Hey Adam,  Typically Artemia are fed to satiation.   We have found that weight gain under a 2x daily (as much as they will eat in 10 minutes) is better than 4-5 x per day smaller feedings, with pellet included in 2 of the 5 feedings.

You could determine dry weight of cysts and feed by percent body weight but isn't that easy to do.  But it is possible, and it can give you a standard to work from.  

It is easier to feed to satiation, however.  Crudely, you can tell is you're going beyond (overfeeding) by the amount of uneaten nauplii in the tanks.  The "right" amount is when the fish look like their guts are full after feeding events and there is no or little uneaten nauplii afterwards.    You could in practice find this amount, and then correlate it to the dry weight of nauplii it takes to get you there to determine a percent body weight.   For adults, my guess is that it would be somewhere between 5 and 10%, but it is difficult to say for sure.  That would be interesting, and useful data to have, actually.

Hey Adam,

 Sorry it has taken me a while to respond and I won't have much more to add.  I agree with Chris, at my old facilities and most that I work with now the fish are fed to satiation.  I remember that we would have to adjust the amount of decapsulated brine every few weeks based on the observation of left over feed in the tanks.  This could change based on fish being used how many tanks of young fish etc.

 There was an estimate we would follow when starting new rooms to feed 2 milliliters of rinsed brine per 2 liter tank of adults.  We generally had a stocking density of 10 fish per liter.  Not scientific at all but based on observation.  This was done using a calibrated pipette, now it is the squeeze bottle method so it could be much more variable.

Thanks,  Joe

Sorry, error in posting; I will repost. I cannot delete the original. Could an admin please remove this?

Thanks, Adam

So they hatch at 4-5 days post-fertilization with no problems.

Have you looked at their developmental stage as they progress? in other words, are they where they "should" be at 3 days developmentally?

Obvious things you've probably thought of are changes in environmental conditions, particularly temperature.  dropping the temp even a few degrees below 26-28 will slow them down considerably. 

Sometimes you will see delays in hatching in poor quality lines. In some instances, you may see this in a few individual within a single clutch.  These types of observations suggest a genetic component.    If you are seeing it throughout your stocks then it is more likely to be environmental.  

Any changes that may have been made in the diet and/or environment over the past month or two could be underlying this.

Not easy to pinpoint but there are simple tests you could do to narrow things down.

Interesting. 

We have recently found a similar effect.  Larval fish are reared in up to 5ppt static water until about 10 days post fertilization. We started doing this because rotifers, which we culture at 7-9 ppt, live and reproduce in 5ppt with the fish if we co-feed rotifers with nannochloropsis. So normally by day 10 we have booming cultures of rotifers in the tanks, the fry are huge, and the survival is close to 100% across the board.  Once we start the flow the salinity drops back down to just under ~1500uS which is still under 1ppt.  The rotifers die off but by that point we easily wean onto Artemia so it is not an issue.  We haven't tried to rear them beyond 10 dpf at these salinities b/c we haven't found the need to.  But up until day 10 it seems to be the way to go b/c of increased performance and very low corresponding labor input.    

3000uS is a good deal higher than what these fish typically experience in nature (from the limited data out there), but it isn't out of the realm of the ordinary to run freshwater fish in culture at elevated salinities because of the energy savings and potentially reduced parasite loads. 

My opinion is that conductivities under 500uS are too low for zebrafish in culture.  This is based upon the fact that although they are adapted to osmoregulate at extremely low salinities (presumably b/c of monsoonal rains) there is steep energetic price associated with this, which is borne out by reduced egg production. It is the same energy budget that is working the other way in elevated salinities.  There is likely an upper physiological limit, but I don't know where it is.   The literature indicates that the fish do not perform well above 2ppt but this doesn't seem to be the case for you or us, so clearly more work needs to be done on this.

In the interim I see no reason not to rear early on at elevated (brackish) conditions, but beyond that I have no direct experience and the data is limited.  It may very well be fine.   If you are rearing fish from egg to egg under these conditions it would be very beneficial for the field if you were to document and report it.   

CL 

I don't have much experience raising fry at these levels but do have some anecdotal experience with adults a a higher level of conductivity. 

At my last facility we had some problems with salt dosers that caused the conductivity to go up over 3000 microsiemens.  The normal setpoint was 1000.  I cannot say with any certainty if it was just the change in salt levels or just being that high but the adult fish nearly stopped breeding for a few weeks.  The conductivity was noticed to be this high after a weekend and then was gradually brought back down by normal water changes but this affect was seen for a couple weeks later where we didn't get many eggs at all.  The only water parameter to change durign this episode was the salt level.

 Now obviously you are keeping the fish normally at 3000 so you must not be having a problem but I play off of what Chris said and say that this could be taxing from a body system maintenace standpoint, just like lower conductivities. 

 Just for some background we used 1000 as our setpoint because for us it seemed like a happy medium between the ranges people were using and it did seem that the parasite load was kept in check using this level.

Thanks, Joe

Re: CL's comments

That is so cool about the rotifers!  It had crossed my mind to try adding nannochloropsis to the water, but I never got around to it.  I was only hoping to prolong their nutritional value a little, and never considered that they would actually reproduce.

My bosses are interested in conducting a long-term experiment on the effects of salinity.  Growth rate, fecundity, longevity and, most potentially exciting, sex ratios would be some things we would look at; if anyone has any other suggestions, I'm open.  We talked about comparing 1000 uS and 3000, but maybe we should go lower on the low end?  

 Re: Joe's comments

 I have only been raising zebrafish for about six months now, and in that time we've gone from 6000 uS (that was when I got here, and I changed it fast!) to 500 to 2000 to 3000.  We have reasons for all these, but I'll spare you the details. 

As far as performance, the fish are mostly being used in a different way than I am familiar wih.  They do IVF on  combined clutches, but I don't know what the average yield is.  The few times I've set up natural crosses the fish have not done well, but we buy our fish from the Ekkwill farm pretty frequently and they seem to vary a lot from batch to batch. 

 It will probably take us a few weeks to get set up, but I'm excited to see what this experiment reveals.  

 Joy

Keep us posted on how these experiments turn out.

We have done some simple comparisons but will likely expand on these a bit more in the coming months.

We are particularly interested in the tradeoff between labor and performance, and the efficacy of conventionally utilized diets (paramecium).  The sex ratio aspect is also quite interesting.

CL 

Just out of curiosity, how will you quantify labor?  I'm assuming you'll be using paramecia for fry only, right?

Joy