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.

2 thoughts

  1. Hey minustide, I think even I could tell the difference now, if I had one that wasn’t wiggling too much. Thanks for sharing!

    1) Do the juveniles look different from mature, in terms of color patterns and contrast? or are the color patterns consistent through life?
    2) The female looks like she has no color on her anal fin. Is that red spot on the male typical, or is he just showing off?

    Unrelated to this specific post, but I’m curious: Do the females get fat and spew large numbers of babies all at once? or do they have them developing at different stages and drop a few here and there, and keep their girlish figures? Or maybe they just make little babies so mom’s body doesn’t get distorted. All the fish you’ve shown so far look pretty sleek, it’s hard to imagine them fat like a momma guppy (or person).

    1. Cool, glad I could help. As for juveniles, yes the color changes as they mature, but more in some species than others. That makes me think I should spend some time exploring ideas about color and maturity. Thanks for asking that question. As for color on the anal fin, that also varies. In red-tailed surf perch, featured in this post, the anal fin of both sexes doesn’t have any pattern to speak of; the individual in the photo you refer to is an anomaly. In other species like silver surf perch we occasionally see spots on the anal fin of both sexes. Other species always have a spot on the anal fin. So, this is the kind of thing we study. Finally, females produce large babies which they have all at once, they get pretty fat right before they give birth, but not like a pregnant guppy or human.

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