With the further development of the fish farming industry, extruded fish feeds have obtained more and more wide applications in virtue of unique advantages including high nutrients, good palatability, strong digestibility, and so on. As a new technology to produce feed, extrusion processing means that in an environment of high temperature(110-200°C), high pressure(25-100kg/cm2), and high water content(10%-20%, even 30%), fish feedstuff mixture, through heating tempering, deep mixing and particles formation, would puff and afterward shape into extruded feed when out of fish feed extruder machine.
Extruded Floating & Sinking Fish Feed Pellets Production Process
On the basis of density variation and puffing degree, extruded fish feed can be segmented into floating fish feed and sinking fish feed. Currently, the floating feed is the most widely used extruded feed in fish farming, and it has relatively mature technology. That is, floating extruded feed pellets are both produced through a modulator for heating and modulation, via a continuous mixing process to fish feed raw materials after entering the extruder machine, heating up, pressurizing, ripening, extruding, and then puffing and granulating. Compared with floating fish feed, sinking pellets have different requirements for fish feed manufacturing techniques because of the diverse requests for specific gravity, even when they use the same fish feed machine. Briefly, the fish feed extrusion process requires a hammer mill to grind raw materials, a mixer to blend raw materials including vitamin-mineral premix, the wet type fish feed extruder with steam preconditioner (yes, steam is required for quality pellets), and a cutter head to shape the pellets, and finally a dryer-cooler to ensure pellet shelf-life and stability.
There are many factors affecting the expansion situation of feedstuffs, but expansion is mainly closely related to the tempering condition, operating conditions of the fish feed extruder machine, and property and shape of raw materials, which means changing the extruding conditions can control the floating and sinking status of extruded fish feed.
- Tempering plays an important role in producing extruded fish feed. When producing extruded sinking feed, operators should weaken the intense effect of extruding and strengthen the function of tempering at the same time. It is necessary to add water and vapor when tempering and prepare enough tempering time so as to make materials soften and ripen, creating conditions for materials to reach better plasticity within the puffing chamber in the next step. Thus, it will keep materials continuing to ripen without generating too big a puffing degree but getting sinking fish feed. So, adequate tempering works well in promoting feed digestibility, water tolerance, and extruding stability.
- Extruded sinking feed should adopt a lower screw speed. That is because lower screw speed can not only provide the required extruding and shearing action but without generating too high pressure, avoiding materials energy from growing rapidly and leading to too large extrusion.
- The control of temperature in the extruder chamber is another important aspect of controlling materials’ energy. When feedstuffs enter the melting section, operators need to heat the temperature reaching 120-125°C for shearing and mixture; then cooling the chamber (lowering the temperature to 40-50°C) at the tail end homogenizing section, lowering the supersaturation state of water content in materials, preventing too big puffing when materials enter the atmosphere from die hole.
- Other than that the puffing degree of floating fish feed can reach 2 or even 3, and sinking extruded fish feed is often less than 1.3. The pressure in the extruder chamber is relative to screw configuration, material character, mold aperture ratio, and charging rate, etc. If the aperture ratio is big, the discharge flow would be bigger. In order to get suitable extruded sinking fish feed, it is possible to change the number of mold holes according to actual situations at production.
Applications of Extruded Floating & Sinking Fish Feed
Compared with traditional powdery compound feed and pelleted feed, extruded fish feed can overcome some conventional disadvantages, such as bad water stability, feed disappearing and waste, water quality pollution, and so forth. In particular, floating extruded feed makes feeding management convenient because aqua feed can float on water for a long time and there is no need to set a feeding station, just at a fixed point to feed. Moreover, fish farmers can observe the food intake situation of their fish, adjust feeding quantity timely, and master fish growth and health status in time. In a word, extruded fish feed can contribute to scientific feeding and management, saving much time and boosting labor productivity. So as the ideal fodder of modern aquaculture, extruded aqua feed has quite good market prospects and wide application fields.
Generally, different aquatic culture animals have various ingestion features, and that is the principle that should be followed when choosing diverse extruded fish feed types. For instance, river crab is accustomed to looking for food in the water bottom and their eating speed is relatively slower, then Aqua feed should not be too hard or too firm, and also needs to reduce the loss in the nibble process. By this token, extruded sinking feed is more suitable for river crabs because it is easy to soften in water and fit for nibbling with longer water resistance time and less crumb loss, decreasing feed waste and water contamination.
In addition to those benthonic animals, most aquaculture species can ingest floating extruded fish feed very well, not only for the famous-special fish species (like aquarium fish) but also for conventional cultivation (like grass crap, crucian, catfish, tilapia, and so on). What’s more, in the aspect of the breeding method, the floating fish feed has more extensive applicability, that is to say, for pond fish farming, culturing fish in rice fields, running water fish culture, cage culture, and especially for fish farms with lower breeding density, the extruded floating feed has much more superiority than other fish feed.
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