114 Fish as feed inputs for aquaculture – Practices, sustainability and implications
giving rise to fish diseases and the need to use veterinary drugs and chemicals for their
prevention and treatment, leading to many problems associated with food safety.
In the Asian context, disease transmission resulting from the use of trash fish/low-
value fish in aquaculture is scantily documented (Figure 22). One such example is
the reported by Subasinghe and Shariff (1992), who attributed mass mortalities of
cage-cultured barramundi (Lates calcarifer) in Malaysia to infections of Pseudomonas
anguilliseptica, Vibrio alginolyticus and the spoilage bacterium Shewanella putrefaciens,
possibly brought about by poor husbandry and the feeding of spoiled coarse fish.
By contrast, the risks and impacts on local fish populations and ecosystems from
the use of imported fish to feed the tuna farming industry in the Mediterranean (WWF
Mediterranean Programme, 2005) have been highlighted. This report, however, fails
to show a direct cause and effect between the use of imported fish to feed the tuna
and negative impacts. All in all, it has to be agreed that there are risks associated with
using trash fish/low-value fish (particularly imports) to feed cultured stocks and that
precautionary approaches have to be applied. However, in most Asian practices, such
feed is often obtained from the immediate habitats.
In a recent study on southern bluefin tuna farming in Australia, Fernandes et al.
(2007) demonstrated that the amount of phosphorous available for leaching from solid
waste ranged from 5–6 percent to 17–21 percent from pellet and baitfish [Sardinops
neopilchardus (syn. of S. sagax)]-fed tuna, respectively, and the corresponding nitrogen
discharge was 15 and 35–43 percent.
A number of strategies have been suggested to reduce the use of trash fish/low-
value fish in aquaculture, and thereby contribute to minimizing the sector’s impact on
a dwindling biological resource. Among these are reducing fishmeal use in aquafeeds
and enhancing the efficacy of trash fish/low-value fish use in aquaculture, culminating
in the weaning of stocks to pellet feeds. The limitations on the reduction of fishmeal
content in aquafeeds in the region are discussed in Section 4 (also see De Silva and
Hasan, 2007).
The environmental gains that are made through the use of trash fish/low-value
fish for aquaculture purposes have often gone unnoticed. For example, the live fish
restaurant trade, a lucrative upper-end market, was almost entirely dependent on wild-
caught reef fish, primarily groupers (Box 13). Destructive fishing methods that not onlyBOX 13
Grouper culture and coral reef preservation
Among the major fish species cultured using trash fish/low-value fish are the groupers
(family Epinephalidae). In the past, almost
the entire market for grouper, especially that
of the live fish restaurant trade, was based on
wild-caught fish that were often obtained using
destructive fishing methods such as poisoning
and explosives. These destructive practices
resulted in major environmental impacts on
aquatic habitats, mainly coral reefs, which
resulted in public denunciations. However,
this niche market is increasingly being filled
by cultured groupers, and this has contributed
significantly to the conservation of tropical coral
reefs.
Photo: Brown-marbled grouper (Epinephelus fuscoguttatus) and humpback grouper
(Cromileptes altivelis)