“The Fundulus notatus/F. olivaceus issue is fairly well known to American ichthyologists,” says Bruce Turner, “and has attracted attention from several, including Jim Thomerson (who did his dissertation research on the two forms) and Robert Cashner of LSU,” who surveyed their variation and described a third form, F. euryzonas, from the Lake Pontchartrain drainage in Mississippi and Alabama. Thomerson and the late Carl Hubs had both recognized that the F. euryzonus form was divergent, but had no proof.
F. olivaceus and F. notatus now appear to be “sibling” species, since they are morphologically difficult to distinguish but are genetically distinctive. There is much research still to be done, however. Does their separation remain the same over seasonal fluctuations in habitat size, movement, water temperatures, etc.?
F. olivaceus and F. notatus – “I’ve only [collected] F. olivaceus types in the Wolf drainage [of Tennessee],” says Shane Essary. “But F. olivaceus has that ‘faint’ yet distinctive notatus looking line that runs from head to tail. Yet all these fish fit more the olivaceus provile (lots of specks) and that notatus line is VERY faint. On the other hand, in the Hatchie drainage I find nothing but dark banded killies (notatus), with faint spots. Really, the two fish look almost just alike,” and both occur in the western Tennessee range projected by Etnier and Starnes in The Fishes of Tennessee. According to them, F. olivaceus seems to prefer slightly faster flowing streams, and in unchannellized streams seems to avoid the sluggish downstream areas. F. notatus tends to prefer the more sluggish areas. This ecological separation was also noted by Braasch and Smith (1965).
“Both these species that I have collected were in shallow water [1 to 6 inches],” reports B. G. Granier, “regardless of the flow or lack of flow in their respective habitats, which is generally backwater areas or a captive population … in a pond or in the shallow, fast moving current of a creek. They are very difficult to collect, since they are very wary … of [anthing resembling] fish-eating birds.” F. notatus has also been collected in the drainages of southwestern Ohio.
F. euryzonus – This species appears to only inhabit “the deeper part of the streams in Louisiana and Mississippi, and while they may be found against the bank, the depth of the water is generally over the 1-6 inch depths that F. olivaceus and F. notatus are commonly found in,” says B. G. Granier. “I have had to wade out to chest deep water to find F. euryzonus congregated around any current break, such as log jams, man-made breakwaters or deep pools … beneath a bridge, to catch them.”
– G.C.K.A. Newsletter, August 1999