Detailed Explanation of Key Points of Rainbow Trout Pellet Feeding Technology

Water, seed stock and feed are the basic conditions for fishery production. In order to obtain better rearing results and reduce fish farming costs, the following issues should be noted during feeding:
1. The shape, structure and specification of the feed are very important for whether fish accept or reject a certain food. Feed pellet size not only affects palatability, but also affects digestibility. Therefore, when choosing the size of pellet feed to be fed, attention should be paid to making it suitable for fish to swallow at each growth stage. If the fish are large but the feed is too small, the fish cannot easily ingest it and it sinks to the bottom of the pond; on the contrary, if the fish are small and the feed pellets fed are very large, it is unfavorable for the fish to swallow and dissolves and is lost in the water, so the feeding utilization rate of such feed is low.
In rainbow trout feed, for fry and fingerlings below 12 grams, pellet feed of 0.3-2.2 mm may be selected according to their individual size; for fingerlings of 12-60 grams, pellet feed with a particle size of 2.2-3.2 mm and a length of 3.4 mm may be selected respectively; for individuals of 60-195 grams, pellet feed with a particle size of 3.5-4.5 mm and a length of 4-5 mm may be selected respectively; for individuals above 195 grams, pellet feed with a particle size of 5 mm and a length of 6-8 mm is fed.
2. The level of dissolved oxygen in the water has a great influence on fish feeding, digestion and absorption after feeding, and fish growth. When the dissolved oxygen in the water is low, the fish have poor appetite, the feed digestion and absorption rate after feeding is low, the growth rate is slow, and the feed coefficient is high. When dissolved oxygen is above 9 mg/L, rainbow trout have vigorous metabolism, grow well, and have a high feed utilization rate. Below 5 mg/L, the respiratory frequency increases. Below 4.3 mg/L, floating head appears, and they do not feed. Therefore, when feeding, attention should be paid to changes in dissolved oxygen in the water. If dissolved oxygen in the water is low and the fish are floating at the surface, do not feed; wait until the dissolved oxygen in the water changes before feeding. In rainbow trout culture, oxygen deficiency generally occurs in the rear ponds of a series connection, so attention should be paid to the stocking density of the rear ponds, which should be appropriately lower than the density of the ponds in front. In addition, sewage should be discharged in a timely manner to maintain good water quality.
3. Attention should be paid to water temperature changes. The survival water temperature for rainbow trout is 0-25°C, and the optimal growth water temperature is 16-18°C. Below 8°C or above 20°C, appetite decreases and growth slows; above 24°C, feeding stops. In actual production, where conditions permit, pumping well water to lower the temperature in high-temperature seasons and introducing hot spring water to raise the temperature in winter so that the pond water temperature remains at 16-18°C can greatly increase the weight gain rate of rainbow trout and the utilization rate of feed.
4. Intraspecific behavior restricts the feeding of rainbow trout. The adverse effects of size and aggressiveness on feeding are commonly seen in rainbow trout farms. Aggressive fish in the cultured population (generally large fish) will affect the appetite or feeding of small fish, thereby affecting their growth. Only after the large fish are full and disperse can the small fish feed. Increasing the number of feedings or spreading the feed evenly helps small fish feed. In addition, because rainbow trout fingerlings grow unevenly, they should be screened once a month, different specifications should be selected, and they should be fed separately to facilitate their growth and improve feed utilization.
5. The daily feeding amount should be appropriate. If the feeding amount is too low, the fish remain in a semi-starved state and growth and development are slow; if the feeding amount is too high, not only is the feed utilization rate low, but it also spoils the water quality and breeds diseases. An appropriate feeding amount ensures the fastest growth speed of fish and the highest feed conversion efficiency. The daily feeding amount is expressed as the feeding rate, that is, calculated and fed as the percentage (%) of feed dry weight in the body weight of the feeding fish. The feeding rate differs with different feed quality, different fish growth stages, and different water temperatures. When the protein content of rainbow trout fry pellet feed is 45%, feed at 3.7% at a water temperature of 14°C and at 4.3% at 16°C; when the protein content of pellet feed at the adult fish stage is 40%, feed at 1.8% at 14°C and at 2.1% at 16°C, which can meet the nutritional needs for normal growth of rainbow trout.
In rainbow trout culture, their body weight will increase. According to the weight gain situation, adjust the feeding amount in a timely manner. At the fingerling stage, weigh 3 times per month and adjust the feeding amount 3 times; at the adult fish stage, adjust the feeding amount once every 15 days.
6. Feeding should be timed, and the number of feedings should be appropriate.
Timed feeding can keep fish full a certain number of times every day, and their growth, assimilation efficiency and feed conversion rate will all remain at a relatively high level. Too many feedings cause incomplete digestion and reduce feed utilization rate; too few feedings inevitably make each feeding amount very large, causing serious feed loss. If the feed has high nutritional value, it may be appropriately less; if the nutritional value is low, it may be appropriately more. When water temperature and dissolved oxygen are high, it may be appropriately more; otherwise, feed less or stop feeding. At the rainbow trout fry stage, feed 4-3 times daily; at the fingerling stage, 3-2 times; for adult fish and broodstock, 2 times. For 2 feedings per day, it is best at 9-10 am and 4-5 pm; for 3 feedings per day, at 8-9 am, 12-1 pm, and 5-6 pm; for 4 feedings per day, 4 feedings may be evenly set between 8 am and 6 pm.
7. When feeding, attention should be paid to the feeding speed, and one should be patient and meticulous and pay attention to the method.
When feeding, each feeding should put the feed into the water little by little at a certain frequency. Do not put the feed into the water all at once, as this will cause the feed to dissolve and be lost. Research on rainbow trout has found that at the beginning of feeding, the amount eaten is large, and afterward it rapidly decreases to cessation of feeding. Therefore, the duration of each feeding for rainbow trout should not be too long or too short. If too long, the feed will sink to the bottom and be lost, and the feed utilization rate will be low; if too short, most of the fish will not yet be 80% full. The duration of each feeding for rainbow trout should be 15-20 minutes. Do not feed moldy and spoiled feed.