In the past years, aquaculture industry has developed with great speed, which has also given rise to the wide applications of the aquatic feed industry. 
Specially designed for aquatic animal breeding, the aqua feed can be divided into fish feed, shrimp feed, and crab feed according to feeding varieties, divided into pelleted feed and extruded feed on the basis of the production process, and divided into mixed feed, concentrated feed, and premixed feed in the light of fodder features. The raw materials of aquatic feed are mainly constituted of fish meal, cereal materials, and grease, thereinto the previous two always account for over 50% of feed cost. Because fish have small intestines and stomachs, and lack good digestion and absorption ability, the requirements for the processing technique of fish feed are far higher than that of livestock feed, so it’s particularly important to choose a suitable fish feed-making machine and process.
As is well known, aquatic feed production development has been through several phases, including the hand feeding process, cold forming of moist diets, pelleting presses via pellet milling technique, and extrusion technology via feed extruder. Currently, pellet feed and extruded feed have become two main popular fish feeds due to the profits they bring for fish farmers. Here, as the pioneers of various fish feed machines and professional manufacturers, we will discuss the respective manufacturing processes, advantages, and disadvantages of both pelleted fish feed and extruded fish feed.
Contrast of Pelleted Feed & Extruded Feed
With the development of processing craft, fish feed can be produced as pelleted feed and extruded aqua feed. Compared with natural feed, they have higher density and less humidity, not only allowing for long time reserve but decreasing the isolation of raw and processed materials. Although these two aquatic feeds have the same ingredients, there are obvious differences after being put into the water: pelleted feed sinks in the water bottom while extruded feed floats on the water within a certain time due to their physical characteristics. Even if with the same formula, the cost of extruded aqua feed is higher than that of pelleted feed, extruded feed can still create more benefits by virtue of its remarkable advantages.
1. Manufacturing process
The principle of choosing raw materials is to select the lowest cost on the premise of ensuring that feed contains the required nutrient substances. In addition, choosing materials should be based on the upper limit and lower limit dosage of ingredients probably used as raw materials, stipulating the upper limit dosage of materials with natural toxins and the lower limit dosage of some materials so as to improve the palatability and water stability of fish feed. For instance, feed producers should control the floor level of rice vermicelli processing by-products and other starch-type materials in order to promote cohesiveness and stability in the water of feed pellets while providing energy.
Besides, the thinner the particle size of raw materials, the higher the digestive utilization ratio, and the better the cohesiveness and water stability of fish feed. Remember to dilute and add the mineral premix compound before crushing and the vitamin premix compound after crushing step by step.
As to their manufacturing processes, conclude as the following figure shows. Clearly, the difference between these two aquatic feeds is the third step, that is, pelleted feed mainly uses the pelleting mill technique while extruded feed chiefly adopts extrusion technology via a high-performance fish feed extruder. In contrast, the processing craft of extruded fish feed is more complicated.
2. Advantages & disadvantages of pelleted aqua feed
As far as production is concerned, pelleted feed has a series of advantages, such as low-cost investment, high yield, low unit production charge, fast capital return, and so on. Moreover, compared with natural food and unprocessed grain feed, pelleted feeds via pelleting press are easier to store, package, and transport. For fish farmers, the pelleted feed has a low price but a high feed coefficient, which not only makes major cultured fish (like grass carp, crucian, and cyprinoid, etc.) grow well but also brings mixed culture fish (like silver carp and dace, etc.) good growth.
Well, as the saying goes, every coin has two sides, and pelleted feed also has some obvious shortcomings. To be specific, it’s hard for feed plants to earn money if demand is not enough big because of the low unit profit. What’s worse, pelleted feeds sink a litter faster after being cast in water, which is too late to eat for fish, so many of them fall to the bottom. Statistically, there are about 10%-15% of pelleted feed wasted due to the fast sinking, heavily polluting water quality, affecting the ecological environment and increasing
feed cost as well. Meanwhile, lots of nutrients are dissolved underwater, resulting in the lower mixed feed original quality, all of which have become prominent problems in the aspect of aquatic feed technology.
3. Merit & demerit of extruded fish feed
Nowadays, extruding technology is very common and widely used in producing kinds of feed. In fact, various fishes should be fed according to the feeding habits of different fishes, broadly separated into three categories – floating, sinking, and slow sinking, and feed should stay in water completely for a certain time so that to fish have enough time to eat. For now, only by using extruding technology can achieve the above features. With incomparable superiority, the extruded fish feed has low pollution, high efficiency, and high conversion, playing a vital role in the improvement of the digestive utilization ratio.
- During the extruding process, heat, humidity, pressure, and various mechanism actions can enhance the starch gelatinization degree, damage and soften the cell wall fraction of fiber structure, and release some begirt digestible substance, thus boosting the digestion and utilization.
- During the extruding process, moderate heat treatment can passivate some proteinase inhibitors (like antitryptase or urease), eliminate the side effects, kill harmful germs in raw materials, and change the properties of protein molecules to increase contact with enzymes in fish bodies, which makes feed easier for fish to digest.
- Extruded feed can lower the content of cottonseed and gossypol dramatically, bringing a better detoxification effect. Meanwhile, its long-time stability in water, up to 12-36 hours, makes it convenient to observe and control fish feeding.
Certainly, there are always two faces to everything, and it’s without exception for extruded aquatic feed. Although extruded aquatic feed has a distinct preponderance than pelleted aqua feed and its manufacturing process gains acceptance from lots of feed plants, its initial investment of the production line is much larger, which also scares many feed enterprises or fish farmers.
Option of Pelleted Feed & Extruded Feed
The option of aquatic feed should consider the feeding characteristics and habits of different aquatic livestock. For instance, river crab and other benthic animals are accustomed to searching for food in the water bottoms and eating food very slowly, so aquatic feed for them cannot be too hard, and the loss of fragments caused by biting food should be reduced as far as possible. 
Then extruded sinking feed would be a better choice because it is convenient to soften and suitable to gnaw, reducing feed waste and water pollution with less fragment loss. Moreover, extruded aquatic feed has a long water-resistant time and a high cultivated degree. Additionally, when the aquatic products market condition is well, using high-class pelleted feed or extruded feed can fatten fish quickly for selling on the market as soon as possible. Feeding with aquatic feed cannot only lower the occurrence rate of fish disease and make fish taste better, but also decrease the waste of resources under the condition of fishing resources starvation day by day.
However, using extruded feed through the whole feeding process can also lead to the feed/meat ratio rising, bad sensitivity and intolerance for long-distance transport. In the adult fish phase, continuing to use extruded fish feed can cause fish guano, big fish tripe and high moisture content in the body so customers are not willing to purchase.
In a word, during the process of freshwater aquaculture, the mixed using of pelleted feed and extruded feed can not only regulate water quality and reduce fish feed waste but also improve the output of aquatic products, achieving the perfect combination of water quality control and economic benefits. Therefore, the combination of pelleted feed and extruded feed is the most significant feeding mode deserving promotion so far.
