Similar families occurring in the area
Marine eeltail catfishes differ from all other catfish
families in possessing a dendritic organ at the
base of the anal fin. Furthermore, additional
characters can be used to distinguish them from
the following families that are found in the region:
Ariidae: caudal fin forked, adipose fin present,
anal-fin base short, not confluent with caudal fin;
anterior and posterior nostrils close together; no
nasal barbel.
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Siluridae (fresh water): dorsal procurrent rays not
extending onto dorsum past posterior extent of anal
fin; caudal fin usually forked or truncated, rarely
rounded or pointed; dorsal fin without pungent spine.
Clariidae and Heteropneustidae (fresh water):
dorsal fin without pungent spine, and not confluent
with caudal fin.
Non-catfish families:
Macrouridae: body scaled; pectoral fins without spine; mouth not surrounded by barbels.
Ophidiidae: body scaled; pectoral and dorsal fins without spines.
Key to the marine species of Plotosidae occurring in the area
1a. Body very elongate, depth at first dorsal-fin origin less than 11% of standard length
(Fig. 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Euristhmus spp.1/
1b. Body less elongate, depth at first dorsal-fin origin usually greater than 15% of standard
length (Figs 3 and 4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . _ 2
2a. Anterior nostril a round tube situated within folds of upper lip, opening directed ventrally
(Fig. 2); second dorsal-fin origin situated immediately behind first dorsal fin and anterior
to vertical line extending from pelvic-fin origin, appressed first dorsal fin extends past
origin of second dorsal fin; gill membranes joined broadly across isthmus and attached