Salmonids, commonly referred to as "trout" in the carp family, are a group of fish known for their unique cold-water adaptations. These species can thrive in low-temperature environments where most other fish cannot reproduce or survive. They are widely distributed across the northern hemisphere, from the frigid zones down to temperate regions, typically found above 35 degrees north latitude. For over two centuries, salmonid farming has developed significantly, leading to the establishment of a globally recognized aquaculture industry in more than 120 countries. In China, the introduction of trout farming began in the 1950s, and by the 1980s, rainbow trout had evolved into a thriving industry spanning over 20 provinces. This development has led to increased awareness of the importance of cold-water resources and the potential for sustainable aquaculture.
Biologically, these fish have specific requirements that set them apart from other aquatic species. One key characteristic is their sensitivity to day length, with gonadal development closely tied to decreasing daylight hours during autumn and winter. This allows farmers to manipulate light conditions to control spawning times. Their breeding season typically occurs between November and February, with peak activity between December and January. Some species spawn in spring when ice begins to melt, and they require water temperatures below 8°C for successful reproduction.
The upper temperature limit for reproductive processes such as gonadal development and hatching is around 13°C. Beyond this, malformations increase significantly. Interestingly, there is no clear lower temperature threshold for maturation, as embryos can develop normally even at 0.5°C. After fertilization, it takes approximately 300–600 degree-days for larvae to hatch, and once hatched, they enter the juvenile stage.
Optimal growth occurs between 8°C and 20°C, but at temperatures above 21°C, metabolic rates decline, reducing feed efficiency and disease resistance. At 25°C, survival becomes extremely low. These fish prefer flowing, well-oxygenated waters with high clarity. Due to these traits, they have been traditionally farmed in Europe, the U.S., and Japan, and the term "cold-water fish" has been adopted internationally, including in China.
In addition to their biological characteristics, salmonids exhibit diverse ecological behaviors. Most species fall into two eco-groups: sea-run and freshwater types. Sea-run species migrate between saltwater and freshwater, while others are strictly freshwater inhabitants but can adapt to marine environments. Juveniles often display distinctive markings like parr marks, which may persist throughout their lives in some species.
Spawning typically occurs on gravel river bottoms, with large eggs laid in clusters. These fish are predatory, feeding on insects, small fish, crustaceans, and even snakes or rodents. Many species now rely on artificial diets in captivity.
There are about 16 species of salmonids that can be fully farmed in freshwater, with China also exploring seawater cultivation. The most commonly farmed species include rainbow trout, golden trout, Yamagata, and Daylight White Spot. Each has unique growth patterns, market value, and environmental needs. Rainbow trout, for example, reach sexual maturity in 2 years and can be farmed in flow-through systems, achieving high yields per square meter.
Water quality is crucial for successful salmonid farming. Temperature must remain below 22°C in summer, with dissolved oxygen levels maintained above 4 mg/L. Ammonia and pH levels also play a significant role, with rainbow trout being particularly sensitive to ammonia toxicity. Turbidity affects feeding behavior, so clear, clean water is essential.
Aquaculture facilities vary depending on the species, but generally involve hatcheries, juvenile rearing ponds, and adult fish tanks. Hatching eggs are kept in controlled environments to avoid light exposure, which can reduce hatching success. Juvenile rearing requires careful management of feeding schedules, water flow, and disease prevention.
Feeding strategies differ based on the developmental stage. Early-stage fry rely on yolk sacs, while older juveniles transition to artificial diets. Proper nutrition is vital for growth and disease resistance. Feeding rates are adjusted according to water temperature and fish size, with overfeeding posing risks of health issues and poor growth.
The economic potential of salmonid farming is significant. With growing demand for high-quality protein and the nutritional benefits of salmonids, the industry continues to expand. Cold-water resources, both in rivers and oceans, offer vast opportunities for sustainable aquaculture. As global consumption of salmonids increases, the future of this sector looks promising, driven by technological advancements, market demand, and environmental stewardship.
Therefore, amino acids are not only essential for human health, but also play an important role in beauty and skin care products.
Amino acids are the basic units of proteins and are essential organic compounds in life. There are about 500 different amino acids in nature, but among the amino acids that make up the proteins of living organisms, 20 are standard amino acids, which are connected in different sequences to form proteinaceous proteins that perform various physiological functions in living organisms.
Amino acids can be divided into the following categories according to their location and function in proteins
1.Essential amino acids
9 amino acids that the body cannot synthesize by itself or the synthesis speed cannot meet the needs, and must be ingest through food, including lysine, tryptophan, phenylalanine, methionine, threonine, isoleucine, leucine, valine and histidine (infants also need histidine).2.Non-essential amino acids
The human body can synthesize by itself and does not need to obtain directly from food, including glutamic acid, aspartate, alanine, serine, glycine, proline, cysteine, etc.3.Conditional essential amino acids
Under specific conditions (such as disease, stress), the human body's synthetic ability is reduced, and additional supplements are needed, such as arginine, glutamine, etc.Amino acids are also widely used in the field of skin care, as skin care ingredients, they mainly have the following effects
1.Moisturizing
Some amino acids such as glycine, alanine, etc. have good hygroscopic properties, which can help the skin retain moisture and enhance its moisturizing ability.2.Repair
Such as arginine, glutamic acid, etc. participate in the repair and regeneration process of skin cells, promoting wound healing.3.Anti-aging
Certain amino acids have antioxidant effects that can help fight free radical damage and slow down skin aging.4.Cleansing
Amino acid surfactants, such as sodium lauryl sarcosine, are commonly used in cleansing products for sensitive skin due to their mild, non-irritating properties.Therefore, amino acids are not only essential for human health, but also play an important role in beauty and skin care products.
Amino Acids,Taurine,L-Tyrosine, Food additives
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