How to Make a Preliminary Judgment on the Quality of Pelleted Fish Feed

In recent years, along with the growing popularity of high-yield @#@233@#@, the use of complete pelleted fish feed in fishery production has become very common. However, because there are many feed brands on the market and great differences exist in quality and grade, the vast number of farmers are unable to judge the merits of its quality. This article introduces a simple method for judging fish feed quality by sensory means. That is: "one look, two sniffs, three twists, four soaks, five chews," for everyone to use as reference when purchasing pelleted feed.

1. Look

1.1 Look at color: Pelleted fish feed is made by uniformly mixing several main raw materials such as fish meal, soybean meal, cottonseed meal, rapeseed meal, wheat middlings, and meat-and-bone meal in a certain proportion and then pelletizing them. The color of the finished product can, to a certain extent, reflect the amount of the raw materials used. If there is more fish meal and soybean meal, the feed color will be somewhat yellow; when there is more miscellaneous meal, the feed color is dark red; when there is more wheat middlings, the feed color is somewhat grayish-white, and so on.

1.2 Look at granule size: Fish feed is formed into pellets after processing by the pelletizing process. By observing the granule size, one can judge the raw material ratio, the fineness of raw material grinding, the degree of conditioning uniformity, the pelletizing process, and the selection of the ring die. High-quality fish feed has a uniformly smooth granule surface, neat cross-sections, a length 1.5 to 2 times the diameter, and a fines rate not exceeding 1%. If, when observing the fish feed granule size, you find that the granules are rough, the cross-sections are uneven, and the fines rate is relatively high, it is estimated to be caused by the following reasons: (1) insufficient grinding fineness of raw materials, (2) unreasonable raw material ratio, (3) uneven conditioning, (4) improper selection of the ring die, (5) improper adjustment of the cutter distance, and so on.

1.3 Look at gloss: The pellet surface of high-quality fish feed is smooth, uniform, and glossy. Such feed has better palatability, stores well, and has a relatively high utilization rate. Low-quality fish feed has a rough, lusterless surface. The above phenomena are mainly caused by the following reasons: (1) insufficient grinding fineness of raw materials, (2) improper compression during the pelletizing process, (3) insufficient addition of feed oil, and so on.

1.4 Look at sinking speed: When feeding pelleted fish feed, it is necessary to ensure that the feed has a certain buoyancy and sinking speed. Fish feeding on the upper surface layer of the water body can not only save feed but also make it convenient to observe the fish's feeding situation.

Generally, fish feed should be ensured to float on the water surface for 3 to 4 seconds. If it sinks too fast, the fish will not have time to eat it, causing waste; if it floats for too long, it proves that the feed has a relatively high crude fiber content and poor quality.

2. Smell

Pelleted fish feed is made by mixing various raw materials and then cooking and aging them through steam conditioning. After the raw materials are cooked and aged, they emit a distinctive aroma. Grab a handful of feed that has just been opened from the bag and sniff it in front of your nose. If you find a musty-bitter smell, burnt smell, artificial fishy smell, raw fish meal smell, or raw flour smell, it indicates that the following problems exist in the processing process;

(1) poor raw material quality, (2) excessive moisture and deterioration during storage, (3) inappropriate conditioning temperature, and so on.

3. Twist

Fish feed needs to be transported many times from production to feeding, so objectively it must have a certain mechanical strength. Under normal circumstances, it is sufficient if it does not break after being twisted a few times with the fingers, but it must not be too hard. If it breaks as soon as it is twisted, it indicates that the feed hardness is insufficient, the fines rate during handling is relatively high, and feed waste is easily caused; if the hardness is too great, the palatability is relatively poor, affecting the movement of the feed in the digestive tract and easily causing the occurrence of enteritis in fish.

4. Soak

Putting the feed into water to soak can, on the one hand, check whether the feed can meet the needs of the fish digestive tract in terms of physical properties. On the other hand, it can also analyze the approximate composition of its raw materials. The specific method is to grab a handful of feed and put it into water, then observe the time it takes for the feed to disperse. Generally, the feed completely disperses after 3 to 5 minutes. If the feed disperses too quickly, it easily causes bloating in the fish digestive tract and affects their feed intake; if the feed disperses too slowly, it affects the intestinal peristalsis of the fish and is not conducive to the fish's digestion and absorption.

5. Chew

Although fish swallow feed when eating, whether the mouthfeel is good or bad is the main factor affecting their feeding behavior. Through the touch and taste of our oral cavity, we can feel the hardness of the pellets and whether there is any off-flavor, whether the feed has deteriorated, whether the feed is mixed with impurities (such as sand grains, soil, etc.), and so on.