My research and readings indicate that paddlefish almost exclusively eat larger zooplankton of sizes 200 -1000 um (0.20 – 1.0mm or 0.0078 – 0.0393”) and not algae. See below. Note – Immature stages of Crustacean zooplankton consumed are often greater than 150um. However there are many other types of zooplankton including rotifers and protozoans present in the zooplankton community less than 200um. Paddlefish are able to uniquely locate and strain out mainly larger zooplankton of Cladocerans and or Copepods depending on seasonality. When available they will strain out small stages of insect larvae and fish fry. Feeding methods also cause them to at times inadvertently ingest up to 50% of their gut content as very small sand grains and detritus particles strained from the water column .
Because paddlefish gather food by methods of filtering – straining the water, the long strands of filamentous algae IMO are rarely if ever eaten because these spaghetti like strands and mats would plug, clog and become entangled in their physical feeding mechanisms and process. Thus their feeding mechanisms are very counter- productive for eating FA.
Planktonic food items will be highly dependent on the types of plankton endemic to each water body.
Reference Notes – “Our study supports the argument that paddlefish do not selectivity feed and can be described as indiscriminate feeders.”
One example food items:
From one of the referenced articles below, they identified seven different taxonomic groups in order of most abundant prey items: Copepoda, Cladocera, Insecta, Ostracoda, Amphipoda, Decapoda, and diatoms (Table 2). Amphipods and decapods (bottom living crustaceans) were rarely found in paddlefish stomachs.
Study Note- It is possible that the importance of algae in the diets of subadult and adult paddlefish has been underestimated. We found that diatoms (are non FA algae) dominated the stomachs of Louisiana paddlefish in May 2003. This is similar to other southern rivers where Hageman et al. (1986) found “prominent green masses of algal and/or plant cells” in one particular month (October). (Note many forms of larger unicellular and colonial soft bodied algae would not be readily identifiable in gut contents). Although few studies have reported algae as a diet item, some paddlefish populations apparently do consume algae during certain times of the year. IMO probably due to the common preponderance of seasonal types of usable sizes of planktonic algae.
Note – IMO fish that normally do eat filamentous algae (FA) do not gather FA by filter feeding and use a different feeding mechanism or method.
https://fisheries.org/docs/books/54066P/4.pdfhttps://fisheries.org/docs/books/54066P/1.pdf
