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Danionella priapus – males quarreling or spawning behaviour?

Home Forums Fresh and Brackish Water Fishes Danionella priapus – males quarreling or spawning behaviour?

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    Great pictures.This appears to be more complex than I thought.

    The stripe you might be calling greenish in D. dracula I would call yellowish, maybe. It may be surrounding of the spinal cord.

    I have attached another picture of one of the Danionella translucida. I got these fish through a friend Joel Sohm who some how convinced Herbert Axelrod to fund in some way Tyson Roberts to get a bunch for researchers bunch on a collecting trip. This makes me think these are really D. translucida. They also have a short body axis (fitting with being a smallest freshwater fish). This was some time in the 1990’s, I think before the other members of the genus were known. I got some because Joel knew the PI of the lab I was in, Scott Fraser. At the time they were the smallest known freshwater fish and we were interested in non-invasively looking at the internals of a live vertebrate. It worked well except for the are I was most interested, in the hindbrain (which I did my thesis on in zebrafish).

    Getting to a point here: In this picture you can see an obnoxious (to me) yellow coating over the brain (behind the eye and in front of the spinal cord). The spinal cord in this animal is the translucent white stripe that ends at the upper right side of the picture. It maybe that the color is an extension of this yellow brain covering. However see comments below.

    You can see what I would call birefrigence green just below where the skin exits the the picture at the top. Also a spot just below the vertebrae, behind the gills.This picture was shot through a microscope, probably with a 40x objective and Nomarski optics (fancy phase contract). The black background is the dark field of the microscope illumination.

    All these apparent colors will be affected by the illuminating light and the background.

    The vertebrae are the clearish (but in areas shiny) things lined up directly underneath the spinal cord. The black spots are individual pigment cells. You can see blood vessels especially in the gills. The heart should be medial at the back of the gills, maybe the darker red area.




    When I got around to ordering some D. translucida from a commercial source a few years ago, at first I assumed they were the right sps. Eventually they seemed too long in proportion to their other dimensions so I knocked one out and took some pictures with a digital microscope I could plug into my laptop (no longer in a lab). This scope was a bit difficult to focus and get the illumination right, but not bad for $200-300.

    I figured it was mirifica based upon the ventral medial pigment stripe which I read about somewhere in a paper. I think this was before dracula was described, not sure about priapus. This fish was dead by this time which is why I don’t like knocking them out. It is turning opaque. This fish does seem to have pigment stripes dorsally, which is confusing. This also shows what seem to be more than one pigment stripe dorsally. This would indicate priapus according to your list above.

    The next picture shows the anal fin (before I realized the rays would be good to count). It has a lot of fin rays, my guess is about 18 (which puts it in your mirifica range) but it is not the perfect picture for this.

    It also has a yellow stripe in the tail region which fades away above the body cavity. This stripe extend over the spinal cord but also below to cover the vertebrae in this view and into the tail. So much for the spinal cord covering explanation.

    There are other possibly relevant pieces of anatomy in this area. The longitudinal pigment cells stripes down the dorsal-ventral middle of the tail are probably along the lateral line nerve which innervate neuromasts (clusters of haircells that are lateral line sensory cells; not to be mistaken for the lateral line seem macroscopically in scales). This nerve usually runs between the dorsal and ventral blocks of the muscle segments. in zebrafish a different kind of muscle develops between these two muscle blocks. Slow muscle instead of fast muscle. It might look different perhaps because of having more mitochondrial or something. You should be able to see two lines from either side, but in places there are three. Perhaps one is at the midline. it might be along a midline blood vessel.





    I suppose it is possible that here are not yet described species being distributed commercially which could increase the difficulty of identifying these guys.




    Wow. That’s a great picture in that link Oaken.

    Seems like a good trait to keep an eye out for.




    @coelacanth and @pablito were breeding Danionella a few years back (maybe still are?) so might be able to help?


    We are, we’ve been a bit tied up recently and so have been unable to respond, we’ll be able to look at it properly this week.



    probably not in the next week or so I’m afraid as we’re shorthanded unless Pete replies from home from memory. 





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