“To dive or not to dive, that is the question.” - Hamlet if scuba diving was available back then, probably.
Let’s talk about hamlets. The fish which make up the Hypoplectrus genus can delight divers with their bright colours and curious behaviours. They generally live their lives between 3m and 20m (10-65 feet), though some can be found as deep as 40m (130 feet). They also display remarkably diverse colour differences from species to species. It should be no wonder why divers have been fascinated by them for years. However, don’t be fooled. These seemingly innocent fish have caused many a fight in the scientific community. It all started with their beautifully varied colours…
Colour morphs
"God hath given you one face, and you make yourself another." - Hamlet Act 3, Shakespeare
Debate runs rampant in certain circles as to whether the different hamlets are merely different colour morphs of the same species, or if each colour morph is a different species altogether. You see, the first thing we need to recognize about hamlets is that they are genetically very similar to one another to the point that different types can mate and produce fertile offspring, creating hybrids. Scientifically, this is often used to define creatures as being of the same species. However, hamlets and their strikingly different colorations between the different species has been the first indicator to mark them as different species.
The masked hamlet is a sight treasured by divers for its beautiful pale coloration and striking blue ventral fins, whilst the barred hamlet will boast of dark brown cryptic coloration that colours most of its body. The blue hamlet boasts a striking uniform shade of blue that covers their entire body, but the shy hamlet favours yellow and golden colourisation on its head and fins, but dark black shading covering most of its body. Currently, not counting hybrids, 17 colour morphs or species of hamlets have been identified. The diverse visual differences between hamlets is what first attracted the scientific community’s attention, and remains a point of debate.
Mating
“My lord, he hath importuned me with love, In honourable fashion.” Hamlet Act 1, Shakespeare
Courtships between hamlets are relatively predictable affairs. Hamlets are synchronous hermaphrodites, meaning that they can move between “male” and “female” roles during mating. At the start of courtship, two hamlets will seek each other out and spend about an hour “playing” together - they chase each other around the reef while occasionally eating off the bottom of the reef.
When they are ready, the hamlet which plays the “female” role will begin a dance to seduce the male. She will point her nose up and flare her fins for the male, who will be below her. They will then rise together in the water column separately over some structure they find on the reef (such as a coral head) before they clasp together. After a few seconds, they will come apart and release the gametes. They will clasp together multiple times, taking turns between who is releasing the eggs and who is fertilising.
The mating habits of hamlets does fuel back into the discussion of whether they are separate species or not. Hamlets will generally only mate with hamlets of the same colour morph. They only mate with another colour morph if there is no other mate of the same type available. This only happens about 2-3 percent of the time. The dislike of mating with other colour morphs is one of the main considerations taken into account when people discuss their speciation.
Eating habits
"Your fat king and your lean beggar is but variable service - two dishes, but to one table.” Hamlet Act 4, Shakespeare
The eating habits of hamlets are quite similar between the different species. By and large, they enjoy munching on your crabs, shrimp and other mobile invertebrates. They are known to occasionally branch their diet out to smaller fish too. The indigo hamlet H. indigo in particular is known to regularly prey on the blue chromis C. cyanea. This plays into another subject that the hamlet has divided the scientific community on - mimicry.
Mimicry
“One may smile, and smile, and be a villain; at least I'm sure it may be so in Denmark.” Hamlet Act 1, Shakespeare
Hamlets are notorious for being aggressive mimics. Aggressive mimics are predators which mimic harmless or beneficial species, and gain enhanced access to prey. This behaviour has been noticed amongst several species of hamlets. For instance, when a butter hamlet H. unicolor is in the same vicinity as the foureye butterflyfish C. capistratus both species will have a higher chance of success in their hunts.
This is perhaps the root cause of the second argument hamlets bring about in the scientific community. While specific hamlets do have a higher success rate in hunting around certain fish, they lack many of the usual indicators which mimics usually have.
For instance, as mentioned earlier, the indigo hamlet is suggested to mimic the blue chromis in order to prey on it. Indeed, they do share a gorgeous shade of blue, but the similarities end there. The indigo hamlet has a vastly different patterning across its body, boasts a much greater size and does not seem to mimic the chromis’ behaviour sufficiently.
It has been suggested that rather than mimicry, the hamlets instead follow a “social-trap”. The social-trap hypothesis suggests that the hamlets are more likely to find areas to live in with fish of similar colourations for social reasons. However, these arguments are not necessarily exclusive as the social-trap hypothesis has also been suggested as the very earliest stages for the evolution of mimicry.
Last Words
“So tell him, with the occurrents, more and less, Which have solicited. The rest is silence.” Hamlet Act 5, Shakespeare
Hamlets are always a pleasure to see underwater. Their beauty and variety are a diver’s delight. But beyond their physical appearance, they may just hold the keys to understanding more about the development of different species that we haven’t had before. So come on over! While science fights over this fishy apple of discord, see how many different hamlets you can find at our beautiful reef at Cobalt Coast!
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