In a communication on the Killiefish Mailing List (e-mail) in June of 1997, reporting on his trip to Tanzania last year, Barry Cooper commented, “One of the new fish … is of the red-tailed Notho class, but the other will remind you of something you’ve never seen before.” He goes on to describe the male collected then adds, “The wild females have color to the point that I found it confusing in the field as to whether I had caught juvenile males or females.”
This immediately prompted the question, “How do you tell in the field, under these conditions, whether [fish] are male or female? How do you even realize in the first place that it is females with color, since that is not very normal?”
A Question of Gender
“After collecting several fish,” Barry Cooper replied, “you begin to realize that there are two consistent forms one is the brightly colored male, and the other, the less brightly colored form … you decide must be the female. Having an expert like Ruud Wildekamp with you helps he can look at other features such as fin shape, etc.”
Nothos display considerable sexual dimorphism, so distinguishing males from females in the field or in the fishroom is generally not a problem. However, “In the case of the new species .. . the color pattern on the body of the female is quite similar to that on the body of the juvenile male, and this can lead to some initial confusion. However, closer inspection [showed] a ready distinction” on the basis of the less well developed finnage of the females, the more pointed shape of the anal fin, and the general lack of a strong patterning on the fins. “Even immature males showed some black bars in the anal, dorsal and caudal fins.”
In some situations, Barry noted, specific water conditions made differentiation between male and female difficult. Where water had a particularly milky, turbid quality, the males might be pale and almost devoid of color. “However, the rounded shape of the anal fin, compared with the more pointed shape of the anal fin of the female, provides the necessary clues. In all cases, the fish regained normal color when placed in clear water in the aquarium.”
What Happens When Similar Species Are Collected at a Single Site?
However, the problem of sexual identification may pale in comparison to matching up the right males with the right females when several species are collected at a single locality. “In a number of the localities” [where we collected] Brian Watters said, “there were as many as four different Notho species co-existing in the pool. However, even under such circumstances, identifying the correct females for the different males is generally not a problem, although it does require a degree of familiarity with known Notho species. Remember, the fish also have to be able to tell the difference, and while those differences may be subtle, they are always there. To the experienced (human) eye the differences … are always identifiable.”
“I just want to emphasize that I, as a beginner collector, at first had difficulty being sure that the females of this new species were, in fact, just that,” says Barry. “I can’t emphasize enough how much help it was to be in the company of experienced people like Ruud Wildekamp and Brian Watters. Even so, after collecting several fish you start to realize that there is a pattern.”
— G.C.K.A. Newsletter, January 1999