that were significantly different were analyzed further by a Fisher multiple-comparison test. An a level of 0.05 was established a priori for all statistical tests.
3. Results
Significant differences in specific and tissue activities of all four digestive enzymes were found among the yolk-sac stages with a general pattern of increase from 161 to
Ž .
276 dd Table 1 . Trypsin activities reached their highest values at 230 dd, whereas those of lipase and alkaline phosphatase peaked at 276 dd. Amylase activities were
detected only in the 230 and 276 dd stages, at statistically indistinguishable levels. When expressed in mUrmg protein, the activities of lipase and alkaline phosphatase decreased
significantly from the 161- to the 179-dd stage, paralleling an increase in soluble protein content. Based on percentage comparisons, specific activities of trypsin and amylase in
whole 276-dd larvae were only 12 and 2, respectively, of those measured in the digestive systems of metamorphic larvae, whereas specific activities of lipase and
alkaline phosphatase in 276-dd larvae were more than 50 of those determined for metamorphic larvae.
Mean specific activities of the digestive enzymes in Artemia nauplii are given in Ž
. Table 2. At least 200 nauplii range 200–300 were found in the digestive system of
Table 1 Activities of digestive enzymes and content of soluble proteins in whole larvae at four yolk-sac stages
Ž .
Ž .
U
161–276 dd and in the whole digestive system of metamorphic larvae 660 dd of Atlantic halibut Ž
. EnzymerProtein
Larvae dd Yolk-sac
Metamorphic 161
179 230
276 660
Specific actiÕities mUr mg protein
a b
d c
Trypsin 3.40.1
9.30.8 16.70.7
11.60.5 98.618.6
a a
b b
Amylase 0.00.0
0.00.0 27.06.2
32.96.1 1633.6401.0
c a
b d
Lipase 15.70.9
9.50.4 13.40.5
22.60.7 37.32.8
b a
b c
Alkaline phosphatase 34.22.1
21.91.1 38.51.1
61.23.4 111.97.2
Tissue actiÕities mUr mg tissue
a c
d b
Trypsin 0.10.0
0.30.0 0.40.0
0.20.0 4.41.8
a a
b b
Amylase 0.00.0
0.00.0 0.50.1
0.60.1 74.120.2
a a
a b
Lipase 0.30.0
0.30.0 0.30.0
0.40.0 1.70.2
a a
b c
Alkaline phosphatase 0.60.1
0.60.1 0.80.0
1.00.0 5.00.5
Soluble protein contents m g r mg tissue
a c
b a
16.81.2 27.11.1
21.21.0 17.21.0
44.92.8
U
Ž Means1 SE ns 5 pooled samples of 10 yolk-sac larvae or ns 5 digestive systems of metamorphic
. Ž
larvae were compared among yolk-sac stages only. Specific activities, F s85.3, trypsin; 20.5, amylase; 75.8, lipase; 58.2, alkaline phosphatase. Tissue activities, F s82.2, trypsin; 11.4, amylase; 32.7, lipase; 29.0,
alkaline phosphatase. Soluble protein contents, F s 24.1. P - 0.001 and df s19 in all cases, except, df s17 .
for amylase . Location and number of significantly different means are designated by different superscript Ž
. letters Fisher test .
Table 2 Ž
. Specific activities mUrmg protein of digestive enzymes measured in Artemia prey and their percentage
contribution to the total specific activity of these enzymes calculated for the whole digestive system of metamorphic larvae of Atlantic halibut containing 200 Artemia nauplii per larva.
a
See Section 2.2 for additional details
Enzyme Activity in
Calculated activity Contribution of
Artemia Artemia enzymes
200 Artemia Digestive system
Trypsin 52.66.7
4.2 50.3
8.4 Amylase
5,44930 435.9
833.1 52.3
Lipase 6.30.7
0.5 19.0
2.6 Alkaline phosphatase
68.89.2 5.5
57.1 9.6
a
Ž Means1 SE
ns 3 pooled samples of ca. 14,000 Artemia nauplii or ns 3 digestive systems of .
metamorphic larvae .
metamorphic larvae. The percentage contribution of 200 such nauplii to total enzymatic activity in the digestive system of these larvae was less than 10 for all enzymes except
amylase for which the contribution was estimated to be more than 50.
4. Discussion
