Yes, it does indeed sound like your male Mustang is flirting with your Sunburst stallion. He is brightening in coloration and assuming the typical posture of courting seahorses. It’s not at all unusual for juveniles or inexperienced males to flirt with other males and practice their dance moves and courtship maneuvers with one another.
Don’t worry about those male-male courting episodes you’ve observed. It doesn’t mean your male Mustang is a sissy or has no interest in the female Mustang, just that he is young and inexperienced and perhaps a little too overexcited at the moment. But sooner or later he’ll settle down and get things right, and in the meantime, it’s a very good sign that you’re new arrivals are already displaying a healthy interest in breeding. It indicates they are comfortable in the new aquarium and are adjusting very well to their new surroundings, which they appear to find very much to their liking. It’s nothing to worry about, even if the male Sunburst is none too thrilled about the unwanted advances.
It’s not that uncommon to see same-sex courting behavior or even homosexual mating attempts in seahorses under certain circumstances. The genetic imperative 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 (Abbott, 2003). They may court their own reflection and sometimes even direct their courtship displays toward their keepers (Abbott, 2003). If no females are present, over-stimulated stallions will sometimes soothe themselves by basking in the air stream from an airstone, content with the tactile stimulation provided by the gentle barrage of bubbles. They may even flirt with inanimate objects. If all else fails, a hitching post may actually suffice as a suitable surrogate when no better alternative is available (Abbott, 2003)!
Same-sex courting displays (both male and female) are also common, especially when no member of the opposite sex is present. Under such circumstances, these passionate ponies are not picky about their partners — males will dance with other stallions and frustrated females will sometimes flirt with other fillies (Abbott, 2003)!
Captive-bred seahorses are far more social and gregarious than their wild conspecifics, so it’s not surprising that cultured seahorses are particularly irrepressible in that regard. They seem to court constantly and the urge to procreate dominates their lives. If given a choice, they are apt to change partners often, and courtship, flirting and dancing are the activities that consume their days. Long before they are sexually mature, juvenile males will spend hours dancing with one another, just horsing around, practicing their moves and perfecting their technique for the real thing to come. Likewise, mature males often compete actively and aggressively with one another through harmless pouch displays and tail-wrestling tug-o-wars whether or not there is a female nearby to appreciate their efforts.
Under crowded conditions, in particular, seahorses occasionally attempt to mate with members of the same sex. These homosexual copulations are usually the result of confusion (Vincent, 1990). For example, sometimes a male and female will rise together as usual — the final phase of courtship leading to copulation — only to have a rival intrude at the crucial moment when the transfer of eggs is about to take place; just as the couple is about to merge in midwater, a rival will swim up and wedge itself between them, mistakenly resulting in a male-male (or female-to-female) mating attempt. Other times, a three-some will rise together, only to have the female fall back at the last moment, leaving two males to complete the copulatory rise.
On occasion, however, two over-stimulated stallions will persist in their futile attempts to pair with each other, as if oblivious to the sex of their ill-chosen partner. 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, despite the presence of a very frustrated female who actively intruded several times. Further, in her famous study on the reproductive ecology of seahorses, Amanda Vincent found that on the average such male-male copulatory rises lasted fully as long as heterosexual mating attempts (Vincent, 1990)….
Female-female mating attempts are not uncommon either, and they will often result in an overly-ripe female dropping her eggs. When that happens, the competition is all over, since a female that has lost her clutch has nothing to offer a prospective mate. In fact, some females are thought to use this as a ruse to deliberately eliminate their competition (Vincent, 1990). These cunning courtesans will entice a rival female to rise with them, and then hang back slightly beneath her, in a position to pose as a receptive male. If the ploy is successful, the ripe female will dutifully attempt to transfer her eggs, losing her entire clutch in the process.
In short, your mixed-up Mustang’s ill-directed flirtations are quite harmless and fairly normal for young inexperienced stallions. He’s just your typical over-stimulated hormone-driven adolescent, operating purely on instincts and with a little too much energy for his own good right now — a virgin male going through some growing pains and courting everything in sight. But when your female Mustang is receptive, you can be sure he will rise to the occasion and provide you with a brood of young.
Best wishes with all your fishes, Heather!