There have been some questions about the dead fish at 72nd. Dr. Andy White, retired biology professor at John Carroll University, researched this phenomenon many years ago. I ask for a summary of his work and here it is. At temperatures less than 4 degrees Celsius, gizzard shad are unable to metabolize their fat stores (again, they are a southern species that are at the edge of their range up here, and not well adapted to the colder temps).  Once this happens, they begin to break down their liver tissue in order to meet their energy demands (and then eventually muscle tissue as well).  Once the fish get to the point where they have essentially metabolized all of their liver tissue, they have a very large problem:  They are unable to create all of the enzymes necessary for metabolism and cell transport.  Among other things, glucose cannot cross the blood brain barrier at an appropriate rate.  To compensate for this, the fish must increase its serum glucose levels greatly (to force some glucose across the blood brain barrier and across cell membranes in general).  Now they have an even bigger problem....they are right on the edge, so to speak, barely hanging on.  At this point, with their non-fat energy stores severely (or completely) depleted, and lacking many essential enzymes, if the temperature drops even a tiny amount more...they can no longer cope.  They become completely disoriented and roll over.   If at this point they happen to float through some warmer water, they will often right themselves and be able to hang in there a little longer...but when the temperature drops again, they are done for. The largest gizzard shad generally are not affected by this phenomenon, because their behavior pattern is such that they swim offshore and hang out in deeper water where the temperature never drops below 4 degrees celsius...at this temperature, they can still metabolize fat and don't get to the point of needing to live off of their liver tissue.  Smaller fish however have a different behavior pattern - they hang out near shore in shallower (and therefore colder) water.  Smaller fish also expend more energy fighting the waves that are in shallower water near shore - that increases their energy demand as well.  All of that adds up to the fact that smaller gizzard shad simply don't survive the entire winter in Ohio, unless it's a really mild winter.

Sandy Buckles, M.S.Education ChairAudubon Society of Greater Cleveland
 
"We must strive to touch the land gently and care for it as true stewards that those who follow us may see our mark on the land was one of respect and love....."( From a trail marker at Settler's Cove, near Ketchikan , Alaska.)
Robert B. Oetting 

                                          
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