The Effects on Fish Eating Artemia Shells

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It has been said by some that eating the shells from hatched artemia cysts will cause juvenile fish to die. I have heard theories ranging from the shells clogging the intestine, to actually tearing the intestine open, causing death.

My past experience has been that relatively small numbers of these hatched cysts caused no harm on the fish I have kept. For decades, I've always had 5%+ quantities of hatched shells in each feeding of artemia. I have never had a problem with juveniles dying because of this. However, I wanted to know if large numbers of hatched cysts would make a difference. Also, I have come to think that size of the fish may be an important variable. Although, I don't experience deaths at any age in my hatchery from these shells, I began to think that maybe it was because my fish don't eat enough of them, so this test is designed to take these variables into account.

(1/22/01) I started this test. I put 25 fish into a 20 gallon tank with one large pore sponge filter. I chose 5 fish in five different age groups. They are approximately 3, 4, 5, 6, and 7 weeks old. At each feeding, I put in approximately 1 teaspoon of hatched artemia shells. I noticed that about 5-10% of these were un-hatched shells and a very small amount was live shrimp, though not enough to keep them going long term.

At the first feeding, they were quite hungry and very accustomed to getting live brine. They actively attacked the shells, appearing to eat them. After a few minutes, I could see that they were spitting most out and frantically looking for live shrimp. Their stomachs did fill out a bit, so I could tell they ate a fair number of shells and un-hatched cysts. Up to this point, they had four feedings. They were so hungry, that they became frantic when the shells were put in and they ate quite a large quantity of the shells. I'm was putting in far more than they could eat even if they wanted to, so there were lots of eggs shells floating in a big mass at the surface and many un-hatched cysts on the bottom. I had a couple corydoras in the tank to keep those cysts stirred up. I couldn't tell if the catfish are eating the cysts or not, but the angelfish gave up on it after several minutes of a feeding frenzy where they appear to be eating quite a few.

At this point, there were no deaths. Not even one that looked like it had a stomach ache, but I did have some real hungry fish. If none died after a few days, I was planning on adding a feeding of flake, just so they wouldn't die of starvation.

(1/24/01) I must admit, last night the fish ate so many of these shells, I thought they might become impacted in the intestines and cause some problems. This morning all fish look very normal. Stomachs have receded to normal size. The tank has many feces casings scattered around the tank. I examined a few of these under a microscope. What I found is a group of shells that appear unaffected in any way by either bacteria or digestive enzymes. Most were encased in intestinal cells. This is the clear gelatinous material you see fish pass, when they haven't eaten in awhile.

So far, the water is still clear with no increase in ammonia levels. There is no "chop" starting on any fin tips, which is indicative that bacterial levels are still low. It's rather strange to see fish so full after eating and yet know that they will starve to death with full stomachs if I don't add other food to their tank. A stark reminder that it's not just the quantity of food, but the quality that will affect the growth and color on your fish. Full bellies will not necessarily translate into optimum growth.

(2/7/01) It has been 16 days since I started the test. So far, the fish are looking great, no deaths or ill acting fish. At day 10, I started altering my feeding a bit to see if other combinations would be detrimental. I reasoned that each person who thinks that the shells are killing their fish, are not actually starving their fish. The fish are getting food and shells. Each feeding now has approximately equal amounts of un-hatched cysts, hatched shells, and live shrimp. The juveniles continue to eat large amounts of shells, both hatched and un-hatched, with no noticeable problem.

There has been a raft of hatched shells on the surface that the fish pretty much ignore. I think they have a learned response that those are empty shells and the things mid-water are possibly shrimp, so they will eat the shells mid-water or on the bottom. I don't believe anyone has to worry about heterotrophic bacteria rising to large numbers because of these extra shells. So far, there has been no noticeable rise in ammonia or nitrites. Fins tips have remained straight and pointed. This all suggests that this bad-bacteria has remained low. I think a good test would be to compare the decomposition rate of an artemia shell to that of other organic material like flake food, or dead shrimp. I think you would find that it decomposes very, very slowly. I would imagine, that this is part of the survival mechanism for the cyst. After more than two weeks, I see no decomposition at all.

Conclusion: I have always been under the impression, that when fish die after eating shrimp, shells, etc., it is because of bacterial problems, not the shells. The results of this experiment seem to support that any deaths are not from eating hatched artemia shells, though I realize that there may be another factor missing in my tanks that could contribute to the shells being dangerous. I have been feeding these shells for many years in several different water conditions without problem, so I suspect that these results will hold true under most water conditions. The other conclusion that this supports, is that extra shells and un-hatched eggs in the tank, is not harmful, nor does it contribute to the bio-load of the tank in any significant way. I will design another experiment to more fully test this.

I will keep this going for awhile longer. I will report any changes, but will not make any more updates unless there is a change.

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