Backyard Aquaponics
A place to discuss aquaponics

A commercial producer of tilapia recently told me it is very easy to sex tilapia - and that you need to in order to stop stunting growth through over-breeding. He wouldn't tell me how though. I have been watching my fish to see if there is any noticeable difference..... can't see it! Anyone know the secret?

Chelle

Well, this can be an easy answer or a complex answer.

In commercial growing they need to raise all male stock in order to keep it profitable. Many do it by feeding hormone laced feed to force all the fry/fingerlings to develope as male. Another way to do it is through special hybrid cross breeding that will produce all male offspring.

For smaller scale home production, it may not be that necessary. Janet has been raising mixed stock for a while now.

As far as actually sexing the fish. It isn't so hard though you probably want to see it done sometime in person since a description or pictures rarely give the full impression. Anyway, I was shown. ya catch a fish that is around 4" since much smaller and they may not be fully developed yet and that is where the errors come in I guess. So you catch the fish and hold it gently but firmly upside down so you can clearly see the body just in front of the tail. Give a little swipe with some Gentian Violet (anti-infective first aid antiseptic that will stain things a strong violet color) then wipe off with a bit of paper towel or tissue. This usually makes the sexual parts easier to see. The female will have a slit that goes from side to side while the male will not. Some people have tried food coloring for this process but the gentian violet seems to work better as far as I can tell.

If you are planning on large stocks then doing this manually is going to be a big drain and it might therefore be better to get some special breeders so you can get the all male offspring. If you are just growing for family consumption, then mixed stock is probably not such a big problem. I've got mixed stock and I put them in a mesh cage within the tank so hopefully little/no successful breeding is going to take place in there but I still have the mixed stock so I can pull out some fish and place them in a breeding tank when I want to increase my stock.

Wow. Thanks! I think I will just leave them be for now. They are not growing very fast but I think that might be due to the lack of heating in winter. The pond is outdoors. When my greenhouse is finished and they are more protected then I will re-evaluate. I would like to get them to a sizeable growth as quickly as possible but using the most low-tech methods possible....within reason. I probably have to power the pump. I know tilapia grow rapidly in warm water. Maybe a solar water-heating system together with the new GH will step up growth. Thanks again TCLynx! Most helpful.

What is your water temp? My tilapia didn't really want to eat all the well until my water temp got over 25C. If you search the web, there are plenty of sites that have good photos of the male vs female genitals. It's a little hard to tell with the smaller fish but in general, if you can see two openings, it's a female. Good luck!

Sexing Tilapia is not that easy,,,,for beginners a bottle of water soluble dye ( one drop on genetalia area) helps.The squeeze methods also helps,,white water = male.
Several times I've offered my " Prada hand-bag in one corner and beer in the othe ""method" but that doesn't seem popular.

For now , why not keep both,,,after the female has grown her first batch,,remove her , add some dye,,and memorise,,,do same for male and the differences will become obvious,.....,there is nothing equal to ACTUALLY seeing it (far better than pictures).

I agree that actually seeing the sexing of fish take place in person makes trying it yourself much easier! I've seen pictures before but that would not have helped but having seen it done at MorningStar when I went to get my fish, I'm now much more comfortable and confident doing it myself.

Thanks all! I think I will just leave them be for the moment. So caught up in trying to get my Greenhouse built asap and get them into warmer waters. My water temp is nowhere near 25C. More like 10C most of the time and at night drops even lower. They still take food in the middle of the day from me though. I was surprised. The pond even has a bit of algae so they are not starved. When I have that settled then I am going to learn to sex them I think. The first breeding resulted in so many fish but now very slow growth.

Have a great weekend
Chelle

Wow, at that temp, it is amazing the tilapia are even moving!

Yes, it is. I was so ignorant when I bought the fish. Delighted to have some in the old reservoir. Out of 100 fingerlings only 11 survived the first winter. It then went down to 8.... each one counted daily. SInce then they have thrived without heating. I think it was survival of the fittest and acclimation. Now have about 300. I want to give them a bit warmer environment in a greenhouse to accelerate growth. They stop growing much every winter. No surprise!

The mongrel Tilapia we unfortunately have in Australia have distinctly different shaped heads between the sexes. As to water temp. the smaller fish survive low water temps much better than the larger versions. From memory fish kills tend to happen on mass at around 14 degrees celcius water temp. obviously any stressed fish drop first.

Did read some good work on using stocked predators in commercial applications to prevent stunting of stocked populations, nile perch was one fish being used in Africa to do this. Do a google search to find articles. You may be able to stock one predator and not worry about stunting.

Currently working with my fellow volunteers stocking predators into a local Lake to overcome the stunting problem and make the population more vunerable to cold snaps. Hopefully good bye Tilapia and hello our own native fish.

I found what you wrote interesting Shayned. I plan on day to fill in between 2 hills to have a miniture "lake". The idea of predator fish might well bear thought to keep the stock healthy.

I seem to have a hybrid tilapia but the heads of all the fish are the same in shape. No ease of selection for me there. I put in 4 different kinds and ended with 2 kinds. The one kind of the 2 remaining only has 2 fish.... a darker fish with running spots on the sides. They have never bred and so must be of the same sex. The other kind has bred prolifically. It is pearl coloured with turquoise and green colouring. I must admit to being quite delighted with them. I have looked everywhere on the net to find a match and a name but have not been able to do so and now assume them to be a hybrid.

If your observation that only the smaller fish survive very low temperatures also applies to mine then I am more greatly motivated to place them in the warmer temperatures of a greenhouse by next winter. It is interesting that when the old reservoir I have them in has leaked its slow leak to a low water level that they will not come to me for food, but when topped up to a depth of 2 meters they will readily swim around and investigate what I give with interest even in the middle of winter. I think greater water depth protects from extreme temperature fluctuations and so plan to build this into my new project.

more water = more stable temps = happy

Cyara,,,be a little carefull going too deep with your ponds,,you'll run into an issue called "stratification".Nothing that cannot be rectified,,but something to be aware of in the planning stages.

.Predator fish to control excess breeding is standard practice in basic set-ups throughout SE Asia,,in Thailand they use "snake-head fish".

Hi Chappo,

What exactly is stratification?

I want to slope the planned new circular raceway down to 2 meters from 1 meter (or 1.5m) ....and a meter in width. This is to manually sweep solids down the slope and then along the bottom of the slope to a slightly lower pit - near the pump - for easier extraction. I am considering a separate little manual pump for that aside from the normal water flow pumping to the beds. This is to place the solids straight onto the beds without possible clogging of pipes.

Would manual sweeping of solids disturb any "stratification"?

Cyara... stratification generally occurs in lakes/ponds deeper than the 1.5-2mtr you intend...

Basically light/heat will only penetrate the top 1.5 mtrs of a water body.... thus the top layer (1.5mtr) can be considerably warmer than water below it.....

i.e it forms a distinct layer or strata .....

The lower layer is often so cold that bacterial decomposition of rotting material/algae etc tends to cease and anerobic conditions take over... this sucks the oxygen out of the bottom pond layer...

Problem with stratafication is that under certain conditions... the layers invert/flip.....

Result ... sudden major change in water temperature and DO levels.... almost always certain and total fatalities of any fish stock....