Greenwater Techniques vs. Selcon Enrichment of Rotifers for larval rearing

[mwp]

OK, so this is a basic question for all the more experienced breeders than myself.

In a nutshell, time and time again, I find my larval tank turning into a high-density rotifer culture. I'm simply not sure if this is truly the most effective thing to be happening. I.e. this last time around, in 48 hours I fed 2L of phytoplankton (T-Iso, Tetra, Nano) into my larval tank and harvested approximately 2L worth of Rotifers (SS and L Strain), enriched with selcon, and fed them in. At the end of 48 hours, my tank went from 0 rotifers to looking extremely jam packed. Adding more selcon enriched rotifers at this point seems like it would be, well, pointless.

So, what's the "real deal" here. Am I better off simply harvesting Rotifers and enriching with selcon, feeding 3-4 times per day with NO phytoplankton (only black tank walls), or am I better off forgoing selcon enrichment once the tank reaches "critical mass" and instead just keeping the phytoplankton levels where they need to be? OR am I forced to do water "filtrations" where I seive the water of let's say 50% of the rofiters in the tank, take those and enrich with selcon, and then RETURN them to the tank?

It seems that when utilizing the greenwater technique (1 L per day of phyto added) that sooner or later you end up with too many rotifers. I'm aware that this population level probably has to be controlled through regular water changes at that point, but when your larval fish are 1-2MM, that's a pretty tall order. Obviously, NOT using greenwater would make it easier to keep the rotifer population under control.

So I guess the final question is what balance are you guys striving for in your larval rearing when it comes to greenwater and/or HUFA enrichment?

MP

 

[Kathy55g]

I can only speak from my limited experience with clownfish.
With clownfish it is the density of rotifers that is important. In a 5 gallon tank you need 8-15 rotifers per ml whether you have 5 larvae or 500. They can't learn to hunt them if they never see them.

Empty, hungry rotifers are worthless. Without full guts, there is no nutritive value.
Not using greenwater in the larval tank means that you would have to remove all the rotifers every 4 hours and enrich with selcon or whatever and return.


When it comes to rots, having more is not necessarily better. Having too many rotifers is bad! Water quality deteriorates, ammonia rises, O2 decreases, larvae die.

If you have more than 15 rotifers per ml, then throw some out each day, until you have 15 rotifers per ml. You will use less phyto to keep them fed, and the water quality will be better.

Measure out a ml of culture with your transfer pipette, and count the rots under the scope.

 

[David M]

Matt, when I get in that situation (too many rots in the rearing tank or I want to feed fortified rots to the larvae) I just set a large diameter 125um plankton screen into the tank and siphon or scoop out water into a bucket. Then I can return those rots to the culture tanks and feed the larve some freshly fortified rotifers.

 

[tanglovers]

David -

I am assuming a 125 um plankton screen is large enough to let the rots through but small enough to keep the larvae out? Just want to make sure I am following correctly.

Scott

 

[mwp]

Actually, my 120 Micron Seive captures a lot of rotifers Scott - I kinda thought that's what David was getting at.

So let me pose a followup question - which is really "better" if you compared the two methods side by side - clean water being fed constantly with Selcon, or Greenwater only. It's my understanding that Selcon can generate much more nutritially sound rotifers, but obviously it has polution issues and the rotifers wouldn't "stay" nutritional without greenwater.

Is the reality that only a combitination of the two concepts is the only "good" way to go?

Matt