While visiting the O. Orkin Insect Zoo at the National Museum of Natural History earlier today, I was surprised to encounter some familiar faces (or should I say anterior cephalothoraxes?).
The freshwater pond display — typically home to a range of aquatic beetles, Odonate larvae (dragonfly and damselfly nymphs), and assorted Hemiptera (water boatmen, backswimmers, water striders, and Belostomatid water bugs) — instead housed just a handful of Hydrophilid beetles alongside a dozen-odd freshwater prawns (most likely Macrobrachium lanchesteri).
M. lanchesteri gathering loose detritus from the substrate with its second pereiopods.
Though I couldn’t help but wonder whether the other tenants had been eaten by the new additions, they exhibited little aggression towards the remaining beetles … which is not to say that the tank was sedate — far from it. The water column and substrate were a constant crustaceous blur of swimming and scurrying forms — as two prawns would squabble over tatters of shed exuvium under the watchful gaze of a dominant male at one end of the tank, an ovigerous female would be aerating the lime-green brood amidst its fluttering pleopods at the other.
Despite the shallowness and slack circulation of the water, the Zoo’s prawns seemed to be in good condition. M. lanchesteri, unsuprisingly, tolerates a broad range of habitats throughout Thailand, Peninuslar Malaysia, Myanmar, southern China, and Java, including not only streams and rivers but also rice fields, ponds, and reservoirs (Cai et al., 2004).
Dominant male M. lanchesteri (~5 cm in rostrum-telson body length; note development of second pereiopods) lurking beneath a leaf. If the silt and algae swaddling most of the plants were anything to go by, aufwuchs appear to make up only a small portion of these prawns’ diet.
Female M. lanchesteri with green ovary mass.
As Wong (1994) noted, M. lanchesteri produces large, floating larvae able to complete development in freshwater; berried females notwithstanding, I didn’t notice any juveniles. If their parents weren’t just very recent additions, it may be that they’re being consumed by older tankmates for want of cover — or that they’re succumbing to that latterday Charybdis of the filter intake.
Cai, Y., Naiyanetr, P., & Ng, P. (2004). The freshwater prawns of the genus Macrobrachium Bate, 1868, of Thailand (Crustacea: Decapoda: Palaemonidae). Journal of Natural History, 38, 581-649.
Wong, J. T. Y., 1994, Larval development of the Palaemonid prawn, Macrobrachium lanchesteri (De Man) reared in the laboratory (Decapoda, Caridea), Crustaceana, 67(3), 297–315.