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can determine the majority of the sexes in a clutch of eggs but with darts what determines it? To date there have been no cases of TSD found in amphibians.. (either XX/XY (male heterogamety) or ZZ (male)/ZW (female heterogamety).
Do you know the chances of that with a 50/50 chance of m/f for every egg? If this is further combined with with a thermal modification of expression of gender then you could easily see all of one sex or another. Sex determination in fish may be due to a lot of different factors including multiple sex chromosomes or none at all..
This would not change the genetic make-up, only it's behavior and function.
If you started genetically with a 50/50 mix(male/female), then subjected them to, in this case, temperatures that are too high during development, you could effectively end up with a 100males?
and this doesn't include potential effects on survivial of one sex or another based on some of the husbandry methods used.
There can be differences in survivial rates between sexes that can skew a sex ratio in one direction or another..
in some animals, maternal diet can affect offspring sex ratios (for one citation see Rosenfeld CS, Grimm KM, Livingston KA, Brokman AM, Lamberson WE & Roberts RM 2003 Striking variation in the sex ratio of pups born to mice according to whether maternal diet is high in fat or carbohydrate.
Now if this species is of the ZZ (male)/ZW (female) system then a breeding between a functional female and a (I don't want to use the word phenotype as its not correct in this usage) temperature altered female would only produce 25% genetic males... The other possible causes seem more difficult to test (i.e.
endocrine disruption, epigenetics, survivability and maternal diet.) As for azureiventris, assuming you had real males and females (not altered ones), wouldn't it be simple to confirm or eliminate temperature as a source for the large percentage of males.