I may have answered a couple of my own questions (and importantly, question #2 in blue). I came across the following article:
Ajiaco-Martínez, R.E., Ramírez-Gil, H., & Arias -Castellanos, J.A. 2012. Fisheries aspects and reproductive biology of Hemiancistrus guahiborum, in a scree in the Bita river, Puerto Carreño - Colombia. Orinoquia, 16(2), 40-51. ISSN 0121-3709.
The paper is written in Portuguese and I am currently working on translating it to English. However, what I did already find is the following:
The size range for mature females was between 4.4 - 9.1 cm SL, with an L50% (estimated average size at gonadal maturity) of 6.4 cm SL. For mature males the sizes ranged between 5 and 12 cm SL, with an L50% at gonadal maturity of 7.5 cm.
I think this answers my question about how big the fish need to be before they can be sexed accurately; they should be sexable by 2" SL.
Another interesting point was:
The gonadosomatic index fluctuated from 0.3 in May to 8.1 in December, but there were no significant differences between the monthly values (P> 0.05) because of the high variability within each month's data.
In other words, at first glance this might suggest that they reach a peak spawning rate around December, followed by a big drop in spawning by May; however, because of the high variation from fish to fish, this probably means nothing and there are no real month-to-month differences in relative gonadal size. Unfortunately, data points are missing for the months of June-September because the area is inundated with high water flow so fish couldn't be collected; who knows what is going on during that time. Consistent with the statistical insignificance of this same data, the authors also found that females carried mature eggs throughout the year, suggesting that the species is an asynchronous spawner (continuous spawning throughout the year). And by inference, they should not be dependent on an environmental cue like a sudden drop in water hardness, which might selectively occur with seasonal flooding. However, I imagine that inference might be too simplistic.
As to potential egg mass numbers to expect, the authors wrote,
The absolute fecundity was 48 ± 19 oocytes, varying between 39 and 143 oocytes per female.
This is based on the number of developed oocytes present in the ovaries at any time; it is not, as far as I can tell in my translation, a count of actual eggs laid. Interpretation: If 39 eggs is minimum and the average is only 48, then the typical clutch size is probably going to be in the range of 40-60 eggs per female; don't expect females with 140 eggs very often.
Also, I found some potentially useful habitat information:
The Alizal is a typical rocky region along the Bita River [Eric's note: Bita = Vita?], located 21.3 km upstream from the Orinoco River (6° 12' 0.8" N, 67° 38' 20.5" W). It has a heterogeneous structure consisting of porous rocks interspersed with solid rocks, all of which will offer great possible niches for wildlife that inhabits it. The river water is warm, with an average temperature of 30.9 ± 0.3°C (maximum, 31.1°C; minimum, 30.1°C); the water is highly oxygenated (8.2 ± 0.1 mg O2/L) and slightly acidic (pH 6.6 ± 0.1).
In fairness, this pretty much states what we already know about other Hemiancistrus - warm, well oxygenated, slightly acidic water, and they like to hang out in rocky areas. None the less, it is reassuring to find this documented here....
...Wait, what?!?
Average temp 30.9°C ??? That's 88°F! That's hot!
(steaming hot, not steaming mad). At least it's a lot hotter than indicated in the CLOG (75-81°F). I wonder if that means they won't spawn eagerly in my tank at 80°F?
Curiously, I also found a sentence which read,
The red doghouse ("La cucha roja") lives in the Alizal at a density of 0.06 individuals per square meter
... Is the local name for
Hemiancistrus guahiborum the "red doghouse?" Please, tell me this is a mistranslation!
So blue question #2 is answered, but I'm still interested in people's feedback on blue question #1 from the last post... And about that "red doghouse" thing, too.
Cheers, Eric