Fish as feed inputs for aquaculture: practices, sustainability and implications

106 Fish as feed inputs for aquaculture – Practices, sustainability and implications

Philippines, China and Viet Nam, and to a lesser extent India and Sri Lanka. The crabs

demand a relatively high market price and are almost always sold live even at the end

point, the consumer.

The production of softshelled crabs for the up-market restaurant trade is a relatively

recent development that enables under-sized crabs to be sold (Figure 17). Wild-caught

crablets are farmed in intensive operations in which no more than two crablets are held

together and all are checked every other day for molting. This is a relatively labour-

intensive farming process, but the economic value of softshelled crabs more than

compensates for the increased labour costs. On average, a crablet goes through over

eight molts during fattening for the market, whereas a softshelled crab is ready for the

market after two molts. Based on the prevailing market price and demand, farms that

have the required infrastructure may switch from fattening crabs to a weight of 400 g

to producing softshelled crabs weighing up to 150 g.

In all the countries, the number of operations producing softshelled crab is

relatively small. For example, in

Myanmar there are only two crab

fattening farms. In India, crab

farming commenced primarily as

a means of reviving the livelihoods

of 2004, tsunami-affected fishing

communities (M. Sakthivel,

Aquaculture Foundation of India,

personal communication, 2005). A

major factor that has encouraged

the rapid growth of crab farming

along the southeastern coast

of India is the ready availability

of trash fish/low-value fish at a

relatively low price of IDR10 to

12/kg (US$1 = IDR48) during

the grow-out period of the crabs

(during the northeast monsoon of

November to February). Hardshell

crabs take eight months to reach a

market size of approximately 1 kg or more (price of IDR400/kg), whereas the turnover

period for softshell crabs (price of IDR325/kg) is only 25 days. In both cases, the

average conversion efficiency is 6.

In Thailand, softshell crab farms maintain an average of 50 000 individual rearing

boxes. Crablets, wild-caught locally, are purchased at approximately THB85 to 90/kg

(10 to 15 individuals per kg) (US$1=THB38) and are kept for 45 to 90 days until

molting. The molting size ranges from 70 to 175 g, and the farmgate price varies

according to the size. For example, 70 to 100 g crabs are sold at THB180/kg, as

opposed to crabs exceeding 175 g, which bring THB240/kg. Crabs are fed once every

other day with trash fish, and approximately 60 to 70 kg of feed per 10 000 boxes are

used at any one feeding.

FIGURE 18

Changes in cultured mangrove crab production over the years

and estimates of trash fish/low-value fish required as feed at

conversion efficiencies of 4 and 6

Source: Production data is based on FAO (2006a)

7 5 10 6 11 11 9

14

(^113117)
0
20
40
60
80
100
120
0
100
200
300
400
500
600
700
800
1995 1996 1997 1998 1999 2000 2001 2002 2003 2004
Feed inputs (thousand tonnes) Production (thousand tonnes)
Years
Feed 4:1 Feed 6:1 Actual production
TABLE 17
Comparison of the production of softshelled crab in Thailand using trash fish and formulated
feed
Feed type % molting % survival Feed/crab (kg) Cost/molted crab (THB)
Trash fish 51.7 52.3 0.292 19.8
Formulated feed 60.7 61.0 0.042 15.6
Softshell crab production trials based on four-month average.
Source: Modified from Wilson (2005)