Sensory methods for judging the quality of pelleted fish feed
With the rise of intensive aquaculture, the use of pelleted fish feed has become very common. However, there are many feed brands on the market today. There are also great differences in quality and grade. Some farmers may feel at a loss about this and can only choose based on manufacturers' advertising or fellow farmers' evaluations of a certain feed, or even try frequently changing between different brands of feed, and so on. To some extent, these practices are all somewhat blind. Here we recommend a simple sensory method summarized from practical experience for preliminarily judging the quality of pelleted fish feed, which can be summarized as one look, two smells, three twists, four soaks, and five chews. For everyone's reference.
One: look at the color, look at the particle size, look at the gloss, and look at the sinking speed. Fish feed is made by mixing several main raw materials such as fishmeal, soybean meal, cottonseed meal, rapeseed meal, and wheat middlings in a certain proportion and then pelletizing them. The color of the raw materials can, to a certain extent, be shown in the finished feed. For example: when the content of fishmeal and soybean meal in the feed is relatively high, the feed color is slightly yellow; when the content of miscellaneous meals (low-quality meals such as cottonseed meal and rapeseed meal) is high, the feed color is black-red; when the content of wheat middlings is high, the feed color is slightly white, and so on. By observing the feed color, the usage amount of certain raw materials can basically be judged.
High-quality fish feed should have uniform particle size, neat cross-sections, a pellet length about 1.5-2 times the diameter, and a fines rate not exceeding 1%. If the fish feed is seen to have rough particle size and uneven cross-sections, it may be caused by the following reasons: ① insufficient fineness of raw material grinding; ② an insufficiently reasonable raw material formula; ③ uneven conditioning during the feed-making process; ④ improper coordination between the cutter and the ring die, and so on. Such fish feed has a certain impact on palatability and digestibility.
The pellets of high-quality fish feed have a smooth and uniform surface and are glossy. Poor-quality feed has a rough surface without luster. The reasons for poor glossiness may be ① insufficient grinding fineness of raw materials; ② insufficient compression ratio during the pelletizing process; ③ insufficient addition of oils and fats in the feed, and so on.
Pelleted fish feed is generally swallowed by fish in the surface layer of the water after entering the water. Therefore, the feed is required to have a certain buoyancy and must not sink too quickly.
Two: smell. Pelleted feed is a cooked material made from mixed raw materials after steam conditioning. High-quality feed gives off a pleasant cooked aroma. If a musty smell, scorched smell, artificially synthesized fishy aroma, flour smell, raw fishmeal smell, or other off-odors are found, it indicates that there are certain problems in the quality of the raw materials, the feed processing and conditioning process, or the storage of the feed. Attention should be paid to this.
Three: twist. Fish feed is scattered in water for fish to eat, so objectively it must have a certain mechanical hardness and not scatter immediately upon entering water. Under normal circumstances, if it does not break after being twisted a few times by hand, that is sufficient. 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 it easily scatters upon entering water, causing waste of feed.
Four: soak. Throw the fish feed into a water container and soak it for a while. On the one hand, this can test the stability and sinking speed of the feed in water. On the other hand, it can be observed what the raw materials are roughly composed of after the feed disintegrates. The stability time of high-quality feed in water is 3-5 minutes.
Five: chew. Put the pelleted feed in your mouth and chew it. Through your own sense of taste and touch, you can feel whether the feed has deteriorated, whether it has off-odors, and whether the feed contains impurities.