I get the impression that they are able to spawn constantly and aren't restricted to a season.
this might also be caused by the fact that the tanks are run with parameters compatible with the rainy seasons.
think in terms of day-length, temperature, hardiness etc.
the fidh might feel like it's an eternal "september in brasil" and keep on staying in spawn-mode.
some catfishes have clearly a well-run inner clock, especially wildcaughts and F1's. Callichthydae and Loricariids are notorious in this aspect.
maybe these Auchenipterids are not like this and are more flexible with their spawnings, any time the circumstances are OK they can switch into spawning mode
this makes sense in a way; Callichthyds and Loricariids are in here for the long run. many species easily reach 10-15 years or more, so they have plenty oppertunities in the rain seasons.
these tiny Auchenipterids give me the impression of a life-in-the-fast-lane catfish.
like the smaller Schilbeids (pareutropius for example), small Silurids (kryptopterus), small Bagrids (Nanobagrus etc) none of these are fish that live for 15 years. so spawn succesfully they might be more oppertunistic and hence have a more flexible approach to spawning activities
Marc, this might also be the cause of one of your problems: intraspecific agression between the Tatia's.
if they keep "being stuck" in spawning mode, they also keep being stuck in fighting mode. spawning time is the time when males will fight much harder for territory, females to mate with and females will fight harder for territory to lay eggs and food to get gravid.
by keeping these fish in a perpetual rainseason you might end up with agressionlevels not seen in the wild.