Substrate in tilapia tank?

[James Stratton]

I have a simple ebb and flow system with a 200 gallon fish tank and two grow beds totaling approximately 27 square feet of media grow space.

Problem is that, although I've been told by everyone how prolific tilapia are, mine must be eating all their young because only a couple of newborns have made to past the fry stage in the year and a half I've had my system. I have white nile tilapia from a local source down here in Southeast Alabama.

I guess my topic for discussion is this: Is it okay to use some pea gravel in the bottom of the tank to aid in breeding and growing out of fry? I currently have a triangle of large pvc drainage pipe for shelter. I originally thought that my fish were simply not breeding or were eating all of their young until a couple of young fish made it to adolescence. My water stays kind of murky but the fish seem to like it. That is why I don't see babies in the bottom of the tank.

What say you? any ideas or suggestions of how I can get my tilapia to breed in a way that I can, at least, maintain my population in the tank. Right now, I'm down to about 12 tilapia as some have died, and I ate some. Hey, I got hungry.

[Alex Veidel]

Yes, well, tilapia are incredibly hardy, but I don't know of a fish that's hardy against being eaten. Kind of a trump card for animal kingdom :D

It's usually recommended that you separate your fry from your adult fish for that reason. How did your 12 tilapia die? Did they have bites taken out of them? What does your water chemistry look like right now?

[Jim Joy]

Gravel or other media in the bottom of the fish tank will collect solid waste.  A bare bottom will actually improve the reproduction success as the female has to pick up fertilized eggs in her mouth.  Gravel will hide some eggs.  So, no gravel or substrate is the best approach for breeding.

Try assembling a matrix of PVC pipe to create a protective area the adults are too large to enter.  I used 4" PVC sewer pipe for the adult females to take shelter in.  The area between pipes is a good fry shelter area.   Or, you could build a baby habitat using 1" PVC pipe that only the babies can get into.  

Another idea is to use the plastic grate covering ceiling florescent lights to make a wall or floating basket that adults can't get through, but the fry and small fingerlings can.  Some plastic plants to provide cover will attract the fry seeking shelter.  Home Depot and Loews both stock rectangles of this lighting grid.

After the fingerlings grow to around 3" they can survive with other larger juvenile tilapia.  Large adults generally won't eat other fish.

Or, just accept this is natural birth control in your aquaponics tank.  Bring one male and four females inside to live in a 50 gallon or larger tank to make babies.  You will still have to protect the fry from other adults.  I use 20 gallon holding aquariums to keep the fry and fingerlings away from adults.  YouTube videos show how to tell when the female is pregnant and how to take the fry from her.  Females don't eat until the fry are large enough to take care of themselves.  It is better to remove the fry from the mothers mouth and let her start eating again.

[James Stratton]

Thanks for the reply, Jim. I know this is going to seem odd, and I believe what you say about the harmful affects of pea gravel in the bottom of my tank. Strange thing though, shortly after posting this, I found a large number of tiny fry swimming around my tank. I quickly prepared a twenty gallon tank as a nursery and transferred them to their new home. I continued to scoop fish out of the tank for the next two weeks and had to add a ten gallon tank to expand the nursery. It could have been the weather that caused this sudden spike in new babies.

Anyway, I have so many fry now that I'm getting ready to harvest most of my large tilapia and put the fry in the 200 gallon tank. Before I put the new fish in the big tank, I'll take the opportunity to remove as much of the gravel as I can.

As long as my tilapia have babies like this at least once a year, I should not have to worry about restocking!

[Jim Joy]

One other thing to think about.  Over several generations - a few years - genetic inbreeding will happen.  It's not a bad idea to buy or trade a few fish to introduce new genes to your herd over time.

Good luck.  Tilapia are tasty fish that know how to keep ahead of predator appetites - including mine.  Blue tilapia remind me of little swimming fish taco's.