Moray eel egg bound!? (Warning Dissection pictures)

[TheDragonsReef]

So let me start off with the fact this is not my eel nor did i dissect it. I was sent these pictures by a friend looking for help as to what he found after his eel passed. I am aware morays have never been bred in captivity and even how they reproduce in the wild is a total mystery. I just dont know what else it would be.

Background info:
They had this white cheek moray eel for 2 years. Never showed any signs or stress or ill health. Ate 2 days prior to passing. It did appear to be getting bloated over the past few weeks but otherwise was acting normal. When he left in the morning it was fine and when he came home it was dead. It was housed with other morays but no bites marks or even previous bouts of aggression between them. He decided to go ahead and dissect in case he found something that could be harmful to the other eels in the tank.

So what are these? eggs? Internal parasites? Some sort of medical condition? Ive honestly never seen anything like it.

 

[vetteguy53081]

So let me start off with the fact this is not my eel nor did i dissect it. I was sent these pictures by a friend looking for help as to what he found after his eel passed. I am aware morays have never been bred in captivity and even how they reproduce in the wild is a total mystery. I just dont know what else it would be.

Background info:
They had this white cheek moray eel for 2 years. Never showed any signs or stress or ill health. Ate 2 days prior to passing. It was fine in the morning and when he came home it was dead. It was housed with other morays but no bites marks or even previous bouts of aggression between them. He decided to go ahead and dissect in case he found something that could be harmful to the other eels in the tank.

So what are these? eggs? Internal parasites? Some sort of medical condition? Ive honestly never seen anything like it.

Yes indeed. While egg-bound this pic(s) show little as to cause of death

@lion king

 

[TheDragonsReef]

Yes indeed. While egg-bound this pic(s) show little as to cause of death

@lion king

Thank you for the quick answer

 

[Jay Hemdal]

Those are eggs, but can be a normal finding for a gravid female fish.
In truly egg bound fish, the egg mass will have a more solid feel almost like amber.
Jay

 

[TheDragonsReef]

Those are eggs, but can be a normal finding for a gravid female fish.
In truly egg bound fish, the egg mass will have a more solid feel almost like amber.
Jay

Thanks, ill relay the info.

 

[ISpeakForTheSeas]

Just to add, there has been one reported instance of successful breeding with morays (Rhinomuraena quaesita - the ribbon eel, at the Vienna Zoo to be exact), though I don't think it was intentional. Some of the eggs hatched, but the larvae all died after seven days. Interestingly, they note with this that the color of the eel does not reflect the eel's sex or sexual maturity.

https://www.researchgate.net/publication/268079682_First_Observations_of_Fertilized_Eggs_and_Preleptocephalus_Larvae_of_Rhinomuraena_quaesita_in_the_Vienna_Zoo

 

[lion king]

I've never dissected an eel, could you ask if he has any pictures of the liver, or around the liver. Look for alot of fat around the liver, discoloration, or even hemorrhage. Do you known what he was feeding and how often. Quick demise many times point to some sort organ failure, did he see any blood in the cavity.

 

[TheDragonsReef]

Just to add, there has been one reported instance of successful breeding with morays (Rhinomuraena quaesita - the ribbon eel, at the Vienna Zoo to be exact), though I don't think it was intentional. Some of the eggs hatched, but the larvae all died after seven days. Interestingly, they note with this that the color of the eel does not reflect the eel's sex or sexual maturity.

https://www.researchgate.net/publication/268079682_First_Observations_of_Fertilized_Eggs_and_Preleptocephalus_Larvae_of_Rhinomuraena_quaesita_in_the_Vienna_Zoo

Learn something new every day, thanks for sharing. Always happy to learn new fish facts haha

 

[TheDragonsReef]

I've never dissected an eel, could you ask if he has any pictures of the liver, or around the liver. Look for alot of fat around the liver, discoloration, or even hemorrhage. Do you known what he was feeding and how often. Quick demise many times point to some sort organ failure, did he see any blood in the cavity.

Ill ask, i dont know how far he went.

 

[TheDragonsReef]

I've never dissected an eel, could you ask if he has any pictures of the liver, or around the liver. Look for alot of fat around the liver, discoloration, or even hemorrhage. Do you known what he was feeding and how often. Quick demise many times point to some sort organ failure, did he see any blood in the cavity.

He said he did not go that far. He was only worried about intestinal parasites and hes never really done it before.

 

[ISpeakForTheSeas]

Out of curiosity, does your friend have any idea what may have triggered the eggs forming - temperature fluctuation, lighting changes, a water change, moon cycles, flow/wave patterns, change in diet, the eel finally maturing enough, phyto/pod population increase, any other water quality/parameters changes, etc.?

Did the eel show any signs of developing eggs like color changes, behavioral changes/exhibition of new/unique behaviors, etc.? (I know you mentioned the slight bloated look and that it was acting normal, I’m just wondering if the bloating was caused by whatever killed it or the eggs, and if the eel was actually acting normal or just not acting sick).

 

[Slocke]

Interesting. I have been looking into this topic recently.
As @ISpeakForTheSeas says moray eels have only been bred once. European river eels are regularly bred in the last couple years but they have also never successfully raised the larvae past the larval stage. I believe the adult eels die after spawning though. I do not know about morays and that life cycle would seem strange for a non-migratory eel but I do not know. (I'm not sure anyone knows.) However that may have something to do with this eels demise. Also am I right in thinking that a morays eels last life stage is the female lifestage and that it isn't a very long one?

 

[ISpeakForTheSeas]

Interesting. I have been looking into this topic recently.
As @ISpeakForTheSeas says moray eels have only been bred once. European river eels are regularly bred in the last couple years but they have also never successfully raised the larvae past the larval stage. I believe the adult eels die after spawning though. I do not know about morays and that life cycle would seem strange for a non-migratory eel but I do not know. (I'm not sure anyone knows.) However that may have something to do with this eels demise. Also am I right in thinking that a morays eels last life stage is the female lifestage and that it isn't a very long one?

Not to derail the thread here too badly, but Japanese Eel (Anguilla japonica) have been aquacultured successfully (though the settlement rates are only about 10% from what I've read*) - they haven't been able to figure out how to scale it up enough for commercial production yet, though, and it's pretty expensive. I know at least the Japanese Eel is confirmed to be a polycyclic spawner (meaning they spawn multiple times, so they don't just spawn once then die) - a recent finding also suggests that this may be the case for the European Eel (Anguilla anguilla) as well.** Some morays are protandrous hermaphrodites (they start as males and end as females), but others have been shown to be simultaneous hermaphrodites (being both male and female at the same time).***

*Japanese Eel aquaculture info sources:

Closed-cycle eel breeding advancing in Japan | SeafoodSource

Closed-cycle breeding of glass eels is advancing in Japan, where preparations of eel such as kabayaki are culinary specialties.

www.seafoodsource.com

Reinventing the eel: Can the Anguilla loop be closed? - Responsible Seafood Advocate

Japanese scientists have been trying to replicate spawning conditions for eels in captivity for decades. They’re getting closer, but major hurdles remain.

www.globalseafood.org

Reproductive farming technology in Japanese eel and chub mackerel

Japanese eel (Anguilla japonica) and chub mackerel (Scomber japonicus) are commercially valuable species in Asian aquaculture. The reduction in eel an…

www.sciencedirect.com

**Polycyclic spawning info source:

Histological Evidence of Multiple Spawning in Wild Female Japanese Eel Anguilla japonica

The post ovulatory follicle (POF) is an important and reliable tissue structure used to investigate the spawning history in teleost fish. Fresh POFs shortly after spawning are comprised of cellular (follicular cells) and acellular (basement membrane and ...

www.ncbi.nlm.nih.gov

***Muraenidae Hermaphroditism info source:

Hermaphroditism in fishes: an annotated list of species, phylogeny, and mating system - Ichthyological Research

Fewer than 1% of vertebrate species are hermaphroditic, and essentially all of these are fishes. Four types of hermaphroditism are known in fishes: simultaneous (or synchronous) hermaphroditism (SH), protandry (male-to-female sex change; PA), protogyny (female-to-male sex change; PG), and...

link.springer.com

 

[Slocke]

Not to derail the thread here too badly, but Japanese Eel (Anguilla japonica) have been aquacultured successfully (though the settlement rates are only about 10% from what I've read*) - they haven't been able to figure out how to scale it up enough for commercial production yet, though, and it's pretty expensive. I know at least the Japanese Eel is confirmed to be a polycyclic spawner (meaning they spawn multiple times, so they don't just spawn once then die) - a recent finding also suggests that this may be the case for the European Eel (Anguilla anguilla) as well.** Some morays are protandrous hermaphrodites (they start as males and end as females), but others have been shown to be simultaneous hermaphrodites (being both male and female at the same time).***

*Japanese Eel aquaculture info sources:

Closed-cycle eel breeding advancing in Japan | SeafoodSource

Closed-cycle breeding of glass eels is advancing in Japan, where preparations of eel such as kabayaki are culinary specialties.

www.seafoodsource.com

Reinventing the eel: Can the Anguilla loop be closed? - Responsible Seafood Advocate

Japanese scientists have been trying to replicate spawning conditions for eels in captivity for decades. They’re getting closer, but major hurdles remain.

www.globalseafood.org

Reproductive farming technology in Japanese eel and chub mackerel

Japanese eel (Anguilla japonica) and chub mackerel (Scomber japonicus) are commercially valuable species in Asian aquaculture. The reduction in eel an…

www.sciencedirect.com

**Polycyclic spawning info source:

Histological Evidence of Multiple Spawning in Wild Female Japanese Eel Anguilla japonica

The post ovulatory follicle (POF) is an important and reliable tissue structure used to investigate the spawning history in teleost fish. Fresh POFs shortly after spawning are comprised of cellular (follicular cells) and acellular (basement membrane and ...

www.ncbi.nlm.nih.gov

***Muraenidae Hermaphroditism info source:

Hermaphroditism in fishes: an annotated list of species, phylogeny, and mating system - Ichthyological Research

Fewer than 1% of vertebrate species are hermaphroditic, and essentially all of these are fishes. Four types of hermaphroditism are known in fishes: simultaneous (or synchronous) hermaphroditism (SH), protandry (male-to-female sex change; PA), protogyny (female-to-male sex change; PG), and...

link.springer.com

Very interesting thanks for all that research. Shows I need to get better at research. Whenever I search for eel breeding it always brings up stuff on Anguilla anguilla and that is too big a rabbit hole.