No matter whether you are a human, a bird or a fish, growing up is not an easy feat. Not only does growing up involve drastic changes in morphology, physiology and behaviour, it usually also signifies the most vulnerable time in an animal’s life. Consequently, many animals rely on strategies such as camouflage and mimicry to make it past their early life stages.
The dusky dottyback, Pseudochromis fuscus, is a small coral reef fish (~ 8 cm) that can be found in various different colours (yellow, brown, grey and pink) across the Indo-Pacific. Dottybacks are vicious predators that consume up to 30 juvenile fishes per day, making them important regulators of coral reef fish communities. Recently, we found that adult dottybacks from the Great Barrier Reef change colour to imitate the colouration of the prevalent damselfish community (either yellow or brown). Dottybacks are doing this because by looking like ‘harmless’ damselfish, they are able to deceive their juvenile fish prey, which greatly enhances their predatory success. However, little is known about the early life stages of this fish.
In this study we investigated how the colour as well as the visual system of dottybacks change when growing up. We found that dottybacks change colour twice during development. First, larval dottybacks change from nearly transparent to dark grey when returning from the open ocean to settle on coral reefs. Being transparent in the open ocean or grey on a coral reef is an efficient camouflage strategy when perceived through the eyes of their predators. Teenage dottybacks then change colour again to imitate the damselfish in their surroundings as soon as they are big enough to prey on juvenile fish. At this stage, mimicking damselfish to increase predation clearly outperforms a general camouflage strategy. However, adult dottybacks are still likely to deceive their own predators by hiding amongst a school of similar looking fish, or when seen against specific habitats types (yellow on life coral and brown on coral rubble).
We also found that dottybacks change their visual system when growing up. Likely to start their life as dichromats that can only distinguish a limited set of colours, bigger larval fish acquire a trichromatic visual system before switching to a potentially tetrachromatic system as larger juveniles. Hence, dottybacks progressively increase the complexity of their visual system, which might better their ability to discriminate between colours and thus, to solve more elaborate visual tasks. Interestingly, the changes to the visual system always precede changes in colour (and habitat transitions) indicating that dottybacks need to first acquire the appropriate visual performance before transitioning into a novel life stage.
In conclusion, we find that starting out as ‘lambs’, small dottybacks rely on various camouflage strategies to avoid being eaten. However, once they are big enough to feed on juvenile fish, they morph into the proverbial ‘wolf in sheep’s clothing’ to become very efficient predators themselves.
Contributed by Fabio Cortesi, Postdoctoral Fellow at the Queensland Brain Institute