Fish Nutrition & Feed Technology

Unit 16 - Storage of fish feeds

16.1.Storage

The manufacture of an aquaculture diet inevitably entails a storage period for the finished ration within the factory warehouse or farm store prior to feeding. Adequate storage conditions are provided so as to prevent deteriorative changes occurring in nutrient composition through oxidative damage and/or through microbial, insect or rodent infestation. Prolonged storage may have deleterious effect on the stability of dietary vitamins and lipids.

The most important environmental factors governing the storage or shelf life of a manufactured feed are ambient temperature and humidity. Bacterial infestation only generally occurs within stored feeds posessing a moisture content in excess of 25% (equivalent to a relative humidity above 90%). The most common fungi involved in the spoilage of feedstuffs include Aspergillus, Cladosporium, Penicillium and Helminthosporioum .

Reduced nutritional value of the stored feed: mould growth results in the loss (through enzymatic digestion or destruction) of dietary lipids, amino acids (lysine and arginine being most affected) and vitamins. Estimated losses in metabolisable energy in corn due to moulding range from 5% to 25% depending on the mould species involved. Mould growth can cause feeds to cake or clump, to change colour consistency and flavour, and to become generally less palatable

Certain mould species, and in particular the mould Aspergillus flavus, produce toxic metabolites or mycotoxins of which Aflatoxin B1, is the most toxic form causing cancer (tumors) and liver damage in virtually every animal species, including fish. Feedstuffs which are especially prone to attack by A. flavus include groundnuts, cottonseed and copra, and to a lesser extent maize, sorghum, sun flower, soybean and cassava.

A common fault in the design of storage buildings is to neglect to provide for an adequately constructed floor. This, like the walls should be effectively damp-proofed, and bags containing feeds should always be stored on wooden pallets. Ideally, moist/semi-moist aquaculture rations should be stored under refrigeration or used on the same day of preparation to avoid vitamin losses. Similarly, dry pelleted feeds should be stored under clean dry ventilated conditions, avoiding high temperatures and direct sunlight. Preferably the prepared feed should be utilized within three months from the date of manufacture.