the fish flock at the intake, the dissolved oxygen in water has dropped to less than 3 mg/l. At this time, the life of the fish has been threatened. In quiet environments, fish oxygen consumption decreases. Temperature, light, vibration and other stimulating factors will increase oxygen consumption and reduce the safety of dissolved oxygen environment. Oxygen consumption can be increased by 30%-70% under the stimulation of water temperature change, 20%-30% under the stimulation of light and 40%-50% under the stimulation of vibration, respectively. Oxygen consumption can be increased by more than one fold under the combined stimulation of various factors. When salmon trout are fed in a running pool, the dissolved oxygen in the drainage outlet should be kept above 4 mg/l.

3. water quality

The water quality factors affecting the growth of salmon trout are very complex, mainly the acidity and alkalinity of water and the concentration of ammonia nitrogen. The tolerance range of rainbow trout to acidity and alkalinity is 5.5-9.2, and the suitable range is 6.5-7.5. Acidic environment, especially strong acidic environment, can inhibit the growth of rainbow trout.

Nitrogen, especially ammonia nitrogen and nitrite, derived from non-decomposing organic matter such as bait and feces, is a toxic substance of salmon trout. The tolerance concentration of rainbow trout to ammonia nitrogen is 0.0125 mg/l. If the pH is about 7, the tolerance concentration can reach 0.05-0.6 mg/l. In near neutral water, ammonia nitrogen generally does not cause great harm. The higher the water temperature and ph, the stronger the toxicity of ammonia nitrogen. The higher the dissolved oxygen content in water, the stronger the resistance to ammonia nitrogen. When the dissolved oxygen content reaches 0.8-1.0 mg/l, rainbow trout will not be harmed within 6 weeks in the environment with more than 7 mg/l of dissolved oxygen. When the dissolved oxygen content is less than 5 mg/l and the ammonia nitrogen content is more than 0.5 mg/l, the growth of rainbow trout slows down, the gills are easily damaged, and even lead to kidney and liver dysfunction.

The turbidity of water quality is also an important factor affecting the growth of salmon trout. The turbid water quality can interfere with fish’s vision and affect their feeding and growth.