Sustainable stocking of tilapia fish tank(s)

[S.E. Bastian]

Hello:

Greetings! I am new to aquaponics. I am trying to figure out, how does one stock fish, Tilapia, such that:

• the 'weight' or 'size' or 'number' of fish will supply the grow beds nutrient requirements at any instant in time
• that fish can be removed at intervals (weekly, monthly or quarterly) for the table
• that fingerlings are added back to the system to maintain the dynamics - fish; fish waste; bacterial conversion; plants nourished; clean water re-circulated

Assuming eight months to table weight, it would appear that maybe new fingerlings need to be introduced say every two months as older (eight month old) fish are removed.

Does this mean that one needs four independent fish tanks (one for every two months)? And when the mature (eight month old) tank is emptied, this is the entrance point for new fingerlings to the system? Or can one tank be used, with simply hunting down (fishing net) the mature ones and subsequently adding new fingerling stock to this same tank? In other words, that different sized Tilapia can happily co-exist with each other?

Further, how does breeding/hatching of new fingerlings by 'occupants' of the fish tank complicate this dynamic?

Thanks. 

[Suzanne Hayes]

As far as can the different sizes coexist, the answer is yes with the exception perhaps of newborn fry, they get eaten.  I have 1, possibly 2 females that are breeding about once a month.  I've only been able to harvest 2 partial batches of fry, the rest get eaten by the adults, which works out alright as I only have 100g tank and 25 gal sump.  The fry I save go into a separate tank to grow and I have sold or traded most as there were just too many.  I just harvested about 50 or so more 4 days ago and these will be the last I try to catch for a while.  I have had 1 or two fry survive in the big tank on their own as I have pipes and pots for hiding.

The other thing to keep in mind is that unless you are using males only, not all the fish will reach plate size in 8 months. Even with all males the more aggressive ones will grow faster as they will get more food.

[S.E. Bastian]

Interesting.......THANKS!

I saw a design some time back with a 'fingerling' tank atop the regular fish tank. Is a fingerling tank the place to raise recently spawned batches of fry? In other words you harvest the batches of fry from the main fish tank and place them in the fingerling tank? Would a 55 gallon blue barrel serve this purpose? How long are the fry kept in the fingerling tank before being introduced (returned) to the main fish tank?

With respect to male growing faster than female - is it practical to sex the fingerlings before returning them to the main fish tank?

All sounds interesting.....fun.....work.

[Suzanne Hayes]

That sounds like it would work, as long as there is some filtration either separately or as exchanging water from the main tank.  One method I have considered but haven't been able to put in place yet is to put a divider in the tank itself to protect the fry without having to create a separate system.  Some type of mesh divider or screen.  Pet stores sell these for breeding/spawning but none are the right size for my tank.

As far is when to move them back, I read somewhere that tilapia will eat anything they can fit in their mouth so it would depend on the size of the adults.  I have had a couple little ones survive on their own, but that was 1 or two out of hundreds. 

For me it really isn't practical to sex the fingerlings as I traded or sold most of them and I want a sustainable population.  Besides catching them is quite a chore even in a small 20 Gal tank, they move pretty fast and can jump out of the nets.  I guess a but based on size since all were hatched at the same time and there was a noticeable size difference.  Also somewhere in this forum (just can't remember where) there is a lady who posted an observation about dorsal fin shape and gender with males having more sharply pointed ones.  From observation on a couple fish that I know the gender that seems to be confirmed but I don't know how reliable it truly is.

Good luck!

[S.E. Bastian]

Thanks for your comments. Much appreciated.