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Wakatobi's Colourful Babies  

It's always fascinating to observe the difference between juvenile and adult fishes. If you're not sure what to look for, many times juvenile fish are hard to identify, because their appearance is so very different to the grown-ups. It's a great theme to look for on the diverse and rich coral reefs of Wakatobi and this was a theme concentrated on in July. Here, a juvenile Spotted Boxfish shows off his bright yellow hues.


Yellow Boxfish Juvenile - Doug Richarson photo


Pacific Boxfish - Liquid Motion Film photo
 
Spotted Male Boxfish - Bill Nyitray photo

The transition from juvenile to adult takes place when the fish reaches sexual maturity. As juveniles grow, appearances change - some more than others, some faster, some slower. Adults are often very differently coloured to juveniles, like this Adult Spotted Boxfish, whose Juvenile is the brightest of yellows.

Adult males are often more colorful than females and males and females can become significantly different to each other, advertising their maturity through color patterns. Like a number of other fishes, the Adult Spotted MALE Boxfish is wearing more blue than the female.


Warty Frogfish Juvenile - Saskia Van Wijk photo

Adults often appear different - but they can also act differently. As juveniles, a fishes main concern is to find food and avoid predators, but once reaching adulthood, reproduction goes straight to the top of their list. As a result, a fish might become more aggressive as it seeks to stake claim to a territory, especially towards members of their own gender who are now competitors for breeding opportunities. The adults start to defend their territory, while attempting to court potential mates. Here we see the colouration of a juvenile Warty Frogfish.

Here below left, in contrast, we see the adult Warty Frogfish, with a distinctly altered colour pattern.


Warty Frogfish Adult - Eric Cheng photo
  The ribbon eel is an elegant creature with a long, thin body and high dorsal fins. The ribbon eel can easily be recognised by its expanded anterior nostrils. Juveniles and sub-adults have jet-black bodies, making it hard to differentiate their eye. Their bodies have a yellow dorsal fin and they appear so different to the adult, that they were once thought to be a separate species entirely!

 

 


Blue Ribbon Eel Juvenile - Ken Knezick photo

Reef fish are able to see colours extremely well, albeit often in quite diferent ways to us humans. The differing color patterns between juvenile and adult is thought to prevent adults from seeing the juveniles as a potential threat to their territory.

The ribbon eels are protandrous hermaphrodites - meaning males changing into females. At approximately 85cm, males begin to develop female sex organs and change colour to yellowish blue, to entirely yellow with a black anal fin with white margins. Female sightings are uncommon. The adult males are easier to spot and are brilliant blue with a yellow dorsal fin, snout, lower jaw and eye.


Blue Ribbon Eel Adult - Paul Sutherland photo

Like many other fish, Parrotfish can change gender during their lives, with their colouration and patterns varying greatly, even between males, females and juveniles of the same species.


Parrotfish Juvenile Bicolor Phase - Ken Knezick photo
 
Bicolor Parrotfish Adult - Liquid Motion Film photo

The Juvenile Pinnate Batfish is a dream for every photographer, but they are often camouflaged under the overhangs, hiding from predators.

As a juvenile, the Batfish is brown with orange stripes outlining its entire body. Adults become dull silver. This fish grows to a maximum size of 45 centimeters and has been observed to contribute significantly to reducing algal growths on coral.


Pinnate Batfish Juvenile- Liquid Motion Film photo
 
Pinnate Batfish Intermediate Phase - Liquid Motion Film photo

The closest fish in appearance to Nemo is the brilliantly coloured Yellowtail Coris Wrasse juvenile, sometimes known as the Clown wrasse, despite having no relation to the little movie star. In its juvenile stage, the yellowtail coris is bright red with five white spots or "saddles", outlined in black, which are scattered across the top of its body from nose to tail.


Yellowtail Coris Juvenile - Liquid Motion Film photo
 
Yellowtail Coris Intermediate Phase - John and Lauri photo

On its way to adulthood, this attention-grabbing wrasse with gold-rimmed eyes ceases to appear like Nemo completely and instead moves on to a greenish-blue phase, developing iridescent blue spots and a sunshine-yellow tail.

When fully grown, the yellowtail Coris assumes a predominantly reddish-orange or reddish-brown base color, along with dorsal and anal fins edged in electric blue. Males differ from females by being darker in hue with a light-colored bar vertically bisecting the center of the body. Among wrasses in general, adult males come in two distinct types: large colorful ones, called terminal males, and small drab ones. If a large male disappears from the scene or an abundance of females proves to be more than one big guy alone can handle, the most dominant female will "become" a male. The change is dramatic, involving a transformation in reproductive organs, appearance and behavior.


Yellowtail Coris Adult - Liquid Motion Film photo

Most fishes change colour and pattern as they grow, passing through different phases until they reach adulthood. Here, a juvenile Emperor Angelfish (below left) contrasts brightly with the reef.


Emperor Angelfish Juvenile - Ana Sofia Ribeiro Fonseca photo
  The adult Emperer Angelfish reveals the variation in colour from its juvenile form. in addition to changing colour throughout life, numerous species develop the ability to alter their colours or patterns to match mood, readiness to mate, blend in with their surroundings or to mimic another species for defence or feeding.

 


Emperor Angelfish Adult - Liquid Motion Film photo

So how do fish change colour? Chromatophores are irregular shaped cells that contain pigments and these cells are found in many fish, crustaceans and marine species. These cells can be stimulated by nerves or in some cases hormones, causing them to concentrate or expand, varying the intensity of the colours. When the chromatophores hold different pigments overlaying each other, they produce colours in the longer wavelengths: red, yellow, orange, brown and black. Brilliant and complex colour patterns on fish indicate a high density of chromatophores in their skin.


Yellowtail Damselfish Adult - Ginnie Reynolds photo
 
Yellowtail Damselfish Juvenile - Ken Knezick photo

Amongst other less common pigment cells, many fishes have cells called irridophores, which contain light-reflecting crystals. These cells produce permanent colours in the short wavelengths: pink, green, blue, silver and irridescence. When illuminated they generate iridescent colors because of the diffraction of light within the stacked plates. Silvery fishes have several layers of irridophores in their skin, reflecting almost all light from their body and helping them blend into their background.


Manderinfish - Glenn Patton photo

 


Emperor Snapper - Liquid Motion Film photo

The control and mechanics of rapid pigment translocation has been well studied in a number of different species and the process can be under hormonal, neuronal control or both. A juvenile Masked Grouper displays his colours brightly.

The adult Masked Grouper wears an entirely different color scheme to the juvenile - perhaps to blend and reflect the change of his everyday habitat and lifestyle.


Masked Grouper Juvenile - Dieter Freundlieb photo


Masked Grouper Adult - Collin photo

One thing is certain - whether changing colour slowly throughout a lifetime, or rapidly for camouflage, defense or to communicate a specific message to another creature, marine animals colouration and colour change is a significant and vital aspect of their daily lives.

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