What is the nutritional requirements of seahorses in regards to fatty acids (poly and HUFA's). I hear quotes of the Steinhart raising one breed of seahorse on enriched brine shrimp, clownfish and bangi cardinals do alright as well. Orchid dottybacks (P. friedmani) cannot be raised exclusively on brine shrimp (even if you feed strictly rotifers the first week).

Yep, there is one aquarist at Steinhart who has taken over the seahorse program, and he's had great success with them, from what I hear. I'll have to make my way down there one of these days to take a look at their setup and talk to him. I've raised pygmies (H. zosterae) on entirely on unenriched premium SFB brine (not great success, but about 10% survived to adulthood), but in general, with proper enrichment, most cultured fish larvae of which I am aware have been successfully raised on brine (most of the aquaculture industry uses them).

The reason that I am so specific about the source of my brine nauplii is that there have been a number of studies showing that there is no difference in the growth and survival of the larvae of a variety of fishes (milkfish, striped bass, hybrid bass, cod, and others that I can't remember anymore) fed premium instar-I SFB nauplii and those fed enriched instar-II Utah nauplii (e.g., Gaspin et al. 1998; Ozkizilcik & Chu, 1994; Burkhardt-Holm, et al. 1989). A variety of studies presented at a recent meeting I attended showed that unenriched instar-I premium SFB nauplii and enriched (in a variety of ways) instar-II Utah nauplii were approixamtely equivalent in terms of growth and survivorship (there were no statistic differences among the treatments), but that both outperformed (showed significantly higher growth and/or survivorship than) unenriched Utah nauplii. It is difficult for hobbyists to get premium cysts, and there is far higher variability among SFB cysts (from premium to hobby-grade) than there is among the Utah cysts. That may be one factor in the variable success of hobbyists in rearing larvae.

Another thing is that the rep from the largest tank aquaculture facility in the US told me that the growth and survivorship of their larvae was always greatest among the cannibalistic fry. He lamented that no one has yet developed an "artificial sibling" food for the larvae, so obviously Artemia nauplii are not the best food for fish fry. There is also a bell-shaped relationship between feeding density and larval growth in some studies as well (e.g., Samocha et al., 1989). This particular study compared growth of shrimp larvae on rotifers and Artemia nauplii under different conditions, and found that too little (<10 rotifers per ml) or too much (>40 rotifers per ml) food significantly decreased survival and growth rates of the larvae. The same result was obtained with Artemia nauplii (ideal feeding amount was 9 nauplii per ml). The tendency of hobbyists to ensure all the larvae are "getting enough food" by providing an excess of prey may also directly impact the success of rearing the young, and it would be worthwhile for some feeding density experiments to be done by small-scale breeders as well. You may well lose a few larvae to starvation & cannibalism, but end up with much higher success rates overall as a result.

The intersting thing about the Samocha et al. study was that a comparison of growth rates on the two food-types showed that higher survival rates were obtained by feeding with rotifers, but higher growth rates with Artemia. The final conclusion of the study (that Artemia is a better food) is indicative of the goals of aquaculture, but the best overall results were obtained when larvae were fed a combination of the two foods. Obviously in the wild, fry will never receive a monoculture of any prey type (especially Artemia) and it has been shown experimentally that larvae fed a mixed diet do better than siblings fed either prey type in isolation, therefore I generally try to diversify the feeding as much as possible. In addition to the brine nauplii and rotifers, I would include copepods in that mix for fish larvae as well, because they are more "nutritious" (in terms of enhanced survivorship) than Artemia alone for seahorse fry, IME.