Feed quality and storage are related to the success of the operation. Feed is expensive in trout production. In addition, good storage will help to maintain the quality of the feed-in time.
In this chapter, we will review management feed quality and storage. We encourage you to review not only these points but also our in-house Feed Trials on our website:
Read our Feed Trials
Trout feeds have significantly been improved in the past decade. Fish meal is still the primary source of protein, but protein digestibility has been improved, and ash content has been reduced by using fish meal processed at lower temperatures (“low-temp” fish meal). Also, diets now have higher energy levels that help fish use protein more efficiently.
Increasing the energy level in the diet limits the fish’s use of protein as an energy source. Trout are grown efficiently with dietary fat levels (mainly from fish oils) as high as 18 to 28 percent, provided the ratio of digestible protein to energy remains in the correct range. This ratio is expressed as grams digestible protein per megajoule of digestible energy.
Ask your feed manufacturer to tell you the ratio of digestible protein to energy in your fish feed, especially if you plan to use high-energy diets. For typical high-energy diets the ratio should be about 20:1. Feeds with ratios significantly higher than 20 may contain excess protein or large amounts of protein that trout cannot digest easily.
Feeds with lower ratios may contain excess fat and could affect flesh quality and dress-out percentages. However, specific diet formulations may vary considerably from this ratio and still be highly efficient if adequately formulated.
Since feed is the highest cost component of a trout farming operation, consideration needs to be given to proper feed storage and handling. Freshness of feed is another consideration, although feed manufacturers use ingredients that are much more stable than they used to be. Some manufacturers have extended shelf life guarantees to 12 months.
A good example of a feed storage room. The space is clean, with no outside light, and the walls are insulated.
Purchase feed that has been recently manufactured and stored adequately by the feed supplier. Feeds that have the manufacturer’s date stamped on the bags will prevent the purchasing of old feed. Where possible, feed should be stored in an air-conditioned building for temperature and humidity control. Otherwise, feed should be stored in a cool, dry area off the ground on pallets and at least one foot away from any walls to avoid condensation. Make sure to rotate inventory; first in, first out. If silos are being used, try to move feed through silos regularly.
Feed that will be used quickly, can be stored in a barrel with a lid, as long as the room does not experience significant temperature changes.
When feeds are stored for long periods or under poor conditions, fish health problems may arise from molds and fungi and from vitamin degradation and rancidity of oils in the feed. Controlling rodents and insects is also important in maintaining nutrient quality and aflatoxin-free feeds.
Poor feed storage- The feed is stored in the incubation room, which will lead to excess moisture entering the feed bags. This can lead to mold colonizing the feed.
Feeds stored for a long time and probably contaminated with molds appear stale, are discolored, lump together and smell musty. Moldy foods are often saturated with moisture and appear to ‘sweat.’ Any containers used to store food (bins, automatic feeders) should be cleaned thoroughly on a bi-monthly basis to prevent mold growth on their surfaces (which may be hidden by newly placed fresh feed).
Mold in fish feed becomes a problem when toxic species of molds exist in sufficient quantities to produce aflatoxins. Aflatoxins are chemicals produced by some species of naturally occurring fungi(Aspergillus flavus and Aspergillus parasiticus), commonly known as molds. Aflatoxins are common contaminants of oilseed crops such as cottonseed, peanut meal, and corn. Wheat, sunflower, soybean, fish meal, and complete feeds can also be contaminated with aflatoxins. These molds can grow in grains and prepared feeds intended for fish production when storage conditions are suboptimal: temperatures of 27°C (80°F) or warmer and moisture at levels greater than 14%.
Consumption of aflatoxins can result in a disease known as aflatoxicosis. Fry are more susceptible to aflatoxicosis than adults. Initial findings associated with aflatoxicosis include pale gills, impaired blood clotting, anemia, poor growth rates, or lack of weight gain. Prolonged feeding of low concentrations of aflatoxins causes liver tumors, which appear as pale-yellow lesions and which can spread to the kidney. Increases in fish mortality may also be observed. Aflatoxins can cause disease indirectly through their effects on essential nutrients in the diet. These toxins can destroy fat-soluble antioxidants, such as vitamin A, and water-soluble antioxidants and vitamins such as vitamin C (necessary for immune function) and thiamin (essential for metabolic and nervous function). Aflatoxins depress the immune system, making fish more susceptible to bacterial, viral, or parasitic diseases. These subtle effects often go unnoticed, and profits are lost due to decreased production efficiency, such as slow growth, reduced harvest weight, higher FCR, and increased medical costs.
Aflatoxicosis is now rare in the rainbow trout industry due to strict regulations in most countries for aflatoxin screening in oilseeds, corn, and other feed ingredients.
Vitamin degradation in feed can’t be seen or detected by smell. Vitamin degradation is accelerated by:
Improvements over the years include:
Lipids (fish oils and poultry oils), lipid-containing ingredients, and complete feeds primarily degrade through oxidation reactions resulting in rancidity. Antioxidants are added to the feed to counteract this process, but they are gradually depleted over time. Rancidity is typically associated with loss of nutritional value and the development of off-odors. Rancid feed smells like paint, turpentine, or other similar chemical smells. The oxidation of lipids can also result in lower feed conversion, decreased weight gain, and increased disease or mortality in cultured fish. Lower energy value, protein quality, and vitamin retention in feed can be accompanied by the formation of toxic oxidation metabolites. Higher moisture feeds are more susceptible to rancidity. Temperature swings can accelerate lipid oxidation by creating pockets of high moisture. Proper storage and handling of feed can significantly increase the lifespan of the feed. The rancid feed should be disposed of and not used. If the feed has passed its expiration date, you can choose to still feed as long as there is no mold or rancidity. Mix with newer feed to be safe. Ideally, feed is used before the expiration date, but we sometimes recognize that you may have feed left over from the year before.
