Rainbow trout are one of the most popular and valuable fish species in aquaculture, both for freshwater and marine production.
They are prized for their high growth rate, good flesh quality, and adaptability to various environmental conditions. However, feeding rainbow trout properly is not as simple as it may seem.
There are many factors that affect the nutritional requirements, feeding methods, and environmental impacts of rainbow trout farming.
Nutritional Requirements of Rainbow Trout
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Rainbow trout are carnivorous fish that need a high-protein diet to support their growth and health.
According to the FAO Technical Guidelines for Responsible Fisheries, "Inland Fisheries" (2010), the optimal ratio between protein and fat recommended when compiling granular feed is from 2:1 to 3:11.
The protein content of the feed should be between 40% and 50%, depending on the size and age of the fish. The fat content should be between 15% and 25%, depending on the water temperature and the energy expenditure of the fish.
The feed should also contain adequate amounts of vitamins, minerals, and essential amino acids and fatty acids.
One of the challenges of feeding rainbow trout is to balance the dietary intake of phosphorus and calcium, which are important for bone formation and metabolism.
Rainbow trout have a high demand for phosphorus, but they also excrete a large amount of it in their feces, which can cause nutrient pollution and eutrophication in the receiving waters.
To reduce the phosphorus discharge, rainbow trout feed should contain highly digestible phosphorus sources, such as fish meal, fish oil, or monocalcium phosphate.
The feed should also have a calcium to phosphorus ratio of at least 1.2:1 to prevent skeletal deformities and ensure optimal growth.
Another challenge of feeding rainbow trout is to provide them with sufficient amounts of carotenoids, which are natural pigments that give the fish their characteristic pink or red color.
Carotenoids are not synthesized by rainbow trout, but they are obtained from their natural food sources, such as krill, shrimp, or insects.
However, in aquaculture, rainbow trout are usually fed with artificial feeds that lack carotenoids, resulting in pale or white flesh.
To enhance the color and appeal of rainbow trout, farmers can supplement their feed with synthetic or natural carotenoids, such as astaxanthin, canthaxanthin, or paprika extract.
The optimal dosage and duration of carotenoid supplementation depend on the desired color intensity and the market preferences.
Rainbow trout are fed by hand, mechanical feeder, or demand feeder. Each feeding method has its advantages and disadvantages, depending on the scale, type, and location of the production system.
The choice of the feeding method should consider the feeding behavior, appetite, and welfare of the fish, as well as the labor costs, feed efficiency, and environmental impacts of the operation.
Hand feeding is the simplest and most common method of feeding rainbow trout, especially in small-scale or family farms. It allows the farmer to observe the fish closely and adjust the feed quantity and quality according to their condition and behavior.
Hand feeding also enables the farmer to interact with the fish and establish a bond with them, which can improve their welfare and reduce stress.
However, hand feeding is also labor-intensive and time-consuming, and it can result in overfeeding or underfeeding, depending on the skill and experience of the feeder.
Overfeeding can lead to wasted feed, poor water quality, and reduced growth and health of the fish, while underfeeding can lead to hunger, aggression, and cannibalism among the fish.
Mechanical feeders are devices that deliver feed to the fish automatically or semi-automatically, using timers, sensors, or remote controls.
These feeders are widely used in commercial production, especially in intensive or offshore systems, where manual feeding is impractical or impossible.
Moreover, these machines can reduce labor costs and human errors, and they can provide frequent and consistent feedings to the fish, which can enhance their growth and performance.
However, mechanical feeders also require regular maintenance and calibration, and they can malfunction or break down, resulting in feed loss or starvation.
Mechanical feeders also lack the ability to monitor the fish behavior and appetite, and they can cause overfeeding or underfeeding, depending on the accuracy and reliability of the device.
On the other hand, Dldemand feeders are devices that allow the fish to feed themselves, by triggering a mechanism that releases a small amount of feed into the water.
Demand feeders are widely used in freshwater trout farming in the United States of America. These offer several benefits, such as low labor costs, little wasted feed, and high feed efficiency.
These feeders also improve the welfare and behavior of the fish, by giving them control over their feeding schedule and reducing boredom and stress.
However, demand feeders also have some drawbacks, such as high initial costs, potential vandalism or theft, and possible overfeeding or underfeeding, depending on the adjustment and regulation of the device.
