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These fish are almost all suitable for maintaining and breeding in an unheated aquarium. their usual range is from 60 degrees to 77 degrees. These fish can tolerate temperatures between 46 and 86 degrees F. In their natural locations the temperature varies similarly and the fish need this natural variation seasonally to remain healthy. The winter temperatures of these fish in their natural ranges are can be 46 to 61 degrees. G. balzani populations do occur much deeper into to Brazil and they will need slightly warmer temperatures.
I have kept at least 5 species, and found if kept at tropical temps all year round, they become prone to disease and fungal infections. So I started putting Gymno gymnogenys “yerbalito” in my unheated basement in the winter. Temperatures would dip into low 50s and high 40s F. When they came out in spring they’d color up very brightly, and spawn almost immediately. – Duane Stuermer
During the summer these fish can tolerate water as high as 86 degrees without problems. The winter cooling period is not only normal but is needed. When kept year round at higher tropical temps like most keep heated tanks, they tend to get disease. They need a winter rest. In the unheated tank or basement they are treated to a winter break of 60 degrees for 2 or 3 months. This is a normal cycle for them and helps keep them healthy and also primes them for spawning."
