Fish as feed inputs for aquaculture – Practices, sustainability and implications: a global synthesis 21
3.3.5 Fishmeal and fish oil use in agriculture
The agriculture sector uses predominantly Peruvian and Icelandic fishmeal, with
Moroccan and other minor sources making up the balance. With fishmeal and fish
oil production predicted to remain stable over the next decade and the proportion
being utilized by aquaculture increasing considerably, there is likely to be a fall in the
proportion utilized by agriculture.
For most domestic animal species, fishmeal is included in animal diets as a feed
supplement in order to increase the protein content of the diet and to provide essential
minerals and vitamins. In general, fishmeal is considered an excellent protein source
for all animal species, and fish is rich in amino acids, particularly lysine, cysteine,
methionine and tryptophan, which are key limiting amino acids for growth and
productivity in the major farmed species. Manipulation of protein quality during
fishmeal production is important in the manufacture of specialist feed supplements.
For example, low temperature (high digestibility and biological value, BV) products are
used in diets for fish, young piglets and poultry, whereas products for ruminant diets
are heated differently to reduce the breakdown of the protein by the rumen microflora
and thus increase the content of rumen undegradable protein (RUP) and to reduce the
soluble nitrogen content.
Typical inclusion rates for fishmeal in animal diets are around 2–10 percent for
terrestrial animal species. Efficiencies of conversion of feed to live weight gain are
usually quoted in terms of feed conversion ratio (FCR, units of weight gain per unit
of feed consumed). In general, efficiencies of feed conversion are higher for fish at 30
percent compared with poultry, pigs and sheep at 18 percent, 13 percent and 2 percent,
respectively (Asgard and Austreng, 1995). It is important to note, however, that with
the lower inclusion rates of fishmeal in poultry and pig diets, production per kilogram
of edible product from these species requires less fishmeal than for fish products.
- The use of fishmeal in ruminant diets^4 : Although sheep and cattle diets are
predominantly forage-based, there is increased use of concentrate diets and
supplements at times of increased productivity, such as during pregnancy,
lactation and rapid growth. The use of fishmeal in these situations has considerable
advantages over other protein sources such as soybean meal and bone meal in
supplying RUP at times when metabolizable protein requirements may be greater
than can be supplied by microbial protein synthesis and forage RUP. - The use of fishmeal in diets of non-ruminants: Fishmeal use in pig diets accounts
for approximately 20 percent of total fishmeal use, and fishmeal is recognized as
a key protein source with a good balance of essential amino acids. Pigs fed diets
containing fishmeal show improved feed conversion efficiencies and generally
produce leaner carcasses (Wood et al., 1999). The protein is well tolerated in
pigs of all ages and has a high digestibility. As with fishmeal used in ruminant
diets, however, processing has a significant impact on protein quality in pig diets.
Excessive heat treatment results in a significant reduction in digestibility and
biological value, due mainly to loss of lysine, a key limiting amino acid in growing
pigs. One major environmental benefit in the use of fishmeal in pig diets is that the
high digestibility of the added protein results in an improved efficiency of dietary
protein use with a concomitant reduction in the production of high N-containing
effluent.
(^4) Currently, the inclusion of fishmeal and fishmeal products in feed for ruminants is banned under EU
legislation as a consequence of the bovine spongiform encephalopathy (BSE) crisis. While there is no
inherent risk of the transfer of transmissible spongiform encephalopathies (TSE) via fishmeal, the ban
was introduced in response to fears about possible contamination of fishmeal products with processed
animal proteins.