[1] It is especially vulnerable to changes in water chemistry that affect local fish populations, such as nitrate and phosphate concentrations.

They bury themselves in the stream bed, leaving only their siphons exposed through which they inhale oxygen and food (algae and microorganisms) and expel waste.

[4] They are tachytictic (short-term) breeders, meaning the cycle of fertilization to juvenile takes place in one season.

Like most Unionidae mussels, the larvae have a parasitic stage where they are required to attach and feed off a host fish.

[9] The most frequent host fishes have been identified as bullhead (Cottus gobio), minnow (Phoxinus phoxinus), chub (Leuciscus cephalus and Squalius cephalus), rudd (Scardinius erythrophthalmus), bleak (Alburnus alburnus), nase (Chondrostoma nasus), stickleback (Gasterosteus aculeatus), ide (Leuciscus idus) and perch (Perca fluviatilis).

For example, in the Danube drainage, European chub (Squalius cephalus) is considered the most suitable host for U. crassus.

Invasive species such as round goby (Neogobius melanostomus) and rainbow trout (Oncorhynchus mykiss) were also unable to keep larvae alive.

Archaeological evidence from shell collections in Hungary as far back as the Neolithic period indicate that several mussel species were gathered from a nearby river and consumed raw as an important supplementary food source.

[10] Unio shells used as tools, including U. crassus, have been found at archaeological sites dating to the 5th millennium BC.

[1] In addition to being a parasite in its larval stage, the thick-shelled river mussel also acts as a host for the endangered European bitterling (Rhodeus amarus).

[4] A 2020 study identified habitat destruction, predation by muskrat, and lack of host fish as the major factors for decline.