I keep a 180 gallon brackish tank for small natives, 1.004–1.007, that includes many South Louisiana fresh water fish known to tolerate light brackish, including mollies, inland silversides, mosquito fish, and least Killi.
I frequently collect in the local ponds around Baton Rouge for grass shrimp, and all of the above are commonly netted. My bucket is always filled with tank water, with a battery-powered aerator, so that acclimation can begin immediately. Usually, the tank water is also cooler, which I think helps.
I have caught both gizzard and threadfin shad as well. I have never been able to keep the threadfin alive more than 24 hours. It is the much preferred fish to me, since it stays relatively small. Gizzards can get huge and usually tolerate acclimation without difficulty, but often slowly dwindle, similar to the inland silversides, whose numbers decline slowly over 12-18 months. The gizzards also tend to lose their beautiful shine and just begin to look unhealthy over time.