Nowadays, fish farmers are confronted with the choice of using either pelleted feeds or extruded feeds. Those who do not know better may just select pelleted feeds on the basis of price because it is usually cheaper than extruded feeds on a per kilogram basis. Let us look into the cost and benefit by first clarifying the difference between the extrusion process and pelleting.
In both the extruder and the pelletizer, the feed is pulverized. But the similarity in the process ends there. In a pelletizer the moist feed mixture is not necessarily cooked with steam or if cooked, this is done under normal atmospheric pressure. In extrusion, the moist mixture is cooked with steam before it is extruded out with a screw into a die with a desired shape. The steam creates a high pressure which makes it possible to cook the feed at a higher temperature. With pressure above one atmosphere, the cooking temperature goes above 100°C. The higher temperature cooks the feed ingredients more thoroughly. The process is similar to cooking meat in a pressure cooker which makes the meat more tender in a shorter period than when cooked in an ordinary pot.
The pelletized feed, even if subjected to steam in the process, can be considered only half-cooked and have lower digestibility rate due to the partially broken bonds of molecules and the presence of anti-nutritional factors from plant ingredients which limits the availability of several compounds, nutrients, vitamins, and minerals. The extruded feed on the other hand, is more fully cooked due to the higher temperature and pressure it is subjected to. This makes it more digestible and more of its nutrients is converted into flesh and tissues. This means a lower feed conversion ratio or FCR.
One big advantage of extrusion process which can easily be seen even without special equipment is the high stability of the feed. Feed which are merely pelletized are more crumbly and results in more “powder” as a result of handling. These fines are usually blown away especially when the wind is strong and are just wasted, thus, contributing to more feed being used, and therefore a higher FCR.
Another advantage of the extrusion process, which again is easily visible, is the fact that extruded feeds can be made to float. This is very important in fish cages. With extruded feeds, wastage is greatly minimized and all of it are available to the fish. Pelletized feeds sink as soon as it becomes wet when not immediately ingested by the fish. Upon sinking, they are no longer available to the fish. This is not only a big waste economically but is also bad to the environment, because they will invariably decompose on the bottom.
Research has shown extruded feeds to be as much as 30% more available than the pelleted versions of the same feed. The cooking process involved with extrusion improves digestibility and availability of all nutrients in a feed including fiber, starch, proteins, minerals, and fats, resulting in higher absorption. The extrusion allows for much more fat to be added to feeds. It ensures that ingredients are getting into the fish and not being wasted, so you feed significantly less feed. Extruded feeds virtually eliminate dust and fines. Less dust at the bottom of the bag means more nutrients actually getting into the fish, less waste and lower FCR.
The extrusion process breaks down the primary bond holding the chain of amino acids together. The heat of extrusion also denatures undesirable compounds such as urease and the trypsin inhibitor present in raw soybeans.
The utilization of carbohydrates is significantly enhanced by the extrusion process. As starch is extruded, it is gelatinized, and when it leaves the extruder, it expands. Once the starch granule is gelatinized, it cannot revert to the original state and is water-soluble.
During the extrusion process, oil from soybeans and other raw ingredients is released from the seed cell, making the fat more available for absorption. The oil helps fulfill the fatty acid requirement and increases the energy density of the feed.
The high temperature during the extrusion process helps kill the microorganisms in the feed that will cause decay. This extends the shelf life of feeds from weeks to months.
One of the biggest hindrances to venture into aquaculture is capital. Several new-comers, usually not fully equipped with the basic knowledge in the industry, think that they can save cost by using cheap feeds like the pelleted one. But due to the fact that FCR is higher in using pelleted feeds, the cost to produce one kilogram of fish is increased. Instead of saving, the use of pelletized feeds actually increases the cost of production. In addition to that, the risk of poor growth, pollution and mortalities are higher with pelletized feeds. On the other hand, extruded feeds significantly reduce the feed cost by an average of 18.28 % and 16.80 % in milkfish and tilapia, respectively, in intensive cage culture systems.
In the Philippine aquaculture industry, there is a glaring difference between using the two forms of feeds. In intensive milkfish farming, FCR using pelleted can be as high as 2.7-3.2 in marine cages, while using extruded feeds the FCR is as low as 2.0-2.5 when growing 10 grams juveniles to 500 grams harvest size in high density cages. If the average price of pelleted feeds is 28 pesos a kilo, an average of P82.60 will be spent for feeds alone in every kilo of milkfish. While if the average price of extruded feeds is P30 per kilo, an average of only P67.50 is spent for feeds to produce a kilo of fish.
In the tilapia industry, the FCR is 1.9-2.3 for pelleted feeds but only 1.5-1.8 with extruded feeds in high density cages in Taal Lake (50-100 fishes per cubic meter at harvest). If pelleted feeds cost P28.20 per kilo, an average of P59.22 is spent for feeds to produce a kilo of tilapia. On the other hand, if extruded feeds cost an average of P30 a kilo, you would only spend an average of P49.50 for feeds to grow a kilo of tilapia averaging 350 grams per fish.
Due to its better form, extruded feeds give even lower FCRs in ponds of both milkfish and tilapia because of better nutrients absorption, lesser waste in pond resulting to better water quality, lesser cost of production, and more profit.
It is clear that extruded feeds result in higher profits and cleaner aquatic environment, all of which contribute to sustainability of the aquaculture industry. Extrusion allows efficient and increased use of plant ingredients, thus, reducing the dependence on fishmeal coming from the sea. Waste and uneaten feeds is reduced by 27%-33% more minimizing the incidence of pollution in the coastal and inland waters.
Using extruded feeds in any culture system and species ensures higher efficiency, profitability and sustainability. In aquaculture, be this for milkfish, tilapia or even shrimps, the cost of feeding to produce one kilogram of fish is what determines profitability – not the price per kilogram of feeds.
This appeared in Agriculture Monthly’s July 2018 issue.