Fish Growth Stage Management

[Cameron Smith]

I have a question for when I start to grow edible fish in my next, bigger system. When the fish are small fry, I can fill the tank with many fish. When the fish get too big for the tank capacity, obviously I have to move some of them to another tank. Generally speaking, how do aquaponists manage this movement and keep their systems filled with fish at all stages without overcrowding and without wasting tank space? 

[Robert Rowe]

Cameron

I am also new to Aquaponics but in pretty deep. My 1st FT 220 Gal. has 23 Red Comet Fish. My 2nd FT 700 Gal. with a 10 ft geodesic shell, will house my 30 Tilapia presently in an aquarium indoors. My plan is to  Let nature take its course and let the Tilapia feed my Media beds and raft tanks and see what happens with reproduction. My estimated capacity is 140 adult Tilapia, and I have provisioned for a nursery area for fry and fingerlings. I hope to be able to sell some of the new fingerlings to keep the population down. If the population gets out of control, I plan to add a catfish which reportedly will take care of the fry, fingerlings?

[TCLynx]

Unless you are planning a rather complex and extensive operation, I'll recommend to keep it a bit more simple.  Few backyard system operators are going to weigh their fish weekly to make sure they are feeding the exact right % of feed and keep it balanced with an exact right % of plants in the right stage of development.

I generally say, stock the right number of fish so that when they are grown out, you do not exceed the max amount of fish in your system.  When fish are small, they may not meed the supposed recommendation of fish weight int he system but remember that small fish will eat more food compared to their body weight and you can feed them a higher % of protein as well to provide more nutrients for your plants.  And if you are doing a system where you are not removing the solids, you don't necessarily need to keep up an exact amount of feed per amount of plants in order to keep up a steady supply of nutrients once the system matures a little bit.

Aquaponics is a balance but for backyard growing, you don't necessarily have to get too wrapped up in numbers and weights to get good growth.

[Jim Fisk]

What they said.

I really like TC's relaxed but educated approach to things. She is one of my main gurus here.

I keep my counts way under which is a benefit to having a large home system. I don't even try to max anything out, not even veggies as crowding breeds such things as white flies. (have I mentioned those %&^$# flies before) Under 70 fish in the system till Spring and warmer temps as bacteria are half asleep at Winter temps and by that I mean 50 - 60F. (Trout temps.) The cat fish are always asking me to turn up the t-stat as is the Comet and the one remaining bluegill but they'll live. (knock on wood) I would wait till you are way further down the road before you worry about keeping anything at the max. Designing and building the system is the fun part. Figuring out what's killing fish and breeding insects, now that's the real challenge.

[Linda Logan]

I have a 300 gallon tank.  Right now there are 10 5 - 6" tilapia and about 60 1-2" goldfish.  My system is about 2 +months old.   I have 3 grow beds 3X6.  I have one bed planted but things are small as I'm not doing added light and I live in Portland OR.  I know starting Feb/Mar I want to up my planting.  About how many tilapia (they will be fingerlings) can I add to support my expanded planting?

TCLynx said:

Unless you are planning a rather complex and extensive operation, I'll recommend to keep it a bit more simple.  Few backyard system operators are going to weigh their fish weekly to make sure they are feeding the exact right % of feed and keep it balanced with an exact right % of plants in the right stage of development.

I generally say, stock the right number of fish so that when they are grown out, you do not exceed the max amount of fish in your system.  When fish are small, they may not meed the supposed recommendation of fish weight int he system but remember that small fish will eat more food compared to their body weight and you can feed them a higher % of protein as well to provide more nutrients for your plants.  And if you are doing a system where you are not removing the solids, you don't necessarily need to keep up an exact amount of feed per amount of plants in order to keep up a steady supply of nutrients once the system matures a little bit.

Aquaponics is a balance but for backyard growing, you don't necessarily have to get too wrapped up in numbers and weights to get good growth.

[TCLynx]

What kind of grow beds Linda?  Are they media filled grow beds or are they rafts?

ya know with 60 goldfish, as the weather warms up, you many not need to add that many fish.  Just feed more.

If growing fish out to 1 lb each, that much raft bed could support say up to 18 fish, that much media bed could support about 54 fish.  Now since you are probably not planning to grow out the goldfish all that big you may be ok with the number of fish you have if the beds are media beds.  If they are raft beds, you may be over stocked.  Goldfish can eat and poop a lot.  If you feed high quality feed and feed the fish as much as they will eat in 10-15 minutes up to 3 times a day, you may find you will have too much nutrients.

[Linda Logan]

I have 3 (3' X 5') 12" deep media beds filled with large lava rock on the bottom and pea gravel above.  I don't plan to grow the goldfish out but I do the tilapia.  I had the impression with that I could have a lot more tilapia.  Right now they eat everything I give them in under 3 minutes and want more.  I feed 2 to 3 x a day a combination of good goldfish food and tropical fish food.  When these are finished I was going to look into another feed.  Any suggestions?

TCLynx said:

What kind of grow beds Linda?  Are they media filled grow beds or are they rafts?

ya know with 60 goldfish, as the weather warms up, you many not need to add that many fish.  Just feed more.

If growing fish out to 1 lb each, that much raft bed could support say up to 18 fish, that much media bed could support about 54 fish.  Now since you are probably not planning to grow out the goldfish all that big you may be ok with the number of fish you have if the beds are media beds.  If they are raft beds, you may be over stocked.  Goldfish can eat and poop a lot.  If you feed high quality feed and feed the fish as much as they will eat in 10-15 minutes up to 3 times a day, you may find you will have too much nutrients.

[TCLynx]

Ok if you have to ask how much fish you can have, the recommendation, if you will grow the fish out to 1 pound each, you can stock as many fish as you have cubic feet of media bed.

So, 3x5=15 x 3 = enough filtration for 45 fish growing out to 1 lb provided you also have enough fish tank water, circulation and aeration for those fish.

Now I know people do manage to grow more fish than that but often they are skirting the edge of sanity especially if anything goes wrong as the fish are nearing full grown.

Remember that if you still have lots of goldfish in there, they will be utilizing some of that filtration capacity and growing and using oxygen etc so you need to adjust the total number of tilapia you keep if you are going to also keep the large number of goldfish (just because you don't plan to eat them doesn't mean they don't count in the system bio-load.)

Now if you are an expert fish keeper and do your water testing religiously and often to gauge how much to feed and harvest fish to keep the overall fish load within bounds and have plenty of aeration and backups etc I'm sure you can keep more fish but if you are that expert, you wouldn't have asked the question.

[Linda Logan]

You're right I'm not that expert.  Is there a guide on how much aeration to have.  Right now I have 4 small air stones.  I have probably about 250 gallons in fish tank.  In terms of testing I am.  Feeding is a question for me.  I'm feeding so all is eaten in under 3 minutes and everyone still acts hungry, (e.g.  nothing left on the floor of tank etc)

Based on what you've said I'll add 10 - 15 more tilapia fry and stick with that.  I am keeping a back up aquarium for sick fish.  But would love to have another tank just for tilapia fry but space and heating, aeration, etc seem too much to take on.

Thanks for your help and more information to my lack of experience is always appreciated.

TCLynx said:

Ok if you have to ask how much fish you can have, the recommendation, if you will grow the fish out to 1 pound each, you can stock as many fish as you have cubic feet of media bed.

So, 3x5=15 x 3 = enough filtration for 45 fish growing out to 1 lb provided you also have enough fish tank water, circulation and aeration for those fish.

Now I know people do manage to grow more fish than that but often they are skirting the edge of sanity especially if anything goes wrong as the fish are nearing full grown.

Remember that if you still have lots of goldfish in there, they will be utilizing some of that filtration capacity and growing and using oxygen etc so you need to adjust the total number of tilapia you keep if you are going to also keep the large number of goldfish (just because you don't plan to eat them doesn't mean they don't count in the system bio-load.)

Now if you are an expert fish keeper and do your water testing religiously and often to gauge how much to feed and harvest fish to keep the overall fish load within bounds and have plenty of aeration and backups etc I'm sure you can keep more fish but if you are that expert, you wouldn't have asked the question.

[TCLynx]

One step at a time Linda, learn as you go, sounds like you are doing pretty good.

Aeration, one rule of thumb I've been told was 1 CFM (cubic foot per minute) of air for every 400 gallons of fish tank.I know there are plenty of people who don't have that much, I was setting that up for my battery backup aeration for when the pump went out but I leave the aeration running even when the pumps are working too and the fish seem to like it better that way.  Anyway, to figure out aeration is a bit like figuring out flow rates since it takes some pressure to push air through the air stones and then it takes a certain amount of pressure to push air down below the water.  So you have to find the chart or graph that tells how much air your pump supplies at different water depths or psi and how much restriction your air stones cause.  Some charts will tell you how much air the pump supplies at different water depths and others will give you the information in psi.  Some air stones will require the same pressure as about 10" of water depth and 28" of water depth is the same as 1 psi.  Now I'm sure that might be more confusing than helpful for you at the moment but this is mostly to say, how much air can your air pump provide, rather than simply how many air stones do you have in the tank.  There are some air stones that can deliver 1 whole CFM while small air stones might only deliver 0.05 CFM.

As for feeding, you can likely increase the feed to as much as they can eat in a 5, 10, even 15 minute time period but as you increase the feeding you need to keep checking your ammonia and nitrite to make sure your bio-filtration keeps up.  If the ammonia or nitrite levels start to climb above 0 ppm, back off the feed amounts a little bit until the levels are back to 0.  Daily water testing while increasing feed rates can be a good idea to make sure you don't increase the feed too much too quickly.