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
to isthmus anteriorly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (Paraplotosus) _ 3
2b. Anterior nostril a round tube situated dorsal to upper lip, opening directed anteriorly;
second dorsal-fin origin posterior to vertical line from pelvic-fin origin, appressed dorsal
fin not reaching origin of second dorsal fin; gill membranes narrowly attached across
isthmus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (Plotosus) _ 5
3a. Dorsal-fin height greater than length of head; pectoral-fin margin angular; nasal barbel
extends well beyond opercular margin . . . . . . . . . . . . . . . . . . . . .Paraplotosus butleri
(northern and western Australia, from Shark Bay to the Gulf of Carpentaria)
3b. Dorsal-fin height less than, or equal to, length of head; pectoral-fin margin rounded;
nasal barbel not extending beyond opercular margin, often falling far short of margin . . . . . _ 4
4a. Dorsal fin short, its height 50 to 70% of head length; eye small, its diameter 5 or more
times in head length . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Paraplotosus albilabris
4b. Dorsal-fin height 75 to 100% of head length; eye larger, its diameter 4 times or less in
head length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Paraplotosusmuelleri
(northern Australia, from Dampier Archipelago to the Gulf of Carpentaria)
5a. Nasal and maxillary barbels long, reaching at least to pectoral-fin base; body uniform in
colour, without stripes; total fin rays in confluent median fins 247 to 281 . . . . . .Plotosus canius
5b. Nasal and maxillary barbels short, reaching to, or only slightly past, posterior margin of
eye; body usually with 2 or 3 whitish stripes, 2 of which extend onto head; total fin rays in
confluent median fins 139 to 200 . . . . . . . . . . . . . . . . . . . . . . . . . .Plotosus lineatus