20 Fish as feed inputs for aquaculture – Practices, sustainability and implications
40 percent, respectively (Tacon,
2007), although these feeds
vary highly in their protein and
oil levels depending upon the
species and life-cycle stage being
fed. Starter diets are typically
rich in protein and lower in oil
than grower feeds. Smaller fish
also have different nutritional
requirements that may favour
the use of a particular fishmeal
such as the histidine-rich South
American feeds. Carp diets have
lower fishmeal inclusion rates of
around 5 percent, but still account over 13 percent of the fishmeal used by aquaculture
due to the high volumes of fish cultured.
Given a combination of the rising cost of fishmeal, the growing demand for a finite
resource and growing concern over the “food miles” involved in transporting fishmeal
around the world (Huntington, 2004), feed suppliers have focused on the potential to
substitute fishmeal and fish oil with plant-based alternatives. However, the level of
substitution possible is restricted by their lack of essential amino acids (such as lysine,
methionine and histidine), which may limit growth at high substitution levels. Another
issue is consumer opinion and the effect that this may have on the continued acceptance
of farmed fish as a “high quality” product similar to its wild counterpart.3.3.3 Fish oil
Fish oil is a proven energy source and, as well as providing essential fatty acids to
farmed fish and crustaceans, it imparts to the final product with high levels of omega-3
fatty acids, increasingly sought by the consumer. Fish oil is an important component
of salmon and trout feeds (25 percent and 17.5 percent, respectively), and nearly 65
percent of all fish oil used by aquaculture goes to these two species alone. Marine fish
also require fish oils (around 7.5 percent), but cyprinids, tilapia, catfish and shrimp
require lower amounts, typically 1–2 percent. To produce a product as “near to the wild
product as possible”, research is also focusing on the “dilution” of vegetable oils in the
flesh when the fish are fed diets containing 100 percent marine fish oils for six months
prior to harvest. In addition, vegetable oil substitutes do not necessarily improve the
environmental sustainability of the product (e.g. increased soybean production may
lead to further rainforest clearance).3.3.4 Future trends
Projections concerning the future availability, price and use of fishmeal and fish oil vary
widely depending upon the viewpoint and assumptions used (Shepherd, 2005; Tacon,
2005; Jackson, 2006; Tacon, Hasan and Subasinghe, 2006). For example, according
to Tacon, Hasan and Subasinghe (2006), fishmeal and fish oil use in aquaculture is
expected to decrease in the long run; assumptions used included rising prices due to
limited supplies and increased demand, increasing competition for pelagics for direct
human consumption and the desire on the part of consumers for sustainability and
a concern for the state of the oceans. However, according to industry estimates, and
in particular that of the International Fishmeal and Fish Oil Organisation (IFFO),
fishmeal and fish oil use is expected to steadily increase, such that by 2012 aquaculture
would use 60 percent of the global supply of fishmeal and 88 percent of the global
supply of fish oil (Jackson, 2006).FIGURE 8
Estimated use of fishmeal and fish oil in compounded aquafeeds
by major cultured species, 2004Source: Tacon (2006)