Awesome photos.
It's been a while since this info was shared, and since aquanero emailed me about same fish this week, I figured this may be a good place to paste that same info (see below).
The distinction that my collector/shipper made in regards to this fish versus citrinellus is as follows:
The name 'Isletas' means 'islands' in spanish. That name is given because these fish were collected behind islands in the great lake where they occupied a specific niche.
Citrinellus are found in and among the rocky habitats in relatively deeper waters, whereas these 'Isletas' were found exclusively in a totally different biotope.
The area where they were collected was shallow, muddy, marshy.. It's important to note that all ages and sizes of this fish were represented in this same habitat.
They were not found outside this area and appeared to be utilizing the very niche that citrinellus does not occupy.
The collector is a PhD and has spent many years studying and teaching biology and ecology of Nicaraguan fauna.
His observations and conclusions were based on countless hours of diving experience in many of Nicaragua's lakes and rivers. I was lucky to have someone with his knowledge to recognize the significance of these observations.