I have done it myself in varying degree for some years. This year is no exception, although the project is not as big as I initially intended because I need time for other things too.
So, sometime mid-march, me and my son started setting up the tubs from last year:
It does not look like much, but once settled and the green leaves start to spread it gets quite nice:
The last pictured tub is planted with some Callitriche sp. and Fontinalis sp. found in a local pond.
It's a great way to find various plants and save money on the expensive ones at the garden centre!
The most problematic is to get the plants to stay where you put them when having this little guy around:
Placing the tubs is not always easy. I would like for mine to get more direct sunlight, but that is not possible due to different reasons. A place that gets a good amount of sun midday has worked well for me in the past, but is not possible at this time.
Fish-wise there is loads of choices you can make. There is a lot of readily available fish that do well outside. Common Xiphophorus from the local petshop, Tanichthys albonubes, Danio margaritatus etc.
Living in Denmark I look for fish that does well between 12C. and 25C. Soem that can go as low as 0-2C. expands the season a lot. The really hardcore enthusiasts have their fish fishes in insulated garden sheds during the winther to keep the just above freezing.
Danio margaritatus is a good garden fish in temperate climate.
You can also choose to get more "special" fishes like wildtype Xiphophorus. I have kept X. milleri outside for several years with excellent results. Also X. xiphidium does a good job on the tubs. For larger tubs/ponds, larger Xiphophorus, Jenynsia and Goodeid species is a good choice.
A classic; Xiphophorus variatus, wild form from Rio Nautla.
If it is warm enough fish like Poecilia wingei and reticulata are good fish for small tubs too. Another small livebearer that a favourite of mine is Heterandria formosa. If kept in a good tub, they can multiply really well during the season.
Looking in another direction, a lot of killifishes from Aphanius, Cyprinodon, Oryzias etc. can be kept outside. Although not something I have done a lot, I have kept a few Aphanius outside with varying luck. This year I am keeping Aphanius danfordi:
Aphanius danfordi "Soysalli" female.
Their tub has gotten a load of chalk to keep the watervalues at the hard end.
I have not looked for eggs yet, but will probably do so soon. From last year I have a picture of an egg in the filamentous algae:
More updates on my outdoor project and fish will follow over the summer. There is more to tell. I am trying some shrimps outside as well. Also, my tubs are in a more shaded area than I would like them to be so time will tell what works and what doesn't.