Fish are very finnicky, the slightest change can be traumatizing to their health, and could possibly cause death. You will want to be sure that the fish have plenty of time to acclimate to their new environment. It’s not just the temperature of the water they are acclimating to…there is also pH levels, oxygen levels, nutrient contents, and many other things to consider.
We have heard back from customers who waited until mid-summer to treat their pond and stock fish. Adding fish to their overgrown ponds and immediately hammering the growth with chemical almost always ends in fish fatalities. Acclimating fish are not used to either the chemical or the drastic change in oxygen levels and can end up being too much for them to handle. This is just one reason why you must be cautious with when and how you stock your fish for the best results.
So when is the best time to stock fish? The safest time would have to be in the spring and fall months. The cooler temperatures and higher oxygen levels are factors that allow for an easier transition for the fish. Stocking fish in extreme temperatures can potentially be hazardous to your fish. You’d rather be safe than sorry and stock your new fish at a time that is less risky for their well-being.