A Contribution to the Biology of the Convict Surgeonfish 
of the Hawaiian Islands, Acanthurus triostegus sandvicensis 1 
John E. Randall 2 
The surgeonfishes (family Acanthuridae ) , 
which are distinctive chiefly in their possession 
of a knifelike spine or spines at the base of the 
tail, are one of the dominant groups of tropical 
inshore marine fishes. Over much of their vast 
range, including Hawaii, where they are espe- 
cially prominent on the reefs, they are important 
components of subsistence fisheries. Little is 
known of their biology, however. There are only 
scattered references to the herbivorous food hab- 
its of the group and general remarks on the 
habitat of certain species. 
An analysis of the generic classification of the 
family and taxonomic revisions of some of the 
genera have been published (Randall, 1955 a, 
c, d\ 195 6b). The largest genus, Acanthurus , 
contains 32 species, 4 of which occur in the 
Atlantic, and the rest in the Indo-Pacific. The 
present paper constitutes a report of a study 
made during 1952-55 upon the life history and 
the ecology of one Hawaiian subspecies of this 
genus, A. triostegus sandvicensis, the convict 
tang or convict surgeonfish. In Hawaii and else- 
where in Polynesia this surgeonfish is known as 
the manini, and hereafter it will usually be 
referred to by that name. 
The manini is the most abundant species of 
surgeonfish in the Hawaiian Islands and com- 
mercially the most important. Judging from its 
prevalence in museum collections, it is also com- 
mon elsewhere in the Indo-Pacific region. Jordan 
and Seale (1906: 354) wrote, "This species is 
the most abundant of the genus about Samoa, 
swarming everywhere on the reefs.” The young 
reside in tidepools, and are therefore more ac- 
cessible for observation and experimentation 
1 Contribution No. 149 of the Hawaii Marine Lab- 
oratory and No. 301 of the Marine Laboratory, Uni- 
versity of Miami, Florida. Manuscript received April 
4, I960. 
2 The Marine Laboratory, University of Miami, 
Miami, Florida. 
than the young of other acanthurids in Hawaii 
which are usually found in deeper water. The 
species has the widest distribution of all of the 
surgeonfishes — East Africa to the Gulf of Cali- 
fornia (a single record from West Africa by 
Fowler, 1936, should be confirmed). Thus in- 
terest in its biology may be greater than that 
of a localized species. 
A. triostegus (Fig. 1) has been described un- 
der 10 different scientific names and placed in 
six different genera. Nomenclatural considera- 
tions and description of the species and variants, 
with special reference to fin-ray counts and col- 
oration, have been dealt with previously (Ran- 
dall, 1956* ). 
ACKNOWLEDGMENTS 
This research was done in partial fulfillment 
of the doctoral thesis requirement at the Uni- 
versity of Hawaii. The author wishes to express 
his sincere thanks to the members of his doctoral 
committee, headed by William A. Gosline of 
the Department of Zoology, for their guidance. 
Personnel of the Hawaii Division of Fish 
and Game, then under the direction of Vernon 
E. Brock, helped materially in the tagging pro- 
gram of the manini. The tagging was financed 
by the Federal Aid in Fish Restoration Program. 
The larval fish collection of the Pacific Oceanic 
Fishery Investigations (POFI) of the United 
States Fish and Wildlife Service was made freely 
available. 
H. W. Manter and Leland S. Olsen of the 
University of Nebraska, Paul Illg of the Uni- 
versity of Washington, Cadet Hand of the Uni- 
versity of California, J. Percy Moore of the Uni- 
versity of Pennsylvania, and Alan Lewis of the 
University of Hawaii, assisted in the identifica- 
tion of parasites. 
Most of the photographs were taken by 
Charles E. Cutress of the U. S. National Mu- 
seum. 
215 
