Ocean Rider Seahorse Farm and Tours | Kona Hawaii › Forums › Seahorse Life and Care › Erectus Fry › Dear Sherry:
Mustangs and Sunbursts (Hippocampus erectus) typically produce pelagic fry that go through an abbreviated free swimming or planktonic stage. The duration of this pelagic phase varies considerably in H. erectus, even within the same brood. For instance, a few of the fry from a large brood may begin to orient to the substrate and seek out hitching posts almost from birth, while others may not begin hitching for a week or two. Unlike H. reidi and H. ingens fry, for example, which undergo a pelagic period that lasts for several weeks, the pelagic phase for Mustangs and Sunbursts is relatively short and sweet, and normally lasts anywhere from a few hours (for a precocious few of the newborns) to a few days (for the majority of the fry) to a week or two (for a number of late bloomers).
Pelagic seahorse fry are positively phototactic, meaning that they are attracted to and move towards sunlight or artificial light. So it’s normal for pelagic seahorse fry like Mustang and Sunburst babies to be surface-huggers by day and feed near the top of the nursery tank during the daylight hours but to settle down and hitch at night after lights out. They are still considered to be pelagic even if some or many of the fry seek out hitching posts at night.
In short, it is perfectly natural for newborn Hippocampus erectus to seek out hitching posts at night, if given the opportunity to do so. Folks are sometimes confused regarding the nature of pelagic seahorse fry versus benthic seahorse fry. As you know, pelagic seahorse fry go through a free swimming or planktonic stage, whereas the benthic or demersal fry do not. Benthic fry, such as Hippocampus zosterae, Hippocampus capensis, and Hippocampus barbouri babies, orient to the substrate and seek out hitching posts right from birth, whereas pelagic seahorse fry like your H. erectus babies are positively phototactic and are drawn towards the light, which means they orient to the surface of the water during the daytime, where they drift freely with the plankton feeding on the lipid-rich “soup” of larval crustaceans and zooplankton. However, at night time, pelagic fry are no longer attracted towards the surface by the light and will therefore settle down and seek out hitching posts after dark.
That behavior confuses some hobbyists. They mistakenly believe that pelagic fry cannot hitch, and since H. erectus fry will hitch at night, that means they must be benthic rather than pelagic in nature. That’s incorrect. Pelagic fry can use their prehensile tails and hitch onto objects right from birth, but they are attracted to the light and therefore feed at the surface during the daytime amidst the planktonic soup. It is that behavior that makes them pelagic and that sets him apart from benthic seahorse fry, which will stay away from the surface of the aquarium, seek out hitching posts during the daytime, and wait for live prey to pass within striking distance while they remained anchored in place.
Of course pelagic seahorse fry use their prehensile tails right from birth, which often causes problems when a pregnant seahorse gives birth to a large brood within the confines of the aquarium. Gravid males normally give birth in the early morning hours (Vincent, 1990), and the hapless hobbyist is apt to be confronted with his first crisis immediately upon arising in the form of a writhing mass of newborn sea horses, hopelessly tangled together at the top of the tank (Giwojna, Jan. 1997).
This dangerous situation develops because a newborn’s first instincts are to head to the surface to fill its air bladder and then to anchor itself to something solid. In the vastness of the ocean this is not a problem, since strong currents rapidly disperse the young, but in the confines of an aquarium, the first hitching post it finds will very likely be the tail or snout of one of its siblings (Giwojna, Jan. 1997). The same mistake is apt to be repeated by the rest of the pelagic fry, as they cluster at the surface, until the entire spawn is snarled together tail-to-tail, head-to-tail, tail-to-snout and so on (Giwojna, Jan. 1997). This is a very common experience when raising seahorses such as Hippocampus erectus, H. reidi, and H. ingens, which produce large broods of pelagic fry.
So how do you know when your pelagic fry have passed beyond their free-swimming planktonic stage of development? The babies that will seek out hitching posts during the day and feed on the newly hatched brine shrimp (or rotifers or larval copepods) while they are perched, rather than feeding on the baby brine shrimp while they are suspended in the water column, as the fry are swimming, have begun their benthic phase of existence. They can be moved to a standard nursery tank at that point.
Pete Giwojna, Ocean Rider Tech Support