Further Notes on the Identification and Biology of Echeneid Fishes 
Donald W. Strasburg 1 
Attempts to identify several small echeneid 
fishes revealed that some of the more useful 
adult characters are not present in the young. 
Specifically, disk length, pectoral fin rigidity, 
body and fin morphology, and scale size and 
number are features which change with growth. 
Certain meristic characters were found to be 
constant over the 14 to 640 -mm length range 
considered, and were usable in identifying small 
specimens. This paper presents a key to the 
Echeneidae with further observations on their 
biology. 
The methods employed require only brief 
description. The leathery membranes were re- 
moved from the fins of all but the smallest 
individuals in order for the rays to be counted. 
This was particularly necessary for the dorsal 
fin, the anterior rays of which are recumbent 
and would otherwise escape detection. The up- 
permost pectoral ray, a short bony splint, was 
counted as a ray. Scale examination involved 
removing a small square of skin from the side 
below the rear edge of the disk, staining this 
square with alizarin, and removing the rubbery 
epidermis. Both lateral line and ordinary scales 
were then visible in this piece of tissue. No type 
material was examined, nor was it possible to 
see specimens of all species. The names used 
are in accordance with Maul (1956). 
Table 1 presents the meristic data obtained 
from specimens in the collection of the Bureau 
of Commercial Fisheries Biological Laboratory 
in Honolulu. These data are the main basis for 
the following key, although supplementary in- 
formation was used for the species not seen and 
to broaden the range of some characters. This 
information was obtained from the following 
reports: Bigelow and Schroeder (1953:485- 
1 U. S. Bureau of Commercial Fisheries Biological 
Laboratory, Honolulu, Hawaii. Manuscript received 
September 26, 1962. 
487), Breder (1936:43), Cadenat (1950:265; 
1953:674-680), Clemens and Wilby (1949: 
329), Clothier (1950:51), Follett and Demp- 
ster (1960:172-176), Fowler (1941:269-275), 
Hildebrand ( 1946:479), Jordan and Evermann 
(1898:2268-2273), Krefft (1953:278), Maul 
(1956), Meek and Hildebrand (1928:896- 
899), Munro ( 1955:268), Schultz (1943:258- 
260), Smith (1950:341-342; 1958:319), and 
Szidat and Nani (1951:399-407). 
The two species of Remoropsis recognized by 
Maul (1956) do not differ meristically, nor are 
they clearly distinguishable by other means. In 
general, the body scales of brachypterus are 
large, closely spaced, and superficial, while those 
of pallidus are small, scattered, and embedded. 
In large brachypterus, however, the scales are 
partially embedded, and, in addition, some pal- 
lidus have large scales. The shape and spacing 
of the lateral line scales varies from point to 
point along the lateral line, and Strasburg (1959: 
244) found specimens with the coloration of 
pallidus but the lateral line of brachypterus. 
These facts suggest that pallidus and brachyp- 
terus are very closely related, if not synonymous. 
In the absence of a definitive monograph, they 
are retained as distinct species characterized 
solely by color pattern. 
The length of the sucking disk has sometimes 
been used as a taxonomic character in the Eche- 
neidae (cf Maul, 1956:18). Rhombochirus has 
been distinguished from the other genera, ex- 
clusive of Remile gia, by the fact that its disk 
reaches to or past the pectoral tips. The pos- 
terior extent of the disk and pectoral fins of 
echeneids of various lengths is shown in Figure 
1. Below 65 mm standard length the pectorals 
of Rhombochirus extend farther posteriorly than 
the disk, as is always the case with Remora, 
Remoropsis, and Phtheirichthys. While this 
character may be used for large individuals, it 
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