Gramma loreto sexing

[ThRoewer]

I found this research paper which confirms what I had already suspected:
Bisexual juvenile gonad and gonochorism in the fairy basslet, Gramma loreto

To make it short: Gramma loreto doesn't change sex after maturing. The same can be assumed for G. dejongi and likely also for G. melacara. Individuals above 25 mm (1") have to be assumed to be set in their sex. It is not yet clear if specimens below that size are already set in their sex or if social interactions can determine the sex of an individual. To be on the safe side it is best to assume the sex is set until further research shows that juveniles still have a "choice".

I currently have a trio of Grammas that I got as fairly small individuals. Of those three two are males and one is female. The dominant male and the female spawn regularly. The subordinate male pretends to be a female towards the dominant male but shows mating behavior towards the female. He generally tries to avoid interactions with the dominant male.

The dominant male is significantly larger than the female and more slender in his body proportions.
I also noticed a coloration difference between males and females: adult males have silver speckles on some of their scales while these are completely absent with females. However, this may be difficult to spot in a fish store system.
The female and the subordinate male are of equal size and body proportions but show clear color and behavioral differences.

Since the sex ratio among small specimen favors females and because subordinate males are tolerated within a group, the easiest way to get a pair or a harem is to acquire 3 or more small specimens of equal size.
When going to pair adults size can be used as a primary indicator. Females stay significantly smaller (below 50 mm SL) than fully mature dominant males (larger than 50 mm SL). Dominant males also have longer ventral fins and a slimmer body.
However, the fact that subordinate males mimic females in size and body proportions makes it difficult to pick females by size. The above-mentioned coloration difference may help but may not be visible with stressed individuals at the store.

For those interested in breeding Gramma, this paper might be of interest:

Development of morphology and swimming in larvae of a coral-reef fish, the royal gramma, Gramma loreto

 

[OrionN]

I don't know about this. My experience with this species is clearly different from your summarize. I had a harem of 5 for many years with 1 male. The male got old. A female change sex and promptly kill him. All of this was in my 420 DT.
Royal Gramma are sexually dimorphic with the male have longer pelvic fins and the transition from purple to yellow further down the body thus give him a lot more purple and less yellow than the female.
I wrote about this before and posted pictures of this before.

 

[ThRoewer]

Your female was likely a covert male.
The research on this seems to be pretty solid.

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[OrionN]

Male build nest in his dent. He court the female and entice her to return to his dent with him where they mate. Male keep watch over the eggs until hatch. It is very difficult to see the egg mass because my tank is large with a little of rock and the nest is deep in the rock structure.
However as the male get older he start to get weak and start to look “raggedy”. This is when the larger female attack, killed him and assumed the male role. My tank is large and I was not able to intervene to save him.

 

[OrionN]

It is possible that the sub male looks like females. The dimorphic physical characteristics is really clear once one know what to look for. I was never sure which female was the mother of which egg mass. Certainly in my 8 foot tank there was not enough territory for 2 terminal males.

 

[ThRoewer]

Have you read the research article? It makes it pretty clear that Gramma have fixed sex once mature.
Subdominant males hide among the females and look largely like them. Once the top position becomes vacant they grow to full length and start looking like dominant males.
I can easily tell my 3 apart and only the true female ever spawns with the dominant male.

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[Michael Hoaster]

Very interesting article. This appears to be quite the Myth-Buster. Though I wonder if it will change the way we keep Grammas in harems, in aquaria.

If I may, I'd like to sum up what was written in the article. Please correct me if I am wrong. Royal Grammas' sex changing is limited to it's time as a juvenile (an inch or less). Once it reaches maturity, a female CANNOT change into a male. So, what we thought was happening - a female changing to a male, to replace the dominant male in a harem, was actually a non-dominant male, who previously acted like a female to avoid harassment by the dominant male, becomes the new dominant male.

Does this new information change the way we keep gammas in harems, in our tanks? Probably not. Since non-dominant males pretend to be female, in our aquariums, they may as well be. The exception would be for breeders of this fish. They'd likely want all 'true females', for maximum egg production.

I kept a harem of seven grammas for around three years. In the early phase of the harem there was a lot of fighting and bickering. I presumed it was part of the Darwinian process of picking the dominant male. Once 'Big Daddy' was established, they became much more peaceful. Occasionally, I witnessed what looked like spawning behavior between two 'females'. In reality, this must have been a non-dominant male getting some action on the down-low!

 

[Boochika]

Is it possible there are different species of Grammas and we are missing minute differences between those in this study and in the trade?

 

[ThRoewer]

Is it possible there are different species of Grammas and we are missing minute differences between those in this study and in the trade?

There is a near identical species from Brazil but they don't make it into the trade (anymore).
Also, it is highly unlikely that those would be different in their sex structure from the Caribbean Gramma loreto, Gramma dejongi, or Gramma melacara. Just see the Amphiprion species which are all following the same sex change pattern, or the worldwide found Callionymidae (dragonets) which all have fixed sex.
Fixed sex is actually far more common with fish than the ability to change sex.


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[OrionN]

Gramma brasiliensis is a little larger than Gramma loreto and does not have the black line through the eyes.
They are yawning, not attacking anybody. Images from the internet, not mine.

Royal Gramma

Brazilian Gramma

 

[ThRoewer]

...
I kept a harem of seven grammas for around three years. In the early phase of the harem there was a lot of fighting and bickering. I presumed it was part of the Darwinian process of picking the dominant male. Once 'Big Daddy' was established, they became much more peaceful. Occasionally, I witnessed what looked like spawning behavior between two 'females'. In reality, this must have been a non-dominant male getting some action on the down-low!

I noticed the same during the first months when I had my trio in a 10 gallon QT. But it always was the (now) dominant male quarreling with the (now) subordinate male. The female was barely involved in this. I could keep them apart by some markings/damages they had when I got them.
If you still have your Grammas I would suggest having a closer look at those females displaying spawning behavior. The disguised males should have white/silver/golden spots like the specimen in the picture below while those spots should be missing on females. At least that's how it is with my female.

from https://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=723

 

[ThRoewer]

I don't know about this. My experience with this species is clearly different from your summarize. I had a harem of 5 for many years with 1 male. The male got old. A female change sex and promptly kill him. All of this was in my 420 DT.
Royal Gramma are sexually dimorphic with the male have longer pelvic fins and the transition from purple to yellow further down the body thus give him a lot more purple and less yellow than the female.
I wrote about this before and posted pictures of this before.

Did you buy all of those individuals at once and are you sure they all came from the same location? There is a variation where the yellow-purple transition is but it is more likely a local variety coloration than sexual dimorphism. Gramma loreto from the Cayman Islands, for example, have far more yellow than "regular" G. loreto.

 

[OrionN]

I ordered a group of 6 from a LFS here in Corpus. Specified that they get small ones and put them all together on arrival. My experiences was that any Royal Gramma that stay alone for any length of time will become male and will fight with other RG once they put back together. This occurred at an early age and very small. I have seen RG barely 1 inch fight each other very aggressively.

I have not keep any RG for the last 10 years or so. Maybe I should try my hand at thai again in the near future.

 

[OrionN]

I did not dissect the fish. I think my observation is c/w the finding of the papers. I did not see any phenotypic differences of the non dominance fish. It is possible that there are sub-males in the group and I did not pay enough attention to the to see the differences between females and sub-males.

I am confidence that the amount of yellow is less is the dimorphic characteristics of the dominant males. Both of my dominant males started the same as females but change with time once the become the dominant male of the harem.