Why newly-arrived Otos can die like flies. Otocinclus are notorious for dying like, well, like Otos,—when you first get them home, though once they've acclimated to your planted tanks they live for years. Aquarists beat themselves up over this, but I think it's not our fault. Here's the thing: no vertebrate vegetarian can digest cellulose, not one! so each carries a species-specific community of anaerobic bacteria (and some protozoans) that do the work. Ruminants even have a special fore-stomach (the rumen) where grass is fermented in a rich bacterial soup, protected from stomach acids. Dairy cows are nourished, not so much by grass, but by bacterial by-products, which include some vitamins, and by digesting some bacteria: cow breath! Now, look at the size of the Oto. Scarcely room for a billion gut bacteria in there to do the work, eh? Starved Otos in transit can lose so much of their gut bacteria that the internal ecosystem doesn't revive,— even with a glut of tasty algae in your tank! It just passes through their system, like when you were too hasty eating that corn-on-the-cob, remember? Not much nutrition when the kernels passed right through, because your system couldn't digest them open. Otos need a jungley tank with lots of leaf surfaces to run over. (If you can count your Otos, you haven't got enough plants.) But the vegetable supplement we give them (zucchini, spinach, etc.) has to be constant, or else they won't have the gut bacteria to process the green treat when it finally does arrive. Hopefully with your algae, and plenty of natural green cover, and your constant feedings of spirulina flakes or algae wafers plus veggies every few days, Otos that aren't too far gone should thrive with you. Females are noticeably wider and plump, but though a healthy male is leaner, he shouldn't have a concave look, when seen from the side.
from time to time.
