Fish feeding is one of the most important factors in commercial fish farming because feeding regime may have consequences on both growth efficiency and feed wastage. During the last decade, there has been a marked increase in the use of extruded fish feed pellets for feeding fish. These feed pellets have superior water stability, better floating properties and a higher energy. The main effects on fish are: an increase in fish growth and an improvement in feed conversion.
Hygienic Quality of Extruded Fish Feed
Ingredients are cooked at high temperatures and pressures in fish feed extruder. Therefore, extrusion cooking provides hygienic processing of feed destroying the pathogens and most viruses and reducing the toxin levels in the feed ingredients. In extrusion cooking avian influenza virus is destroyed during the processing (greater than 70ºC). Also, Newcastle disease virus is inactivated by the extrusion and drying process where temperatures exceed 75ºC for one minute. Growth inhibitor, allergens and other anti-nutritional factors largely inactivated during extrusion cooking.
Manufacturing Soft Aquatic Pellets
Some species like blue fin tuna prefer very soft pellet. Extrusion processing allows us to make a very soft pellet (moisture content up to 30 percent in finished feed), which is not possible by other methods.
This is accomplished using a preservation system in aquatic feeds (final product moisture of 16-28 percent) during extrusion processing.
Lower Aw, (water activity) below 0.70 can be controlled with humectants at 10-12 percent levels and by reducing pH to 4.0-4.5 with acids at 1-2 percent levels or with fish silage/soluble. Mould inhibitors are also added at 0.2-0.5 percent level in the formulation.
Recent developments indicate that soft, gel-like aquatic pellets can be processed by coupling alkaline extrusion with a post-extrusion acid bath to adjust ph and set or ‘firm up’ the texture and pellet integrity.
Water Stable Fish Feed Pellet
Pellets that break down quickly in water will lose nutrients.
Some farmers hydrate feed in water and nutrient solution prior to feeding and require rapid and excellent water stability for handling and feeding purposes. Pellets that breakdown quickly in the stomach of fish loses nutrients (during regurgitation) and may contribute to GDAS (Gastric dilation and air sacculitis) in certain species.
Extrusion processing allows us to make pellets which are very stable in water for a long duration.
Water Absorption of Pellets
Extrusion moisture content during processing can be controlled over a wide range, which helps to increase the water stability of the final feed.
These pellets absorb more water, retains shapes for longer time and results in reduced losses of nutrients. Water Absorption and integrity after hydration is very important. It benefits pellet technical qualities and fish health.
Fewer Fines of Pellets
Extrusion reduces 75 percent of the amount of fines which normally enters the water and ends up decaying on the bottom of the pond.
In other words, fewer fines means: increased water stability; clearer ponds; lower fatality rates; less undesirable bacteria growth; increased conversion rates (10 – 20 percent); higher production yields; improved digestibility and reduced feed cost.