These seahorses have given up on monogamy

This article was first published in the May 2016 issue of WIRED magazine. Be the first to read WIRED's articles in print before they're posted online, and get your hands on loads of additional content by subscribing online.

Shortly after arriving at Ocean Rider Seahorse Farm, on Hawaii's lava-crusted Kona Coast, I am invited by a tanned young woman who's wearing short shorts, an in-ear-microphone and a turquoise Hawaiian shirt patterned with seahorses, to steeple my fingers into a structure that Teddy could hold on to.

Teddy is one of six dark-brown seahorses wrapped around one another in a many-snouted knot at the bottom of a large, blue, plastic tub. "He's really into people," she says. And sure enough, as soon as I put my finger into the water, Teddy makes a beeline for me, steering with pectoral fins that look like children's water wings. He is startlingly graceful and wraps his long tail lightly around my index finger and leans back, angling his face in our direction. "Is he looking at me?" I ask. "Probably," she says. "We breed them for friendliness."

Seahorses are fish, but maybe because they look like tiny, gentle horses, humans find it easier to acknowledge their emotional lives and individual personalities than other species'. Teddy is popular on the tours because he is so gregarious. But he's one of thousands. Ocean Rider Inc may be the world's busiest paternity ward. It looks and sounds a lot like the aquatic section of a garden centre, with its low hum of pumps, gurgling water, rolls of black shade netting and plastic tubs. But instead of a scrum of duckweed or fat koi, the tubs are full of expectant fathers; fathers who've just given birth; or fathers who are about to get pregnant.

This farm has perfected the art of raising seahorse dads, their female companions and their offspring, referred to as "ponies" by enthusiasts who have them shipped from here to Minnesota or Malaysia or anywhere in-between. Some of Ocean Rider's males have been continuously pregnant for more than ten years. After gestating the babies from ten days to six weeks, they give birth to anything from 100 to 800 individuals (depending on their size and species), expelling the seahorse babies from a marsupial-like pouch on their bellies. In addition to their fame as one of the few animals to have a male pregnancy, the genus Hippocampus has long been known as monogamous.

Both in the wild and in captivity, pairs greet each other every morning with a languid, promenading dance, possibly a colour change, and then spend the rest of the day sucking up snacks of zooplankton or crustaceans together through their snouts. Seahorse sex happens after a many-hour courtship dance – the male and female gliding and spinning in tandem, as synchronised as water ballet dancers1. When she's ready, the female deposits her eggs into the male's pouch and he releases sperm to fertilise them.

In the wild, seahorses seem to prefer dancing and mating with a particular seahorse – possibly because breeding successive times with the same partner means that, with practice, they're more successful at delivering and fertilising the eggs2. Monogamous seahorses also spend less time between pregnancies. The daily dance ritual allows the female to keep a close eye on her male and keep track of exactly what stage he's at in his pregnancy. She will begin ripening her eggs before her partner is due to deliver, so she's ready to mate again as soon as he gives birth.

This romantic dedication to one another has sometimes made it hard for aquarists to keep seahorses happy in home tanks. Seahorses can refuse food and waste away after the death of a mate or when they're taken away from them in the wild. Pete Giwojna is Ocean Rider's "tech support" – a dedicated and knowledgeable aquarist who makes sure every prospective buyer has completed the lengthy Seahorse Training Programme. After a purchase, he often responds to customers dealing with seahorses' emotional issues. One pair of pony owners wrote to him after their eldest seahorse died because the second-oldest seemed upset. "He is not eating as much. He seems depressed, is that possible?"

"A widowed seahorse certainly can be traumatised by the loss of its mate," Giwojna responded. They can "languish, experience loss of appetite and lapse into a general state of decline. Many hobbyists equate this to a state of depression or melancholy. Although it's safe to say widowed seahorses don't die from a broken heart, there may well be a kernel of truth behind such accounts." According to Giwojna and many other seahorse aficionados, it's quite common for pair-bonded seahorses to suffer emotionally and physiologically if separated from one another. The survivor experiences hormonal changes associated with everything from suppressed immunological function to lack of sex 
drive and appetite, things that can cause mortal problems if the seahorse doesn't recover soon enough.

At Ocean Rider's farm, this is a problem they don't face all that much. On the tour, the guide motions to a tub of tiny seahorse babies drifting in small, sociable clouds and declares: "We have a created a domesticated seahorse that doesn't die of loneliness." One way that Ocean Rider has done this is by raising the seahorses not in pairs as they live in the wild, but in groups. "Non-monogamy3 is just something that naturally happens when you are raising young adults together at greater population densities than they ever experience in the wild," Giwojna explains. "The seahorses are surrounded by prospective partners at all times."

Some of these prospective partners are trademarked. Ocean Rider is best known for breeding the "Mustang", a dun-coloured pony with dark-brown zebra stripes, on sale for $75 (£50), mate not included. But they've bred other varieties, such as the bright yellow "Sunburst" ($250 per pair) and the "Fire Red" ($450) said to have all "the personality of the Mustang" but coloured like a Hawaiian sunset. As Ocean Rider sees it, its tinkering has made a creature that's better suited to living with humans, and its business relieves pressure on wild populations who've been plundered for the aquarium, souvenir and medicine trades and are losing habitat as their preferred seagrass beds, shallow reefs or mangroves are destroyed or polluted. 

But studies suggest that a few populations of wild seahorses may have taken up swinging too. So, has Ocean Rider really created a domestic seahorse, or have their ponies simply agreed to make do in a world of faux treasure chests, peering human giants and the arrival and departure of tempting companions via FedEx? Sex-advice columnist Dan Savage says that being "monogamish" might be the best way to save a long-term relationship. Perhaps the ponies got there first

1. Vincent ACJ, 1995. A role for daily greetings in maintaining seahorse pair bonds. Anim Behav 49:258-260.
2. Vincent ACJ and Sadler LM, 1995. Faithful pair bonds in wild seahorses, Hippocampus whitei. Anim Behav 50:1557-1569.
3. Kvarnemo C, Moore GI, Jones AG, Nelson WS, and Avise JC, 2000. Monogamous pair bonds and mate switching in the western Australian seahorse Hippocampus subelongatus. J Evol Biol 13:882-888.

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