Startled by an oyster

[Ochtapodi]

A couple of months ago, I purchased a red sea fan attached to a small rock. I placed it low in my aquarium resting on the gravel. At one point, I tried to turn the rock in order to avoid the fan touching the side of the equarium, and that's when I got the fright of my life: the rock moved!! I retrieved my hand so fast, I nearly fell off the stool I was standing on.
At closer inspection, I realised that the sea fan was not attached to a rock, but to an oyster.
I tried to look-up on the internet how to feed an oyster, but found very little infomation. Could someone give me some advice?

[Ninong]

Oysters are filter feeders. In fact, all bivalves are filter feeders but some, such as Tridacna clams, also have symbiotic algae (zooxanthellae) in their mantles that provide nourishment via photosynthesis.

I'm not sure exactly what oysters require as far as captive feeding. I don't know if phytoplankton would help or not. I guess I've never given it any thought.

You might be able to find that information using Google's scholar search feature.

[Ninong]

I just did a quick search using Google scholar and it appears that oysters feed on phytoplankton, particulate organic compounds, and bacterivorous ciliates.

I found this information about the American oyster, Crassostrea gigas:

The oyster Crassostrea gigas obtains energy resources by filtering microalgae (~5 to 100 µm). However, in turbid estuaries, light-limited phytoplanktonic production cannot entirely account for oyster energy requirements. Conversely, picoplankters (<2 µm), which are main effectors of coastal energy flow and matter cycling, are not efficiently retained by oyster filtration. Ciliate protozoa, as both micro-sized cells (~5 to 100 µm) and bacteria grazers, may represent a major intermediary in trophic transfer between picoplankton and metazoa. The ciliate Uronema was intensely cultured and labelled, using the cyanobacteria Synechococcus as an autofluorescent biomarker. The labelled ciliates were offered as potential prey to oysters. We report here the first experimental evidence of a significant retention and ingestion of ciliates by oysters, supporting the role of protozoa as a realistic trophic link between picoplankters and filter-feeding bivalves and thus enhancing their potential importance in estuarine microbial food webs.

[Ochtapodi]

Thanks Ninong.
I am using Kent Marine Phyto Plex phytoplancton between 2 and 15 microns to feed the sea fan. So I guess it should also be OK for the oyster, as there is a greater probability that the phytoplancton will be >5 microns vs below, right?

[Ninong]

I'm really not familiar with the exact preferences oysters have when it comes to size, shape, density, etc., of their food items. The bivalves that are most commonly discussed in the reefkeeping hobby are the Tridacna clams and they do have exact preferences when it comes to size, shape, density, etc. of food items. Food items that do not fit in with their exact requirements, as determined by millions of years of evolution, will be rejected.

[Ochtapodi]

I guess I'll have to keep feeding it some phytoplancton and hope for the best. In fact, last week, I thought the oyster was a gonner. It stayed completely closed for three days. So I decided to take it out of the tank and clean it before it contaminated all the aquarium. When I tried to open it, I was surprised to see it was keeping well shut. So I put it back on the gravel and qtuite quickly it opened again and seems to be doing fine ever since.