NOTE Sekiguchi and Best: In vitro digestibility of some prey species of dolphin 
387 
5 red squids (Todaropsis eblanae, Ommastrephidae); 
and 6) 5 pelagic gobies (Sufflogobius bibarbatus, 
Gobiidae) and 5 lanternfishes. These taxa are com- 
monly found in stomachs of dolphins (including com- 
mon dolphins, Delphinus delphis, dusky dolphins, 
Lagenorhynchus obscurus, and Heaviside’s dolphins, 
Cephalorhynchus heavisidii ) along the west coast of 
southern Africa (Sekiguchi et al., 1992). Table 1 shows 
the sizes of sample species used: all were collected in 
trawls by the RV Africana, November 1987 or Janu- 
ary 1988, and frozen at -20°C. 
For the first experiment, the procedure followed 
that of Jackson et al. (1987). Four liters of a diges- 
tion solution of 0.15% HC1, 0.05% Na 9 C0 3 (buffer) 
and 1.0% pepsin (pepsin A powder, BDH Chemicals 
Ltd.) were adjusted to an initial pH of 2.30, near the 
midpoint of the range of that recorded for cetacean 
stomachs (pH=1.4 to 3.0, Ishihara, 1960; pH=1.8 to 
3.0, Smith, 1972; pH=1.5 to 3.5, Jobling and Breiby, 
1986 ). A Beckman expanded scale pH meter was used 
to monitor pH. The solution was then divided into 
240-mL portions in each of seven 600-mL beakers, 
and 1,150 mL portions in each of two 5-L beakers. 
The beakers were placed in two water baths con- 
tinuously agitated (rocked) 20-30 times per minute 
at 38°C. Each fish was put in a small fiber glass bag 
(mesh size 0.5 x 0.5 mm) and then suspended in the 
solution. Four samples were placed in each of the 5- 
L beakers and a single sample in each of the 600-mL 
beakers. The pH for each beaker was maintained 
between 1.90 and 3.37; pH increased with time and 
was adjusted by adding HC1. 
Owing to the effort required to maintain pH in in- 
dividual beakers, one large PVC container (40 x 28 x 
20 cm) made specifically to fit in the water bath was 
used in subsequent experiments. Ten liters of diges- 
tion solution, consisting of 0.50-0.56%- HC1, 0.27- 
0.29% Na 2 C0 3 , and 1.0% pepsin, were maintained 
at 36.0 to 39.i°C in the PVC container. A Beckman 
expanded-scale pH meter was placed in the corner 
of the container to monitor pH constantly. The pH 
was maintained between 2.25 and 2.51 by occasional 
Table 1 
The species used in the artificial digestion experiments; their total length (TL, cm) or dorsal mantle length (DML, cm) and 
corresponding weight (WT, g). (L=large size and S=small size groups.) 
Sample species 
Length (cm 
) and weight (g) 
Cape anchovy (L) 
TL 
13.6 
12.7 
12.7 
12.8 
11.7 
WT 
19.48 
17.28 
21.25 
18.09 
16.45 
Cape anchovy (S) 
TL 
9.9 
9.6 
9.6 
9.4 
9.6 
WT 
8.25 
8.05 
8.01 
7.81 
7.56 
Round herring (L) 
TL 
19.5 
18.7 
19.5 
21.0 
19.8 
WT 
68.95 
63.49 
79.03 
96.27 
79.47 
Round herring (S) 
TL 
14.4 
14.8 
14.8 
14.8 
15.2 
WT 
28.28 
33.47 
34.88 
36.77 
34.69 
Pilchard (L) 
TL 
20.8 
20.0 
20.8 
20.0 
20.3 
WT 
108.70 
104.55 
105.27 
103.11 
103.72 
Pilchard (S) 
TL 
13.7 
13.0 
14.0 
14.1 
13.5 
WT 
31.0 
27.88 
30.59 
30.89 
30.65 
Hake 
TL 
17.0 
17.4 
17.3 
17.5 
16.5 
WT 
46.1 
51.2 
48.4 
52.2 
41.5 
Maasbanker 
TL 
18.8 
19.4 
18.9 
19.1 
16.5 
WT 
79.5 
83.3 
80.2 
80.4 
53.6 
Goby 
TL 
8.7 
7.8 
8.2 
8.5 
8.6 
WT 
10.2 
7.1 
8.6 
8.9 
10.0 
Lanternfish 
TL 
5.3 
5.1 
3.5 
3.9 
4.5 
4.4 
4.4 
4.2 
4.1 
4.6 
WT 
1.85 
1.64 
0.61 
0.93 
1.16 
1.1 
1.1 
0.8 
1.0 
1.0 
Chokka squid 
DML 
16.0 
18.5 
16.5 
15.8 
15.8 
WT 
118.3 
152.9 
120.7 
104.4 
98.8 
Red squid 
DML 
10.4 
9.6 
10.7 
9.9 
9.2 
WT 
60.6 
55.8 
61.2 
49.1 
40.8 
