Suicidal mother fish

[DaveOponic]

A couple of days ago my son found an adult Tilapia on the concrete outside of the 1000 litre tank. I was in the shower at the time so asked him to pick it up and throw it back into the tank. He came back inside and said it had just swam around straight away when he dropped it into the water.

A while later when I went outside to feed the fish, I could smell a fishy odour near the tank. It usually means a fish has jumped out onto the ground. I looked around but couldn't see another fish. What I did notice was scores of tiny fish on the damp spot on the concrete where the Tilapia had landed and flapped around.

So a mother fish had leaped out and the impact had forced some of the fry out of her mouth.

Perhaps Kellen or someone else more knowledgeable on Tilapia might be able to shed some light on the behaviour here. ...

My tank is 1000 litres and currently houses around 50 Tilapia.. mostly adult size around 500g to 1 kg in size. A handful of smaller fish around the 100 - 150g mark also introduced recently. There are probably roughly equal numbers of male and female fish, based on past experience as I often find when harvesting that the chances of cutting open a female with eggs are about 50 - 50.

There are probably many reasons why fish jump out of the tank. Tilapia seem to be easily startled if there is a sudden movement, or when I try to net them they will become airborne. We also have a cat (that shows little interest in the fish usually) and there are often strays in our yard though again, never seen one near the tanks.

Would protecting the babies be enough reason to try to jump out of the water to a safer (?) place??
It made me wonder how aware the fish is of its artificial environment. Do Tilapia in the wild look for a quieter place to protect their young? Should I move the pregnant fish into a confinement tank?


Dave

[svc]

I don't know anything specific about tilapia, but my oscar's (an american cichlid) used to go a bit mental and eventualy jump out of the tank when it got too acidic.

[kellenw]

That's some good insight SVC! A majority of cichlids prefer 7.0+ ph. Acidic water makes ammonia and nitrite more toxic to them, and as a result they will often jump out of the tank. It's a possibly that they believe there might be cleaner water on the other side, though they've never given me a straight answer when I've asked. :) Tilapia like ph to be between 7.0 and 8.0 ideally.

Now, Dave, with your female tilapia holding eggs/fry... When the female is holding, she's very vulnerable to attacks from her other tank mates. As you know, tilapia can be pretty aggressive fish, and they have a tendency to pick on the weaker fish, often to the point of killing them. It's likely that your female was being bullied and was just trying to escape the mistreatment. For that matter, tilapia are jumpers by nature anyway. I've been hit in the head by flying tilapia more than once while doing water changes, trying to net out a fish or even during feeding. I would suggest covering the tank with netting and trying to maintain a ph of 7.0-7.4. If you aren't growing plants, but just raising tilapia in a RAS, a ph closer to 8.0 is even better. I would also suggest putting in some "hides" for females to find shelter in while holding. Clay pots or cut sections of large PVC pipe work well. Just try to position them so that they interfere with water circulation as minimally as possible (so they don't become solids traps).

Trying to move the fish to a confinement tank will usually backfire. More often than not, the female will spit the eggs/fry while you are chasing her with a net. If you manage to net her before she spits, she'll almost certainly begin spitting once in the net. If you get lucky enough to keep her from spitting still, placing her in a new tank will often cause her to spit as well. A better solution is to provide hides and hope for the best. You'll get plenty of fry production this way as long as long as you are at the ready with a fine mesh net when you inspect the tank.

Also, the worst culprits for eating newly released fry are the juveniles in your tank. The smaller fish have an enormous appetite for protein, and they aggressively target smaller fish until they get to about 4 or 5 inches in size. Even as adults, they'll eat some fry, but since fry are not the "big meal" they once were, in proportion to their own body size, the fry become a less desirable meal simply because they have to work so hard to catch so many just to fill them up (you would't work very hard for a grain of rice either... you're looking for a whole bowl). Basically, well fed adults will leave most of the fry alone. If they are hungry, all bets are off however. It's those small fish that are the fry eaters, so grading the fish and placing the smaller ones into separate tanks or even cages inside the tank will substantially reduce predation.

If you are seeking to breed a very large number of fish, establish a breeding colony of 4 or 5 females and a single male in a large aquarium (55 gallon or larger). It is the best method. If you can synchronize spawning (tightly controlling light cycles helps to synchronize them), you can simply remove the male when his job is done. Maternal mouthbrooding tilapia (Oreochromis) spawn about once a month if left to brood the fish themselves (only about 2.5-3 weeks if you strip eggs and artificially hatch them). This means, you can easily rotate a male in and out of the breeder tank on a monthly schedule. He'll likely only need to be in the breeder tank for about 5 days or so until being removed. This allows the females to brood their eggs and young (about a 10 day process), and provides them with about 10-15 days to rest and eat well before going again... all without being attacked and abused by the male who thinks it's spawn time ALL the time.

Hope that all makes sense. Let me know if you have any questions. :)

[Ravnis]

The hides and clay pots are very beneficial to raising fry. I put pvc pipe peices cut ~4-5 inches long over various sizes from 1/2", 3/4", 1", and 1 1/4". These were simply leftovers from various plumbing jobs. After this I noticed fry.

If you really want to get a lot of fry going, try putting a female and male in a tank outside in the sunlight with nothing but an air bubbler. The greenwater that will result will provide initial food for the fry.

Once you see the fry free swimming, remove the parents and transfer the fry when they are 1 cm or so long.

[Cecil]

Acidic water makes ammonia and nitrite more toxic to them, ...

Kellen,

I thought it was the other way around in that the higher the PH the more unionized ammonia there is? Or is this something just endemic with the tilapia's physiology?

[kellenw]

Kellen,

I thought it was the other way around in that the higher the PH the more unionized ammonia there is? Or is this something just endemic with the tilapia's physiology?

You're exactly right Cecil. You could probably explain this better than me actually, but I'm going to give a brief one for the benefit of anyone else reading who I could have potentially confused with my previous statement. hehe :)

With basic water, unionized ammonia (NH3) have no real way of "converting" to the less toxic ionized version, ammonium (NH4+). In fact, there is a danger with basic water, in that ionized ammonia (ammonium, NH4+) will "convert" back to unionized ammonia (NH3). Acidic water can help to keep the ammonia "locked" in the NH4+ form, which is less toxic to fish. The danger is actually in having acidic pH with high levels of ionized ammonia present. It's a time bomb waiting to explode. Your fish may appear to be coping fine with a high level of ammonia/ammonium in the water, but should the pH be raised through using a buffering agent, via a water change/addition or even things many people wouldn't think of (like adding some new limestone gravel to a growbed for instance), the quickly rising pH will result in a massive "conversion" of NH4+ back to NH3, and a total fish kill could likely be the end result. A person could say that for this reason, basic water can actually be viewed as "safer" since it isn't giving you any false expectations of what your fish can really handle.

Most Tilapia like a higher pH. Interestingly they are able to tolerate much higher levels of ammonia/ammonium in basic water.... levels that would be fatal to the large majority of our native North American fishes. It's a contradiction to conventional wisdom. This was the part I was pointing out, but should have explained a lot better. Sorry for the confusion my man! :)