Raising Caridina cf. propinqua, ‘Borneo Orange shrimp’

Several years ago these bright orange shrimp started showing up in aquarium shops and on importer lists. They are hardy, brightly-colored, and largely diurnal, so they attract a lot of attention. The also attract a fair bit of suspicion — nearly every web forum discussing them ends with debate about where they come from and whether or not their coloration is natural. Importers generally state either that they are wild-caught in Indonesia or raised and dyed in Malaysian fish farms. I asked a shop-owner in Singapore about his source, thinking that he might have better information being only a hundred or so miles from either of those places, but he just shrugged and said “probably dyed.”

One thing that’s clear is that they do not have a fully freshwater life-cycle. Many people have collected larvae from their orange shrimp but these larvae inevitably perish in fresh water. I’ve raised a few dozen of these from infancy using a method similar to that used for Yamato shrimp, but there are a few marked differences.

Gathering larvae

Unlike Yamato zoaea, newly-hatched larvae of this species are not attracted to light. Indeed, shining a light on a tank full of larvae makes them dash for cover. This makes gathering them from a decorated tank quite difficult as they tend to lurk at the bottom rather than collecting under the lights. Generally I’ve let the eggs hatch in a jar or bowl, then removed the mother with a large-mesh net, and poured the entire contents of the bowl through a fine-mesh net. Keeping the female happy during this time can be difficult; if she gets stressed out she may drop or eat her eggs. A bit of shelter and something for her to hold on to (like a stalk of moss or piece of wood) seems to help.

Raising larvae

A modestly-controlled experiment with a variety of brackish waters showed that the larvae are happiest at low salinities in the neighborhood of specific gravity 1.008. Some survived at ranges up to 1.016, bit 1.008 seems to be the sweet spot. Tetraselmis algae can’t survive with so little salt, so I cultured these larvae in tandem with Nannochloropsis instead; otherwise the process is the same as that used for Yamatos. These larvae are well along their development upon hatching, and they grow quickly; many of mine transformed to adult form after only 24 days.

Another dramatic difference from Yamato shrimp is that young of this species do /not/ need to be transferred into fresh water immediately. Post-larvae continue to eat and flourish in brackish water. I have not seen eggs laid by adults in brackish water, but that may be due to lack of patience vs. biology.

Coloration

After a few months of growth in fresh water, the next generation looked like this:

Brown! So, that’s one vote in favor of the orange coloration being related to artificial colors or diet. However, a sibling of the above shrimp, raised in brackish water (1.012) looked like this:

Yellow!

Speculation

Everything about the captive lifecycle suggests a life in an intertidal area; my guess is that these are salt-marsh dwellers and don’t spend much if any time in the open ocean or river. The salinity levels that they like are consistent with an estuary or salt marsh, and the photophobic behavior of the larvae suggests that they don’t want to wash out to sea, but rather stay right where they were hatched.

As to the color variations, I can only guess. Presumably different colors are adaptive in different degrees of murk, so it may be that the orange color is a reaction to particular water chemistry. Or, it may yet be a miracle of chemistry — only Malayan shrimp farmers (or, possibly, Indonesian shrimp-fishermen) know for sure.

Rename

Moments after writing this, I discovered that this species has been identified as Caridina thambipillai.