It’s not as easy as simply dumping a cooler or bag full of new fingerlings into prepared tanks and hoping for the best when you first get your order of fish. Whether you’re setting up fish tanks for the first time or are just adding the latest batch of fingerlings, you’ll need to quarantine the fish and perform tempering procedures to acclimate them to the system’s water supply.
Brand new systems can function as the quarantine area for the first round of fish, but all future additions must start out in a tank separate from the rest of the facility. Even when you’re buying from the most reliable suppliers, it only takes a single infected fish to introduce diseases and parasites that spread rapidly and costs you thousands of dollars to fight. Keep new fish in a purge tank for at least one week, preferably two, before introducing them into the stock tanks. Watch for signs of infection such as low feeding rates, sideways swimming and floating, reddened or tattered gills, and tucked fins.
All new fish need tempering, even the very first batch introduced into empty tanks that have cycled and tested. Check the water the fish are packed in for pH and temperature. Fish can only handle a single degree of pH change and two degrees of temperature change per half hour, so you may need to spend a few hours slowly introducing them to the water. Use the hauling tank they arrived in or set up a separate tank for tempering and fill it with the hauling water. Replace 10% of the tank’s volume with the system water every half an hour to slowly acclimate the fish without shocking them. It takes hours to eventually reach a level where they can be released into the main tanks, but the time spent on tempering pays off with healthier fish that start eating and growing almost immediately, rather than lingering or dying off from stress and subsequent disease.