Re:live rock

Pete Giwojna

Dear Karen:

You’re very welcome to all the information I can provide to help keep your seahorses happy and healthy!

Yes, there’s no reason a bow front corner tank wouldn’t work well for seahorses as long as you equip it with an efficient filtration system and suitable lighting. I would suggest an aquarium of at least 40 gallons for the following reasons. When keeping the larger breeds of seahorses, it’s best to start with the largest aquarium you can reasonably afford and maintain (the taller, the better). In general, a tank of at least 40 gallons (150 L) is preferable since that’s the size when one begins to see significant benefits in terms of the greater stability a larger volume of water can provide. An aquarium of 40-gallons or more will be more resistant to overcrowding and to rapid fluctuations in temperature, pH, and salinity than smaller setups. The larger the aquarium the larger the margin for error it offers the aquarist and the greater the benefits it provides in terms of stability.

It is equally desirable to select an aquarium at least 20-inches high when keeping the greater seahorses. They need the vertical swimming space to perform their complex mating ritual and successfully complete the egg transfer, which is accomplished while the pair is rising through the water column or drifting slowly downwards from the apex of their rise. If the aquarium is too shallow, eggs will be spilled during the transfer from the female to the male’s brood pouch, and mating becomes increasingly difficult or impossible below a certain minimum depth. A tall aquarium can also help protect the seahorses from depth-related health problems such as bloated pouch and certain forms of Gas Bubble Disease.

The optimum height for a seahorse tank would be greater than 36 inches (research shows that a water depth of 36 inches or greater effectively prevents most forms of gas bubble disease). In actual practice, however, tanks that are 3 feet tall or better are quite impractical for the home hobbyist. For one thing, few tanks that size are available; you would have to have something custom made to achieve those dimensions and that gets to be prohibitively expensive with such a tall aquarium. In the second place, it’s very difficult to clean and maintain an aquarium that is 36 inches deep or more since you cannot reach the bottom of the tank with your arms.

For this reason, most seahorse keepers compromise on the height of the aquarium. I find that a height of 24 inches is a good compromise. Standard, off-the-shelf aquariums 24-inches tall are available so that you can obtain such a tank at a reasonable cost, and a height of 24 inches still provides significant protection against gas bubble disease, while being quite manageable when working in the aquarium. So I would suggest that you shoot for a depth of about 24 inches, Karen.

As far as filtration goes, an external power filter is a valuable addition to any seahorse setup for several reasons. It will provide added water movement and circulation for your aquarium, as well as accommodating any mechanical or chemical filtration you may desire. A bewildering array of filtration options are available today, including a myriad of canisters and hang-on-the-back models, most of which will do the job reasonably well. Even the trusty old standbys, undergravel filters and air-operated sponge/foam filters, are still reasonable choices for a standard seahorse setup under some circumstances.

If you are using 1-2 pounds of live rock per gallon as your primary biofilter, then a basic canister filter or hang-on-the-back filter is all you need to provide mechanical/chemical filtration and additional water movement. Otherwise, you’ll need to include a filter that can provide biological filtration. Undergravel filters and air-operated sponge filters can accomplish this and work well for some applications, but there are better choices available for seahorse keepers nowadays.

For example, wet/dry trickle filters are probably the most desirable units for the seahorse keeper if the aquarium has adequate space (behind or beneath it) to accommodate such a unit and the hobbyist can afford one. They are top-of-the-line units that feature a thin film of water trickling over filter media with an ultra-large surface area, thereby allowing maximum air-water contact. This provides excellent oxygenation with efficient offgassing, which is very important for seahorses. It helps keep dissolved oxygen levels high, CO2 low, and effectively prevents gas supersaturation, which can sometimes contribute to serious problems for our aquatic equines. As a added benefit, wet/dry trickle filters can also provide remarkable biological filtration, which can give you a real nice edge by further increasing your carrying capacity and boosting your margin for error accordingly.

The type or brand of supplemental filter you choose for your seahorse tank is not critical, but there are certain desirable features you want to look for in any filter that will be used for seahorses. For example, it should provide good surface agitation and water movement with adjustable flow. The intake tubes should reach all the way to the substrate (add extenders if they do not) and be screened off or otherwise shielded so they cannot "eat" a curious seahorse. The filter must provide efficient oxygenation and gas exchange and be able to accommodate mechanical and chemical filtration media such as activated carbon and polyfilter pads. A prefilter is very desirable, as is a "waterfall" return (or a spray bar attachment, if you decide on a good canister filter instead).

Males seahorses can indeed be aggressive with one another under certain circumstances, Karen. When a male displays aggression, it’s almost always directed toward a rival male and involves competition for mates, as discussed below.

As a rule, competition over mates is nothing to be overly concerned about with captive-bred seahorses. Believe me, such encounters tend to be much more stressful on the attentive aquarist than on the actual participants. Competition for mates is a highly ritualized affair in seahorses and though it can be chaotic at times, it’s mostly harmless bluster and serious damage is almost unheard of as a result of such jousting and sparring among the males.

Here is an excerpt from my new book (Complete Guide to Greater Seahorses in the Aquarium, unpublished) that discusses tail-wrestling and other antagonistic behavior in Hippocampus, Karen:

Competition for Mates

In the aquarium, both males and females compete for mates, but there is a big difference in the way they go about it. Females compete with one another passively, each trying to outdo the other and be the first to attract a mate simply by increasing the intensity of their courtship activities and displays. Their competitive behavior is therefore directed at the eligible males rather than any rival females. Males, on the other hand, compete much more actively and much more antagonistically. Their behavior is often aimed directly at their rival(s) and includes aggressive behaviors such as tail wrestling and snapping or sparring, which are never seen in the fairer sex. In other words, females respond to the presence of rivals by getting more flirtatious, whereas males often react to rivals by getting surly and carrying a testosterone-induced chip on their shoulders.

This is rather surprising when you think of it. Since, with seahorses, it is females that "impregnate" males, so to speak, and the males who undergo a prolonged pregnancy, many researchers have speculated that sex roles should also be reversed in Hippocampus and that females would thus exhibit typically male traits. According to the role-reversal theory, since males carry the young and limit the female reproductive rate, females are predicted to assume the male role and compete more vigorously for mates.

Several studies have shown that this is emphatically not the case (Vincent 1990, 1994a), however, and that male seahorses compete more actively and aggressively than females, and basically try harder to get pregnant than female seahorses try to give their eggs away. In the kinky world of seahorse sex, the boys still chase the girls, even though it’s the boys who get pregnant as a result!

And when two or more evenly matched young studs are butting heads and aggressively contending for the right to reproduce, chaos and confusion can sometimes result. Such cutthroat competition often brings out surprising, seldom-seen behaviors in Hippocampus. This is how I described the sort of fireworks and festivities that can ensue in an article entitled "Seahorse Breeding Secrets" (FAMA, Vol. 20, Num. 1 & 2, January-February 1999):

<quote>"What do I mean by chaos and confusion? I’m talking about normally passive, totally nonaggressive fish suddenly engaging in no-holds barred wrestling matches and exchanging sucker punches and knockout blows. I’m talking spousal abuse, with hapless females taking a beating when they get trapped in the middle of a melee between two rival males. I’m talking about shameless homewreckers trying everything from lies, trickery, and deception to brute force in order to come between would-be mates. As for confusion, crowded conditions often result in homosexual mating attempts, with over-aroused males trying to copulate with other stallions and frustrated females rising to mate with other fillies (Vincent, 1990)!

"In its mildest form, this sort of competition begins when the odd-man out in a trio of unpaired seahorses attempts to interfere with the other couple by interposing its body between them, as if ”cutting in” on their courtship dance (Vincent, 1990). If this simple ploy fails to break up the budding romance, the intruder may then decide to take matters into his own hands by wrapping his tail around his rival and actively restraining him (Giwojna, Jan. 1999)." <end quote>

If the opponents are evenly matched, a strenuous wrestling match will ensue, with each adversary trying its best to hog-tie the other and forcibly remove him from the female’s presence. If unable to break free, the loser will eventually signal that he’s had enough by darkening dramatically in coloration while flattening his body so that he’s lying parallel to the bottom. This is the way a seahorse cries "Uncle!" and the victor quickly recognizes this submissive display and releases his vanquished foe.

However, certain unscrupulous males are not above using this as a ruse, feigning submission in order to trick their rival into letting down his guard so they can launch a sneak attack. The moment the unsuspecting male relaxes his grip, the supposedly submissive scoundrel will take advantage of this lapse in order to deliver a sharp blow to the head of his unwary victim. One of these sucker punches is often enough to KO the would-be winner, thus enabling the crafty coward to snatch victory from the jaws of defeat. Like they say, "All’s fair in love and war," and, as we have just seen, when that war is over the right to mate with a frisky filly, the competition can quickly escalate in violence until the stallions come to actual blows.

With seahorses, this takes the form of "Snapping," an aggressive maneuver in which the attacker stretches out his head and flicks his snout against his rival with a violent snap, thus delivering a nasty blow to the adversary. The snap is often aimed either at the opponent’s eye or gills — particularly sensitive areas — and the force of a well-directed snap will knock the unfortunate recipient reeling across a distance of 10cm or more. Stunned by this sudden assault, the victim of one of these vicious blows invariably throws in the towel, flattening in submission and darkening in coloration. The loser’s dusky body coloration stands out in stark contrast to its brightly colored conqueror.

The winner may then celebrate his conquest with a curious kind of victory dance directed toward the female he’s been fighting over. The victorious male begins by tilting his body, often leaning over so far he is almost lying horizontally on his side, and then rapidly righting himself, repeating this motion several times in quick succession so he seems to be shuddering. At times it looks almost as if shivers are travelling down his spine until the male’s entire body is trembling and quivering with a rhythmical rippling motion that would put a hula dancer to shame. It’s as though the male anchors its tail to a solid object in order to wag his body, like a baby shakes a rattle. As suddenly as they began, the male will bring these amazing vibrations to a complete halt, only to resume them a short while later, repeating the whole procedure again and again.

This tremulous victory dance is a solo version of the displays of reciprocal quivering conducted during courtship and, of course, it is performed solely for the benefit of the nearby female, who often stands by motionlessly, as if rapt with sheer adoration. To the victor go the spoils, and the conquering hero will soon begin to court his lady fair in earnest.

<quote> "Short of a knock-out punch, this sort of sparring only serves to get the competitors all the more excited, which can be rough on the nearby female, who, of course, is the object of the entire exercise in the first place. Overzealous males sometimes swim right over the female, trampling her underfoot in their haste to get at their adversary, and woe to the luckless lady who gets caught in the crossfire between two sparring males (Vincent, 1990). She will certainly be snapped at inadvertently, and may even find herself stuck smack dab in the middle of a tail-wrestling tug-o-war, pulled in opposite directions by her admirers — the same sort of rough treatment Olive Oyl so often received from Popeye and Bluto in the cartoons.

"In self-defense, the harassed female often attempts to evade sparring males by darkening and flattening herself against the bottom in submission, or by swimming to the top and suspending high in the water column in order to escape the notice of her pumped-up paramours, since courtship and competition take place on the bottom and seahorses seldom look upwards. But in the close confines of the aquarium, it is impossible for a female to escape the attention of her over-sexed suitors for long, and even submissive females sometimes get dragged around the tank by rival males in the heat of combat…

"Worst of all, under crowded conditions, seahorses sometimes 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 such male-male copulatory rises lasted fully as long as heterosexual mating attempts (Vincent, 1990)….

"…Female-female mating attempts are even more disastrous, since they 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… (Giwojna, Jan. 1999)" <end quote>

Lest you get the wrong idea, I should emphasize that competition for mates is highly ritualized in Hippocampus. Let me repeat: 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 serious injuries are virtually unknown when these armor-plated adversaries throw down the gauntlet. In short, intrasexual 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.

In short, Karen, it’s not too unusual for male seahorses to use their tails aggressively under certain circumstances. Because of the seahorse’s bony plates and body armor, even when a tail is wrapped around the neck of an adversary, there is no real danger of strangulation, asphyxiation or injury. Seahorses breathe through their gills so their breathing isn’t impaired in such situations. They don’t like it one bit, and will certainly struggle and do their best to break free, but they’re not really in any danger. Of the agonist displays rival males may engage in, snapping is far more worrisome, particularly when it’s directed at the eye or head of the adversary, as is usually the case.

Male potbelly seahorses (Hippocampus abdominalis) are particularly prone to this type of aggression because they are polygamous by nature. Pot bellies are promiscuous ponies and groups of males will often compete actively for the favors of receptive females. Many other seahorse species form lasting pair bonds, which tends to limit the need for such aggression.

So the male H. abdominalis you rescued from your LFS were just doing what comes natural to them — butting heads and tail wrestling with rival males to assert their dominance and win the right to mate.

Best of luck with your new seahorse tank, Karen! I hope you find a bow front corner aquarium with just the right height.

Happy Trails!
Pete Giwojna

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