It has been said that when a juvenile fish feeds heavily on non-hydrated decapsulated brine shrimp eggs (decaps), the fish will or can die when the decapsulated egg swells in the gut.
(2/9/01)I first wanted to see what the hydration process of the artemia cyst looked like under a microscope. I looked at some dry decaps under the scope. They appeared somewhat wrinkled and odd shaped - not round. I then took some dry decapsulated artemia and placed it in water. I let this sit for 4 hours to hydrate them and then removed cysts that had sunk to the bottom and looked at them at 30X under the scope. They appeared to be a nice round shape. I would guess they were 20-30% larger than the dry decaps.
Next, I added a drop of water to a group of dry decaps that were under the scope and observed them while tracking time. It was quite amazing how rapidly they absorbed the water. Within seconds, they were popping around as they rapidly expanded with water. Within one minute they looked identical to the eggs that had been hydrated for 4 hours.
Feedings: I wanted the fish to eat enough at one feeding to cause the problem if swelling of the artemia cyst was a legitimate concern. I decided to feed them once a day as much as they would eat, in an attempt to stimulate the greatest hunger and feeding response. I have always observed higher than normal bacterial problems in tanks being fed decaps, so I decided to do a 90% water change each day, two hours after feeding. This was to remove any uneaten decapsulated eggs and try to keep bacteria from interfering with the results. The first feeding was given on 2/10/01, to a group of twelve 5-7 week old juvenile angelfish. They were in a 20 gal tank at 83° F with one large pore sponge filter.
(2/13/01) After three feedings I could see no problems. Fish were eating well and filling up nicely, but not attacking the decaps as they would a good flake fish food or live brine shrimp. This morning, I took a couple fecal samples and looked at them at 30X under the scope. The excreted decaps were encased in the clear gelatinous material that is commonly seen in fish that haven't eaten in a few days. The individual cyst could still be clearly seen. The transparent outer-layer of the cyst appeared to be intact. The material inside the shell was still present in varying amounts. Some looked completely as they did before being fed, some looked almost completely empty, but most looked as if about 1/2 the food matter was gone or shrunk. This was an eye opener and explained previously observed slow growth when feeding decapsulated artemia as well as the higher than normal bacterial problems when feeding them. Huge water changes seem even more critical after seeing the amount of food still present in the fecal matter. If after about two more weeks, I do not see any deaths or problems, I will switch to testing 2-3 week old fry.
(2/26/01) Fish are thriving. No deaths or ill acting fish. At no point in this test did any of the fish appear to have eaten enough to even be stressed, although they all fed vigorously at each feeding. I have concluded that fish that are 5 weeks or older are unlikely to be affected by decapsulated dried artemia that is not hydrated before feeding. This coincides with my previous experience with this product.
Conclusion: Decapsulated artemia is a food that is not readily absorbed through digestion. The undigested food in the fecal matter is a potential hazard to water quality and will likely raise bacterial levels greatly. This makes it a poor choice for fish like angelfish that are very susceptible to high bacterial levels. In addition its low digestibility makes it an overall poor value in fish foods.
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