Sunday, May 05, 2013

Most Wanted : Reticulated Dragonet.

Following on from my last "Most Wanted" post, another example of where misidentification can easily occur is between common and reticulated dragonets. Indeed, following discussions with fellow species hunter Ross Johnston about some of the dragonets we caught last year at the Cornish Lure Festival, I had some doubts about the ones I caught being commons as I assumed at the time. Oops! Subsequently I've been doing a bit of research so that I can decide if my initial identification was correct and so that future dragonet captures can be properly identified.

A small dragonet I caught last year at Megavissey Harbour in Cornwall. At the time I thought it was a common dragonet but there was a small element of doubt in my mind follow a discussion I had with my mate Ross.

To start with adult males of both species are distinct from the females. Like the male cuckoo wrasse, adult male common and reticulated dragonets are quite unmistakable as they have bright, striking markings.

The male common dragonets above display their sail like dorsal fins. Vivid orange and electric blue markings make it quite distinctive. The first ray of the first dorsal fin is unusually elongated. The electric blue markings on the second dorsal fin run almost parallel to the body.
Male reticulated dragonet photos seem to be quite rare. The first ray on the first dorsal fin is not as long as that of the male common dragonet but the second fin is much taller by comparison. The markings on the second dorsal fin are quite different too comprising of bands of light blue spots with thin darker blue borders and yellow halos divided by dark bands and the bands run diagonally back down towards its base.
Two superb images depicting the typical male dorsal fin patterns of both species. Common dragonet on the left and reticulated dragonet on the right

Obviously from the above identifying adult males is not an issue. Females of both species and juvenile males too however can easily be mistaken due to their much less colourful appearance and indeed many of the different descriptions of the colouration of them I've found are somewhat contradictory. In fact I believe that some of the photos that can be found online are mislabelled in a similar way to some photos of gobies. Also in relation to colouration, various sources state that the saddle markings found on their backs can be used to distinguish them because the common dragonet only has three of these whilst the reticulated dragonet has four, the borders of those on the reticulated dragonet also being much more clearly defined. Again in many of the photos I've found online these saddles aren't clear or the labelling of the photos contradicts the number of saddles or how pronounced the borders are. Here are a couple of images that do match the general descriptions of their colouration.

A common dragonet. Pretty bland and the three saddles aren't really obvious due to the fairly mottled colouration.
The saddles are more apparent on this picture of a common dragonet. Note that there are four present but the second one back is quite faint. Perhaps this is actually a misidentified reticulated dragonet?
A reticulated dragonet. Slightly more exciting with some nice turquoise markings and the four saddles are easy to see and reddish brown in colour.

Whilst these example photos above seem to best match the common aspects of most descriptions given other photographs show that not every dragonet is so easy to identify using colouration alone. With this becoming apparent whilst researching I have tried to find some anatomical differences and thankfully there does seem to be a few ways to reliably distinguish between the two that do not rely on colouration or markings.

Size can be used to identify which species is which in larger specimens as reticulated dragonets only grow to about 11cm so any exceeding this length must be common dragonets as they can grow up to about 25cm.

Applying this simple rule means that this must be a female common dragonet and indeed it is one of specimen proportions.

Snout length can also be used. The common dragonet has a much longer snout being two to three times the diameter of their eyes where as the snout of a reticulated dragonet is usually only slightly longer than the diameter of their eyes.

Dragonets have a group of small sharp prickly spines at the edge of their preoperculum. They use this as a defensive mechanism. When threatened they flair their gill plates and these spines stand out giving anything that touches them a rather unpleasant surprise. Common dragonets have four spines in total, one faces forward whilst the remaining three face upwards and backwards. Reticulated dragonets only have three spines and all face upwards and backwards.*

Finally a count of the rays in the second dorsal fin can be used. When doing this bear in mind that the final ray in both species is branched into two so you have to count both of these as one! Common dragonets normally have nine rays whilst reticulated dragonets have ten. Occasionally however common dragonets may have eight or ten so this identifying feature should be used in conjunction with others above if the count is ten.

There is a third species of dragonet found in U.K waters, the spotted dragonet. It's another small member of the dragonet family, only growing to 14cm, and is normally found offshore in very deep water so the chances of ever catching one are extremely remote.

Easily identifiable due to their electric blue spots.

I'm fairly confident now that the dragonets I caught last year were all common dragonets and that armed with the above knowledge I'll be able to positively identify any dragonets I catch in the future. A bit like my problem of differentiating between common gobies and sand gobies last year this is an area of species identification I'm determined to fully master that will of course require catching more dragonets to examine and also photograph. Like I need another excuse to species hunt!

Tight lines, Scott.

*Update: Further research has revealed that this forth spine is not visible to the naked eye. It can however be detected my running a fingernail back along the gill plate towards the other three spines. If it is present your fingernail will catch on it. I have applied this simple test to all dragonets I have caught since writing this post and all of them possessed the forth spine confirming them as the common variety.


  1. nice article on dragonets.
    do you have an email address as I would like to find out more about this species

  2. Click the link at the end of the "About me" section at the top left of the page. :-)