Very occasionally I notice small, white worms to be present amongst brine shrimp.

What are these white worms and is it okay for my fish to eat these?

 

   Those small white worms are the larvae of brine flies (Ephydra sp.), also called ‘salt flies’ or ‘shore flies’. As the name implies brine flies live in and near saline lakes, saline ponds and solar evaporation ponds in saltworks. Brine fly and brine shrimp are what’s called ‘co-inhabiting species’[1], which basically means that ‘where you find one of the species, you will more than likely also encounter the other’. And indeed, brine shrimp and brine fly are the only metazoan (so multicellular) species known to be able to permanently live in such saline lakes.

   Brine fly larvae live on the bottom of the lakes where they graze on microalgae, bacteria and detritus. They occasionally get dislodged by currents caused by wind or rain and can therefore end up getting harvested together with brine shrimp. Although maybe unsightly to some people, these larvae are actually very nutritious and will be readily eaten by your fish, amphibians and aquatic invertebrates. In nature the larvae are mainly eaten by wading birds[2] and to a certain extend by water boatmen, as fish and amphibians cannot live in these lakes or ponds due to the high salinities (water boatmen only occur at the lower salinity range in which brine fly larvae can be found). As such brine fly larvae play an important role in the recycling of nutrients in saline bodies of water.

   Adult flies can literally color patches of beach black because of the sheer, massive number of adults gathering together. Do they form a nuisance for us when harvesting brine shrimp? Not really, as the adult flies don’t fly up to people (they more than likely consider us predators). And besides, during the adult phase the flies only live for a couple of days and the only thing they are occupied with is finding a mate.

   Brine fly larvae produce a casing (like a caterpillar producing a chrysalis enabling it to emerge as a butterfly) in which they transform into an adult. After the adults have hatched the empty casings are blown ashore by the wind as shown in the picture below (the dark, brown mass floating on the water surface near the edge of the pond in the lower, right corner).

   We find such empty casings in most batches of harvested brine shrimp as pictured below (the black items). The removal of these empty brine fly casings is the aim of one of the various cleaning steps we utilize when processing a batch of harvested brine shrimp.

   Still occupied casings (that is, casings still containing the developing larva) do occasionally get mixed with the brine shrimp we are harvesting. These full casings are very difficult to separate from the brine shrimp and can only be removed manually during the final cleaning and dewatering step; a very tedious process! If too large an amount of full casings is found to be present amongst the harvested brine shrimp, we do not transport the harvested brine shrimp to our facility for further processing. Instead the batch of harvested shrimp is sold to nearby shrimp or crab rearing farms.

Do such full brine fly casings have any nutritional value for fish? Some … but not much. The developing larva inside does have a high protein and fat level, but the surrounding casing is mainly made of chitin, which most fish can poorly digest. As such the digestibility of a full casing is quite low. Empty brine fly casings in the ponds, or blown ashore, are slowly degraded by bacteria and fungi, which in this way recycle the nutrients and get them back in the cycle of life.