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#4200-6270 University Blvd.
Vancouver, BC

Functional morphologist and evolutionary biologist


Building Ontogenetic Series I: Halichoeres and Thalassoma

Vikram Baliga

I'm starting to build my collection of specimens from museum loans and pet trade purchases, and I thought I'd share a few photos. I'm interested in building an ontogenetic series for each of the species I show here (and many more), so I can better understand how morphological traits may change over ontogeny. This will help me understand how ontogenetic shifts in morphology, and thus feeding mechanics, may be associated with ontogenetic shifts in diet. I'm looking to have at least 15 specimens per series, so each of the pictures shown here represents a work in-progress.

(Photos after the jump.)

First up: Halichoeres bivittatus, commonly known as the slippery dick wrasse. This species is an eater of gastropods, crabs and other benthic invertebrates as an adult, but is also known to exhibit cleaning behavior as an early juvenile. This Caribbean species is thus a facultative (juvenile) cleaner.

Halichoeres bivittatus

H. bivittatus, smallest

H. bivitatus

H. bivittatus

H. bivitattus,  largest (so far)

Next up, we have Halichoeres nicholsi, commonly known as the spinster wrasse. Early juveniles of this species exhibit cleaning behavior, and often form aggregations. As they transition adulthood, members of this species tend to become a bit more solitary, and feed on gastropods, sea urchins and crabs. Thus, this species can be classified as a facultative (juvenile) cleaner.

Halichoeres nicholsi

Unfortunately, the smallest specimen of H. nicholsi I currently have is close to 10cm TL. Individuals of this size or larger rarely (if ever) clean.

H. nicholsi

The largest H. nicholsi I have is roughly half the maximum size of this species.

H. nicholsi -- nasty, big, pointy TEETH!

Here we have Halichoeres nigrescens, the dusky rainbowfish -- another facultative (juvenile) cleaner. Like many other wrasses, this species is a generalist invertivore. Small individuals, however, have been observed to clean other fishes.

Halichoeres nigrescens

At such a small size, this specimen of H. nigrescens probably partakes in cleaning.

H. nigrescens

H. nigrescens

My largest specimen of H. nigrescens seems to be much more deep-bodied than the others. At a TL of just under 7.5 cm, this individual probably no longer cleaned.

My next series, composed of individuals of Halichoeres argus, unfortunately does not show a very broad range in size. Also known as the peacock wrasse or argus wrasse, this species can actually grow up to 12 cm SL. Unlike the other Halichoeres species I currently possess, H. argus is not a cleaner at any point in ontogeny and is a generalist invertivore.

Halichoeres argus

Halichoeres argus

H. argus

H. argus

H. argus

H. argus

We'll depart from the world of Halichoeres and enter the realm of Thalassoma. Below is Thalassoma duperrey, known as the saddleback wrasse. This Hawaiian species is facultative throughout ontogeny, meaning that cleaning behavior has been observed in both juveniles and adults. The majority of its diet, however, is composed of benthic crustaceans and molluscs.

Thalassoma duperrey. Note: specimen 4 is not as deep-bodied as it may seem; a bend in the specimen caused it to curve towards the camera lens, causing distortion.

Thalassoma duperrey

Thalassoma duperrey

Our final species is Thalassoma lutescens, also known as the yellow-brown wrasse, the green moon wrasse, the sunset wrasse, the parrotfish (not to be confused with scarids), the yellow wrasse, and the whistling daughter (my favorite). This species is a facultative (juvenile) cleaner: adults mainly feed on crabs, gastropods and sea urchins and do not partake in cleaning.

A pretty lopsided size series of Thalassoma lutescens.

T. lutescens

T. lutescens

T. lutescens
 My largest specimen of Thalassoma lutescens is actually about half the maximum size reported in the literature for this species. Note that this large specimen lacks the dark lateral stripes that the smaller specimens have.

A closer look at my largest specimen of Thalassoma lutescens.

I hope you've enjoyed this post! It's a shame that preserved museum specimens often appear more drab than fresh specimens from the wild. Species in Halichoeres and Thalassoma are quite often characterized by vivid yellows, reds and greens, and it is partially for this reason that these genera are among my favorites. For more on the species I've mentioned here, be sure to check out resources such as FishBase, the EOL, and Arkive.