92 Fish as feed inputs for aquaculture – Practices, sustainability and implications
Fish fed to cultured stocks can be divided into three broad categories:- Fish landed mostly by small-scale artisanal fishers, usually comprised of a single
species at any one time, and which may be suitable for human consumption
(Figure 10). This category includes slightly larger-sized fish with firmer flesh and
can be and is consumed by local populations. This category is often used in the
culture of crabs and molluscs (such as Babylon snail), often filleted or chopped
into suitably sized pieces. - Fish that are evidently not suitable for human consumption, mostly caught by
trawlers and often equivalent to the grade of low-value fish used in fishmeal
production. The species that fall into this category vary from region to region. In
general, the species included in this category are small-sized, often crushed and
literally “mushy” (Figure 9). - Fish of relatively high quality that are used to feed large-sized broodstock (often
individuals of over 10 kg) of some cultured marine species such as grouper. This
category includes horse mackerel, large oil sardines, etc., and is small in total
quantity.
5.1 Use of trash fish/low-value fish in brackishwater and marine aquaculture
in Asia
5.1.1 Current use of trash fish/low-value fish in brackishwater and marine finfish
aquaculture in Asia and future projections
The very significant increase in marine and brackishwater finfish production in Asia
over the last ten years, amounting to an average yearly increase of 9.6 percent, has
increased the demand for trash fish as the major food source for cultured brackishwater
and marine finfish stocks. These cultured stocks include a range of species belonging
to at least eight major families, the family/species group that currently accounts for the
highest demand for trash fish species being the groupers (Table 10). In the region, fish
is used as feed directly in mariculture in China, Indonesia, Malaysia, Thailand and Viet
Nam, and in the farming operations for southern bluefin tuna (Thunnus maccoyii) in
southern Australia.
Estimates of trash fish/low-value fish usage in aquaculture are available only for
Australia and Viet Nam. In the case of Viet Nam, trash fish/low-value fish use in inland
and coastal aquaculture ranged from 64 800 to 180 000 tonnes and from 71 820 to
143 640 tonnes, respectively, and the total amount used in aquaculture in Viet Nam was
between 176 420 and 323 440 tonnes (Edwards, Le and Allan, 2004). The latter figures
amount to approximately 22 percent of all trash fish/low-value fish production in Viet
Nam. The bulk of trash fish/low-value fish is used for the production of fish sauce
(Dao, Dang and Nguyen, 2005).
Australian southern bluefin tuna fattening, which is based on the on-growing of
wild-caught juveniles, is totally dependent on trash fish/low-value fish as the feed
source. In 2003, 5 409 tonnes of wild-caught tuna (of average weight 15 to 30 kg) were
fattened in cages to produce 9 102 tonnes (processed weight), over a period of three
to five months. The tuna were fed solely on pilchard and mackerel, and their farmgate
value was Australian dollar (AUD)$266 million (US$1=AUD$0.75) (Primary Industries
and Resources SA, undated; EconSearch Pty Ltd., 2004). The approximate increase in
fattened weight of 4 000 tonnes required 50 000 to 60 000 tonnes of imported trash
fish/low-value fish (Allan, 2004), giving a CE that is, at best, 12.5.
The computations given in Table 11 on the use of trash fish/low-value fish in Asian
finfish aquaculture are based on production figures for the major cultured groups
over a ten-year period (1995–2004) and at two levels of CE, 6 and 10 based on the
best and the average conversion efficiencies observed in practices in Asian countries.
Orachunwong, Thammasart and Lohawatanakiul (2006) estimated the conversion
efficiencies when trash fish/low-value fish are used in mariculture to range from 8 to
15.