As they assimilate nitrogenous and carbon-rich compounds, they hasten the breakdown of sludge, decaying leaves and animals, dead algae, fish waste, and so much more. The cisco (aka lake herring, Coregonus artedi) was one of the most abundant fish in Lake Michigan before unregulated commercial fishing, invasive species, and habitat degradation took their toll.By the mid-1960s, cisco were nearly wiped out. These invertebrates are quite diverse; some are microscopic whereas others are lobster-sized and are considered an absolute delicacy. (.pdf),