Ž further processed using AEQUITAS Image Analysis software Dynamic Data Links,
. Ž
Cambridge, England for individual shell height measurement perpendicular to the .
hinge . This method was chosen in order to ensure the minimum of spat handling, since previous studies have indicated that P. maximus may be sensitive in this respect
Ž .
Ž .
Millican, 1997 . At this stage, the new initial biomass was calculated as above and the ration fed was adjusted, as required. Each experiment was continued for 3–4 weeks.
For each week of each experiment, at each temperature and ration treatment, the Ž
y1
. mean growth rate mm day
was calculated from the measurements on the 8–16 individual scallops in duplicate containers. The data set for temperatures in the range
Ž .
6.58C–23.08C 121 combinations of temperature and ration, Table 1 was processed by Ž
. the G3GRID and GCONTOUR procedures
SAS Institute, Cary, NC, USA . The G3GRID procedure interpolates data sets of irregularly spaced observations to complete
a rectangular grid that is displayed by GCONTOUR, in this case to show growth rates over the full range of temperatures and rations tested. The results for 5.08C were not
included, as there was no growth at this temperature.
Samples of five to six scallops were taken initially and from each of the beakers at Ž
. the end of the experiments. Dry and organic ash-free dry weight estimations were
made on individual spat. For these estimations, spat were washed three to four times in fresh water and transferred to porcelain crucibles previously dried in a heated cabinet at
608C for 4 h and weighed, to the nearest 1 mg, on an automatic electrobalance. The crucibles containing the individual spat were returned to the drying cabinet for 48 h at
608C and then re-weighed to give the total dry weight. The dried spat were then combusted at 4508C for 24 h in a muffle furnace and then re-weighed. Organic weight
Ž
. weight loss on combustion was determined as a percentage of the total dry weight.
Further spat from each beaker were taken and the meats and shells were separated. The Ž
. percentage organic weight of each component was then determined, as described
above. These values were used to calculate, by simultaneous equations, the dry meat and dry shell weights of the spat in the other samples, from the total dry weight and total
organic weight values obtained. Condition index of the scallops was then calculated, as Ž
. the ratio of dry meat weight to dry shell weight Beninger and Lucas, 1984 . For
Ž .
comparison of condition index, an analysis of variance GLM procedure, SAS Institute was carried out on mean values from each beaker. Where a significant difference in
condition was found, individual temperature and ration treatments were compared by least significant difference between means.
3. Results
Ž .
Recorded temperatures were similar to the nominal values, means s.d. were 4.7 0.18C, 6.6 0.18C, 8.0 0.48C, 10.3 0.48C, 14.8 0.58C, 17.2 0.28C, 20.2
1.08C and 22.9 0.28C. At 178C, the full range of rations was used in each of the 3 experiments, and there was no significant difference for the mean ration between
Ž .
experiments F
s 0.846, P s 0.44 . There was also no significant difference be-
2, 27
Ž tween mean growth rate of scallops at this temperature in the three experiments F
2,
. s 0.186, P s 0.90 .
27
Ž
y1
. Fig. 1 shows mean growth rates mm day
of king scallop spat within the range of temperatures and rations investigated. There was no growth at 4.78C. Growth was
limited primarily by temperature at 6.58C and by ration at 22.98C. The relative influence that each of these factors had on growth rate gradually exchanged through the intermedi-
ate temperatures. At each temperature, an increase in ration initially gave an increase in growth, until a point was reached at which higher rations gave either the same growth
rate or, at temperatures above 168C–178C, slightly lower growth rates.
The proportion of the fed ration that was consumed by the scallop spat is given in Table 2. There was no measurable uptake of food at 4.78C. At each of the other
temperatures, as the ration was increased, a smaller proportion of it was consumed. The level at which the proportion consumed fell below about 80 of that fed corresponds
approximately to the point at which a further increase in ration did not give any
Ž .
additional increase in growth rate, at that temperature Fig. 1 . This level of ration Ž
y1 y1
. increased with temperature. The highest amount of food consumed g g
week , at
each temperature is also given in Table 2, together with the corresponding ration fed. Ž
The highest amount of food consumed increased almost fivefold from 6.68C 0.016 g
y1 y1
. Ž
y1 y1
. g
week to 8.08C 0.079 g g
week , then more gradually, and linearly with
Ž temperature, from 8.0 to 17.28C
highest amount of food consumed s 0.0065 =
2
. temperature q 0.0227, R s 0.9745, P s 0.012 for 3 df . Within this range the highest
amount of food consumed at each temperature was close to the fed ration which gave
Ž
y1
. Ž
. Fig. 1. Growth rates increase in shell height, mm day
of king scallop spat at a range of temperatures 8C Ž Ž
.
y1
Ž .
y1
. and rations g organic weight of algae g
live weight of spat week .
Table 2 Mean percentage of the fed ration consumed by king scallop spat held at various temperatures and given
Ž .
y1
Ž .
y1
rations of 0.012–0.492 g organic weight of algae g live weight of spat week
Ž
y1 y1
The asterisk in each temperature column indicates the range of the fed ration in 0.05 g g week
. Ž
. increments in which the greatest amount of food was consumed cleared from suspension . The observed
highest amount of food consumed at each temperature is shown in the bottom row of the table.
y1 y1
Ž .
Ž .
Ration range: g g week
Temperature 8C 6.6
8.0 10.3
14.8 17.2
20.2 22.9
Fed
U
0–0.05 75.42
83.72 93.01
92.80 99.96
– –
U U
0.05–0.10 –
81.94 87.34
79.78 84.19
– –
0.10–0.15 –
69.98 52.23
74.78 78.94
87.65 94.58
U U
0.15–0.20 –
– 24.41
54.31 59.02
83.88 89.87
0.20–0.25 –
– –
– 48.00
81.58 –
0.25–0.30 –
– –
– –
– 88.10
U U
0.45–0.50 –
– –
– –
69.13 76.09
U
Highest amount of food 0.016
0.079 0.084
0.122 0.135
0.320 0.376
y1 y1
Ž .
consumed g g week
Ž .
Ž maximum growth Fig. 1 . The highest amounts of food consumed at 20.28C 0.320 g
y1 y1
. Ž
y1 y1
. g
week and 22.98C 0.376 g g
week were much greater than at the other
temperatures, and were also greater than the ration required for maximum growth. Ž
. Condition index ratio of dry meat weight to dry shell weight is given in Table 3.
With a ‘full’ ration, i.e., one that gave maximum growth, condition of the animals was significantly greater between 10.38C–17.28C than at the other temperatures tested
Ž .
outside this range F s 34.05, P - 0.0001 . Within this temperature range, it was
7, 39
Ž .
not significantly different from the initial value of 163.0 12.9 F s 0.32, P s 0.81 .
3, 20
Condition index was significantly lower at 88C than at 17.28C or 14.88C and was also significantly lower at 4.78C and 6.68C than at all other temperatures tested. ‘Low’
rations, i.e., ones that gave less than maximum growth, gave significantly lower
Table 3 Ž
. Mean condition index ratio of dry meat weight to dry shell weight of king scallop spat held at various
Ž .
Ž temperatures and fed a ‘full’ ration one that gave maximum growth , a ‘low’ ration one that gave less than
. maximum growth , or ‘unfed’ cultured algae. Initial condition index was 163.012.9
Ž .
Temperature 8C 4.7
6.6 8.0
10.3 14.8
17.2 20.2
22.9 Ration
Full 85.7
96.6 150.7
165.9 168.8
171.4 145.4
136.8 Low
– –
– 101.0
110.7 145.4
100.5 94.1
Unfed –
78.1 –
– –
67.0 –
77.7 ANOVA
Value of F –
2.44 –
128.13 97.06
175.11 52.76
55.54 Degrees of freedom
– 1, 5
– 1, 10
1, 10 2, 11
1, 10 2, 11
Probability –
0.18 –
- 0.0001
- 0.0001
- 0.0001
- 0.0001
- 0.0001
condition indices at all temperatures. When no food was added, condition indices were significantly lower than with ‘low’ rations at 22.98C and 17.28C and lower, but not
significantly so, than the ‘full’ ration at 6.68C. Condition index of unfed spat was not Ž
. significantly different at these three temperatures F
s 2.78, P s 0.208 .
2, 3
4. Discussion
