Read and translate the text with the help of a dictionary.
Once a diet has been formulated and the ingredients have been mixed together in the proper proportions, the material is usually made into a pellet. Pellets are made by exposing the material to high pressure in a pellet mill or extruder. Pellet mills may use steam to help bind the ingredients together. Extruders use supplemental heat and extended exposure to high pressure to make pellets. Pressure pellet mills and extruders pass the feed mixture through a small aperture which leads to a product which is not cut to short lengths, would be much like spaghetti strands.
The diameter of the pellets varies, but is typically 0.2 to 0.24 inches (5 to 6 mm). A knife cuts off the strands as they exit the pelleting equipment. Feeds produced by pressure pelleting are more dense than water; thus, they sink. During the extrusion process, on the other hand, the high heat used causes changes within the ingredients so that starches expand when the pellets leave the machine and come into contact with air. This rapid expantion of the material traps air within the pellets, which float when placed in water. Because of the higher temperatures and other factors, extruded pellets are more expensive than pressure pellets.
Advantages of floating pellets are that the aquaculturist can see that the fish eat feed. By watching the fish eat, the producer can control the amount of feed offered and thereby avoid overfeeding. This can save money. If the fish develop a disease, the aquaculturist may be able to identify the problem by observing changes in the behavior or appearance of the fish and can treat the problem before it progress very far. Floating feeds should not be used on all aquaculture species. Shrimp, for example, feed on the bottom and will not swim to the surface for pellets.
However, nutrients will be quickly lost from sinking pellets which may dissolve in a few minutes (floating pellets may take 24 hours or more to disintegrate), so valuable source of nutrition can be lost if the animals do not consume the feed quickly. Also, bacterial and fungal growth on feed particles that are not quickly consumed can lead to disease or toxicity problems.