In recent years, the development of marine fish aquaculture is very rapid with increased aquaculture area by years and diversified aquaculture species, and its production has accounted for a sizeable proportion of worldwide aquaculture. Suitable fish feed forms concern the feed intake of fish, residual feed, fish growth rate, feed efficiency and thus the economic benefits of aquaculture.
Based on form and character, the marine fish feed can be divided into: minced fillet, powder type and feed pellets which includes dry sinking pellets, wet pellets, extruded pellets and slow sinking pellets.
Now the disadvantages and hazards of the minced fillet and powder feed have increasingly attracted people’s attention. Wet feed pellets are made of fresh or frozen small miscellaneous fish and powdery feed with certain nutritional indicators by fish feed pellet machine. It can integrate the strengths of both small fish and pellet feed for carnivorous fish feeding habits and has good palatability. Besides, nutritional levels can be adjusted according to the nutritional requirements of the fish at different stages of growth, improving feed efficiency, reducing feed costs and significantly weakening the dependence on small fish, so as to maintain a balanced supply of fish feed. It is reported that in Japanese cage aquaculture, wet fish feed pellets account for 65% of feeding amount.
Extruded fish feed pellet has a good stability and can float on the water for a long time, so it is easy to observe fish feeding conditions. Moreover, high temperature and pressure during extruding can damage the anti-nutritional factors in feed and improve feed digestion rate. But if directly feed extruded feed pellets, some fish may not be accustomed and the palatability will not be satisfactory. In addition, extruded feed pellets are not suitable for the middle and lower fish feeding habits.
As to sinking fish feed pellets, the requirements for formulation integrity are particularly high and it is difficult to master fish feeding conditions. But, with low processing cost and convenient storage and transportation, this sinking fish feed pellet is the main feed form for intensive marine fish farming.
Slow sinking pellet is a new form of fish feed developed in recent years, and it has a slow sedimentation rate (between extruded feed pellets and sinking feed pellets), particularly suitable for fish living and feeding in the middle level water (such as large yellow croakers).
Fish living habit and feeding habit should be taken into consideration when decide the suitable forms of marine fish feed pellets. According to reports, salmon grouper can feed on both wet and dry feed pellets, while the dry feed pellets have a better result on weight gain rate, feed efficiency and protein utilization. Perch generally eat wet feed pellets, but after being soaked in water, dry pellets and extruded pellets are also suitable for them to take. Wet feed pellets and slow sinking feed pellets have the best performance for large yellow croaker.
The size of the feed pellets should be 40% -60% of fish caliber so as to be fit for fish feeding, because too big or too small feed pellets will increase feeding difficulties and feed waste.