Tropical seahorses such as your Hippocampus kuda typically brighten or lighten in coloration during their various social interactions. So, the basic coloration a seahorse assumes is often a reflection of its emotional state: when excited, seahorses typically brighten in coloration, reflecting a state of high arousal. On the other hand, fear, anxiety and distress are generally accompanied by dark, somber hues.
Seahorses will typically brighten during social interactions, such as their courtship displays, morning greeting rituals, and mating attempts. Likewise, when competing for mates, seahorses may go through characteristic color changes during their confrontations and competitions.
It sounds like that may be what is happening with your male kudas who have turned a bright white and become more aggressive when interacting with one another, Stacie. If one of them is actually a female, the bright coloration they have adopted is associated with courtship and pair formation.
On the other hand, if the trio of survivors are all males, then the change in their coloration and behavior is likely due to the following:
In a same-sex environment, it is not unusual for eager stallions (or fillies) to play around and practice their courtship moves with one another. That’s just an indication of how strong the mating instinct can be in Hippocampus.
It’s not at all 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 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 and females may 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.
In short, Stacie, what you are witnessing is pretty normal behavior for male seahorses in a same-sex environment, and is generally completely harmless and nothing to be concerned about.
All my condolences on the loss of your female, and best of luck with the rowdy males.
Pete Giwojna, Ocean Rider Tech Support