Not too long ago, I was studying shrimps. 🙂

No no, I did not forget my first love, the giant clams. It was purely coincidental when my colleagues and I came across a pair of shrimps latched onto the giant clam’s gills (or respiratory organs). Based on our earlier literature review on ‘The ecological significance of giant clams in coral reef ecosystems‘, we knew that giant clams hosted shrimps in a relationship known as commensalism.

Commensalism refers to the association between two organisms in which one benefits and the other derives neither benefit nor harm. In this case between the giant clams and shrimps, we think that the shrimps likely had more to gain from living inside the body of a big ‘bodyguard’ and pinching food off from the gills of the clams. Some scientists suggested that the shrimps may cause some harm to the clam host by nipping off tissues from its gills, but this is anecdotal.

Figure 1. A pair of Anchistus miersi shrimps collected from a fluted giant clam, Tridacna squamosa. a) Male shrimp and b) Female shrimp.

We consulted the experts and the shrimps were both identified as Anchistus miersi, and they were a male-female pairing (Fig. 1). The male (Fig. 1a) tends to be smaller than its female counterpart, and the female (Fig. 1b) was brooding eggs (in pale green).

The most interesting observation here was that the same species of shrimps exhibited different spot colours within a single population (found in a single giant clam)! Here, when alive, we observed that the male shrimp had red dots and the female shrimp had blue dots. Upon preservation in ethanol, both specimens revealed a mixture of red and blue pigments. We concluded that the species, Anchistus miersi exhibit dichromatism.

Dichromatism means the occurrence of two different colours in animals. So why do they exhibit dichromatism in the same species? We simply have no idea yet! There are no obvious advantage or disadvantage being colourful as they live inside the clam host for their entire lives. The simultaneous occurrence of red and blue pigments does suggest that the colour pattern is not fixed.

So can the shrimps change their spots? Even more questions!


  • Neo, ML, BY Lee, K Vicentuan & PA Todd (2015) Dichromatism in the commensal shrimp, Anchistus miersi (De Man, 1888). Marine Biodiversity 45: 877-878.