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Table 4.3.6 The length of culture period (Days), number per cubic meter (N/m 3 ), initial weight
(IW), final weight (FW), initial stocking density (ISDkg/m 3 ), final stocking density (FSDkg/m 3 ),
stock retention (%SR) and daily percentage growth (G%/day) for silver perch (Bidyanus
bidyanus) from the 02/03/01 up to 27/09/01 in 7 and 14m 3 raceways
R’way Start Finish Days N/m 3 IW FW ISD FSD %SR G%/day
(g) (g) (kg/m 3 ) (kg/m 3 )
SR1 03/05/01 18/07/01 76 826 3.2 3.3 2.6 2.8 99.8 0.1
SR2 04/07/01 18/07/01 14 1608 7.6 10.5 12.1 16.4 98.2 2.8
On the 02/08/01 all caged fish from C8 were transferred to SR1 to give a new stocking density of
19.1 kg/m 3 or 3,709 fish/m 3 (Table 4.3.7). The second of the small raceways (SR2) was graded on the
02/08/01 to reduce the numbers of fish to 5,543 and give an average weight of 20.4 g at a density of
16.0 kg/m 3 . A third 14 m 3 raceway (MR1) was also stocked on the 02/08/01 with 129.6 g fish at a rate
of 255 fish/m 3 or 33.1 kg/m 3 . Fifty six (SR1 and SR2) and 28 days later (MR1) the average weights of
fish in all raceways had increased only marginally to 6.0, 22.2 and 142.1 g respectively. This equates
to a daily growth rate of 0.3, 0.2 and 0.3 per cent. Mortality in the three units was minimal and stock
retention was equivalent to 99.2, 99.1 and 97.6 per cent of fish stocked.
On the 07/11/01 three 7 m 3 and three 14 m 3 raceways were re-stocked (Table 4.3.8). The three 7 m 3
raceways were stocked at rates of 1,393 (SR1), 1,453 (SR2) and 977 (SR3) fish/m 3 with fish weighing
15.9, 5.9 and 10.4 g respectively. These raceways were operated for 83 days before being harvested.
At harvest, the average weights had increased to 35.3, 25.3 and 22.5 g respectively. The rates of
growth in these three raceways were 1.5, 3.9 and 1.4 per cent per day. Survival was high in all
raceways with the lowest being 92.9 per cent (SR1). The FCRs in these three 7 m 3 raceways were
1:1.8, 1:1.5 and 1:4.1 respectively. The three 14 m 3 raceways were stocked with 69.7 (MR1), 31.1
(MR2) and 198.3 g (MR3) fish. The respective numbers stocked were equal to 358, 1,063 and 332/m 3 .
Survival was again high with 100, 92 and 100 per cent of stock retained at harvest. However, growth
in raceways over this period was variable with average weights in MR1 and MR2 increasing to 98.5
and 77 g while the average weight of fish in MR3 decreased to 189 g. The raceway with the highest
rate of growth of 1.8 per cent per day (MR2) also returned an FCR of 1:1.6. In comparison the other
14 m 3 raceway with 0.5 per cent per day growth (MR1), had an FCR of 1:6.9. In the raceway with no
apparent growth 453 kg of feed was used for a net loss of biomass. This inconsistent FCR values for
raceways during the period from 07/11/01 to 29/01/02 indicates significant operator over feeding in
some instances. This may have been the result of poor feeding response and/or overfeeding by the
operator in some raceways.
On the 05/02/02 all raceways were graded and re-stocked with various size classes of fish
(Table 4.3.9). A number of new TAMCO raceways were also added. In the only remaining 7 m 3
raceway (SR3), 64.5 g fish were stocked at a rate of 165/m 3 giving a density of 10.6 kg/m 3 . At the
same time similar sized fish averaging 68 g, were stocked into a larger 14 m 3 raceway (MR2) at a rate
of 393/m 3 or 26.7 kg/m 3 . The 7m 3 raceway was harvested after 91 days on the 07/05/02 when fish
weight averaged 132.8 g. This represents a growth rate of 1.3 per cent per day. Stock retention was
high with only 14 mortalities observed and 979 fish harvested. The final operating density was
18.6 kg/m 3 . The 14 m 3 raceway was harvested after 91 days with stock averaging 135.2 g. The final
operating density in this raceway was 53.0kg/m 3 . Survival was again high with only 19 observed
mortalities and 4,502 fish harvested. Growth in the 14 m 3 raceways did not appear to be detrimentally
affected by an increase in density. Similar results were observed for 137 g and 140 g fish stocked at 76
and 168fish/m 3 in identical 1m 3 raceways (MR4 and MR6). In this case, both raceways were stocked
and harvested at the same time (after 91 days). Fish from the lower density raceway (MR4) averaged
216.5 g and fish in the higher density raceway (MR6) averaged 232.2 g at harvest. Stock retention and
therefore survival was unaffected by density with 95.0 and 99.8 per cent of stock being harvested from
the low and high density raceways respectively.
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