With regard to crossbreeding, as a High-Health aquaculture facility, there is NO unauthorized breeding at Ocean Rider, sir. Each strain of seahorses is necessarily kept in a biosecure area that strictly segregate it from all of the other types of seahorses. In short, the 20 different species of seahorses raised at Ocean Rider are never mixed together; each line has its own biosecure area, it’s own rearing tanks, and it’s own grow out tanks.. Needless to say, this effectively presents crossbreeding and interspecific hybridization.
In home hobby tanks, however, where different species of seahorses are often mixed freely, crossbreeding or interspecific hybridization does occasionally occur, but it is quite uncommon, especially when seahorses have potential partners of their own species available to them. The prolonged, elaborate courtship ritual that seahorses go through before mating occurs generally prevents seahorses from different species from breeding successfully. Suffice it to say that seahorses are much, much better at species recognition than we are, and that given a choice, they almost always prefer to mate with their own kind. Almost always.
However, the urge to reproduce is very strong in seahorses. For example, solitary males often go through the motions of courtship when there are no other seahorses present in their aquarium. They may court their own reflection and sometimes even direct their courtship displays toward their keepers. Dwarf seahorse stallions in particular are irrepressible in that regard, and a hitching post may suffice for them as a surrogate, when no better alternative is available! Homosexual mating attempts (both male and female) are also common when no member of the opposite sex is present. (Fielder reported a case where two male Hippocampus hippocampus courted one another for over two hours and unsuccessfully attempted at least 20 copulatory rises together.)
Now, where a male and female seahorse of different species are confined together, they may simply ignore one other. But many times the instinct to breed overwhelms any interspecific inhibitions, and with no other available partner, the male will attempt to flirt with the female regardless of their differences. Results vary when this occurs, but the resulting offspring are generally perfectly viable.
As a matter of fact, the first strain of hybrid seahorse has actually been with us for some time now. It was developed not by hobbyists here in the USA but by the Chester Zoo in the UK and is known simply as the Chester strain of seahorse or "Hippocampus chesteri" for fun (Neil Garrick-Maidment, pers. comm.). It has been widely distributed to zoos and public aquaria and has been very well accepted. A recent survey showed that the Chester hybrid is the most frequently kept seahorse in European exhibits, displayed by no less than 45.5% of the public aquaria sampled (Bull & Mitchell, Seahorse Husbandry in Public Aquaria: 2002 Manual). It apparently owes its popularity to the fact that it is readily available and completely captive bred and raised — a hardy, easy to feed, eco-friendly display animal for zoos and public aquaria in Europe that helps relieve the pressure on wild seahorse populations. I believe the Chester hybrids do breed and produce viable offspring.
In short, Charlie, it is possible that your male Hippocampus fuscus and female Hippocampus kuda may attempt to breed in your aquarium. If they are successful, they will probably produce healthy young. But that’s a cross that I’ve never seen before and there’s no way of predicting if the offspring of such a union would be fertile themselves or would be sterile like mules. Keep us informed as to how their budding romance works out, sir.
Best wishes with all your fishes, Charlie!