168 
PACIFIC SCIENCE, Vol. XVIII, April 1964 
TABLE 1 
Location and Amounts of Bobo Taken for Use as Tuna Bait, by Date of Capture 
DATE 
LOCATION 
SCOOPS 
OF BAIT 
REMARKS 
29 Mar. 1953 
12° 30' N 88° 47' W 
60 
187 specimens 46-67 mm 
returned, identified as 
P. opercularis 
30 Nov. 1953 
40—50' SW Cape Corrientes, Mexico 
700 
1 Apr. 1955 
12° 05' N 88° 23' W 
200 
5 Mar. 1956 
12° 17' N 90° 33' W 
100 . 
27 Aug. 1956 
30—40' WSW Cape Corrientes, Mexico 
150 
2 Feb. 1957 
60-70' SW San Benito, Mexico 
amount not 
logged 
19 specimens 58—72 mm returned, 
identified as P. opercularis 
2 Feb. 1957 
13°32'N 92° 54' W 
60 
2 Feb. 1957 
13° 58' N 93° 53' W 
85 
2 Feb. 1957 
13° 13' N 92° 29' W 
300 
2 Feb. 1957 
13° 43' N 93° 10' W 
100 
3 Feb. 1957 
13° 17' N 92° 26' W 
410 
4 Feb. 1957 
SW San Jose, Guatemala 
250 
2 Mar. 1957 
12° 02' N 89° 08' W 
100 
4 Mar. 1957 
22° 09' N 106° 30' W 
30 
5 Mar. 1957 
22° 09' N 106° 30' W 
48 
5 Mar. 1957 
22° 09' N 106° 30' W 
115 
9 Mar. 1957 
22° 30' N 106° 07' W 
250 
with "crowder” 
9 Mar. 1957 
22° 09' N 106° 30' W 
100 
10 Mar. 1957 
22° 09' N 106° 30' W 
175 
11 Mar. 1957 
22° 09' N 106° 30' W 
50 
11 Mar. 1957 
22° 09' N 106° 30' W 
65 
3 Apr. 1957 
12° 30' N 91° 07' W 
100 
3 Apr. 1957 
13° 05' N 91° 48' W 
100 
Commission personnel sampled 
103 specimens 63-89 mm, 
P. opercularis 
4 Apr. 1957 
off Acajutla, El Salvador 
some bait 
bobo 
9 Apr. 1957 
17° 38' N 104° 47' W 
90 
20 Apr. 1957 
17° 29' N 104° 23' W 
130 
As may be seen from Figure 1 and Table 
1, the catches have been centered around Cape 
Corrientes, Mexico, in the north and off Guate- 
mala and El Salvador in the south. Approxi- 
mately equal amounts have been taken from 
each locality. The only species identified has 
been P. opercularis from three samples taken off 
Guatemala — El Salvador. We have, therefore, 
definite proof of only one species that schools 
in large aggregations offshore. We believe, how- 
ever, that P. approximans also schools in large 
aggregations as its occurrence offshore is well 
documented (Table 2) and threadfin in other 
localities, i.e., the Gulf of Mexico, are known 
to school offshore (Bullis, 1961). 
Although the bobo is used occasionally for 
bait by tuna fishermen, offshore catches of this 
bait fish are on the whole negligible when com- 
pared with the total bait catch. In 1957 slightly 
more than 2,500 scoops of threadfin were taken 
on the high seas as compared with the total bait 
catch of all bait species in the eastern Pacific of 
3,700,000 scoops. 
It is interesting to note that the coloration of 
P. opercularis collected off San Jose, Guatemala 
(see above), showed adaptation to the pelagic 
habitat from which these fish were removed. 
The fish were bluish-gray dorsally and whitish- 
silvery ventrally. We were told by some of the 
tuna fishermen that when the young threadfin 
with the bluish coloration are kept for a few 
days aboard the vessel in the baitwells, they 
assume the adult coloration, i.e., inshore colora- 
tion, which is a greenish-brown color with some 
