I spent a bit over 18 ,months working in Saudi Arabia in the late 1970s. I experienced 130F (54.4F) in the shade. This was in the summer on the Gulf side. I was then transferred to Jeddah. There I met one of the workers from Scotland. He was a fish keeper. He built a tank for SW fish, and then collected the fish from the Red Sea to stock it. The fish looked fine when I saw them, Unfortunately, some time later the seals on the tank let go., and that was the end of that
And I am not so sure that fish which did not develop over time to deal with very warm water are not at all harmed when their water is on the too warm side. Metabolism changes with temperature. So it is not a big leap to assume that while keeping goldies in overly warm water may not kill them, but I would bet it does shorten their lifespan if the water is warm enough for long enough.
Most fish do not require an exact temperature to the degree. They have a range in which they will thrive. In most places water temp is not constant 24/7, 365. It changes day to night and back again, it may also change seasonally. I have fish I have to raise the water to over 90 F when simulating a dry/rainy season. For the onset of the rainy I drop the temp from the low 90s into the mid 70s in about 36 hours in two stages. This should trigger them to spawn. This is how it works in nature so the fish are OK with such temps and changes.
So, based on your specific species, you may or may not be in a safe zone for temperature. Here is a research paper which may interest you.
Ford, T. and Beitinger, T.L., 2005. Temperature tolerance in the goldfish, Carassius auratus.
Journal of Thermal Biology,
30(2), pp.147-152.
https://www.sciencedirect.com/science/article/abs/pii/S0306456504001731
Abstract
- 1. Lower and upper temperature tolerances of 240 goldfish, Carassius auratus, were measured at constant acclimation temperatures of 5, 15, 25 and 35 °C via critical thermal methodology.
- 2. Mean critical thermal minima and maxima ranged from 0.3 to12.6 °C and 30.8 to 43.6 ° C, respectively, and were significantly linearly related to acclimation temperature. Acclimation temperature accounted for approximately 90% of the variance in temperature tolerance. Ultimate critical thermal minimum and maximum equaled 0.3 and 43.6 °C, respectively.
- 3. Integrating the temperature tolerance polygon yielded an area of temperature tolerance of 1429 °C2, which is approximately 17% larger than the polygon measured via the incipient lethal temperature approach. This difference is explained by methodological differences in these two techniques to quantify temperature tolerance.
Materials and methods
Goldfish obtained from retail pet stores in north Texas were placed in aquaria filled with dechlorinated Denton tap water under a LD 12:12 photoperiod. After attaining the selected acclimation temperature at the rate of 1 °C per day, fish were held for a minimum of 20 days at constant temperatures of 5, 15, 25 and 35 °C.
Basically what the above is saying is that the temperature limits for the fish were partially the result of first acclimating them to a specific higher temperature. That means gradually raising the tremperature so the fish can adapt to it to some extent. That is why the levels for both too cold and too hot, where it becomes fatal, depend on how they were acclimated in advance.