You’d need a much larger container than 125g. Looking for an entire ecosystem where nature feeds everything and likely just the one predator. Easier to just get an automatic feeder with appropriate pellets.
I have to agree with Garriga here, for bigger, predator fish like triggers, you’d probably need something
substantially larger than 125 gallons - particularly if you want to ensure that they are getting a properly balanced diet (remember, what their food eats impacts its nutritional profile, and that impacts the top predator’s health too, so you would need to offer a good, varied diet to anything the triggers might eat).
That said, however, my recommendations for feeders would probably be salt water ghost shrimp (I’ve also seen these called Grass Shrimp and Marsh Shrimp), fiddler crabs, sand fleas, etc. for the crustacean side of things (at least one or more of the better options for this - several of which I haven’t listed - would be incredibly difficult to get to work in a traditional aquarium setup), and (if you can get any and manage to keep them alive and successfully reproducing in your tank) something like bay or buccaneer anchovies, dwarf herring, or some other (preferably multiple other) really small, marine, schooling fish. Some gobies or other small, shoaling fish could potentially work too (and I would recommend them), but, again, you’d need probably several dozen actively breeding (and successfully reproducing) at the least, and that’s really just not super feasible in anything short of an absolutely massive tank.
*As a note here, most fish species that could work really well for this are noted for not handling the transition from ocean to aquaria very well, and they generally are more “bland” colors (basically just silver), so they are both difficult to find and difficult to keep.*
It’s an interesting subject, and one that I admit I am looking into the feasibility of, but the sheer size and scope of what all is needed to make it work in a (almost entirely) closed system is daunting, and even after figuring out exactly what all would be needed to make it work, you would still need to figure out the proper proportions for each step of the food chain (i.e. something like I need X amount of gobies to feed Y amount of bass), and then you would likely need to remove the apex predators on occasion too (and this all only works if everything in the tank is breeding successfully and regularly, which would be difficult to ensure since many animals won’t mate under stressful conditions like being in a tank full of predators).
Anyway, great question with the unfortunate answer of “not in a tank that size.”
. Or dogs/Rabbits. Note this is a facetious comment.
