by Pete Giwojna and Ben Giwojna
Terrific Trio: captive-bred-and-raised seahorses have now achieved a high level of domestication and are available in virtually every color of the rainbow, as indicated by these Pintos from Ocean Rider. Photo by Dr. Clyde Tamaru
Seahorses are truly the chameleons of the sea with a propensity for changing color in response to a wide range of environmental factors, hormonal influences, and behavioral interactions. Hippocampus has exceptional visual acuity and color plays a vital role in every part of the seahorse's life. Seahorses rely on color changes throughout their elaborate courtship displays to express their emotional state and well being, to signal submission and dominance when competing for mates and as a sign of recognition during their daily greeting rituals and other social interactions, as well for their very safety in order to conceal themselves from their enemies. In this article we will discuss the curious ways seahorses use their amazing ability to change coloration.
Concealment through camouflage and crypsis is no doubt the most important way in which Hippocampus employs color changes. Crypsis, or the use of protective coloration to disrupt its outline and break up its body shape, is a vital talent for the seahorse since its awkward method of locomotion is so slow and cumbersome as to be useless when a quick burst of speed or a fast getaway is required to escape from danger. Hippocampus is forced to rely on its suit of armor, spiny exterior, and ability to camouflage itself to avoid harm rather than outrunning its enemies.
Fortunately, it is truly a master of disguise. The seahorse has perfected the art of blending into its background, and it can alter its coloration and even its shape as needed to suit its surroundings. As noted by Whitley & Allen (1958), “Their chameleon-like color changes permit them to become one minute pale in color, the next darkest brown, red or green, light and dark spotted, and so on. Meantime, their bodies sway gently forward and backward like the weeds themselves, with the swell of the water.”
Thus, as described by Alisa Abbott in the Complete Guide to Dwarf Seahorses in the Aquarium, if a seahorse lives among the lush grass flats in Florida Bay it is apt to be green in late spring and summer when the seagrass is thriving, and then change to a yellowish hue later in the season when the grass begins to die back, finally assuming an appropriate shade of brown or black to match the dead, decaying blades of grass in the fall.
A pair of juvenile Hippocampus erectus well endowed with extravagant cirri. The fancy looking filaments give the seahorses an exotic appearance, but their actual purpose is to enhance the ponies' camouflage ability. Photo by Kyle Walczak
Likewise, if Hippocampus has taken up residence in a bed of eel or turtle grass whose blades are heavily overgrown with algae, hydroids, and calcareous encrustations, it will adopt a mottled appearance that perfectly matches these growths (Giwojna, 1990a). On rare occasions, blazing orange and fiery red specimens are found living amidst colonies of orange or red sponges (Giwojna, 1990a). In addition, the seahorse also makes full use of disruptive coloration, so that its basic background coloration is interrupted by a series of lighter or darker contrasting streaks, spots and irregular blotches, which break up its silhouette or profile, thereby further deceiving the eye.
To improve its camouflage all the more, Hippocampus is capable of growing or shedding dermal cirri, which are long filaments and branching extensions of its skin, in order to match its habitat (Vincent, 1990). Specimens inhabiting mudflats or a bed of sponges will remain smooth skinned, for example, while individuals living in a weedy environment are apt to develop extravagant cirri to blend in with their surroundings. This is rather like the military’s practice of using leafy branches and brush attached to the helmets and uniforms of its soldiers in order to enhance their jungle camo.
To complete its disguise, the seahorse allows algae, bryozoans and other encrusting organisms to grow on its body, thereby rendering it all but invisible in its natural habitat. Its skin contains polysaccharides, which are believed to encourage algal growth, thereby helping it disappear into its surroundings. This vanishing act is so convincing that even when they are collected by hand seining, seahorses often go undetected amidst the plant matter that accumulates in the net (Giwojna, unpublished text). Unless the collector is really diligent, he will lose a large proportion of his catch simply because many specimens will be overlooked and thrown back with the debris (Giwojna, 1990a).
Their ability to disguise themselves is no less effective in the aquarium, as I discovered when I brought a pair of black Indian Ocean seahorses home with me one afternoon. They were handsome specimens, quite slender and graceful, with unusually long snouts and an interesting color pattern consisting of charcoal black bodies with pale yellow bands on their tails. Here's how I described the incident in my latest book (The Complete Guide to Greater Seahorses in the Aquarium, in publication):
"The new acquisitions were carefully ensconced in a quarantine tank and seemed to settle in at once, greedily demolishing a portion of live brine shrimp shortly after being introduced to the aquarium. My brothers and I admired them all evening, marveling at their endless appetites, and all seemed well. They were still contentedly exploring their new surrounding when we retired for the night.
"It was therefore quite a surprise when I was rudely awakened the next morning with the startling news that the seahorses were gone. Not that I was too concerned, since they were the only inhabitants of a 10-gallon aquarium and couldn’t possibly have escaped. As a matter of fact, as I got up to take a look for myself, I strongly suspected the whole thing was somebody’s feeble attempt at a practical joke, and I was rather annoyed, ready to unleash my wrath on the perpetrator as soon as I put him to the lie.
"The 8-10 cm seahorses should have been easy to spot, since the quarantine tank was sparsely decorated, but sure enough, at first glance, the tank certainly appeared to be empty. This was ridiculous. The only decorations were a couple of elaborate formations of staghorn and finger coral, and my black beauties should have stuck out like sore thumbs amidst the bleached skeletons of the coral. Where the heck were they?
"When a second, closer examination revealed no sign of the missing seahorses, I began to get a little worried. Things were getting serious now, and I launched a meticulous inch-by-inch search of the entire aquarium. When I had all but completed this painstaking procedure -- just when I was beginning to believe my brothers must have removed the seahorses as a prank -- a flicker of movement caught my attention out of the corner of my eye. I immediately focused on the area where the motion seemed to have originated, but the newcomers were nowhere to be seen. Then another slight movement caught my eye, and all a once a white seahorse materialized right before my eyes, perched on a finger of coral. As long as it remained anchored motionlessly in place, it seemed like a natural extension of the coral (Giwojna, 1990a).
"Now that I knew what to look for, I soon noticed that one of the other tines on the staghorn coral was striped with pale yellow. Upon tracing this suspicious “branch” back to its source, the other snow white seahorse suddenly appeared as if by magic. Our eyes had been deceived because we were searching for black seahorses and, of course, there were no longer any black seahorses to be found. Their camouflage was so perfect they had managed to disappear in plain sight (Giwojna, 1990a)."
Seahorses will often alter their coloration to closely match their surroundings and disappear into their background as described above, but it is actually far more common for Hippocampus to adopt a general, all-purpose form of cryptic coloration featuring irregular patches, streaks and blotches of contrasting colors that serve it equally well in different situations. Mottling or disruptive coloration breaks up the seahorse’s outline and provides effective concealment under most conditions.
Seahorses also rely on dramatic changes in coloration during their charming courtship displays but for exactly the opposite reason. Whereas cryptic coloration acts as camouflage in order to make Hippocampus inconspicuous in its natural habitat, the bright coloration flaunted by courting seahorses leaves them quite conspicuous, thereby signaling their readiness to breed in order to help them attract a mate.
Courtship in Hippocampus is punctuated by a number of remarkable displays. These ritualistic behaviors are quite distinct and have been given descriptive names by researchers. They include "tilting" and "reciprocal quivering," dancelike maneuvers aptly known as "carouseling" and the "parallel promenade," prominent pouch displays usually described as "pumping" and "ballooning," characteristic postures such as "pointing," and the actual nuptial embrace or "copulatory rise." In tropical seahorses, brightening in coloration accompanies all of these displays.
Courtship coloration varies from species to species. However, regardless of the colors involved, the head, dorsal surface (i.e., back), and ventral line (keel) of the seahorse normally remain quite dark while the rest of the body becomes lighter and therefore brighter in color (Vincent, 1990). Of course, courting seahorses flaunt their flashy finery in order to impress prospective mates and the overall effect of this change is to make them stand out from the crowd (Giwojna, Mar. 2002).
This magnificent Mustang has assumed a pinkish-red color in an attempt to match the reddish grape algae that surrounds it. Photo by Leslie Leddo
Indeed, courting seahorses always remind me of a couple of excited teenagers dressing up for the prom. When a seahorse is interested in romance, the stylish stallion dons his most dashing duds to impress his date, while his ladylove likewise dresses up in her most alluring attire, just as their human counterparts do. For example, consider the courtship colors of the Brazilian Seahorse (Hippocampus reidi): males tend to prefer a flamboyant orange outfit while the fashionable females favor more subtle shades of pastel pink (Giwojna, Mar. 2002). Hippocampus fuscus, the Sri Lanka Seapony, exchanges its somber, everyday black attire for a more enticing ensemble featuring pale cream and yellow colors when courting (Giwojna, Mar. 2002). As for the dark-colored European species, the short-snouted seahorse (Hippocampus hippocampus) changes to a shining white or silvery color, and the long-snouted Hippocampus guttulatus often switches to shades ranging from copper to light ochre or sulfur yellow, its body further adorned with tiny silver dots (Giwojna, Mar. 2002). Likewise, our own North American Hippocampus erectus typically swaps its normal dark brown or black ensemble for a wardrobe of pearly white or pale yellow during its courtship displays.
As a general rule, tropical seahorses undergo more pronounced color changes than temperate species, which tend to be more subdued. Dwarf seahorses (Hippocampus zosterae) are not nearly as bright and flamboyant during courtship than their bigger brethren. These pint-sized ponies take on a different sort of glow. They sparkle looking as if they have been sprinkled with glitter, as they take on metallic tints, hues and highlights of their natural neutral colors (Abbott 2003). Tropical seahorse species generally rely on brightening and conspicuous color changes during courtship more than their temperate counterparts, which depend primarily on pouch displays such as Ballooning to impress the females.
The urge to reproduce is so strong in Hippocampus that captive male seahorses will often color up and indulge in courtship this place even in the absence of a mate. Thus it is not uncommon to see a lonely stallion parading back and forth in full courtship regalia, pumping his inflated brood pouch and dancing provocatively before its own reflection in the aquarium glass, vigorously displaying to itself! If no females are present, over-stimulated stallions will sometimes soothe themselves by playing in the stream of bubbles from an airstone, basking in the gentle barrage of bubbles, or flirt with inanimate objects. If all else fails, the nearest hitching post may serve as a suitable surrogate. And when no members of the opposite sex are present, these passionate ponies are not picky about their partners -- males will dance with other studs and frustrated females will flirt with other fillies (Vincent 1990)!
Throughout the male's pregnancy, apair-bonded stallion's mate visits him daily for morning greetings. The female seahorse swims over for 5-10 minutes of intense interaction during which the couple briefly reenact many of their courtship maneuvers. They brighten and change color, wheel around sea grass fronds performing their dancelike displays, and finally promenade, holding each other's tails. Then they drift apart and go their separate ways until the next morning. Daily greetings serve to strengthen and reinforce the pair bond, and recent research demonstrates the colorful greetings are more important in keeping the couple together than mating itself (Vincent 1990; Vincent 1994, Vincent and Sadler 1995).
In fact, seahorses will often extend their greeting displays to include their keeper, prominently parading their most vivid hues at the front of the tank when they detect the approach of the aquarist. Some go as far as perching on your hand or clinging to your fingers whenever you are working in the aquarium -- an equine invitation to dance, perhaps?
The lightening in coloration and bright hues displayed during courtship and greeting are very characteristic of social interactions in Hippocampus in general. For instance, they are typical of seahorse reunions and the color changes that accompany competition for mates as well.
At such times, rival males often engage in bouts of tail wrestling and a form of combat known as snapping, in which a male will cock his head downwards and then deliver a sharp blow to its opponent with a powerful upwards ''snap'' of its snout. Stallions have proportionally longer tails and shorter, thicker snouts than the female seahorses, features that are thought to aid them in these ritualistic contests to determine "who’s the best man.”
When two over-stimulated studs square off, they begin by brightening and flashing through a series of intimidating color changes, and if neither opponent backs down in the face of his rival’s threatening spectral display, things can rapidly escalate from there. It can be surprising and disturbing for the hobbyist to find his normally passive, totally nonaggressive seahorses suddenly engaging in no-holds barred wrestling matches and exchanging sucker punches and knock-out blows, as I described in an article titled "Seahorse Breeding Secrets" that first appeared in the January 1999 issue of FAMA magazine:
Once a stallion has established his dominance over a rival, the subordinate male may automatically darken and assume the submissive posture of lying on its side for the next few days whenever the superior male draws near. The aquarist may easily become alarmed at such a sight if unaware of the dynamics of the situation. If the aquarist does not recognize this as a submission signal, the odd behavior, unusual posture, and obvious darkening of the subordinate male can easily be mistaken for illness.
Lest you get the wrong idea, I should emphasize that competition for mates is highly ritualized in Hippocampus. The idea is to assert dominance, not inflict bodily harm. Tail wrestling and snapping are forms of ritual combat -- little more than glorified shoving matches and tug of wars -- with clear-cut submission signals that are always honored. They seldom do any real damage and the combatants are so well protected that with rare exceptions serious injuries are virtually unknown when these armor-plated adversaries throw down the gauntlet. In short, intraspecific competition for mates can sometimes disrupt courtship and prolong the process of pair bonding, but it's usually nothing to be concerned about and is always extremely interesting to observe.
Other social interactions between seahorses also involve characteristic color changes and dancelike displays. For instance, introducing new additions into the aquarium usually triggers a flurry of colorful activity and greetings as the seahorses reassess the shifting social dynamics of the herd, check out their prospective new partners, and explore possible new pairings. Likewise, if a seahorse has been separated from its tankmates for several days, perhaps after being transferred to a paternity tank to deliver its brood (in the case of a pregnant male) or if isolated in a hospital tank (in the case of a disease), and is then returned to its tank after a prolonged absence, its return will trigger a round of renewed color changes and “dancing” very similar to the previously described greeting ritual. It’s like a family reunion with old friends getting reacquainted and rejoicing over the return of their long lost chums. If the seahorse is pair bonded, watching the happy couple don their greeting garb and dance in tandem as they renew acquaintances when the missing mate is returned to the herd can be particularly dramatic.
Witnessing such a remarkable scene leaves little doubt of the following in the mind of even the most objective observer: seahorses clearly recognize one another, they undeniably experience something akin to our own emotions of excitement and happiness or well-being, and they literally wear their hearts on their sleeves. In fact, one can often read a seahorse’s mood from the changes in coloration it displays. Excitement is portrayed by the same sort of lightening in shade and brightening in coloration seen during courtship, greetings, and competition or ritual combat -- all stimulating times when seahorses are operating at a high state of arousal. For example, a hungry seahorse will often betray it’s excitement at feeding time by brightening in coloration as it hunts down the newly added food or prey. Once its appetite has been sated, it will quickly revert back to its normal base color pattern.
On the other hand, seahorses typically respond to stress by darkening markedly in coloration. A distressed seahorse is thus often darker than its normally coloration due to the expansion of melanophores in its skin. This is often the case when a pair-bonded seahorses loses its mate, and experienced seahorse keepers will invariably tell you that seahorses also experience something similar to sadness. Just as a grieving widow wears black for an indefinite period, widowed seahorses often betray their distress by darkening markedly in coloration. The darkening is similar to the change in coloration a vanquished seahorse displays to signal its submissiveness.
There are numerous anecdotal reports that indicate that the health of a pair-bonded seahorse often suffers when it loses its mate. Widowers are thus said to languish, experience loss of appetite, and lapse into a general state of decline. Many hobbyists equate this to a state of depression or melancholy. While it’s safe to say that widowed seahorses don’t die from a broken heart, there may well be a kernel of truth at the heart of such accounts. It's very likely that a pair-bonded seahorse suddenly separated from its mate will experience altered hormonal secretion as a result. This can cause low levels of certain hormones that are known to have a profound influence on both mental state and physical well being in humans and animals alike, affecting everything from the immune response to sperm production and sex drive.
By now it should be clear that seahorses change color for many reasons, including camouflage, courtship displays and various other social interactions, and also in response to hormonal influences and quite a number of environmental factors. In the next issue of Conscientious Aquarist, we will explain how these changes in coloration are accomplished, discuss the factors that can have an adverse impact on your seahorses' coloration, and go over some suggestions for keeping your seahorses looking their best and brightest in the aquarium.
Abbott, Alisa Wagner. 2003. The Complete Guide to Dwarf Seahorses in the Aquarium. Neptune City, NJ: TFH Publications.
Blake, R.W. 1980. “Undulatory median fin propulsion of two teleosts with different modes of life.” Canadian Journal of Zoology. 12 May 1980.
Bull, Colin D., ed. and Jeffrey S Mitchell, asst. ed. 2002. Seahorse Husbandry in Public Aquaria. Project Seahorse: 2002 Manual.
Cusick, Terry. 2000. “Where'd the Color Come From?” Barbels: Selected Articles. Mar. 2000 (accessed 2 Feb. 2004). http://www.nfkc.info/barbels003.htm
Giwojna, Pete. 1990a. A Step-By-Step Book About Seahorses. Neptune City, New Jersey: T.F.H. Publications.
Giwojna, Pete. 1990b “Color variations in the dwarf seahorse.” Seahorse Update. 11 (5): 3-4.
Giwojna, Pete. Jan. 1999. "Seahorse Breeding Secrets: Ten Common Mistakes and How to Avoid Them." Freshwater and Marine Aquarium. Vol. 20, Num. 1 & 2. http://www.oceanrider.com/articledetail.asp?ArtNo=18 (accessed 8 Dec. 2003), part of Ocean Rider Articles http://www.oceanrider.com/articles.asp
Giwojna, Pete, and Carol Cozzi-Schmarr. Mar. 2002. "Horse Forum." Freshwater and Marine Aquarium. http://www.oceanrider.com/articledetail.asp?ArtNo=2 (accessed 20 Jan. 2004), part of Ocean Rider Articles http://www.oceanrider.com/articles.asp
Giwojna, Pete, (unpublished text). Complete Guide to the Greater Seahorses in the Aquarium. Neptune City, New Jersey: T.F.H. Publications.
Tamaru, Dr. Clyde, and Carol Cozzi-Schmarr. Sep. 2001. "Horse Forum." Freshwater and Marine Aquarium. http://www.oceanrider.com/articledetail.asp?ArtNo=8 (accessed 28 Jan. 2004), part of Ocean Rider Articles http://www.oceanrider.com/articles.asp
Vincent, Amanda C.J. 1990. Reproductive Ecology of Seahorses. Ph.D. Thesis, University of Cambridge, 1990.
Vincent, A.C.J. 1994. “The improbable seahorse.” National Geographic 186(4), Oct.1994: 126-140.
Vincent, Amanda C.J. & Sadler, Laila M. 1995. “Faithful pair bonds in wild seahorses, Hippocampus whitei.” Animal Behavior 50(3), 1995: 1-13.
Whitley, G. and J. Allan. 1958. The Sea-Horse and its Relatives. Adelaide: The Griffin Press.