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Maybe Maurice will jump in here, because I remember him doing some intensive larval rearing. I have to use quasi-intensive larval rearing because I'm so cramped for space. My preference would be to spread the fry out in large enough ponds that they did not need anything except natural forage until they are 4-6 cm and large enough to harvest.
Since I have to augment the fry's food to compensate for the lack of space I designate a couple of units as plankton reactors. There needs to be a green water reactor. This is often a unit with slightly older fish which are being fed dry feed. They will keep the zooplankton stripped out of the water because of the intense competition so the green water gets really dense and stable. I continually siphon water from the green water pond to a zooplankton unit which has a good bloom of rotifers, Moina (a large Cladoceran) or copepods. If the flow rate of green water to the zooplankton pond is right, the zooplankton density stays pretty high - several hundred rotifers/ml or 20-50 Moina/ml or 10-20 copepods/ml. Water is continually siphoned from the zooplankton unit to the fry units(s) where it is stripped away by the fry. Using a small submersible pump with fine screen on the suction (a "bongo" set-up, if you know that term) water is continually pumped from the fry unit back to the green water unit. So, it makes a loop: green water --> zooplankton --> fry --> green water. Since the units are all at the same elevation and the flow rates are low, the difference in water level between units is very small. Getting the correct flow rate is critical so as not to "wash out" the zooplankton unit while providing maximum forage to the fry. The pump could be placed in any of the three units, but I suspend the pump just under the water surface in the fry unit. This way, if the suction screen clogs or a siphon breaks overnight, the pond can will only be pumped down a couple of cm before everything stops.
I also start supplementing with dry food as soon as possible. Last year, I used dry shrimp larvae feeds made by Zeigler. There are different size grades (<100 micron, 100-150 micron, 150-250, 250-450). The particles stay suspended and intact longer than something I would grind myself. They also mill the ingredients very fine so each particle has the same mix of ingredients. Shrimp feed was what I could get quickly (poor planning on my part) but Inve and others also have some fish larvae feeds developed for seabass and such. Don't they have some good barramundi larval diets? I plan to also use a little frozen Cyclopeze starting about day 12 this year. It's frozen copepods from an arctic lake or something (google it). This is, without doubt, the best off-the-shelf food for small fish I have ever come across. It's really expensive, but may actually produce results as good as having higher concentrations of natural forage.
I know growth and survival is correlated with the amount of live forage available. I also see some circumstantial evidence that some of the common deformities are less prevalent in batches with more live forage. In particular, I suspect that the flared gill deformity is related to a nutritional deficiency.
If you are going to augment the zooplankton (as discussed above) or do supplemental feeding, good aeration is essential. Both of these activities have a BOD which will crash the system if there is not enough aeration. I used to borrow a dissolved oxygen meter when needed but finally bought one last year. Some aerated fry ponds were found to have pretty marginal D.O. at times so I'm increasing the aeration for this year.
Koi people always advise against using too rich a diet. It is not surprising to hear that you get better results with a high protein diet for fry though. The shrimp feed mentioned is up there about 45-50% (do not have the can in front of me). I think the high carb thing comes into play later.
-steve hopkins
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