Observations on the Biology of the Lousefish, 
Phtheirichthys line at us (Menzies) 
Donald W. Strasburg 1 
The lousefish, Phtheirichthys lineatus (Men- 
zies), is a slender member of the Echeneidae 
which is often free-swimming but which also 
attaches to immotile objects or slow-swimming 
fishes. It is pantropical, uncommon, and little 
known biologically. 
This paper reports on 24 lousefish in the 
collections of the Bureau of Commercial Fisher- 
ies Biological Laboratory in Honolulu. Capture 
data for these specimens are presented in Table 
1. Most of the other data were derived from 
preserved fish with the exception of one 256- 
mm specimen which was maintained alive in a 
swimming pool for several weeks. 
Mr. Richard D. Samuels and Mr. Richard N. 
Uchida captured the fish, Mr. Everet C. Jones 
identified many of the food items, and Mr. 
Tamotsu Nakata prepared the figure. All are 
employees of the Bureau of Commercial Fish- 
eries Biological Laboratory, Honolulu. 
COMMON NAME 
The American Fisheries Society (1960:48) 
lists the common name of Phtheirichthys line- 
atus as "slender suckerfish." P. lineatus is an 
uncommon or rare fish, however, and no one 
of my acquaintance applies this rather arbitrary 
name to it. In Honolulu, Phtheirichthys is usu- 
ally called "lousefish," a name used earlier by 
Jordan (1907:680). "Lousefish" is used 
throughout this report. 
ATTACHMENT 
The data in Table 1 were grouped to reflect 
the various objects to which lousefish attached. 
Most small fish (ca. 40-130 mm standard 
length) came from essentially motionless ob- 
jects: buoys, baits, and large dead fish hanging 
1 Bureau of Commercial Fisheries Biological 
Laboratory, Honolulu, Hawaii. Manuscript received 
March 31, 1966. 
from the longline gear that caught them. One 
lousefish was attached to a living porcupinefish, 
Diodon hystrix Linnaeus, a notoriously slow 
swimmer. Lousefish have been reported from 
other slow swimmers including turtles (Men- 
zies, 1791:187), barracuda (Jordan and Ever- 
mann, 1898:2268; Schultz, 1943:256; Smith, 
1950:341), and large groupers (Smith, 1950: 
341 ) . It is difficult to accept Jordan and Ever- 
mann’s statement (1898:2268) that lousefish 
occur on spearfishes. 
Six specimens were free-swimming when col- 
lected, including the three largest ones which 
were attracted to a submerged light at night. 
One of the latter was kept alive in the ship’s 
baitwell for 10 days, during which time it was 
occasionally seen to attach to the tank walls for 
1 or 2 seconds at a time. Later it was trans- 
ferred to a circular plastic swimming pool, 
23 ft in diameter and 4 ft deep, which was 
supplied with running salt water. Here its 
attaching and other behavior were observed 
for two 1-hr periods each day for 25 days. 
The captive lousefish attached only under 
two conditions: when I entered the pool or 
when it had been fed to satiety. It was necessary 
to clean the pool’s windows and drain-strainers 
every few days ; when I entered the water to do 
this work, the fish abruptly ceased swimming 
and attached to the pool’s bottom or side. It 
usually remained attached for a few minutes 
and then darted toward me, especially if I was 
swimming. When I swam, it accompanied me | 
around the pool, staying about 1 ft from my 
bare feet, but making no effort to attach to me. ' 
The lousefish was fed once or twice a day. 
Feeding was avid to the point of greediness, jj 
the satiated fish having a bulging belly and 
cheeks, and usually being unable to dose its 
mouth. In this state its swimming movements t 
appeared to be hampered. It sank to the pool’s : 
bottom and did one of three things: either it 
swam slowly back and forth with a great deal I 
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