Backyard Aquaponics
A place to discuss aquaponics

So my system is cycled and its time for me to add fish. I was going to start with some feeder goldfish and eventually get some channel catfish and/or bluegill. My FT is an old claw foot bathtub which is about 80 gallons... its not completely filled so I would guesstimate there is about 65-70 gallons of water in it. Additionally I've got two GB's around 20 gallons each and a sump that's around 30-35 gallons. So my question is how heavily should I stock my FT with goldfish?

The rule (at least for eating fish that will get big) is to stock according to the amount of flood and drain grow bed that you have.
3 kg of fish per 100 liters of grow bed
or
6 lb of fish per 25 gallons of grow bed

Use the grown out weight of fish, ya wouldn't want to put in 6 lb of fingerlings to a system with only 25 gallons of grow bed because they would immediately outgrow the filtration of the system.

As to how many goldfish to put in, I suppose that depends on how much you want to spend on goldfish. What will you do with the goldfish when you get the other fish? Just remember that whenever you suddenly increase the stocking density of a system, there will likely be a bit of cycle up to the new load and possible ammonia/nitrite spikes so monitor water quality carefully and go easy on the feed whenever adding many new fish to a system.

A bathtub is pretty shallow and there might not be much excess rim to keep a fish from jumping out, be sure to add the inverted fish trampoline (fish tank cover) over the top of such a fish tank to bounce the fish back into the tank if they start wondering too much about what is on the other side of the tank wall. (Even channel catfish jump sometimes, my second fish fatality was a catfish that jumped out of the tank.) Tank covers also help protect fish from hungry birds.

I honestly have no idea how to figure out the # of fish I need based on weight... can you tell me how much say an inch long fish weighs? Then maybe I can figure it out... As far as a fish tank cover, I've put on a screen mesh to keep out flower pedals and Racoons. It should be fine enough to keep the fish in as well. Metal mesh won't hurt them will it?

The problem with trying to give an inch of X fish equals X pounds, is that when you double the length of a fish, you octuple its mass, and therefore the load on the system. So, using Roz's numbers, you should be able to handle about 10lbs or so of fish at max load, live weight. For bluegill, that would be 10-20 grown fish (unless you expand your growbeds). You will have to decide what that means for your ordering plans.

Is starting with gold fish even a good idea? I wanted to use them first so if I messed something up I wouldn't kill fish that I want to keep... but if I don't kill them then....

gold fish are dirty fish - meaning that not only can the produce a lot of poop, but they can also live in squalid conditions. This makes them good for cycling.

If you are worried about what to do with them when you get your "real" fish in, you have several options:
1- Keep them in, and ignore them.
2- Move them to another system to start it cycling
3- Kill them for fish, chook, or people food

Your call.

I know there are several people that just kept the goldies in there. They can deal with nearly any condition, and they don't eat too much or crowd other fish too much, and eventually, they will pass on to the fishbowl in the sky, so you can send them there, or let them find their way eventually.

Grow out weight is what you are interested in. You'll have to figure out what the ideal eating weight for whatever fish you have is.. So like for tiliapia it's about 1lb when it's a good eating fish.

So grow out weight is easy to figure out there. 6 tilapia per 25 gallons of grow bed space..

If blue gill need 2lb to be eating ready then you'd have 3 of them per 25 gallons of grow bed. And so on...

If you don't kill them then you may want to sell them off, or keep them in your sump tank.

Perhaps you can have an "ornamental pond" (with a couple of grow beds attached) in the front yard?

You could use them to cycle your next system.

Tony

I have some (now) very large goldfish in my big sump, they keep the bottom of the tank clean from stray food.

So for my 2 grow beds I'll need about 10 fish. If I stock my FT with 10 goldfish then by the time I want to put in my "real" fish I will need to get rid of some to make room right? Alternatively I could just put in something like 3-5 instead, but if I do that will they produce enough nutrients for my plants? I've been thinking about getting some koi that I actually would like to keep... then I wouldn't need to worry about getting rid of them. Are they as hardy as feeder gold fish? Thanks for the help so far everyone!

I expect that people will often eat blue gill at 1/2 to 1 lb. Channel catfish can easily get much much bigger than that but the small size of a bathtub for a tank might be inhibiting for growing them very big. We regularly eat channel catfish at 3 lb or so but I'm sure many people will eat them at 1 1/2 lbs.

As far as how many goldfish to get, you don't need to stock to the max with goldfish just to keep the bacteria alive in the system. Get a bag full or something.

"I've been thinking about getting some koi that I actually would like to keep... "
As long as you realise koi can jump