Rotifer density and oxygen depletion

[Tomoko Schum]

I lost the majority of my clownfish larvae on a second day after capturing them with a snagger. I need your help to decipher what seems to be the real cause of this so I can avoid it in the future.

I am suspecting oxygen depletion as the cause of the loss since Seachemfs ammonia badge in the larvae tank showed no ammonia and rotifers and mysis shrimp babies (came in with larvae) are thriving in the larvae tank. I added a large amount of rotifers to the larvae tank a day or two before capturing the larvae and the rotifers have gotten really dense because of live phytoplankton I added while waiting on eggs to mature. Two collonista snails in the tank are doing fine as well.
I use parent tank water (a 120 gallon reef tank with very clean water) for larvae and fry tanks. I aerate the tanks just enough to create a very gentle flow in the tanks.

While I am not new to fish breeding (many years of fresh water fish breeding experience plus raising two batches of Bangaii cardinalfish fry), I am still very new to raising clownfish babies. The lost larvae were from my clown's second clutch of eggs. My clownfish fry from the first clutch are doing really well so far.

TIA,

Tomoko

 

[MYDRAAL]

Seems like I read somewhere that the first couple of batches may not be the healthiest of eggs. Maybe someone can right or wrong me on that . What are you feeding the parents? Is the tank water your using sterilized? I had an issue with my last batch to, so I'm tagging along to see what may come up to cause this that I haven't thought of.GL :rollface:

 

[Tomoko Schum]

I feed my adult fish a variety of frozen food including mysis, squid, krill, cyclopeeze, scallops, clams, etc. in addition to live food (adult brine shrimp, rotifers, copepods/tiggerpods, and daphnia.)

I did not sterilize my tank water.

These two clutches of eggs may not be the parents' very 1st and 2nd clutches since the number of eggs are very high (more than 600 eggs easily) for the first few clutches. They are most likely the 1st and 2nd clutches that "I" noticed.

I almost missed the hatching of the 1st clutch and ended up scooping just eleven larvae (all I could find that night) with a cup after they hatched. I have managed to save all eleven of them and they are looking very cute.

The only differences in the way I handled and reared my two batches of larvae are the number of larvae and the method of capturing. The first batch of larvae was gently scooped up with a cup. The second was captured with a DIY larval snagger rigged up with an airlift tube. This might have been a bit rough. I ended up with 15 to 20% loss in the next morning, but the remainders were swimming fast and eating well.

So you see, I am a bit puzzled about this sudden loss...

Tomoko

 

[FB]

Could be a couple of things!

Can you describe what they were doing before they died.

1. Larvae damage.
When mine were damaged they were swimming in very irregular patterns. i.e. Circles and never hunted. Also if your bubbles are on too high this can damage larvae. When they are really young mine is about 1-2 bps no more. Once past met I increase 5-6 bps.

2. Small yolk sac
Yolk sac supports them for 24 hours or less but they still do not learn to hunt and starve. Were the clowns hunting? Kink and lurch? This would be my bet.

3. Ammonia - this is obviously unlikely in your situation as other critters are living in the same water.

I'm not sure about oxygen depletion but I would doubt it. All the other animals in the tank require oxygen as well!

 

[Tomoko Schum]

The larvae was hunting well. The most of them had the silver bellies (pucked with rotifers) on the 2nd day. There were a few that swam erratically. Some got nearly knocked out by air bubbles. The aeration rate in the larvae tank is about 1-2 bps.

I had a lot of rotifers in the tank to start with, and the density is so high this morning that the larvae tank looked denser than some of the rotifer culture containers.

I am afraid that hypoxia can be an issue for delicate fish larvae with a high density of rotifers. I read somewhere that the dissolved oxygen concentration in a larvae rearing tank should be at least 80%.

Tomoko

 

[FB]

Maybe Billsreef will come in and comment I bet he would know about oxygen levels.

FB

 

[billsreef]

Depending on just how dense those rot's were, hypoxia could be a problem. But it would have to be quite dense for that, along with no phyto or during the night with no lights on.

 

[Tomoko Schum]

Hmm, the rotifer density was very high. After removing one half of the larval tank water and adding the same amount of water from the parent's tank this morning, the rotifer count was still well over 15 per 1 ml. I suspect that I had 30 or more per 1 ml of water before the water change - there were just too many to count.

No light at night with live phyto. Obviously this was not a good thing, either, since phyto consumes O2 with no light on. Do you recommend leaving the light on at night if live phytoplankton is used?

I expect that the parents will lay another clutch in a week. I would like to raise 20 to 30 fry out of each batch since I have only two local shops that would take them, and I can only give away so many to local club members. My objective is to raise a small number of clownfish just for fun. I really don't want to run around to surrounding cities to sell fish (been there done that with FW fancy angelfish and various dwarf cichlids for a few years.)

So the next time, I intend to have the following:

5.5 gallon aquarium (filled halfway up)
Two air stones bubbling at 1 - 2 bps - one on each end of the tank.
15 rots per ml or there about with live phytoplankton
Ammonia badge
Tetra O2 test kit just in case
Light on for 15 hours a day

Am I missing something?

My snagger captured larvae too efficiently. I probably had at least three hundred larvae. I will slow the air down on the air lift tube and try to save only 50 larvae (now this takes a real will power.)

Does this sound okay?

TIA,

Tomoko

 

[billsreef]

That was a lot of rots. Keep the density down around 15/ml with only enough phyto to keep the water tinted nicely and you should be fine, even at night with the lights off

 

[Tomoko Schum]

Thank you, Bill I will follow your advice.

Tomoko

 

[FB]

I knew bill would have some good advice as always.

THANKS BILL!

FB

 

[Tomoko Schum]

I have one more question if you don't mind.

I just got a small bag of Otohime A. Since I don't use but a tiny amount at a time, should I store it in my freezer? I can keep a tiny amount in a small container for everyday use.

Tomoko

 

[billsreef]

Yes, store the Otohime in the freezer.

 

[Tomoko Schum]

Thank you, Bill

Tomoko