A break down on Nemateleotris

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Well, I never thought that I’d write this but I found it rather interesting and I’m sure many others will.
So, you’re likely sitting on a fish that you think is Nemateleotris helfrichi but… It’s not!
Here’s the break down on this genus of Dartfish.

First off what is the genus Nemateleotris for those who don’t go into the scientifics?
Nemateleotris is a genus from the family Gobiidae which is the ‘True’ Goby Family. Now, Nemateleotris was originally split off into 5 species;
Nemateleotris magnifica (The first described of this genus in 1938)
Nemateleotris helfrichi (This species was described in 1973)
Nemateleotris decora (This species was also described in 1973)
Nemateleotris exquisita (This species later came into the genus in 2013)

However recently there was a 6th described species from this genus, Nemateleotris lavandula.

I know I’ve just done a huge information dump but not really explained any differences. So, I guess your question is how do you identify the Lavandula from a Helfrichi or maybe an Exquisita from a Decora?

Well, I’ll happily help there starting with the two older species - Exquisita and Decora.
The Exquisite Firefish is believed to be identified through having a lighter and more yellow anterior whereas the Decora is thought to have a darker, more grey anterior. More minimal ways include the diameter of the eye and length of the first dorsal fin. However it is questioned if these two are actually different species altogether or just simply a variation from different regions.
Nemateleotris exquisita - Exquisite Firefish
006EBB02-8AB6-4124-AE99-26F95A656E9B.jpeg

Nemateleotris decora - Purple Firefish
B31999ED-308E-41BC-A534-C5699E6ED719.jpeg


Now, let’s go into the fun bit… Helfrichi vs Lavandula.
The Lavender-Blushed Firefish is what we used to believe was the ‘Normal’ Helfrichi and the deep water Cook Island Helfrichi Firefish was believed to be just a variant of N. helfrichi. The biggest colour difference between the two is on the head, the Lavender Firefish has the beautiful yellow head and is the most common species we see in captivity. The true Helfrichi Firefish however has a very different head colour and is almost completely purple! A minor difference is with the mouth, the true Helfrichi has a black band on the upper jaw however the Lavandula lacks that band. The other difference is that the true Helfrichi Firefish has a much more restricted region of origin in the Pacific Ocean between the Cook Islands and French Polynesia. Whilst the Lavander Firefish is found all throughout the Indo-Pacific from the north east of Australia right up to Japan.
Nemateleotris helfrichi - Helfrichi Firefish
F838A590-CEE9-4F9B-AB26-7F6EF784A721.jpeg

Nemateleotris lavandula - Lavander-Blush Firefish
A1AC33BD-3B97-4636-892D-B775D68C342B.jpeg


I hope you enjoyed this ‘deep dive’ into this deep water genus of Gobies! And yes, Gobies, Firefish and Dartfish are the same they all go under the same family but are spread out through many genera.

P.S. Any photos used were from quick google searches, none are mine.
 
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If I saw the Lavander in-person I'd probably confuse it for a Helfrichi... All I really know about these fish are that they school, are shaped like torpedos and behave as such (in addition to looking lousy on the floor).
Honestly, only the Magnifica is Communal the rest of them dislike being in more than a pair and tend to kill eachother off.
 

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Honestly, only the Magnifica is Communal the rest of them dislike being in more than a pair and tend to kill eachother off.
...or chase each other out of the tank (same net result). Someone took a chunk out of my new yellow coris wrasse today (don't think he's going to make it). Kind of bummed out about that...
 
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7573DF03-0C29-49CC-99B0-1D8EDA2A3826.jpeg
A really underrated genus. Even the common, cheap magnifica is a truly stunning fish.
Definitely, I saw the two most beautiful specimens of it the other week. They had golden yellow dorsal spines with that beautiful white body
 

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It's always been very interesting to me how the dorals of the other four species don't grow as long as that of Magnifica. A picture I saw in the reefbuilders article distinguishing Lavandula from Helfrichi, however, seems to be an example of a Lavandula with the extended dorsal. I wonder what causes this dorsal growth, and if there's any way to replicate it in aquaria.
Figure_6-scaled.jpg

Nemateleotris lavandula With extended dorsal growth
 
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It's always been very interesting to me how the dorals of the other four species don't grow as long as that of Magnifica. A picture I saw in the reefbuilders article distinguishing Lavandula from Helfrichi, however, seems to be an example of a Lavandula with the extended dorsal. I wonder what causes this dorsal growth, and if there's any way to replicate it in aquaria.
Figure_6-scaled.jpg

Nemateleotris lavandula With extended dorsal growth
I have a feeling it’s likely shorter as the Magnifica has a more robust dorsal spike whilst the other 5 (I personally do think the Exquisita and Decora are two species and not just variants the colouring is incredibly different and much more regional like the Lavandula and Helfrichi) species have slightly more delicate dorsals.
 

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I have a feeling it’s likely shorter as the Magnifica has a more robust dorsal spike whilst the other 5 (I personally do think the Exquisita and Decora are two species and not just variants the colouring is incredibly different and much more regional like the Lavandula and Helfrichi) species have slightly more delicate dorsals.
So do you think the specimens we see in the trade have just had their dorsals broken at some point and they just never fully recover? It seems that most pictures I can find of the 4 "shorter-finned" dartfish species have varying dorsal lengths, even within the same species, so I guess that would lend to the broken dorsal theory since it would likely be a slightly different breakpoint for every specimen. There also doesn't seem to be a huge amount of very long-term documented experience with single specimens of these species, so maybe the dorsal regrowth is a years-long process that we are just not seeing in our aquaria.
 
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So do you think the specimens we see in the trade have just had their dorsals broken at some point and they just never fully recover? It seems that most pictures I can find of the 4 "shorter-finned" dartfish species have varying dorsal lengths, even within the same species, so I guess that would lend to the broken dorsal theory since it would likely be a slightly different breakpoint for every specimen. There also doesn't seem to be a huge amount of very long-term documented experience with single specimens of these species, so maybe the dorsal regrowth is a years-long process that we are just not seeing in our aquaria.
That’s what I’d say as the most likely reason. Going from the oceans to our reefs there’s several times that a long spike can be damaged.
 

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