I ordered some Fancy Goldfishes (about 5 boxes I think) from a wholesaler directly imported and forwarded and I got ....
...dead fish, unprofessinally packed.
Cooling packs were even included to the fishbags containing slimy, smelling water, yellowish and lethal....the bags, not the packs...
All fishes died within one week, although most arrived dead alredy.
I learned that professionality in avoiding distress for fishes is the most important quality a trader should have.
So I never ordered again more than 20 fishes per Box (approx. >200-500 is usual

)...
...and I quarantine bevor I resell...
So if you have trouble with some fishes from one trader it possibly could be bad luck, if it increases...change him/her...
