I got an email question the other day that spurred me to write a fairly concise wrapup of how I found success in incubating the eggs of pelagic spawners. I'm posting my response here for the benefit of anyone else who might be searching for this type of info:
Here's what I can tell you about incubating pelagic eggs.
I always had my best successes, be it with Dragonettes (Synchiropus sp.), Pygmy Angelfish (Centropyge argi), or the Harlequin Files (Oxymonacanthus longirostris), working with a basic philosophy that less is more. I should point out that while O. longirostris is NOT a pelagic spawner, the eggs are similar in size and the shorter development time. If I recall correctly, the Dragonettes took about 16 hours to hatch, the Angelfish around 22, and the Harlequin files around 52.
In each case, I'd collect the eggs from the broodstock tank with broodstock water. Typically this involves shutting down the pumps in anticipation of a spawn, and then scooping/skimming the eggs off the surface with a jar, and pouring them into a specimen cup (in the caes of the filefish, their eggs are removed from the spawning site with a turkey baster).
I should note of critical importance, that specimen cup should be the 1/2 gallon size, and I suggest a quick sterilizing with bleach or at minimum, scalding hot water. I always had poor hatches or even failure with 1/4 gallon size specimen cups. I hypothosize that this is likely due to faster changes in salinity due to the smaller quantity of water. If you don't sterilize the incubation vessel, they tend to be pretty scummy after a prior use, and it seems to bring in a lot of bacteria that just take over.
Now, my water quality is almost guaranteeably not perfect...i.e. I have higher nitrates. Most of my broodstock tanks also run around 78-80F. I found that if I simply hung the specimen cup in the broodstock tank, I almost always had a failed hatch. However, if I took that same specimen cup, and put it in a 10 gallon tank that was running slightly warmer...say 82F, I had a much greater chance of successful hatches, and for that matter, HIGH hatch rates....not 50% but closer to 90-100%. I should mention that this tank would have a glass lid on it, which cuts down on evaporation and keeps humidity above the water high.
It seems that anytime I tried using "clean new water" for incubation I had issues. When I tried flow through arrangments to slowly change the water quality I had issues (as well as eggs being drained from the collection cup). If I tried aeration to prevent stagnation that seemed to cause issues as well. Early on, I tried a propeller type mixing setup which was described by Wolfgang Mai and prior to that, RSMAN on Reef Central, for mandarins. It didn't seem to do anything beneficial either.
I've heard of people treating the eggs with things like Erythromycin or Hydrogen Peroxide. Based on my experiences that clean equipment produces better results, I'd say there's merit to investigating these methods further if all the above doesn't get the job done.
Generally speaking, I had my best successes doing almost nothing. It seemd that the larger volume of incubation water was helpful. It seemed that a slight increase in temperature was helpful (someone theorized that pelagic eggs spawned at depths would rise to the warmer surface waters...I'd say that's certainly a possible explanation as to why a temperature rise would be required / helpful). It seemed that a clean incubation vessel was helpful. It seemed that using the water the eggs were spawned in was helpful.
And that about sums up what I can personally tell you about my expereiences and the methods that seemed to work for me. Let me know what you think :)
Matt