Use of wild fish and other aquatic organisms as feed in aquaculture in the Asia-Pacific 107
In general, in both forms of crab farming the wild-caught crablets are fed chopped
trash fish/low-value fish. Given an estimated production of about 120 000 tonnes
of crab and an average
conversion efficiency of 4 to
6, the total quantity of trash
fish used in mangrove crab
farming is between 480 000
and 720 000 tonnes (Figure
18).
Although crabs are
relatively inefficient in
feeding on pellet feeds and
such feeds are not widely
available, evidence suggests
that pellet feeds can be more
effective than feeding trash
fish and that they can
significantly reduce the cost
of production (Table 17).
In view of the rapid
growth in crab farming
in the last few years, and
taking into consideration
that a proportion of crablet
supplies is likely to come
from hatcheries, an overall
growth rate of 25 percent
from the current level is expected by 2010. This would mean that a trash fish/low-value
fish supply of 600 000 to 750 000 tonnes will be required given an average CE ranging
BOX 9
Production of gravid female crabs for niche markets, Chanthaburi province, Thailand
Crablets weighing about 140–150 g are brought a long distance (travel time of up to 22 hr) from the
Adaman Sea area. They are fattened for two to three weeks in a pond by feeding with trash fish/low-
value fish that is purchased at THB10–13/kg. The crabs are individually observed at the change of the
tide, and when the first signs of eggs appear they are kept in net cages suspended in the ponds. The
fully gravid females, determined by using a torch or by making a small incision in the abdomen, and
weighing on average 240 to 250 g, are exported weekly. Daily feeding is at a rate of approximately
100 kg of trash fish per 10 kg of crab. The mortality rate is nearly 70 percent during the rearing
period; however, the dead crabs are cooked and sold in the local market. An approximate cost-benefit
analysis, per cycle of 45 to 60 days, of the practice is as follows (all figures in THB):
Revenue from crab egg production = 270 000
Revenue from crab meat = 99 000
Total revenue = 369 000
Crablet costs = 282 750
Feed costs = 16 100
Labour costs = 10 000
Total expenses = 308 850
Net profit/loss = 60 150
Photo: Monitoring of early indications of eggs development
in female crabs during low tide in suspended net cagesBOX 10
Lobster fattening in Viet Nam
In addition to finfish, certain aquaculture practices use other
aquatic animals that are collected on a small scale and fed to
cultured stocks. Among these are various molluscs (also see Phan,
2007). However, the use of non-finfish aquatic organisms as feeds
in aquaculture is relatively uncommon and may be specific to
certain regions and culture practices. In Viet Nam, a variety of
aquatic food sources including trash fish/low-value fish, molluscs,
etc., is used in lobster fattening, and the feed material is often
processed prior to feeding.Photos: Cockles used in lobster fattening in central Viet Nam