Pulsatile activity in genital papilla of clown pleco (Panaqolus maccus)

YouTube · Post by **bekateen** » 21 Sep 2015, 01:47

Hi All,

Have you ever observed the genital papillae of either male or female loricariids? Obviously, if you've tried to sex your plecos, you probably have, at one point or another, checked out the genital papillae to see if there is a gender difference. (Okay, sorry; that may not sound right... I didn't mean to suggest that everyone sits around staring at their fishes' private parts.)

During recent attempts to sex my new mustard spot plecos (), I observed that the genital papillae of all three of my fish would pulse when the fish were held out of water, as I tried to get a good look at their papillae for any sexual dimorphism.

Today I was watching one of my female clown plecos (, L104) as she sat against the glass of the aquarium, and I saw that her genital papilla was doing the same thing - a slow, rhythmic pulsation, starting at the posterior tip of the papilla and moving anteriorly through the papilla until it disappeared into the body. A video of this behavior is shown below.

I found a few old references to this pulsing in the forums:

The two explanations I read in the forums are intestinal respiration (also known as "cloacal breathing") and simple colonic peristaltic movements to propel feces out of the body. The former should not be correct, as all the examples of cloacal breathing I'm aware of involve air-breathing animals underwater. Gill-breathers really shouldn't require, or I would expect benefit much from, a secondary aquatic respiratory system. But air breathers (e.g., turtles) which hold their breath when underwater can exchange a certain amount of oxygen and carbon dioxide through the lining of their colon by moving water into/out of their cloacas.

The latter explanation, that it is just simple intestinal peristalsis, is quite possible, although what I witnessed causes me to question that explanation: 1) in my clown plecos and in my mustard spot plecos, the pulsatile wave migrates from the tip of the papilla back to the body, not the other way around; this, I would think, is in the wrong direction to drive feces out of the body. Additionally, I don't know if this is true for loricariids, but I know that some catfish have the reproductive and digestive tracts combined (a common opening), while other spp. do not (separate openings). I suspect that loricariids have a single shared opening, but if they don't, then I wouldn't expect a digestive peristaltic wave to pass through the genital papillae.

Has anyone else ever seen this personally? Does anyone know what it means (if anything)? Do you have any ideas regarding the rate of the pulsation? It's very slow (about 20-30 pulses per minute); is it linked to the fish's heart rate? Is it nothing more than a blood pressure pulse, just as we might feel in our own wrist every time our heat beats? I don't think this is the explanation, since the action seems to be very distinctly a muscular action, not merely a volume surge due to blood flow.

Any thoughts or additional observations/experiences are greatly appreciated.

Cheers, Eric

https://youtu.be/rtJ-blKNP5g