China's farmed salmon mainly comes from Heilongjiang's Astragalus japonicus, hybrid quail, and Russian varieties such as Russian oysters, Glover, and small pods.
First, the nutritional requirements of carp are crucial for their growth and development. Studies have shown that the protein needs in feed are relatively similar across different carp species. For Gaoshouyu (145-300g), the optimal dietary protein content is 36.5%-40.5%, with the highest weight gain rate at 49.6%. This was determined using the broken-line model, with the ideal level being 40.5% ± 1.6%. For Siberian coriander (22-47g), the best protein content is 40% ± 2%, with a maximum weight gain of 49%. The crude protein content in Acer palmatum should be around 47%, while for smaller baits (3-12g), 39% is most suitable, with a growth effect best at 39.76% protein. The suitable protein range for Chinese sturgeon is 35.4%-49.09%, with an optimal range of 39.68%-44.64%.
Although no specific studies have been published on essential amino acid requirements for carp, general fish amino acid profiles can be used as a reference. Research by Wing K. N. and Hung S. S. O. (1994) found that the overall amino acid composition in four sizes of Angelica (19.5-535.4g) is similar, but essential amino acids vary by tissue. Muscle has high histidine and lysine, liver has more cystine and branched-chain amino acids, while loquat has low isoleucine, leucine, and proline, and high glycine and proline.
Fat plays a key role in energy supply for aquatic feeds, and the protein-to-energy ratio significantly affects growth. Xu R. et al. (1993) tested various oils and found no significant difference in weight gain, suggesting carp do not require specific fat sources. Optimal fat levels for high-salmon bait are 9%, while for Chinese bacillus bait, it’s 9.06%. For small baits (12.9-17.2g), the ideal fat range is 5.6%-11.4%, with 7.5% being optimal. Chen Haitao et al. (1998) found that Amur sturgeon grew best on diets with 39.78% protein and 9.5% fat. Juveniles (2.79g) had the best growth when fed 39.46% protein and 9.21% fat.
Carbohydrates are less efficiently utilized by aquatic animals compared to land animals. Juvenile Chinese larvae showed best growth with 25.5% dextrin. Feeding D-glucose at 7% or more improved growth, though it had little impact on protein accumulation. Higher glucose levels increased fat synthase activity. Carbohydrate utilization varies: glucose and maltose lead to higher blood sugar than other sugars, galactose reaches peak levels later, and disaccharides appear in the blood after 4-20 hours. Catfish are influenced by feeding frequency, tilapia by sugar type, and salmon better at utilizing carbohydrates than tilapia.
Most fish cannot digest cellulose well, but small amounts (2%-4%) may improve growth. Hung S. S. O. (1989) recommended 3% cellulose in Gaoshouyu feed.
Vitamin C studies on salmon are limited. Moreau R. et al. (1999) found no growth or survival benefit from adding vitamin C to cockroach feed. Papp Z. C. et al. (1999) also found no significant effect of vitamin C levels on juvenile hybrids.
Second, juvenile fish feeding techniques are critical. After hatching, larvae rely on yolk sacs for nutrients. By day 7-13, they begin to eat plankton. During this mixed nutrition phase, water quality must be maintained to prevent hypoxia.
At the mixed feeding stage, larvae start eating live food. In practice, many hatcheries begin with artificial diets, but survival rates are low. Initially, larvae should be fed live food like leeches and zooplankton, 4-6 times daily, with about 25% of their body weight in feed. Overfeeding leads to waste and pollution, while underfeeding causes aggression.
After 30 days of live feeding, fry reach 3.8-9.4 cm and 0.5-3.9 g, with a survival rate over 60%. They can then be transitioned to artificial diets. Methods include direct feeding (survival 35%-40%), alternating live and artificial feed (survival 40%-50%, longer time), mixing live food into soft pellets (survival >50% in 3 weeks), or soaking dry pellets with live food (survival over 75% in 2 weeks). The last two methods are more effective. During domestication, select non-eaters and gradually introduce artificial feed.
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