J .M. Navarro et al. J. Exp. Mar. Biol. Ecol. 247 2000 67 –83
71
2.2.4. Ammonia excretion Ammonia excretion was determined by the phenol–hypochlorite method of Solorzano
1969. Scallops were well fed and then placed individually in glass beakers containing 0.5 l of filtered 0.45 mm seawater. One additional beaker containing filtered seawater,
but with no animals, served as a control. Following an incubation period of 2 h, samples from the water containing the scallops and from the control were analysed. Values for
21
excretion rate were expressed in mg NH –N h and transformed to Joules using the
4
conversion factor: 1 mg NH –N524.8 J Elliott and Davison, 1975.
4
2.2.5. Scope for growth This physiological index represents the energy available for growth and reproduction
after all metabolic demands have been met from the absorbed ration. Scope for growth was calculated by the equation given by Widdows 1985, after converting all the
21
physiological rates to energy equivalents J h .
2.2.6. Gonad maturation Individual scallops from each conditioning tank were sampled every 6–8 days to
analyse gonad development and to induce spawning at the end of the conditioning experiment. A visual criterion was used to define ripe scallops, characterised by turgid
and highly pigmented gonads. In the present study we consider only gonadal develop- ment and the spawning capacity of scallops conditioned at the different temperatures and
diets. Biochemical analyses of the gonad will be described elsewhere.
2.3. Statistical analysis Physiological rates were related to dry meat weight by linear regression analysis, after
log-transformation of all variables. Analysis of variance followed by a Tukey test of significance was carried out to compare the total weight and organic content of the
different diets and also the effects of the temperature diet treatments on each physiological variable. In all statistical tests differences are considered significant when
P ,0.05. All analyses were carried out with the statistical package Statistica for Windows, v. 4.2.
3. Results
3.1. Diets
6
The three experimental diets were supplied at a concentration of 30310 particles
21
l . The diet composed of a mixture of microalgae 50 Isochrysis galbana 150
21
Chaetoceros gracilis corresponded to a total dry weight of 0.98 mg l , with an organic
21
content of 0.88 mg l 89.8. The diet composed of 70 of the mixture of microalgae
21
plus 30 of lipids represented a total dry weight of 1.89 mg l , with an organic content
21
of 1.46 mg l 77.2. The diet containing a mixture of 70 microalgae plus 30
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.M. Navarro et al. J. Exp. Mar. Biol. Ecol. 247 2000 67 –83
Fig. 1. Total, organic and inorganic content of the experimental diets. Values are means6S.E.
21
carbohydrates represented a total dry weight of 2.13 mg l , with an organic content of
21
1.87 mg l 87.7 Fig. 1. The energetic content of these diets was calculated
according to Whyte 1987 and to our own calculation based on the conversion factors
21 21
for lipid 39.5 J mg and carbohydrate 17.5 J mg
given by Gnaiger 1983. The results of energy content for the different diets are presented in Table 1.
3.2. Clearance and ingestion rates Mean values of clearance rates as well as means of the other physiological variables
from each treatment were compared by analysis of variance followed by a Tukey test of significance. Argopecten purpuratus fed with the diet microalgae1lipid showed a
significantly higher clearance rate. No significant differences P .0.05 were found between the groups treated at the two experimental temperatures Fig. 2. Scallops of
21
standard size 3 g dry tissue wt showed clearance rates as high as 16 l h when fed
with this diet. Significantly P ,0.05 lower values were observed for animals fed with
21
microalgae alone, with clearance rates around 4.5 l h at both experimental tempera-
tures Fig. 2. There were no significant differences P .0.05 between clearance rates measured at 16 and 208C, when microalgae were used as food. The lowest clearance rate
Table 1
6 21
Organic and energetic content of the experimental diets at a concentration of 30310 particles l Total
Organic Inorganic
Energy
21 21
21 21
mg l mg l
mg l J l
Microalgae 0.98
0.88 0.10
13.73 Micr.1Lip.
1.89 1.46
0.43 33.68
Micr.1CHO 2.13
1.87 0.26
30.80
J .M. Navarro et al. J. Exp. Mar. Biol. Ecol. 247 2000 67 –83
73
Fig. 2. Argopecten purpuratus. Clearance rate at different temperatures and diets. Values are means6S.E.
values were observed at the combination 168C and microalgae1carbohydrate. However, feeding rate increased significantly when the scallops were exposed to the same diet but
at 208C P ,0.05. There were no significant differences P .0.05 in clearance rate when various treatments involving microalgae and microalgae1carbohydrates were
compared Table 2.
Ingestion rate followed a similar trend to that described for clearance rate, the highest values being recorded for scallops fed the microalgae1lipids diet Fig. 3a. Total
21
ingestion rate for a scallop of 3 g dry tissue weight was as high as 30 mg h . The
lowest values were observed with the diet of microalgae, but slightly higher values were recorded when microalgae1carbohydrates was supplied. The organic ingestion rate
represented a large fraction of the total ingestion rate. The highest values were observed
21
for scallops fed with the diet microalgae1lipids, with values as high as 25 mg h and
not significantly different P .0.05 to the condition microalgae1carbohydrates at 208C. The lowest organic ingestion rate was observed with the diet composed of a mixture of
21
microalgae, with values near 3.2 mg h Fig. 3b.
3.3. Absorption efficiency Absorption efficiency ranged from 27 to 85 in scallops of 3 g dry tissue weight
within the range of temperatures and diets tested Fig. 4a. There was not significant differences P .0.05 between values for the 168C microalgae group and those for the
208C microalgae treatment or the microalgae lipid treatment at 16 or 208C Table 2, Fig. 4a. The lowest values of absorption efficiency in conditioned A
. purpuratus were observed for the combination microalgae1carbohydrate and 168C. Absorption efficiency
increased considerably when scallops were exposed at 208C and fed with the same diet Fig. 4a. Absorbed ration was significantly higher with the diet microalgae1lipids, the
74 J
.M. Navarro et al. J. Exp. Mar. Biol. Ecol. 247 2000 67 –83 Table 2
Argopecten purpuratus: comparison of mean values for physiological variables at different combinations of
a
diet and temperature Physiological process
Treatments M1L 168C
M1C 168C M 208C
M1L 208C M1C 208C
Clearance rate M 168C
0.0008 0.951
1.000 0.0002
0.067 M1L 168C
0.0003 0.0009
0.578 0.251
M1C 168C 0.935
0.0002 0.0198
M 208C 0.0002
0.073 M1L 208C
0.0249 Absorption efficiency
M 168C 0.9293
0.0202 0.6016
0.2693 0.0632
M1L 168C 0.0385
0.9697 0.6565
0.1737 M1C 168C
0.0667 0.1251
0.3477 M 208C
0.9560 0.3871
M1L 208C 0.7735
Oxygen uptake M 168C
1.0000 0.9999
0.9999 0.9988
0.9991 M1L 168C
1.0000 1.0000
0.9957 0.9966
M1C 168C 1.0000
0.9911 0.9926
M 208C 0.9878
0.9898 M1L 208C
1.0000 Excretion rate
M 168C 1.0000
0.9213 0.9270
0.7936 0.6447
M1L 168C 0.8606
0.8685 0.8693
0.5499 M1C 168C
1.0000 0.2904
0.9904 M 208C
0.2980 0.9889
M1L 208C 0.1213
Scope for growth M 168C
0.0154 0.9991
1.0000 0.0141
0.5534 M1L 168C
0.0494 0.0131
1.0000 0.0914
M1C 168C 0.9999
0.0461 0.6411
M 208C 0.012
0.4704 M1L 208C
0.0825
a
Probability values are derived from an a posteriori multiple range test Tukey’s honestly significant difference following ANOVA. Significant differences at P ,0.05 M, microalgae; M1L, microalgae1lipid;
M1C, microalgae1carbohydrate.
values being very similar at 16 and 208C Fig. 4b. The amount of food material absorbed was greatly reduced for animals fed solely with microalgae, representing only
16 of the amount absorbed from the food containing lipids at the two experimental temperatures. The lowest values for absorbed ration were observed for the diet
containing carbohydrates at 168C, where the food material absorbed represented less than 7 compared with the food absorbed with the diet microalgae1lipids. However,
absorbed ration increased significantly when scallops were exposed to this same carbohydrate diet at 208C Fig. 4b.
3.4. Oxygen uptake Oxygen uptake for scallops of standard size 3 g dry tissue wt showed values around
21
1.5 ml h and there were not significant differences P .0.05 between treatments of
diet and temperature Fig. 5a, Table 2.
J .M. Navarro et al. J. Exp. Mar. Biol. Ecol. 247 2000 67 –83
75
Fig. 3. Argopecten purpuratus. Total ingestion rate a and organic ingestion rate b at three different diets and two temperatures. Values are means6S.E.
3.5. Ammonia excretion There were no significant differences P .0.05 between treatments Table 2.
However, the excretion rate for scallops of 3 g dry tissue weight was higher at the combination 208C microalgae1lipids and lower when the scallops were fed with
microalgae1carbohydrates Fig. 5b.
3.6. Scope for growth This physiological index was significantly higher when scallops were fed with the diet
microalgae1lipids, at both experimental temperatures Fig. 6. At 168C the scope for
21
growth reached a mean value of 337657.4 J h , which was not significant different
21
P .0.05 from the value of 343637.4 J h obtained with the same diet at 208C Table
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.M. Navarro et al. J. Exp. Mar. Biol. Ecol. 247 2000 67 –83
Fig. 4. Argopecten purpuratus. Absorption efficiency a and absorption rate b at three different diets and two temperatures. Values are means6S.E.
2, Fig. 6. When microalgae were used as diet, scope for growth was much lower, with
21 21
values of 15.563.8 J h at 168C and 4.668.4 J h
at 208C. These values represented only 1.5–4.5 of the energy gain in the diet containing lipids. A negative scope for
21
growth 214.2 J h was observed at 168C when the scallops were fed with the diet
containing carbohydrates, although at 208C and the same diet, scope for growth
21
increased to 124616.6 J h .
3.7. Gonad maturation After 72 days under the different regimes of diets and temperatures, the highest
J .M. Navarro et al. J. Exp. Mar. Biol. Ecol. 247 2000 67 –83
77
Fig. 5. Argopecten purpuratus. Oxygen uptake a and ammonia excretion b at three different diets and two temperatures. Values are means6S.E.
percentage of scallops that appeared to be ripe was observed in the group fed with a mixture of microalgae1lipids. At 168C, 68.4 of the scallops fed with this diet looked
ripe, while only 27 of the scallops fed with the diet of microalgae and 30.8 of those fed with the diet containing carbohydrates looked ripe Table3. A similar situation was
observed at 208C, where 42.1 of the scallops fed with lipids looked ripe and the lowest percentage 15.4 of ripe individuals was observed in scallops fed with a mixture of
microalgae1carbohydrates Table 3. When the animals that looked ripe were induced to spawn, the greatest success was obtained with scallops conditioned with the diet
microalgae1lipids and the least with the scallops fed with the diet containing carbohydrates Table 3.
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.M. Navarro et al. J. Exp. Mar. Biol. Ecol. 247 2000 67 –83
Fig. 6. Argopecten purpuratus. Scope for growth estimated at three different diets and two temperatures. Values are means6S.E.
4. Discussion
