Decapsulated Brine Shrimp Eggs

Brine shrimp eggs (cysts) consist of dormant embryos covered with a three-layered shell. Under optimal hatching conditions the embryos break out of the shell and hatch into nauplii, which are then used for larval or fry feeding. However, the hard outer shell of the brine shrimp egg, the alveolar layer can be completely removed through a chemical process known as decapsulation. Consequently, the task of separating the nauplii from the unhatched eggs and shells is eliminated because 100% of the decapsulated eggs (both hatched and unhatched) can be fed. An important application of the decapsulated cysts is that even low-hatch or no-hatch cysts can be used for feeding. Obviously, the time and effort involved in decapsulating brine shrimp eggs may not suit the average aquarist. However, if you have the time and patience, it could be worth trying.

The decapsulated cysts can be used immediately or dehydrated in a brine solution for storage, or further subjected to a drying process for longer term storage. The advantages of decapsulation include disinfection of the cysts, improved hatching and no risk of fish larvae suffering from gut obstruction due to the ingestion of empty egg casings. A number of studies have demonstrated that the growth and survival of fish fed decapsulated cysts is better than or comparable with those fed newly-hatched nauplii. In one study (Lim et al. 2002), it was found that the fry of five common ornamental fish species tested (Poecilia reticulata, Poecilia sphenops, Xiphophorus maculatus, Xiphophorus helleri and Hyphessobrycon herbertaxelrodi) could readily feed on the decapsulated cysts, and their growth and survival was comparable to or better than those fed on nauplii.

Decapsulated Artemia cysts have several advantages over nauplii as a larval diet for freshwater fishes: • Decapsulated cysts are more nutritious due to their high level of unsaturated fatty acids, amino acids and their nutrient-to-energy ratio. • Empty egg casings are not introduced into the fry tanks. • Nauplii that are hatched out of decapsulated eggs have a higher individual weight (30-55 % depending on strain) than regular instar I nauplii. • In some cases, hatchability is improved by decapsulation. • Decapsulation results in disinfection of the eggs. • Can be stored in a fridge for an extended period if dehydrated. • Have a smaller diameter which enables them to be ingested by smaller fish. • Persist for longer in freshwater than nauplii.

Decapsulated eggs can be used as an energy-rich food source for larval rainbowfishes. For example, the larvae of several freshwater fish species grew equally well or better when fed decapsulated cysts compared to those fed a commercial starter feed. The cysts contain an average of 30% more nutrients than newly hatched nauplii. The cysts have the appearance and the practical advantages of a dry feed and, in contrast to nauplii (470–550 µm); their small particle size (200–250 µm) is more suitable for smaller fish. However, despite their apparent nutritional benefits, decapsulated cysts may sink too rapidly to the bottom of the culture tank and the larvae may not feed off the bottom of the tank. If they have been dried before use, they have a high floating capacity, and sink only slowly to the bottom of the culture tank. Dried decapsulated cysts, when treated appropriately, can be stored for years, and hence may be fed off the shelf without the need for hatching.