When I first started examining surfperch it was a bit difficult for me to tell males from females but now I’ve got it down. There are differences in color, pattern and the shape of the anal fin. The top panel on the left shows a female redtail surfperch; the panel below that is a male. The male has a bolder, darker pattern with more contrast. The two sexes seem to be abut the same size but the largest ones I have observed myself are females.
One of the most striking differences between the sexes is in the anal fin. This makes a lot of sense because surf perch have internal fertilization. Males have an intromittent organ on the anal fin that gives it structure not found on the female anal fin. In the two photos to the left you can see the simple anal fin of the female (top) and the complex anal fin of the male (bottom). Internal fertilization has major implications for the kinds of questions we ask about the natural history of surfperch.
Because they have internal fertilization, I’m always thinking about their courtship and the role of vision and color preferences, and what they eat. All of this has to do with questions about how three or more similar species sharing time and space on the outer shore keep from getting mixed up. Maybe they do get mixed up. The orange spot on the anal fin of the male red-tailed surfperch (left) is usually only seen in the silver surfperch.